Chapter 1 – Basic Concepts of Chemistry
Revision Assignment 1
Q.1. State the law of multiple proportions.
Q.2. State Gay Lussac's law of gaseous volumes.
Q.3. State Avogadro law.
Q.4. For an actual result of an observation to be 5; two students A and B reported their readings as follows:
|
|
Observations |
Average |
|
|
1 |
2 |
||
|
Student A |
4.95 |
4.93 |
4.94 |
|
Student B |
4.94 |
5.05 |
4.995 |
Which of the students has made a more precise observation? Is his observation accurate too?
Q.5. Express the following in the scientific notation:
(i) 0.0048 (ii) 6.0012
Q.6. How many significant figures are present in the following?
(i) 0.0025 (ii) 126,000 (iii) 500.0
Q.7. Round off the following figures upto three significant figures:
(i) 0.04597 (iv) 2808
Q.8. How many electrons are present in 16 g of CH4?
[Ans. 6.02 × 1024]
Q.9. Boron occurs in nature in the form of two isotopes, 11B and 10B, in ratio of 81% and 19% respectively. Calculate its average atomic mass.
[Ans. 10.81]
Q.10. If 2 litres of N2 is mixed with 2 litres of H2 at a constant temperature and pressure, then what will be the volume of NH3 formed?
[Ans. 1.33 L]
Q.11. How many atoms are present in 1 ml of NH3 at STP?
[Ans. 1.07 × 1020 atoms]
Q.12. 0.5 mole each of H2S and SO2 mixed together in a reaction flask, react according to equation:
2H2S + SO2 → 2H2O + 3S
Calculate the number of moles of 'S' formed.
[Ans. 0.75 mole]
Q.13. If 6.023 × 1023 molecules of N2 react completely with H2 according to the equation:
N2(g) + 3H2(g) → 2NH3(g),
then calculate the number of molecules of NH3 formed.
[Ans. 1.204 × 1024]
Q.14. Calculate the mass of ferric oxide that will be obtained by complete oxidation of 2 g of Fe. [Atomic weights of Fe = 56 u, O = 16 u]
[Ans. 2.857 g]
Q.15. A sample of drinking water was found to be severely contaminated with chloroform (CHCl3), supposed to be carcinogenic in nature. The level of contamination was 15 ppm (by mass).
(i) Express this in per cent by mass.
(ii) Determine the molality of chloroform in the water sample.
[Given molar mass of CHCl3 = 119.5 g mol-1]
[Ans. (i) 1.5 × 10-3 %, (ii) 1.255 × 10-4 mol/kg]
Q.16. Calculate the mass of sodium acetate required to make 500 ml of 0.375 molar aqueous solution. Molar mass of sodium acetate is 82.0245 g mol-1
[Ans. 15.3795 g]
Q.17. If the density of methanol is 0.793 kg L-1, what is its volume needed for making 2.5 L of its 0.25 M solution?
[Ans. 25.22 ml]
Q.18. What is the concentration of sugar (C12H22O11) in mol L-1 if its 20 g are dissolved in enough water to make a final volume up to 2 L?
[Ans. 0.0292 M]
Q.19. An organometallic compound on analysis was found to contain, C = 64.4%, H = 5.5% and Fe = 29.9%. Determine its empirical formula (At. mass of Fe = 56 u).
[Ans. C10H10Fe]
Q.20. How many grams of Cl2 are required to completely react with 0.4 g of H2 to yield HCl? Also, calculate the amount of HCl formed.
[Ans. 14.2 g of Cl2, 14.6 g of HCl]
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