In-Text Questions and Solutions

11) What happens when dilute hydrochloric acid is added to iron fillings? Tick 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.

Ans) (a) Hydrogen gas and iron chloride are produced.

Fe(s) + 2HCl_(aq) → FeCl_2(aq) + H_2(g)

The hydrogen forms a gas because it is a diatomic atom, it will exist naturally in its gaseous state.

12) What is a balanced chemical equation? Why should chemical equations be balanced?

Ans) The chemical equation in which the number of atoms of different elements is same on both sides of the chemical equation is called balanced chemical equation.

The chemical equation needs to be balanced so that it follows the law of conservation of mass. The Law of conservation of mass states that matter cannot be created out of nothing nor can it be destroyed. This means that during a chemical reaction, the mass of the products should be equal to the mass of the reactants. Therefore, it means that the total number of atoms of each element should be equal on both sides of a chemical equation. Hence, it is for this reason that chemical equations should be balanced.

13) Translate the following statements into chemical equations and then balance them.

(a) Hydrogen gas combines with nitrogen to form ammonia

(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.

(c) Barium chloride reacts with aluminum sulphate to give aluminum chloride and a precipitate of barium sulphate

(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas

Ans) (a) 3H₂ +N₂ → 2NH₃

(b) 2H₂S + 3O₂ → 2H₂O + 2SO₂

(c) 3BaCl₂ + Al₂ (SO₄)₃ → 2AlCl₃ + 3BaSO₄

(d) 2K + 2H₂O → 2KOH + H₂

14) Balance the following chemical equations.

Ans) Step 1: Write down the skeletal equation

Step 2: Calculate the number of atoms each element has on each side of the equation

Make a little table and list the numbers of each atom for the left hand side and for the right hand side

Balance the different atoms on both side of equation by multiplying the chemical species on the side which doesn’t have enough atoms of that type by the number required to bring it up to the same as the other side.

(a) HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + H₂O

Ans) 2HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + 2H₂O

(b) NaOH + H₂SO₄ → Na₂SO₄ + H₂O

Ans) 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O

(c) NaCl + AgNO₃ → AgCl + NaNO₃

Ans) NaCl + AgNO₃ → AgCl + NaNO₃

(d) BaCl₂ + H₂SO₄ → BaSO₄ + HCl

Ans) BaCl₂ + H₂SO₄ → BaSO₄ + 2HCl

15) Write the balanced chemical equations for the following reactions.

(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water

Ans) Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

(b) Zinc + Silver nitrate → Zinc nitrate + Silver

Ans) Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag

(c) Aluminium + Copper chloride → Aluminium chloride + Copper

Ans) 2Al + 3CuCl₂ → 2AlCl₃ + 3Cu

(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride

Ans) BaCl₂ + K2SO₄ → BaSO₄ + 2KCl

16) Write the balanced chemical equation for the following and identify the type of reaction in each case.

(a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)

Ans) 2KBr (aq) + BaI_2(aq) → 2KI_(aq) + BaBr_2(s)

It is a double displacement reaction as there is an exchange of ions between the reactants {‘Br’ (Bromine and ‘I ‘(iodine)}

(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide (g)

Ans) ZnCO_3(s) → ZnO_(s) + CO₂

The above given chemical reaction is a decomposition reaction because a single substance (ZnCO₃) decomposes to two simpler substances (ZnO and CO₂ ).

(c) Hydrogen (g) + Chlorine (g) → Hydrogen chloride (g)

Ans) H_2(g) + Cl_2(g) → 2HCl_(g)

The above given chemical reaction is a combination reaction because two or more substances (Hydrogen and chlorine) combine to form a single substance (hydrogen chloride)

(d) Magnesium(s) + Hydrochloric acid (aq) → Magnesium chloride (aq) + Hydrogen (g)

Ans) Mg_(s) + 2HCL_(ag) → MgCl_2(s) + H_2(g)

The above given chemical reaction is a displacement reaction because magnesium being more reactive than hydrogen displaces hydrogen from hydrogen chloride to form a new product namely magnesium chloride.

17) What does one mean by exothermic and endothermic reaction? Give examples.

Ans) An exothermic process releases heat and causes the temperature of the immediate surroundings to rise. E.g., rusting iron, chemical reaction between quicklime and water to form slaked lime is characterized by release of heat energy.

An endothermic process absorbs heat and cools the surroundings. E.g., producing sugar by photosynthesis, formation of nitric oxide from nitrogen and oxygen.

18) Why is respiration considered an exothermic reaction? Explain

Ans) An exothermic reaction is one in which heat or energy is released. Respiration is considered to be an exothermic reaction because energy is released as heat and ATP. Oxygen and glucose are both reactants of cellular respiration. Oxygen enters the body when an organism breathes. Glucose is got by the breaking down of food (carbohydrates) that we eat into simpler forms (glucose) during the process of digestion. The products of cellular respiration are carbon dioxide and water which are waste products, the production of A.T.P, a high energy molecule, and heat is also released.

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 2805 kJ