Mole Concept Questions and Solve

Mole Concept Questions and Solve

The ratio-proportionality or formula method can be used to solve mole concept questions. We will use the ratio-proportion method in solving the questions.

Mole concept formulas;

Used if gram is given in the question;

Number of Moles = (Mass of the Sample)/(Molar Mass)

It is used if the number of particles is given in the question;

Number of Moles =(The number of particles of the sample)/(Avogadro’s Constant)

This formula is used for gases whose volume is given at NTP;

Number of Moles =(volume of the Sample)/(22,4

Note: One mole of a gas at NTP occupies 22,4 litre.

Ratio-proportion method;

We will use proportion to interpret questions about the concept of moles. In the ratio, the first information is usually written according to 1 mole.

1.Calculate the molar mass of H2O. (H:1g/mole   O: 16g/mole)

Solve;

H2O = 2.H + 1.O =  2.1 + 1.16 = 18 g/mole

The molar mass of H2O  18g/mole

2.What is the mass of one mole H2SO4, in grams? (H:1g/mole S:32g/mole  O: 16g/mole)

Solve;

H2SO4 = 2.H + S + 4.O = 2.1 +32 +4.16 = 98 g/mole

The molar mass of H2SO4   98 g/mole

3.How many moles is 8 grams of CH4 gas? (CH4: 16g/mol)

Solve;

1 mole CH4                16 g/mol

x mole CH4                 8gr

______________________

x=8/16 = 0,5 mole CH4

4.How many moles is 16 grams of NaOH ? (Na: 23g/mole O: 16g/mole H:1 g/mole)

Solve;

Firstly calculate molar mass of NaOH;

NaOH = Na + O + H = 23 + 16 + 1= 40 g/mole

1 mole NaOH             40 g/mole

xmole NaOH            16 g

_____________________

x= o,4 mole NaOH

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