Topic: UNIT 1: Basic Concepts of Chemistry and Chemical Calculations



Topic: UNIT 1: Basic Concepts of Chemistry and Chemical Calculations
Q.1
40 ml of methane is completely burnt using 80 ml of oxygen at room temperature The volume of gas left after cooling to room temperature is
A. 40 ml CO2 gas
B.

40 ml CO2 gas and 80 ml H2O gas

C.

60 ml CO2 gas and 60 ml H2O gas

D.

120 ml CO2 gas

Answer : Option A
Explaination / Solution:

CH4(g) + 2O2(g) → CO2 (g)+ 2 H2O (l)



Since the product was cooled to room temperature, water exists mostly as liquid. Hence, option (a) is correct


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Q.2
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 closest to
A. 201 u  
B. 202 u
C. 199 u
D. 200 u
Answer : Option D
Explaination / Solution:




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Q.3

Assertion Two mole of glucose contains 12.044 × 1023 molecules of glucose

Reason : Total number of entities present in one mole of any substance is equal to 6.02 × 1022


A. both assertion and reason are true and the reason is the correct explanation of assertion
B. both assertion and reason are true but reason is not the correct explanation of assertion
C. assertion is true but reason is false
D. both assertion and reason are false
Answer : Option C
Explaination / Solution:

Correct reason: Total number of entities present in one mole of any substance is equal to 6.022 ×1023.

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Q.4
Carbon forms two oxides, namely carbon monoxide and carbon dioxide. The equivalent mass of which element remains constant?
A. Carbon
B. Oxygen
C. both carbon and oxygen
D. neither carbon  nor oxygen
Answer : Option B
Explaination / Solution:




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Q.5
The equivalent mass of a trivalent metal element is 9 g eq-1 the molar mass of its anhydrous oxide is
A. 102 g
B. 27 g
C. 270 g
D. 78 g
Answer : Option A
Explaination / Solution:

 Let the trivalent metal be M3+

 Equivalent mass = mass of the metal / valance factor

 9 g eq-1 = mass of the metal / 3 eq

 Mass of the metal = 27 g

 Oxide formed M2O3 ;

 Mass of the oxide = (2 x 27) + (3 x 16)

 = 102 g


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Q.6
The number of water molecules in a drop of water weighing 0.018 g is
A. 6.022 × 1026
B. 6.022 × 1023
C. 6.022 × 1020
D. 9.9 × 1022
Answer : Option C
Explaination / Solution:

Weight of the water drop  =0.018 g

No. of moles of water in the drop=Mass of water / molar mass

=  0.018 / 18 = 10-3 mole

No of water molecules present in 1 mole of water= 6.022 x 1023

No. water molecules in one drop of water (10-3 mole)= 6.022 x 1023x 10-3

=6.022 x 1020


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Q.7
1 g of an impure sample of magnesium carbonate (containing no thermally decomposable impurities) on complete thermal decomposition gave 0.44 g of carbon dioxide gas. The percentage of impurity in the sample is
A. 0 %
B. 4.4 %
C. 16 %
D. 8.4 %
Answer : Option C
Explaination / Solution:
No Explaination.


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Q.8
When 6.3 g of sodium bicarbonate is added to 30 g of acetic acid solution, the residual solution is found to weigh 33 g. The number of moles of carbon dioxide released in the reaction is
A. 3
B. 0.75
C. 0.075
D. 0.3
Answer : Option C
Explaination / Solution:



The amount of CO2 released, x = 3.3 g

No. of moles of CO2 released = 3.3 / 44 = 0.075 mol


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Q.9
When 22.4 litres of H2 (g) is mixed with 11.2 litres of Cl2 (g), each at 273 K at 1 atm the moles of HCl (g), formed is equal to
A. 2 moles of HCl (g)
B. 0.5 moles of HCl (g)
C. 1.5 moles of HCl (g)
D. 1 moles of HCl (g)
Answer : Option D
Explaination / Solution:

H2(g) + Cl2(g) → 2 HCl (g)




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Q.10
Hot concentrated sulphuric acid is a moderately strong oxidising agent. Which of the following reactions does not show oxidising behaviour?
A. Cu+ 2H2SO4 → CuSO4 + SO2+2H2O
B. C+ 2H2SO4 →CO2+2SO2+2H2O
C. BaCl2 + H2SO4→ BaSO4+2HCl
D. none of the above
Answer : Option C
Explaination / Solution:




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