NCERT Class 10 Science Solutions: Chemical Reactions and Equations
Question:
What happens when dilute hydrochloric acid is added to iron fillings? Choose the correct answer.
A. Hydrogen gas and iron chloride are produced.
B. Chlorine gas and iron hydroxide are produced.
C. No reaction takes place.
D. Iron salt and water are produced.
Concept in a Minute:
This question tests the understanding of chemical reactions between acids and metals. Specifically, it focuses on the reaction between dilute hydrochloric acid (an acid) and iron (a metal). The general reactivity of metals with acids is crucial.
Explanation:
When a dilute acid reacts with a reactive metal, a salt and hydrogen gas are produced. Iron is a reactive metal. Hydrochloric acid is a dilute acid. Therefore, when dilute hydrochloric acid is added to iron fillings, a chemical reaction will occur. Iron will react with hydrochloric acid to form iron chloride (a salt) and hydrogen gas. The chemical equation for this reaction is:
Fe(s) + 2HCl(aq) → FeCl2(aq) + H2(g)
Here, Fe represents iron, HCl represents hydrochloric acid, FeCl2 represents iron(II) chloride (iron chloride), and H2 represents hydrogen gas.
Option A states that hydrogen gas and iron chloride are produced, which is consistent with the reaction.
Option B is incorrect because chlorine gas is not produced, and iron hydroxide is not the primary product of this reaction with a dilute acid.
Option C is incorrect because iron is a reactive metal and will react with a dilute acid.
Option D is partially correct in that an iron salt is produced, but water is not the other product; hydrogen gas is.
Therefore, the correct answer is A.
Question:
Translate the following statement into chemical equation and then balance it.
Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
Concept in a Minute:
Chemical reactions involve the rearrangement of atoms and molecules. A chemical equation represents this process symbolically. Balancing a chemical equation ensures that the law of conservation of mass is obeyed, meaning the number of atoms of each element is the same on both the reactant and product sides. Key steps involve identifying reactants and products, writing the unbalanced equation, and then systematically adjusting coefficients to balance the atom counts.
Explanation:
1. Identify the reactants and products:
Reactants: Barium chloride, Aluminium sulphate
Products: Aluminium chloride, Barium sulphate (precipitate)
2. Write the chemical formulas for each substance:
Barium chloride: BaCl₂
Aluminium sulphate: Al₂(SO₄)₃
Aluminium chloride: AlCl₃
Barium sulphate: BaSO₄
3. Write the unbalanced chemical equation:
BaCl₂ + Al₂(SO₄)₃ → AlCl₃ + BaSO₄
4. Balance the equation:
* Start with Aluminium (Al): There are 2 Al atoms on the left and 1 on the right. Place a coefficient of 2 in front of AlCl₃.
BaCl₂ + Al₂(SO₄)₃ → 2AlCl₃ + BaSO₄
* Now look at Chlorine (Cl): There are 2 Cl atoms on the left and 2 * 3 = 6 Cl atoms on the right. Place a coefficient of 3 in front of BaCl₂.
3BaCl₂ + Al₂(SO₄)₃ → 2AlCl₃ + BaSO₄
* Now look at Barium (Ba): There are 3 * 1 = 3 Ba atoms on the left and 1 on the right. Place a coefficient of 3 in front of BaSO₄.
3BaCl₂ + Al₂(SO₄)₃ → 2AlCl₃ + 3BaSO₄
* Finally, check Sulphur (S) and Oxygen (O): There are 3 SO₄ groups on the left and 3 SO₄ groups on the right (due to the coefficient 3 in front of BaSO₄). So, S and O are balanced.
The balanced chemical equation is:
3BaCl₂(aq) + Al₂(SO₄)₃(aq) → 2AlCl₃(aq) + 3BaSO₄(s)
(aq) denotes aqueous solution, and (s) denotes solid precipitate.
Question:
Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Concept in a Minute:
Decomposition reactions and combination reactions are fundamental chemical reaction types. A combination reaction involves two or more reactants combining to form a single product. A decomposition reaction involves a single reactant breaking down into two or more simpler products. The opposite nature arises from their differing effects on the number of chemical species.
Explanation:
Decomposition reactions are called the opposite of combination reactions because they involve the breakdown of a single compound into two or more simpler substances, whereas combination reactions involve the formation of a single compound from two or more simpler substances. In essence, combination reactions bring things together, and decomposition reactions break them apart.
Here are the equations for these reactions:
Combination Reaction:
A combination reaction is represented by the general equation:
A + B → AB
where A and B are two or more reactants that combine to form a single product AB.
Example: The formation of water from hydrogen and oxygen.
2H₂ (g) + O₂ (g) → 2H₂O (l)
In this reaction, two gaseous elements, hydrogen and oxygen, combine to form liquid water.
Decomposition Reaction:
A decomposition reaction is represented by the general equation:
AB → A + B
where a single compound AB decomposes into two or more simpler substances A and B.
Example: The decomposition of water into hydrogen and oxygen.
2H₂O (l) → 2H₂ (g) + O₂ (g)
In this reaction, liquid water decomposes into gaseous hydrogen and oxygen.
As you can see from the examples, the decomposition of water produces the same substances (hydrogen and oxygen) that combine to form water. This direct reversal of reactants and products clearly demonstrates why decomposition reactions are considered the opposite of combination reactions.
