mole calculations - Standard Grade Chemistry

National Chemistry

Calculations using mole

If question tells you about mass of grams

or asks for mass or grams

mass given in question

or

if answer is a mass..

Mass of 1 mole

or

gram formula mass

number of mole

number of mole

volume in litre

cm3 divided by 1000 = litres

ml divided by 1000 = litres

concentration..

If question tells you about concentration or mol/l

or asks for concentration or mol/l

Volume will also be mentioned.

1. Calculate the mass mole of SO2 .

2. Calculate the mass of 2.5 mole of NH3 ..

3. How many mole are there in 38.5g of CCl4

ANSWERS

Questions 1 to 3 only use triangle 1. Mass or grams are mentioned. Concentration is not.

1. Triangle not needed. Just calcualte mass of one mole from the formula

SO2 has 1 x S at 32 = 32

2 x O at 16 = 32

64 ans = 64g

2. Use triangle You have both bottom parts so answer will be a multiplication.

*number of mole x mass of 1 mole*

2.5 x mass 1 mole NH3 1 x N at 14 = 14

3 x H at 1 = 3

= 17g

*calculation * number of mole x mass of 1 mole

2.5 x 17

= 42.5g

3. You have top and bottom right of triangle so this will be a division.

mass in question/answer

mass 1 mole 1 mole CCl4 is 1 x C at 12 = 12

4 x Cl at 35.5 = 142

154g

*calculation* mass in question/answer

mass 1 mole

38.5

154

= 0.25 mole

4. Calculate the number of mole in a 50ml solution of 0.1 mol/l socium hydroxide.

5. Calculate the concentration of a 100ml of solution which contains 0.25 mole hydrochlric acid .

6. What would be the volume of solutiion if 0.2 mole silver nitrate was used to make a solution of concentration 0.5 mol/l ?

ANSWERS

Triangle TWO is used

Q4 has the unit of concentration - mol/l

Q5 has the word concentration

Q6 has the word concentration - calculating volume is seldom asked question

4. Asked about top of triangle; given both bottom parts - therefore this is a multiplication.

*calculation* mole = concentration x litres

= 0.1 x 50 ml (divide by 1000 to get litres)

= 0.1 x 0.05

= 0.005 mole

5. Given volume (from bottom of triange) and number of mole (from top) - therefore a division

*change volume to litres* = 100 = 0.1 litre

1000

*calculation* concentration = number of mole

litre

= 0.25 ans = 0.025 mol/l

0.1

6. Given concentration (from bottom of triange) and number of mole (from top) - therefore a division

*calculation* volume in litres = number of mole

concentration

= 0.2 ans = 0.4

0.5

NOTE

In questions not involving mass (or grams) such as questions 4 to 6 there is no need to know the formula of the chemical.

Formulae are only required if mass needs to be calculated.

You are viewing the text version of this site.

To view the full version please install the Adobe Flash Player and ensure your web browser has JavaScript enabled.

Need help? check the requirements page.