Some Basic Concepts of Chemistry

In which case is number of molecules of water maximum?

1. 18 mL of water
2. 0.18 g of water
3. 0.00224 L of water vapours at 1 atm and 273 K
4. 10-3 mol of water

Suppose the elements X and Y combine to form two compounds XY2 and X3Y2. When 0.1 mole of XY2 weighs 10 g and 0.05 mole of X3Y2 weighs 9 g, the atomic weights of X and Y are

1. 40, 30
2. 60, 40
3. 20, 30
4. 30, 20

What is the mass of the precipitate formed when 50 mL of 16.9\% solution of AgNO3 is mixed with 50 mL of 5.8\% NaCl solution ? (Ag = 107.8, N = 14, O = 16, Na = 23, Cl = 35.5)

1. 3.5 g
2. 7 g
3. 14 g
4. 28 g

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