Question:
What do you mean by a precipitation reaction? Explain by giving examples.
Concept in a Minute:
Precipitation reaction is a chemical reaction where two soluble ionic compounds in aqueous solution react to form an insoluble solid product, called a precipitate. This precipitate separates from the solution.
Explanation:
A precipitation reaction is a type of double displacement reaction where the cations and anions of two ionic compounds swap partners. When these new combinations are formed, if one of the resulting ionic compounds is insoluble in water, it will form a solid that settles out of the solution. This solid is the precipitate.
To identify if a precipitation reaction will occur, one needs to consult solubility rules. These rules indicate which ionic compounds are soluble or insoluble in water.
For example, consider the reaction between silver nitrate (AgNO₃) and sodium chloride (NaCl) in aqueous solution. Both silver nitrate and sodium chloride are soluble ionic compounds. When mixed, they undergo a double displacement reaction:
AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
Here, silver ions (Ag⁺) from silver nitrate combine with chloride ions (Cl⁻) from sodium chloride to form silver chloride (AgCl). Silver chloride is insoluble in water, so it precipitates out as a white solid. Sodium ions (Na⁺) from sodium chloride combine with nitrate ions (NO₃⁻) from silver nitrate to form sodium nitrate (NaNO₃), which is soluble and remains in solution.
Another example is the reaction between barium chloride (BaCl₂) and sodium sulfate (Na₂SO₄):
BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)
Barium chloride and sodium sulfate are soluble. Upon mixing, barium ions (Ba²⁺) and sulfate ions (SO₄²⁻) combine to form barium sulfate (BaSO₄), which is an insoluble white precipitate. Sodium ions (Na⁺) and chloride ions (Cl⁻) form sodium chloride, which is soluble.
Question:
Write the balanced chemical equation for the following reaction.
$Zinc+SilvernitrateZincnitrate+Silver$
Concept in a Minute:
Chemical equations represent chemical reactions. A balanced chemical equation accurately shows the reactants and products and ensures that the number of atoms of each element is the same on both sides of the equation, obeying the law of conservation of mass. This is achieved by using stoichiometric coefficients.
Explanation:
The reaction given is between Zinc and Silver nitrate, producing Zinc nitrate and Silver.
First, we write the chemical formulas for each substance:
Zinc: Zn
Silver nitrate: AgNO₃
Zinc nitrate: Zn(NO₃)₂
Silver: Ag
Now, we write the unbalanced chemical equation:
Zn + AgNO₃ → Zn(NO₃)₂ + Ag
To balance the equation, we need to ensure that the number of atoms of each element is equal on both sides.
Let’s count the atoms on each side:
Reactants side:
Zn: 1
Ag: 1
N: 1
O: 3
Products side:
Zn: 1
Ag: 1
N: 2 (since NO₃ is in parentheses with a subscript 2)
O: 6 (since O is 3 inside parentheses with a subscript 2)
We can see that Nitrogen (N) and Oxygen (O) are not balanced. To balance them, we need to adjust the coefficient of AgNO₃.
If we place a coefficient of 2 in front of AgNO₃:
Zn + 2AgNO₃ → Zn(NO₃)₂ + Ag
Now, let’s recount the atoms:
Reactants side:
Zn: 1
Ag: 2 (since we have 2AgNO₃)
N: 2 (since we have 2AgNO₃)
O: 6 (since we have 2AgNO₃, 2 * 3 = 6)
Products side:
Zn: 1
Ag: 1
N: 2
O: 6
Now, Zinc (Zn) and Nitrogen (N) and Oxygen (O) are balanced. However, Silver (Ag) is not balanced (2 on the reactant side, 1 on the product side).
To balance Silver, we place a coefficient of 2 in front of Ag on the product side:
Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag
Let’s do a final count:
Reactants side:
Zn: 1
Ag: 2
N: 2
O: 6
Products side:
Zn: 1
Ag: 2
N: 2
O: 6
All elements are now balanced. The balanced chemical equation is:
Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag
Question:
Write the balanced chemical equation for the following and identify the type of reaction.
$Zinccarbonate(s)Zincoxide(s)+Carbondioxide(g)$
Concept in a Minute:
Balancing chemical equations involves ensuring that the number of atoms of each element is the same on both the reactant and product sides. This adheres to the law of conservation of mass. Identifying the type of reaction involves recognizing patterns of chemical change, such as decomposition, combination, displacement, or double displacement. Decomposition reactions involve a single compound breaking down into two or more simpler substances.
Explanation:
The given reaction is: Zinc carbonate (s) → Zinc oxide (s) + Carbon dioxide (g)
Step 1: Write the unbalanced chemical equation using the chemical formulas of the reactants and products.
The chemical formula for zinc carbonate is ZnCO₃.
The chemical formula for zinc oxide is ZnO.
The chemical formula for carbon dioxide is CO₂.
So, the unbalanced equation is:
ZnCO₃ → ZnO + CO₂
Step 2: Balance the chemical equation.
Count the number of atoms of each element on both sides of the equation.
