Chapter 4- Relative formula mass

Question 1

How do you calculate the relative formula mass?

Answer 1

Add up all the atomic masses of all the atoms present in the formula.

Water, H20 (2xH)+(1xO)= (2x1)+(1x16)= 18

Question 2

What is Avogadro’s number?

Answer 2

Its 1 mole. The amount of substance that contains 6x10^23.

1 mole of Na contains 6x10^23 atoms of Na

Question 3

How do you calculate the mass of 1 mole?

Answer 3

It is simply the Ar expressed in grams.

Hydrogen,
Ar=1,
Mass of 1 mole=1g

Question 4

What is the equation linking mass from amount?

Answer 4

Mass of substance(g)= amount x Mr

NaCl
3mol
Mr-58.8
(3x58.8)= 175.5g

Question 5

What is the equation linking amount from mass?

Answer 5

Amount in moles= amount/Mr

NaOH
Mass- 80g
Mr-40
(80/40)= 2 mol

Question 6

What is the volume of 1 mol of gas?

Answer 6

24dm^3 at room temp and pressure (r.t.p)

Question 7

How do you calculate the volume of gas from the amount?

Answer 7

Volume of gas(dm^3)= amount x 24

Amonia
Amount- 0.02 mol
Volume-(0.02x24)=0.48dm^3

Question 8

How do you calculate the amount of gas from the volume?

Answer 8

Amount of gas(mol) = volume of gas(dm^3)/24

Methane
Volume-225.6dm^3
Amount- (225.6/24)= 9.4mol