Some Basic Concepts of Chemistry

An organic compound contains 78% (by wt.) carbon and remaining percentage of hydrogen. The right option for the empirical formula of this compound is : [Atomic wt. of C is 12, H is 1]

1. CH4
2. CH
3. CH2
4. CH3

Which one of the following has maximum number of atoms?

1. 1 g of Mg(s) [Atomic mass of Mg = 24]
2. 1 g of O2(g) [Atomic mass of O = 16]
3. 1 g of Li(s) [Atomic mass of Li = 7]
4. 1 g of Ag(s) [Atomic mass of Ag = 108]

The number of moles of hydrogen molecules required to produce 20 moles of ammonia through Haber’s process is :

1. 10
2. 20
3. 30
4. 40

A mixture of 2.3 g formic acid and 4.5 g oxalic acid is treated with conc. H2SO4. The evolved gaseous mixture is passed through KOH pellets. Weight (in g) of the remaining product at STP will be

1. 1.4
2. 3.0
3. 2.8
4. 4.4

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