Reactant side:
Zinc (Zn): 1
Carbon (C): 1
Oxygen (O): 3
Product side:
Zinc (Zn): 1
Carbon (C): 1
Oxygen (O): 1 (in ZnO) + 2 (in CO₂) = 3
In this equation, the number of atoms of each element is already the same on both sides. Therefore, the equation is already balanced.
Balanced chemical equation:
ZnCO₃(s) → ZnO(s) + CO₂(g)
Step 3: Identify the type of reaction.
In this reaction, a single compound (zinc carbonate) breaks down into two or more simpler substances (zinc oxide and carbon dioxide). This type of reaction is called a decomposition reaction.
Therefore, the balanced chemical equation is ZnCO₃(s) → ZnO(s) + CO₂(g), and it is a decomposition reaction.
Question:
Write the balanced equation for the following chemical reaction.
$Hydrogen+ChlorineHydrogenchloride$
Concept in a Minute:
Chemical equations represent chemical reactions using symbols and formulas. A balanced chemical equation has the same number of atoms of each element on both the reactant side (left side of the arrow) and the product side (right side of the arrow). This adheres to the Law of Conservation of Mass.
Explanation:
The given chemical reaction is: Hydrogen + Chlorine → Hydrogen chloride
First, identify the chemical formulas for each substance:
Hydrogen is a diatomic molecule, so its formula is H₂.
Chlorine is also a diatomic molecule, so its formula is Cl₂.
Hydrogen chloride is a compound formed from hydrogen and chlorine. The formula for hydrogen chloride is HCl.
Now, write the unbalanced equation using these formulas:
H₂ + Cl₂ → HCl
Next, balance the equation by ensuring the number of atoms of each element is the same on both sides.
On the reactant side (left):
Number of Hydrogen atoms = 2
Number of Chlorine atoms = 2
On the product side (right):
Number of Hydrogen atoms = 1
Number of Chlorine atoms = 1
To balance the hydrogen atoms, we need 2 hydrogen atoms on the product side. We can achieve this by placing a coefficient of 2 in front of HCl:
H₂ + Cl₂ → 2HCl
Now, let’s check the atom count again:
On the reactant side (left):
Number of Hydrogen atoms = 2
Number of Chlorine atoms = 2
On the product side (right):
Number of Hydrogen atoms = 2 × 1 = 2
Number of Chlorine atoms = 2 × 1 = 2
The number of atoms of each element is now equal on both sides of the equation. Therefore, the balanced equation is:
H₂ + Cl₂ → 2HCl
Question:
Write the balanced chemical equation for the following reaction.
$Calciumhydroxide+CarbondioxideCalciumcarbonate+Water$
Concept in a Minute:
Chemical equations represent chemical reactions. Balancing a chemical equation ensures that the law of conservation of mass is obeyed, meaning the number of atoms of each element is the same on both the reactant and product sides. Reactants are the substances that react, and products are the substances that are formed.
Explanation:
The given reaction is between calcium hydroxide and carbon dioxide to produce calcium carbonate and water.
First, let’s write the chemical formulas for each substance:
Calcium hydroxide: Ca(OH)₂
Carbon dioxide: CO₂
Calcium carbonate: CaCO₃
Water: H₂O
Now, let’s write the unbalanced chemical equation:
Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
Next, we need to balance the equation by ensuring the number of atoms of each element is equal on both sides.
Let’s count the atoms on each side:
Reactant side:
Calcium (Ca): 1
Oxygen (O): 2 (from OH) + 2 (from CO₂) = 4
Hydrogen (H): 2 (from OH)
Carbon (C): 1
Product side:
Calcium (Ca): 1
Oxygen (O): 3 (from CaCO₃) + 1 (from H₂O) = 4
Hydrogen (H): 2 (from H₂O)
Carbon (C): 1
Comparing the number of atoms on both sides, we see that:
Ca: 1 on reactant side = 1 on product side (balanced)
C: 1 on reactant side = 1 on product side (balanced)
H: 2 on reactant side = 2 on product side (balanced)
O: 4 on reactant side = 4 on product side (balanced)
Since the number of atoms of each element is already the same on both the reactant and product sides, the equation is already balanced.
The balanced chemical equation is:
Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
Question:
What is a balanced chemical equation? Why should a chemical equation be balanced?
Concept in a Minute:
Law of Conservation of Mass: Matter can neither be created nor destroyed in a chemical reaction. The mass of reactants before a reaction must be equal to the mass of products after the reaction.
Atoms: In a chemical reaction, atoms are rearranged to form new substances, but the total number of atoms of each element remains the same.
Explanation:
A balanced chemical equation is a chemical equation where the number of atoms of each element is the same on both the reactant side and the product side. This ensures that the law of conservation of mass is obeyed.
We should balance a chemical equation because:
1. To satisfy the Law of Conservation of Mass: As stated above, matter cannot be created or destroyed in a chemical reaction. Therefore, the total mass of the elements involved in the reactants must be equal to the total mass of the elements involved in the products. Balancing ensures that the number of atoms of each element is the same before and after the reaction, thus maintaining the mass.
2. To accurately represent the chemical reaction: A balanced equation reflects the actual stoichiometry of the reaction, meaning it shows the correct mole ratios in which reactants combine and products are formed. This is crucial for quantitative calculations in chemistry, such as determining the amount of product formed from a given amount of reactant. An unbalanced equation would inaccurately suggest that atoms are lost or gained during the reaction, which is not scientifically accurate.
