National Chemistry

Calculations using mole

### ONE

If question tells you about mass of grams
or asks for mass or grams

### TWO

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.