A. Very-Short-Answer Questions
1. Classify the following elements, compounds and mixture.
Iron, brass, salt, sugar, air, pure water, sea water, milk, tooth paste, diamond, LPG, smoke, sulphur
2. What is an atom?
3. Are all atoms of an element alike in all respects?
4. What is an isotope?
5. Which is lightest element? What is its atomic weight?
6. What is a molecule?
7. How is the molecular weight related to atomic weight?
8. How are molecular formula and empirical formula related?
9. What is the molar volume of a gas at STP?
10. What is the molarity of pure water?
11. Which concentration unit does not change with temperature?
12. What is a limiting reactant?
B. Long-Answer Question
1. What do you understand by matter? Distinguish between types of matter.
2. What are the different laws of chemical combination? Explain them.
3. What is the difference between the molecular formula and a formula unit? Explain giving examples.
4. What do you understand by atomic weigh (relative atomic mass)?
5. What are the different ways of expressing the concentration of a solution? Explain.
C. Numericals
1. Calculate the molecular mass of the following : (i) H2O (ii) CO2 (iii) CH4
2. Calculate the mass per cent of different elements present in sodium sulphate (Na2SO4).
3. Determine the empirical formula of an oxide of iron which has 69.9% iron and 30.1% dioxygen by mass.
4. Calculate the amount of carbon dioxide that could be produced when
(i) 1 mole of carbon is burnt in air.
(ii) 1 mole of carbon is burnt in 16 g of dioxygen.
(ii) 1 mole of carbon is burnt in 16 g of dioxygen.
(iii) 2 moles of carbon are burnt in 16 g of dioxygen.
5. Calculate the mass of sodium acetate (CH3COONa) required to make 500 mL of 0.375 molar aqueous solution. Molar mass of sodium acetate is 82 g mol–1.
6. Calculate the concentration of nitric acid in moles per litre in a sample which has a density, 1.41 g mL–1 and the mass per cent of nitric acid in it being 69%.
7. How much copper can be obtained from 100 g of copper sulphate (CuSO4)?
8. Calculate the atomic mass (average) of chlorine using the following data :
Isotope | % Natural Abundance | Molar Mass |
35-Cl | 75 | 35 |
37-Cl | 25 | 37 |
9. In three moles of ethane (C2H6), calculate the following :
(i) Number of moles of carbon atoms.
(ii) Number of moles of hydrogen atoms.
(iii) Number of molecules of ethane.
10. What is the concentration of sugar (C12H22O11) in mol L–1if its 20 g are dissolved in enough water to make a final volume up to 2L?
11. 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?
12. Pressure is determined as force per unit area of the surface. If mass of air at sea level is 1034 gcm–2, calculate the pressure in pascal. (1Pa = 1Nm–2)
13. 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 percent by mass.
(ii) Determine the molality of chloroform in the water sample.
14. The following data are obtained when dinitrogen and dioxygen react together to form different compounds :
S.No. | Mass of dinitrogen | Mass of dioxygen |
I | 14 g | 16 g |
II | 14 G | 32 g |
III | 28 g | 32 g |
IV | 28 g | 80 g |
Which law of chemical combination is obeyed by the above experimental data?
Give its statement.
15. In a reaction A + B2→ AB2 Identify the limiting reagent, if any, in the following reaction mixtures.
(i) 300 atoms of A + 200 molecules of B
(ii) 2 mol A + 3 mol B
(iii) 100 atoms of A + 100 molecules of B
(iv) 5 mol A + 2.5 mol B
(v) 2.5 mol A + 5 mol B
16. Dinitrogen and dihydrogen react with each other to produce ammonia according to the following chemical equation: N2 (g) + H2 (g) → 2NH3 (g)
(i) Calculate the mass of ammonia produced if 2000 g dinitrogen reacts with 1000 g of dihydrogen.
(ii) Will any of the two reactants remain unreacted?
(iii) If yes, which one and what would be its mass?
17. How are 0.50 mol Na2CO3and 0.50 M Na2CO3 different?
18. If ten volumes of dihydrogen gas reacts with five volumes of dioxygen gas, how many volumes of water vapour would be produced?
19.Which one of the following will have largest number of atoms? (i) 1 g Au (s) (ii) 1 g Na (s) (iii) 1 g Li (s) (iv) 1 g of Cl2(g)
20.Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is 0.040.
21.What will be the mass of one 12C atom in g?
22.A welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives 3.38 g carbon dioxide 0.690 g of water and no other products. A volume of 10L (measured at STP) of this welding gas is found to weigh 11.6 g. Calculate
(i) Empirical formula (ii) molar mass of the gas (iii) molecular formula.
23.Calcium carbonate reacts with aqueous HCl to give CaCl2 and CO2 according to the reaction, CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2(g) + H2O(l) What mass of CaCO3 is required to react completely with 25 mL of 0.75 M HCl?
24.Chlorine is prepared in the laboratory by treating manganese dioxide (MnO2) with aqueous hydrochloric acid according to the reaction 4 HCl (aq) + MnO2(s) → 2H2O (l) + MnCl2(aq) + Cl2 (g) How many grams of HCl react with 5.0 g of manganese dioxide?
25. A compound contains 4.07 % hydrogen, 24.27 % carbon and 71.65 % chlorine. Its molar mass is 98.96 g. What are its empirical and molecular formulas?
26. How many moles of methane are required to produce 22 g CO2 (g) after combustion? Calculate the amount of water (g) produced by the combustion of 16 g of methane.
27. 50.0 kg of N2(g) and 10.0 kg of H2 (g) are mixed to produce NH3 (g). Calculate the NH3 (g) formed. Identify the limiting reagent in the production of NH3 in this situation.
28. A solution is prepared by adding 2 g of a substance A to 18 g of water. Calculate the mass per cent of the solute.
29. Calculate the molarity of NaOH in the solution prepared by dissolving its 4 g in enough water to form 250 mL of the solution.
30. The density of 3 M solution of NaCl is 1.25 g mL–1. Calculate molality of the solution.
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