Question:
In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
Concept in a Minute:
Chemical displacement reactions. Specifically, understanding the reactivity series of metals to predict which metal will displace another from its salt solution. In this case, copper displacing silver from silver nitrate.
Explanation:
The question describes a process where silver is recovered from a silver nitrate solution using copper metal. This is a classic example of a displacement reaction. In such reactions, a more reactive metal displaces a less reactive metal from its salt solution.
We need to determine the relative reactivity of copper and silver. The reactivity series of metals (a list of metals in order of their decreasing reactivity) shows that copper is more reactive than silver. Therefore, copper will displace silver from its solution.
The silver nitrate solution is represented by the chemical formula AgNO₃.
Copper metal is represented by the chemical symbol Cu.
When copper metal is added to the silver nitrate solution, copper will displace silver ions (Ag⁺) from the solution and form copper nitrate (Cu(NO₃)₂) while the displaced silver ions will get reduced to silver metal (Ag).
The balanced chemical equation for this displacement reaction is:
Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s)
In this reaction:
– Copper (Cu) is the reactant that is being oxidized (losing electrons).
– Silver ions (Ag⁺) in silver nitrate are being reduced (gaining electrons) to silver metal.
– Copper nitrate (Cu(NO₃)₂) is formed in the solution.
– Silver metal (Ag) is deposited as a solid.
Question:
Balance the following chemical equation.
$NaCl+AgNO𝐴3AgCl+NaNO𝐴3$
Concept in a Minute:
Balancing chemical equations involves ensuring that the number of atoms of each element is the same on both the reactant side (left side of the arrow) and the product side (right side of the arrow). This adheres to the Law of Conservation of Mass. Balancing is achieved by placing stoichiometric coefficients (numbers) in front of the chemical formulas.
Explanation:
The given chemical equation is:
NaCl + AgNO₃ → AgCl + NaNO₃
Let’s count the atoms of each element on both sides of the equation.
Reactant side:
Sodium (Na): 1 atom
Chlorine (Cl): 1 atom
Silver (Ag): 1 atom
Nitrogen (N): 1 atom
Oxygen (O): 3 atoms
Product side:
Silver (Ag): 1 atom
Chlorine (Cl): 1 atom
Sodium (Na): 1 atom
Nitrogen (N): 1 atom
Oxygen (O): 3 atoms
Comparing the number of atoms of each element on both sides, we see that:
Number of Na atoms (reactant) = Number of Na atoms (product) = 1
Number of Cl atoms (reactant) = Number of Cl atoms (product) = 1
Number of Ag atoms (reactant) = Number of Ag atoms (product) = 1
Number of N atoms (reactant) = Number of N atoms (product) = 1
Number of O atoms (reactant) = Number of O atoms (product) = 3
Since the number of atoms of each element is already equal on both the reactant and product sides, the equation is already balanced. The stoichiometric coefficients are all 1, which are usually not written.
Therefore, the balanced chemical equation is:
NaCl + AgNO₃ → AgCl + NaNO₃
Question:
Write a balanced chemical equation with state symbols for the following reaction.
Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
Concept in a Minute:
Balancing chemical equations: The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction. Therefore, the number of atoms of each element on the reactant side must equal the number of atoms of that element on the product side.
State symbols: Chemical equations should include state symbols to indicate the physical state of reactants and products (solid (s), liquid (l), gas (g), aqueous (aq)).
Explanation:
The reaction involves sodium hydroxide (NaOH) and hydrochloric acid (HCl) reacting to form sodium chloride (NaCl) and water (H2O). Both reactants and the product sodium chloride are given as solutions in water, so they are in aqueous (aq) state. Water is a liquid (l).
First, write the unbalanced equation with the correct chemical formulas:
NaOH (aq) + HCl (aq) -> NaCl (aq) + H2O (l)
Now, balance the equation by ensuring the same number of atoms of each element on both sides.
Count the atoms:
Reactants:
Na: 1
O: 1
H: 1 (from NaOH) + 1 (from HCl) = 2
Cl: 1
Products:
Na: 1
Cl: 1
H: 2 (from H2O)
O: 1 (from H2O)
The number of atoms of each element is already equal on both sides. Therefore, the equation is already balanced.
The balanced chemical equation with state symbols is:
NaOH (aq) + HCl (aq) -> NaCl (aq) + H2O (l)
Question:
Identify the substances that are oxidised and the substances that are reduced in the following reaction.
$CuO(s)+H𝐴2(g)Cu(s)+H𝐴2O(l)$
Concept in a Minute:
Oxidation is the loss of electrons, gain of oxygen, or loss of hydrogen. Reduction is the gain of electrons, loss of oxygen, or gain of hydrogen. In a chemical reaction, the substance that gains oxygen is oxidized, and the substance that loses oxygen is reduced.
Explanation:
Let’s analyze the given reaction: $CuO(s) + H_2(g) \rightarrow Cu(s) + H_2O(l)$
We need to identify what is oxidized and what is reduced.
Oxidation involves an increase in the oxidation state, typically by gaining oxygen or losing hydrogen.
Reduction involves a decrease in the oxidation state, typically by losing oxygen or gaining hydrogen.
Consider the reactants: CuO and $H_2$.
