Some Basic Concepts of Chemistry

If Avogadro number NA, is changed from 6.022 1023 mol-1 to 6.022 1020 mol-1, this would change

1. the mass of one mole of carbon
2. the ratio of chemical species to each other in a balanced equation
3. the ratio of elements to each other in a compound
4. the definition of mass in units of grams.

The number of water molecules is maximum in

1. 1.8 gram of water
2. 18 gram of water
3. 18 moles of water
4. 18 molecules of water

20.0 g of a magnesium carbonate sample decomposes on heating to give carbon dioxide and 8.0 g magnesium oxide. What will be the percentage purity of magnesium carbonate in the sample? (At. wt. of Mg = 24)

1. 96
2. 60
3. 84
4. 75

A mixture of gases contains H2 and O2 gases in the ratio of 1 : 4 (w/w). What is the molar ratio of the two gases in the mixture ?

1. 16 : 1
2. 2 : 1
3. 1 : 4
4. 4 : 1

Equal masses of H2, O2 and methane have been taken in a container of volume V at temperature 27 in identical conditions. The ratio of the volumes of gases H2 : O2 : methane would be

1. 8 : 16 : 1
2. 16 : 8 : 1
3. 16 : 1 : 2
4. 8 : 1 : 2

When 22.4 litres of H2(g) is mixed with 11.2 litres of Cl2(g), each at S.T.P. the moles of HCl(g) formed is equal to

1. 1 mol of HCl(g)
2. 2 mol of HCl(g)
3. 0.5 mol of HCl(g)
4. 1.5 mol of HCl(g)

1.0 g of magnesium is burnt with 0.56 g O2 in a closed vessel. Which reactant is left in excess and how much ? (At. wt. Mg = 24, O = 16)

1. Mg, 0.16 g
2. O2, 0.16 g
3. Mg, 0.44 g
4. O2, 0.28 g

6.02 1020 molecules of urea are present in 100 mL of its solution. The concentration of solution is

1. 0.001 M
2. 0.1 M
3. 0.02 M
4. 0.01 M

How many grams of concentrated nitric acid solution should be used to prepare 250 mL of 2.0 M HNO3? The concentrated acid is 70\% HNO3.

1. 70.0 g conc. HNO3
2. 54.0 g conc. HNO3
3. 45.0 g conc. HNO3
4. 90.0 g conc. HNO3

In an experiment it showed that 10 mL of 0.05 M solution of chloride required 10 mL of 0.1 M solution of AgNO3, which of the following will be the formula of the chloride (X stands for the symbol of the element other than chlorine)

1. X2Cl2
2. XCl2
3. XCl4
4. X2Cl