Science – Chemical Reaction and Equations
Long Answer Type Questions
Q.1) Explain the following terms on gain or loss of oxygen with two examples each: (a) Oxidation, (b) Reduction.
Ans) (a) Oxidation – A chemical reaction in which gain of oxygen or loss of hydrogen takes place is called oxidation reaction and the process is called oxidation. When a substance gains oxygen during a reaction, it is said to be oxidised. Example –
(i). 2Cu(s) + O2(g) → Heat → 2CuO (s) {Here, copper is oxidised to copper oxide.}
(ii). 2Mg(s) + O2(g) → Heat → 2MgO(s) {Here, magnesium is oxidised to magnesium oxide.}
(b) Reduction – A chemical reaction in which loss of oxygen or gain of hydrogen takes place is called reduction reaction and this process is called reduction. A substance is reduced when it either gains hydrogen or loses oxygen. Example –
(i). CuO + H₂ → Cu + H₂O {Here, copper oxide is reduced to copper.}
(ii). ZnO + C → Zn + CO {Here, Zinc oxide is reduced to zinc.}
Q.2) Explain the following terms with one example each: (a) Corrosion, (b) Rancidity.
Ans) (a) Corrosion – Corrosion is defined as a process where materials, usually metals, deteriorate as a result of chemical reaction with air, moisture, chemicals etc. Corrosion causes damage to car bodies, bridges, ships and all objects made of metals, specially those of iron. Example – Iron, in the presence of moisture, reacts with oxygen to form hydrated iron oxide, which is called rust.
4Fe + 3O₂ + nH₂O → 2Fe₂O₃.nH₂O
(b) Rancidity – The process of oxidation of fats and oils due to which there is change in taste and smell is known as rancidity. Hence, substances which prevent oxidation (antioxidants) are added to foods containing fats and oil. Keeping food in air tight containers helps to slow down oxidation. Change of taste and smell of butter on keeping it for a long time is an example of rancidity.
Q.3) Write the types of following chemical reactions.
(i). 2FeSO₄(s) → Heat → Fe₂O₃(s) + SO₂(s) + SO₃(g)
Ans) Thermal decomposition reaction.
(ii). CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat
Ans) Exothermic reaction.
(iii). Fe(s)+ CuSO4(aq) → FeSO4(aq) + Cu(s)
Ans) Displacement reaction.
(iv). Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq)
Ans)Double displacement reaction.
Q.4) (i) When sodium sulphate reacts with barium chloride. What is the name of this type of reaction and write its chemical reaction.
Ans) Na₂SO₄ (aq) + BaCl₂ (aq) → BaSO₄ (s) + 2NaCl (aq) {It is double displacement reaction.}
(ii) Which type of product produce, when calcium oxide reacts with water? Write its chemical reaction.
Ans) When calcium oxide reacts with water, calcium hydroxide [Ca(OH)2] is produced and heat is released.
CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat.
Q.5) Transform the following statements into chemical equation.
(i). Hydrogen gas combines with nitrogen to form ammonia.
Ans) N₂ + 3H₂ → 2NH₃
(ii). Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
Ans) 2K+ 2H₂O → 2KOH + H₂
(iii). Barium chloride reacts with sulphuric acid to give barium sulphate and hydrochloric acid.
Ans) BaCl₂ + H₂SO₄ → BaSO₄ + 2HCI
(iv). Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
Ans) 2H₂S + 3O₂ → 2H₂O + 2SO
Q.6) Balance the following chemical equations:
(i)HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + H₂O
Ans) 2HNO₃(aq) + Ca(OH)₂(aq) → Ca(NO₃)₂(aq) + 2H₂O(l)
(ii). NaCl + AgNO₃ → AgCl + NaNO₃
Ans) NaCl(aq) + AgNO3(aq) → AgCl(s) + NaNO3(s)
(iii). NaOH + H₂SO₄ → Na₂SO₄ + H₂O
Ans) 2Na(OH) (aq) + H₂SO₄(aq) → Na₂SO₄(aq) + 2H₂O(l)
(iv). BaCl₂ + H₂SO₄ → BaSO₄ + HCI
Ans) BaCl₂(aq) + H₂SO₄(aq) → BaSO₄(s) + 2HCl(aq)