Consider the products: Cu and $H_2O$.
Let’s look at copper (Cu). In CuO, copper is bonded to oxygen. In the product, copper is in its elemental form, Cu. This means that CuO has lost oxygen. The loss of oxygen signifies reduction. Therefore, CuO is reduced.
Now let’s look at hydrogen ($H_2$). In the reactants, we have $H_2$. In the products, we have $H_2O$. This means that $H_2$ has gained oxygen. The gain of oxygen signifies oxidation. Therefore, $H_2$ is oxidized.
So, in the reaction $CuO(s) + H_2(g) \rightarrow Cu(s) + H_2O(l)$:
The substance that is oxidized is $H_2$.
The substance that is reduced is CuO.
Question:
What is the difference between displacement and double displacement reactions? Write equations for these reactions.
Concept in a Minute:
Chemical reactions involve the rearrangement of atoms. Displacement reactions involve one element replacing another in a compound. Double displacement reactions involve the exchange of ions between two compounds.
Explanation:
A displacement reaction, also known as a single displacement reaction, occurs when a more reactive element displaces a less reactive element from its compound.
The general form of a displacement reaction is: A + BC → AC + B
where A is more reactive than B.
Example of a displacement reaction:
When zinc metal is added to copper sulfate solution, zinc displaces copper because zinc is more reactive than copper.
Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
A double displacement reaction, also known as a metathesis reaction, occurs when the ions of two ionic compounds are exchanged, resulting in the formation of two new compounds.
The general form of a double displacement reaction is: AB + CD → AD + CB
Double displacement reactions often result in the formation of a precipitate, a gas, or water.
Example of a double displacement reaction:
When silver nitrate solution is mixed with sodium chloride solution, silver chloride (a white precipitate) is formed.
AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
Question:
Write the balanced chemical equation for the following reaction.
$Bariumchloride+PotassiumsulphateBariumsulphate+Potassiumchloride$
Concept in a Minute:
Balancing chemical equations involves ensuring that the number of atoms of each element is the same on both the reactant and product sides of the equation. This is based on the Law of Conservation of Mass.
Explanation:
The given reaction is:
Barium chloride + Potassium sulfate → Barium sulfate + Potassium chloride
First, we write the chemical formulas for each substance.
Barium chloride: BaCl$_2$
Potassium sulfate: K$_2$SO$_4$
Barium sulfate: BaSO$_4$
Potassium chloride: KCl
Now, we write the unbalanced chemical equation:
BaCl$_2$ + K$_2$SO$_4$ → BaSO$_4$ + KCl
Next, we balance the equation by counting the atoms of each element on both sides.
Reactants:
Ba: 1
Cl: 2
K: 2
S: 1
O: 4
Products:
Ba: 1
S: 1
O: 4
K: 1
Cl: 1
To balance, we need to adjust the stoichiometric coefficients.
We have 2 chlorine atoms on the left and 1 on the right. So, we place a coefficient of 2 in front of KCl.
BaCl$_2$ + K$_2$SO$_4$ → BaSO$_4$ + 2KCl
Now, let’s recount the atoms:
Reactants:
Ba: 1
Cl: 2
K: 2
S: 1
O: 4
Products:
Ba: 1
S: 1
O: 4
K: 2 (from 2KCl)
Cl: 2 (from 2KCl)
The number of atoms of each element is now equal on both sides.
The balanced chemical equation is:
BaCl$_2$ + K$_2$SO$_4$ → BaSO$_4$ + 2KCl
Question:
Give an example of a double displacement reaction.
Concept in a Minute:
Double displacement reaction is a chemical reaction where two ionic compounds react, and the positive ion (cation) of one compound swaps places with the positive ion (cation) of the other compound. This results in the formation of two new compounds. These reactions often involve the formation of a precipitate, a gas, or water.
Explanation:
A common example of a double displacement reaction is the reaction between silver nitrate (AgNO3) and sodium chloride (NaCl).
When a solution of silver nitrate is mixed with a solution of sodium chloride, the silver ions (Ag+) from silver nitrate combine with the chloride ions (Cl-) from sodium chloride to form silver chloride (AgCl), which is an insoluble solid (a precipitate). Simultaneously, the sodium ions (Na+) from sodium chloride combine with the nitrate ions (NO3-) from silver nitrate to form sodium nitrate (NaNO3), which remains dissolved in the solution.
The balanced chemical equation for this reaction is:
AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
In this reaction, the silver cation (Ag+) from AgNO3 has swapped places with the sodium cation (Na+) from NaCl, resulting in the formation of two new compounds, AgCl and NaNO3.
Question:
Identify the substances that are oxidised and the substances that are reduced in the following reaction.
$4Na(s)+O𝐴2(g)2Na𝐴2O(s)$
Concept in a Minute:
Oxidation is the loss of electrons or an increase in oxidation state. Reduction is the gain of electrons or a decrease in oxidation state. In a redox reaction, one substance is oxidized and another is reduced.
Explanation:
The given reaction is:
$4Na(s)+O𝐴2(g)2Na𝐴2O(s)$
To identify the oxidized and reduced substances, we need to determine the oxidation states of each element before and after the reaction.
For Sodium (Na):
In its elemental form, $Na(s)$, the oxidation state of Na is 0.
