Very Short Answer Questions - 1 Mark

Que 1. Why is combustion of Liquefied Petroleum Gas (LPG) a chemical change?

Ans. Combustion of Liquefied Petroleum Gas (LPG) is a chemical change because after its combustion, the substance formed changes chemically and cannot be turned back into LPG.

Que 2. What is wrong with the following equation?

                      Mg + O →MgO

Identify the mistake and balance the equation.

Ans. In this equation, oxygen should be in molecular form (O₂) as oxygen exists as bimolecular gas O₂.

                     2Mg + O₂→ 2MgO

Que 3. Potassium chlorate (KCIO₃) on heating forms potassium chloride and oxygen. Write a balanced equation for this reaction.

Ans.        2KCIO₃ (s) → 2KCI(s) +30₂(g)

Que 4. On heating blue colored powder of copper(II) nitrate in a boiling tube, copper oxide (black),oxygen gas and a brown gas 'X' is formed. Identify the brown gas 'X'.

Ans.       

X' is nitrogen dioxide gas.

Que 5. Convey the following information in the form of a balanced chemical equation:
“An aqueous solution of ferrous sulphate reacts with an aqueous solution of sodium hydroxide to form a precipitate of ferrous hydroxide and sodium sulphate remains in solution.”

Ans.  FeSO₄(aq) + 2NaOH(aq) → Fe(OH)₂(s) + Na₂SO₄(aq)

Que 6. Balance the following chemical equation: 

             

Ans.   

Que 7. Give one example of a combination reaction which is also exothermic.

Ans. When quicklime or calcium oxide (CaO) reacts with water, slaked lime [Ca(OH)₂] is formed. During this reaction, a large amount of heat is released. So, this reaction is an exothermic Reaction.

        

Que 8. Why will the colour of heated copper powder become black when air is passed over it? 

Ans. When copper powder is heated in the presence of air, black copper oxide is formed.

        

Que 9. What is the difference between the following two types of reactions? 

      

Ans. The first reaction is a double displacement reaction whereas second reaction is a single displacement reaction.

Que 10. Why is hydrogen peroxide kept in coloured bottles?

Ans. This is done in order to cut off light because hydrogen peroxide decomposes into water and oxygen in the presence of light.

Que 11. Consider the following reactions:

(i) Fe + CuSO₄ → FeSO₄ + Cu

(ii) Cu + FeSO₄ → CuSO₄ + Fe

Which of these two reactions will take place and why?

Ans. Reaction (i) will take place. This is because Fe (iron) is more reactive than Cu (copper) and so it can displace Cu from its compound (CuSO₄). On the other hand, copper (Cu) cannot displace iron (Fe), so reaction (ii) will not take place.

Que 12. Give one example of a reaction which is a double displacement reaction as well as a Precipitation reaction. 

Ans.   

Que 13. Why is photosynthesis considered an endothermic reaction?

Ans. Photosynthesis is an endothermic reaction because energy, in the form of sunlight is absorbed during the process of photosynthesis by green plants.

Que 14. What type of reaction is represented by the digestion of food in our body?

Ans. Decomposition reaction.

Que 15. How will you test for the gas which is liberated when hydrochloric acid reacts with an active metal?

Ans. When an active metal like Zn reacts with HCl , the gas produced burns with a pop sound which indicates that it is hydrogen gas.

                    Zn(s) + 2HCl(aq) → ZnCl₂ (s) + H₂(g)  

Que 16. Can a double displacement reaction take place when the products are highly soluble or highly ionised?

Ans. No, double displacement reaction takes place when there is a formation of a slightly soluble salt.

Que 17. What changes in the colour of iron nails and copper sulphate solution do you observe after keeping the iron nails dipped in copper sulphate solution for about 30 minutes?

Ans. Iron nails become brownish in colour and the blue colour of copper sulphate solution fades. This is because iron displaces copper from copper sulphate solution and forms ferrous sulphate which is colourless.

Que 18. Name the oxidising and reducing agent in the following reaction:

                   2H₂S + SO₂ → 2H₂O + 3S ↓ 

Ans. H₂S is the reducing agent while SO₂ is the oxidising agent.

Que 19. A dilute ferrous sulphate solution was gradually added to the beaker containing acidified potassium permanganate solution. The light purple colour of the solution fades and finally disappears. Write the correct explanation for this observation.

Ans. Potassium permanganate solution (KMnO₄) is an oxidising agent. It oxidises ferrous sulphate (FeSO₄) to ferric sulphate [Fe₂(SO₄)₃].

Que 20. Define rancidity.

Ans. The oxidation of oils or fats in food resulting in a bad taste and smell is called rancidity.

Que 21. Name one synthetic antioxidant.

Ans. Butylated hydroxyanisole (BHA).