" /> -->

#### Basic Concepts of Chemistry and Chemical Calculations Important Questions

11th Standard

Reg.No. :
•
•
•
•
•
•

Chemistry

Time : 02:00:00 Hrs
Total Marks : 50
10 x 1 = 10
1. An element X has the following isotopic Composition 200X = 90%, 199X = 8% and 202X = 2% The Weighted average atomic mass of the element X is closet to

(a)

201 u

(b)

202 u

(c)

199 u

(d)

200 u

2. When 6.3g of sodium bicarbonate is added to 30g of the acetic acid solution, the residual solution is found to weigh 33g. The number of moles of carbon dioxide released in the reaction is

(a)

3

(b)

0.75

(c)

0.075

(d)

0.3

3. The oxidation number of oxygen in O2 is _______________

(a)

0

(b)

+1

(c)

+2

(d)

-2

4. Which of the following is/are true with respect to carbon -12

(a)

relative atomic mass is 12 u

(b)

the oxidation number of carbon is +4 in all its compounds.

(c)

1 mole ofcarbon-12 contain 6.022 x 1022 carbon atoms.

(d)

All of these

5. The change in the oxidation number of S in H2S and SO2,in the following industrial reaction:
2H2S(g) + SO2(g) $\longrightarrow$ 3S(s) + H2O(g)

(a)

-2 to 0, +4 to 0

(b)

-2 to 0, +4 to -1

(c)

-2 to -1, +4 to 0

(d)

-2 to -1, +4 to -2

6. Unit of Avogadro's number is

(a)

mol

(b)

g

(c)

mol -1

(d)

No unit

7. Equal volume of N2 and H2 react to form ammonia under suitable condition then the limiting reagent is

(a)

H2

(b)

N2

(c)

NH3

(d)

No Reactant is a limiting regent

8. 20.0g of a magnesium carbonate sample decomposes on heating to give carbon dioxide and 8.0g magnesium oxide. What will be the percentage of purity of magnesium carbonate in the sample?

(a)

60

(b)

84

(c)

75

(d)

96

9. How many moles of Hydrogen atoms are present in 1 mole of C2H6?

(a)

18 moles

(b)

6 moles

(c)

3 moles

(d)

1 mole

10. Match the List-I and List-II using the correct code given below the list.

List-I (Empirical Formula)   List-II (Molecular formula)
A Benzene - CH 1 H2O2
B Fructose - CH2O 2 C2H2
C Acetylene - CH 3 C6H6
D Hydrogen peroxide-OH 4 C6H12O6
(a)
A B C D
4 2 3 1
(b)
A B C D
3 4 2 1
(c)
A B C D
4 1 2 3
(d)
A B C D
1 4 3 2
11. 5 x 2 = 10
12. What do you understand by the term oxidation number?

13. Hydrogen peroxide is an oxidising agent. It oxidises ferrous ion to ferric ion and reduced itself to water. Write a balanced equation.

14. Balance the following equations by ion electron method ${ Na }_{ 2 }{ S }_{ 2 }{ O }_{ 3 }+{ I }_{ 2 }\longrightarrow { Na }_{ 2 }{ S }_{ 4 }{ O }_{ 6 }+NaI$

15. Give examples for the following redox reaction "Metal displacement reaction".

16. If 10 volumes of H2 gas react with 5 volumes of O2 gas, how many volumes of water vapour would be produced?

17. 5 x 3 = 15
18. What is the empirical formula of the following?
i) Fructose (C6 H12O6) Found in honey
ii) Caffeine  (C8H10N4 O2) a substance found in tea and Coffee

19. Which one of the two, ClO2- or ClO4- shows disproportionation reaction and why?

20. How many moles of barium sulphate is precipitated when 1 mole of aluminium sulphate reacts completely with barium chloride?

21. Identify the type of redox reaction taking place in the following
$3{ M }^{ 0 }g_{ (s) }+{ N }_{ 2(g) }^{ 0 }\longrightarrow \overset { +2 }{ { Mg }_{ 3 } } \overset { -3 }{ N_{ 2(s) } }$

22. How much volume of chlorine is required to form 11.2 L of HCI at 273 K and 1 atm pressure?

23. 3 x 5 = 15
24. A Compound on analysis gave Na = 14.31% S = 9.97% H= 6.22% and 0= 69.5% calculate the molecular formula of the compound if all the hydrogen in the compound is present in combination with oxygen as a water of crystallization. (molecular mass of the compound is 322).

25. Calculate the empirical and molecular formula of a compound containing 32% carbon, 4% hydrogen and rest oxygen. Its vapour density is 75.

26. Calculate the percentage composition of the elements present in magnesium carbonate. How many kilogram of CO2 can be obtained by heating 1 kg of 90 % pure magnesium carbonate.