In the compound $Na𝐴2O(s)$, Sodium is an alkali metal and its compounds typically have an oxidation state of +1.
For Oxygen (O):
In its elemental form, $O𝐴2(g)$, the oxidation state of O is 0.
In the compound $Na𝐴2O(s)$, Oxygen typically has an oxidation state of -2.
Now let’s analyze the changes in oxidation states:
Sodium changes from 0 to +1. This is an increase in oxidation state, which means Sodium has been oxidized.
Oxygen changes from 0 to -2. This is a decrease in oxidation state, which means Oxygen has been reduced.
Therefore, in the given reaction:
Sodium ($Na$) is oxidized.
Oxygen ($O_2$) is reduced.
Question:
Explain the following in term of gain or loss of oxygen with two examples.
Reduction
Concept in a Minute:
Redox reactions involve oxidation and reduction. Oxidation is defined as the gain of oxygen or loss of hydrogen or loss of electrons. Reduction is defined as the loss of oxygen or gain of hydrogen or gain of electrons.
Explanation:
Reduction is a chemical process where a substance loses oxygen atoms. This can also be understood as gaining hydrogen atoms or gaining electrons.
Two examples of reduction in terms of gain or loss of oxygen:
1. Reduction of Copper(II) Oxide:
When copper(II) oxide (CuO) is heated in a stream of hydrogen gas (H₂), it loses oxygen to form copper (Cu) and water (H₂O).
Reaction: CuO + H₂ → Cu + H₂O
In this reaction, copper(II) oxide (CuO) loses oxygen to become copper (Cu). Therefore, CuO is reduced.
2. Reduction of Iron(III) Oxide:
When iron(III) oxide (Fe₂O₃) is heated with carbon monoxide (CO) in a blast furnace, it loses oxygen to form iron (Fe) and carbon dioxide (CO₂).
Reaction: Fe₂O₃ + 3CO → 2Fe + 3CO₂
In this reaction, iron(III) oxide (Fe₂O₃) loses oxygen to become iron (Fe). Therefore, Fe₂O₃ is reduced.
Question:
Explain the term Rancidity.
Concept in a Minute:
Rancidity is a phenomenon that affects fats and oils. It is primarily caused by oxidation. This oxidation leads to the breakdown of fats and oils, producing unpleasant smells and tastes. Factors like exposure to air (oxygen), light, and heat accelerate this process.
Explanation:
Rancidity refers to the spoilage of fats and oils, making them unfit for consumption. This spoilage occurs mainly due to the oxidation of fats and oils when they are exposed to air, light, and heat. During oxidation, unsaturated fatty acids in the fats and oils react with oxygen, breaking down into smaller molecules. These breakdown products, such as aldehydes and ketones, are responsible for the characteristic unpleasant smell and taste associated with rancid food. For example, when cooking oil is left open for a long time, it becomes rancid. Similarly, fatty foods like potato chips, if not properly packed and sealed, can become rancid due to exposure to air. This process is a chemical change that alters the composition and sensory properties of the food.
Question:
What does one mean by endothermic reaction? Give example.
Concept in a Minute:
Endothermic reactions absorb heat energy from their surroundings. This leads to a decrease in the temperature of the surroundings. Key terms: heat absorption, surroundings, temperature decrease, reactants, products.
Explanation:
An endothermic reaction is a chemical reaction that absorbs energy from its surroundings, usually in the form of heat. This means that the enthalpy of the products is higher than the enthalpy of the reactants. As a result, the temperature of the surroundings decreases, making the reaction feel cold.
Example:
A common example of an endothermic reaction is the decomposition of calcium carbonate (limestone) when heated. The chemical equation for this reaction is:
CaCO₃(s) + Heat → CaO(s) + CO₂(g)
In this reaction, calcium carbonate absorbs heat energy from the surroundings to break down into calcium oxide and carbon dioxide gas. This process requires continuous heating to proceed. Another common example is the melting of ice, where ice absorbs heat from the surroundings to turn into liquid water.
Question:
Explain the following in term of gain or loss of oxygen with two examples.
Oxidation
Concept in a Minute:
The question is about understanding the definition of oxidation in terms of gain or loss of oxygen. This relates to the basic concept of oxidation-reduction (redox) reactions.
Explanation:
Oxidation is a chemical process where a substance loses electrons or gains oxygen. In the context of gaining oxygen, oxidation refers to the addition of oxygen atoms to a substance.
Examples:
1. Formation of Iron(III) oxide (rust): When iron (Fe) reacts with oxygen (O2) in the presence of moisture, it forms iron(III) oxide (Fe2O3). In this reaction, iron gains oxygen.
The balanced chemical equation is: 4Fe(s) + 3O2(g) → 2Fe2O3(s)
Here, iron is oxidized as it gains oxygen.
2. Burning of Magnesium: When magnesium (Mg) ribbon is heated in air, it reacts with oxygen (O2) to form magnesium oxide (MgO). In this reaction, magnesium gains oxygen.
The balanced chemical equation is: 2Mg(s) + O2(g) → 2MgO(s)
Here, magnesium is oxidized as it gains oxygen.
Question:
Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Concept in a Minute:
Chemical reactions, displacement reactions, reactivity series of metals, colour changes associated with metal ions.
