Science – Chemical Reaction and Equations
Very Short Answer Type Questions
Q.1) Write the balanced equation for the following chemical reactions:
(i) Hydrogen + Chlorine → Hydrogen chloride
Ans) H₂(g) + Cl₂ (g) → 2HCl(g)
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
Ans) 3BaCl₂(s)+ Al₂(SO4)3(s) → 3BaSO4(s) + 2AlCl3(s)
(iii) Sodium + Water → Sodium hydroxide + Hydrogen
Ans) 2Na(s) + 2H₂O(l) 2NaOH(aq) + H₂(g)
Q.2) Why does the colour of copper sulphate solution change when an iron nail is dipped in it? Write a reaction.
Ans) When an iron nail is dipped in the copper sulphate solution then iron displaces copper from the copper sulphate because iron is more reactive than copper. Therefore, the colour of the copper sulphate solution changes.
Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
Q.3) Identify the substances that are oxidised and the substances that are reduced in the following reactions:
4Na(s) + O2(g) → 2Na2O(s)
Ans) Sodium (Na) is oxidised as it gains oxygen and oxygen gets reduced.
CuO(s) + H₂(g) → Cu(s) + H₂O(l)
Ans) Copper oxide (CuO) is reduced to copper (Cu) while hydrogen (H₂) gets oxidised to water (H₂O).
Q.4) 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 → 2AICI+3Cu
(d) Barium chloride + Potassium sulphate→ Barium sulphate + Potassium chloride
Ans) BaCl₂ + K₂SO₄ → BaSO₄ + 2KCI
Q.5) Why is respiration considered an exothermic reaction?
Ans) Respiration is considered an exothermic reaction because in respiration, oxidation of glucose takes place which produces large amount of energy.
C6H12O6(aq) + 602(g) → 6CO2(g) + 6H2O(l) + Energy
Q.6) Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Ans)
CaCO₃(s) → Heat → CaO(s)+CO₂(g)
2AgCl(s) → Sunlight → 2Ag(s) + Cl₂(g)
2H₂O(l) → Electricity → 2H₂(g) + O₂(g)
Q.7) In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
Ans) 2AgNO₃(aq) + Cu(s) → Cu(NO₃)₂(aq) + 2Ag(s)
Silver nitrate + Copper → Copper nitrate + Silver
Q.8) A shiny brown-coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black-coloured compound formed.
Ans)’X’ is copper (Cu) and the black-coloured compound formed is copper oxide (CuO). The equation of the reaction involved on heating copper is-
2Cu + 02 → Heat → 2CuO
Shiny brown + colour Oxygen → Black in colour
Q.9) Why do we apply paint on iron articles?
Ans) Iron corrodes or gets rusted on coming in contact with moisture and oxygen present in air. Iron articles are painted because it prevents them from rusting. When painted, the contact of iron article with moisture and oxygen of air is cut off. Hence, it prevents rusting.
Q.10) Oil and fat containing items are flushed with nitrogen. Why?
Ans) Oil and fat containing food items become rancid on coming in contact with oxygen due to oxidation. They are flushed with nitrogen because nitrogen is a less reactive gas and it acts as an antioxidant. It prevents the food items from getting oxidised or becoming rancid.
Q.11) Define rancidity.
Ans) 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.12) Write the following word equation to balanced chemical equation:
Zinc Sulphuric acid → Zinc sulphate + Hydrogen
Ans) Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)
Q.13) For white washing which substance solution is used? Write the reaction.
Ans) A solution of slaked lime produced by following reaction is used for white washing.
CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat
Quick lime → Slaked lime
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