Some More Written Practice Questions

10. You Must Have Tasted Or Smelt The Fat Containing Food Material Left For A Longtime. Such Foods Taste And Smell Bad. What Is The Reason For This? Name To The Phenomenon Responsible For It. List Two Majors For Its Preventions. [CBSE 2016]

Ans) Food material left for a long time is oxidised by atmospheric oxygen. This changes the smell and taste of food.

Majors for prevention:

(i) Keep the food in air tight container.

(ii) Flush the food packets with nitrogen gas before sealing it

11. Give the characteristic tests for the following gases. [NCERT Exemplar]

(a) 𝐶𝑂2 (b) H2

Ans) as explained in the lecture, 

(a) Co2 – Lime water turns milky

(b) H2- Burns with a pop sound

12. During the reaction of some metals with dilute hydrochloric acid, following observations were made. [NCERT EXEMPLAR]
(a) Silver metal does not show any change.
(b) The temperature of the reaction mixture rises when aluminium (Al) is added.
(c) The reaction of sodium metal is found to be highly explosive.
(d) Some bubbles of gas are seen when lead (Pb) is reacted with the acid. Explain these observations giving suitable reasons.

Ans. (a) It is because silver is less reactive than hydrogen. It cannot displace hydrogen from dilute acid.

(b) It is because the reaction is exothermic.

(c) It is because sodium is highly reactive and forms hydrogen gas in the presence of moisture (𝐻2𝑂) which catches fire as the reaction is highly exothermic and 𝐻2 is highly inflammable.

(d) It is due to formation of hydrogen gas. The reaction becomes slow after some time as 𝑃𝑏𝐶𝑙2(𝑠) covers Pb metal.

13. Write Chemical Equation For The Reaction Taking Place When: 
(I) Mangnesium React with Dil. HNO3.
(II) Sodium React With Water.
(III) Zinc React With Hydrochloric Acid. [CBSE 2016]

(i) Mg + 2HNO3(dil) → Mg(NO3)2 +H2

(ii) 2Na + 2H2O → 2NaOH + H2

(iii) Zn + 2HCL→ ZnCl2 + H2

14. Decomposition Reaction Require Energy Either In The Form Of Heat Or Light Or Electricity For Breaking Down Down The Reactants. Write One Equation Each For Decomposition Reaction Where Energy Is Supplied In The Form Of Heat, Light And Electicity. [CBSE 2018]

Ans : Energy supplied in the form of heat:

Ca(OH)2(aq) → CaO(s) + H2O(l)

Energy supplied in the form of light:

2AgCl(s) → 2Ag(s) + Cl2

Energy supplied in the form of electricity:

2H2O→2H2+O2

15. A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of the chemical reaction?

Answer.

KCl(aq) + AgNO3 (aq) ——–> AgCl (s) + KNO3

It is a double displacement reaction. It is also a precipitation reaction as AgCl is a white precipitate.