Explanation:
Copper sulphate solution is blue in colour due to the presence of copper ions (Cu^2+). Iron is more reactive than copper. When an iron nail is dipped in the copper sulphate solution, iron displaces copper from the copper sulphate. This is a displacement reaction. The iron reacts with copper sulphate to form iron sulphate and copper. Iron sulphate solution is greenish in colour due to the presence of iron(II) ions (Fe^2+). The copper displaced from the copper sulphate is deposited on the iron nail as a reddish-brown coating.
Reaction:
Fe(s) + CuSO_4(aq) -> FeSO_4(aq) + Cu(s)
(Iron) + (Copper sulphate solution) -> (Iron sulphate solution) + (Copper)
Therefore, the blue colour of the copper sulphate solution changes to green because the copper ions are replaced by iron(II) ions, which have a green colour.
Question:
What does one mean by exothermic reaction? Give example.
Concept in a Minute:
Chemical reactions involve the breaking and forming of bonds. Energy changes are associated with these processes. Exothermic reactions are a specific type of chemical reaction characterized by their energy release.
Explanation:
An exothermic reaction is a chemical reaction that releases energy in the form of heat, light, or sound. This means that the products of the reaction have less energy stored in their chemical bonds than the reactants. The excess energy is released into the surroundings.
Example:
Combustion of natural gas (methane):
CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g) + Heat
In this reaction, methane (CH₄) reacts with oxygen (O₂) to produce carbon dioxide (CO₂) and water (H₂O). A significant amount of heat and light is released, making it an exothermic process. This is why natural gas is used as a fuel for heating and cooking.
Another common example is the burning of wood, which also releases heat and light energy.
Question:
A solution of a substance ‘X’ is used for white washing.
- Name the substance ‘X’ and write its formula.
- Write the reaction of the substance ‘X’ named in (i) above with water.
Concept in a Minute:
This question relates to common chemical reactions used in everyday life, specifically the process of white washing. It requires knowledge of common chemical compounds and their reactions with water. The key concept is the reaction of calcium oxide with water to form calcium hydroxide.
Explanation:
Part (i):
The substance ‘X’ used for white washing is calcium oxide. It is commonly known as quicklime.
The chemical formula for calcium oxide is CaO.
Part (ii):
When calcium oxide (quicklime) is mixed with water, it undergoes a chemical reaction to form calcium hydroxide. This process is called slaking of lime. Calcium hydroxide is also known as slaked lime.
The reaction between calcium oxide and water is:
CaO(s) + H₂O(l) → Ca(OH)₂(aq)
Calcium oxide reacts vigorously with water, producing heat and forming a milky white suspension of calcium hydroxide. This suspension is then applied to walls for white washing.
Question:
Why is respiration considered an exothermic reaction? Explain.
Concept in a Minute:
Exothermic reactions are chemical reactions that release energy, usually in the form of heat, light, or sound. Respiration is a biological process that breaks down glucose to release energy for cellular activities.
Explanation:
Respiration is considered an exothermic reaction because it releases energy. During cellular respiration, glucose is broken down in a series of steps, and the chemical energy stored in the bonds of glucose is converted into a usable form of energy for the cell, primarily adenosine triphosphate (ATP). This energy release manifests as heat, which is why our bodies feel warm and our body temperature is maintained. The overall process can be simplified by the equation:
C6H12O6 (glucose) + 6O2 (oxygen) → 6CO2 (carbon dioxide) + 6H2O (water) + Energy (ATP + Heat)
The “Energy” term in the equation signifies the release of energy, making respiration an exothermic process.
Question:
Write one equation for decomposition reactions where energy is supplied in the form of light.
Concept in a Minute:
Decomposition reactions are reactions in which a single compound breaks down into two or more simpler substances. Photochemical decomposition is a type of decomposition reaction where energy in the form of light is used to break the bonds of the reactant compound.
Explanation:
A decomposition reaction where energy is supplied in the form of light is called a photochemical decomposition reaction. A common example is the decomposition of silver chloride. Silver chloride (AgCl) is a white solid that decomposes into silver metal (Ag) and chlorine gas (Cl2) when exposed to sunlight.
The balanced chemical equation for this reaction is:
2AgCl(s) –light–> 2Ag(s) + Cl2(g)
In this equation:
– 2AgCl(s) represents solid silver chloride.
– –light–> indicates that light energy is used to drive the reaction.
– 2Ag(s) represents solid silver metal.
– Cl2(g) represents chlorine gas.
Question:
A shiny brown-coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black-colored compound formed.
Concept in a Minute:
This question relates to the chemical reactions of metals with oxygen, specifically oxidation, and the common properties of certain elements. Key concepts include: identifying common shiny brown elements, understanding the process of oxidation (reaction with oxygen), and recognizing the color changes associated with metal oxides.
Explanation:
The element ‘X’ is described as shiny brown. A common shiny brown element encountered in high school chemistry that reacts with oxygen when heated is Copper (Cu).
When Copper is heated in air, it reacts with oxygen (O2) to form Copper(II) oxide. This reaction is a form of oxidation.
The chemical equation for this reaction is:
2Cu(s) + O2(g) —-heat—-> 2CuO(s)
Copper(II) oxide (CuO) is a black-colored compound.
