Frequently asked five mark questions Basic Concepts of Chemistry and Chemical Calculations

11th Standard

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Chemistry

Answer any 20 of the following questions
Time : 01:30:00 Hrs
Total Marks : 100

Part - A

23 x 5 = 115
1. Balance the following equation by ion-electron method In acidic medium.
$Mn{O}_4^-+I^-\rightarrow MnO_2+I_2$

2. Balance the following equation by ion-electron method In acidic medium.
$Mn{O}_4^-+Fe^{2+}\rightarrow Mn^{2+}+Fe^{3+}$

3. Balance the following equation by ion-electron method In acidic medium.
$Cr{(OH)}_4^-+H_2O_2\rightarrow Cr{O}_4^{2-}$

4. (a) Define equivalent mass of an oxidising agent.
(b) How would you calculate the equivalent mass of potassium permanganate?

5. (a) Define equivalent mass of an reducing agent.
(b) How would you determine the equivalent mass of Ferrous sulphate?

6. A compound on analysis gave the following percentage composition: C=24.47%, H = 4.07 %, CI = 71.65%. Find out its empirical formula.

7. A laboratory analysis of an organic compound gives the following mass percentage composition: C = 60%, H = 4.48% and remaining oxygen.

8. An insecticide has the following percentage composition by mass: 47.5% C, 2.54% H, and 50.0% Cl. Determine its empirical formula and molecular formulae. Molar mass of the substance is 354.5g mol-1

9. Calculate the percentage composition of the elements present in magnesium carbonate. How many Kg of CO2 can be obtained from 100 Kg of is 90% pure magnesium carbonate.

10. Urea is prepared by the reaction between ammonia and carbon dioxide.
2NH3(g) + CO2(g) $\rightarrow$ (NH4)2CO(ag) + H2O(I)
In one process, 637.2 g of NH3 are allowed to react with 1142 g of CO2
(a) Which of the two reactants is the limiting reagent?
(b) Calculate the mass of (NH4)2CO formed.
(c) How much of the excess reagent in grams is left at the end of the reaction?

11. (a) Define oxidation number.
(b) What are the rules used to assign oxidation number?

12. Balance the following equation by oxidation number method.
C6H6 + O2$\rightarrow$CO2 + H2O

13. Balance the following equation by oxidation number method.
KMnO4 + HCI $\rightarrow$ KCl + MnCl2 + H2O + Cl2

14. Explain the steps involved in ion-electron method for balancing redox reaction.

15. Define the following (a) equivalent mass of an acid (b) equivalent mass of a base (c) equivalent mass of an oxidising agent (d) equivalent mass of a reducing agent.

16. Balance the following equation by oxidation number method.
KMnO4 + FeSO4 + H2SO4 $\rightarrow$K2SO4 + MnSO4 + Fe2(SO4)3 + H2O

17. Balancing of the molecular equation in alkaline medium.
MnO2 + O2 + KOH$\rightarrow$K2MnO4 + H2O

18. Write balanced equation for the oxidation of Ferrous ions to Ferric ions by permanganate ions in acid solution. The permanganate ion forms Mn2+ ions under these conditions.

19. A flask A contains 0.5 mole of oxygen gas. Another flask B contains 0.4 mole of ozone gas. Which of the two flasks contains greater number of oxygen atoms.

20. (a) Formulate possible compounds of 'CI' in its oxidation state is: 0, -1, +1, +3, +5, +7
(b) H2O2 act as an oxidising agent as well as reducing agent where as O3 act as only oxidizing agent. Prove it.

21. The Mn3+ ion is unstable in solution and undergoes disproportionation to give Mn2+, MnO2 and H+ ion. Write a balanced ionic equation for the reaction.

22. Chlorine is used to purify drinking water. Excess of chlorine is harmful. The excess chlorine is removed by treating with sulphur dioxide. Present a balanced equation for the reaction for this redox change taking place in water.

23. ${ 2NH }_{ 3 }\left( g \right) +{ CO }_{ 2 }\left( g \right) \rightarrow \underset{Urea}{H_2N}-\overset { \underset { || }{ O } }{ C } -{ NH }_{ 2 }\left( aq \right) +{ H }_{ 2 }O(I)$
(i) If the entire quantity of all the reactants is not consumed in the reaction which is the limiting reagent?
(ii) Calculate the quantity of urea formed and unreacted quantity of the excess reagent. The balanced equation is
$\overset { { 2NH }_{ 3 }+{ CO }_{ 2 } }{ \underset { { H }_{ 2 }NCON{ H }_{ 2 }+{ H }_{ 2 }O }{ \downarrow } }$