Therefore, the element ‘X’ is Copper, and the black-colored compound formed is Copper(II) oxide.
Question:
Write one equation for decomposition reactions where energy is supplied in the form of heat.
Concept in a Minute:
Decomposition reactions are reactions where a single compound breaks down into two or more simpler substances. When energy in the form of heat is supplied to cause this breakdown, it is specifically called thermal decomposition.
Explanation:
A decomposition reaction where energy is supplied in the form of heat involves breaking down a compound using heat. One common example is the decomposition of calcium carbonate (limestone) when heated. Calcium carbonate breaks down into calcium oxide (quicklime) and carbon dioxide gas. The chemical equation for this reaction is:
CaCO3(s) heat–> CaO(s) + CO2(g)
In this equation, CaCO3 represents calcium carbonate, CaO represents calcium oxide, and CO2 represents carbon dioxide. The arrow with “heat” above it indicates that heat is supplied to drive the reaction.
Question:
Explain the terms Corrosion
Concept in a Minute:
Corrosion is a natural process that degrades materials, especially metals, over time due to chemical or electrochemical reactions with their environment.
Explanation:
Corrosion is the gradual destruction of materials, usually metals, by chemical or electrochemical reaction with their environment. It is a surface phenomenon. The most common example is the rusting of iron, where iron reacts with oxygen and moisture in the air to form hydrated iron(III) oxide, which is the reddish-brown rust. Other examples include the tarnishing of silver (formation of silver sulfide) and the formation of a green patina on copper (formation of copper carbonates and sulfates). The process generally involves oxidation of the metal. Factors like the presence of electrolytes (like salts) and acids can accelerate corrosion.
Question:
Oil and fat containing food items are flushed with nitrogen. Why?
Concept in a Minute:
Oxidation, Rancidity, Antioxidants, Inert gas
Explanation:
Oil and fat containing food items are flushed with nitrogen because nitrogen is an inert gas. Fats and oils are prone to oxidation, a process that leads to rancidity. Oxidation occurs when fats and oils react with oxygen in the air. This reaction breaks down the fat molecules, producing compounds that have an unpleasant smell and taste, rendering the food rancid and unpalatable. By flushing the food packaging with nitrogen, the oxygen is displaced. Nitrogen does not react with the fats and oils, thus preventing or significantly slowing down the oxidation process. This helps to preserve the freshness and extend the shelf life of the food items. In essence, nitrogen acts as a protective atmosphere, keeping oxygen away from the food.
Question:
Why should a magnesium ribbon be cleaned before it is burnt in air?
Concept in a Minute:
Reactivity of metals, formation of oxides, protective layers on metals.
Explanation:
Magnesium is a highly reactive metal. When exposed to air for a period of time, its surface reacts with oxygen and moisture present in the air. This reaction forms a layer of magnesium oxide (MgO) and magnesium hydroxide (Mg(OH)2) on the surface of the magnesium ribbon. This layer is dull and white. If this layer is not removed before burning the magnesium ribbon, it acts as a barrier between the magnesium metal and the oxygen in the air. This protective layer prevents the magnesium from burning completely and vigorously. Cleaning the magnesium ribbon with sandpaper removes this oxide and hydroxide layer, exposing the fresh, reactive magnesium metal to air, allowing it to burn brightly and completely.
Question:
Write one equation for decomposition reactions where energy is supplied in the form of electricity.
Concept in a Minute:
Decomposition reactions are reactions where a single compound breaks down into two or more simpler substances. Some decomposition reactions require energy to occur. When electricity is used to drive a decomposition reaction, it is called electrolysis.
Explanation:
A decomposition reaction where energy is supplied in the form of electricity is known as electrolytic decomposition. The most common example is the electrolysis of water. Water (H₂O) decomposes into hydrogen gas (H₂) and oxygen gas (O₂) when an electric current is passed through it.
The balanced chemical equation for this reaction is:
2H₂O(l) –electrolysis–> 2H₂(g) + O₂(g)
Question:
Why do we apply paint on iron articles?
Concept in a Minute:
The question relates to the concept of rusting, which is a chemical process that affects iron. Understanding the conditions required for rusting and the purpose of preventing it is key.
Explanation:
We apply paint on iron articles to prevent them from rusting. Iron reacts with oxygen and moisture in the air to form iron oxide, commonly known as rust. Rusting weakens the iron, makes it brittle, and can eventually lead to its destruction. Paint forms a protective layer on the surface of the iron. This layer acts as a barrier, preventing oxygen and moisture from coming into contact with the iron and thus preventing the process of rusting.
Question:
nan
The question provided is “nan”. This is not a valid question for a high school physics problem. It appears to be either a typo, an incomplete question, or some kind of placeholder.
Cannot be answered as the question is not a valid physics problem.
The input “nan” is not a question that can be solved using physics principles. It does not present any physical quantities, relationships, or scenarios that require a scientific or mathematical solution. Therefore, it is impossible to provide a conceptual summary or a detailed explanation.
Concept in a Minute:
Cannot be answered as the question is not a valid physics problem.
Explanation:
The input “nan” is not a question that can be solved using physics principles. It does not present any physical quantities, relationships, or scenarios that require a scientific or mathematical solution. Therefore, it is impossible to provide a conceptual summary or a detailed explanation.
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