Topic 4 - Calculations Involving Masses

Question 1

How do you calculate the empirical formula?

Answer 1

Divide both elements mass by its RFM
Divide the answers by the smallest answer e.g say one element got 0.5 and one was 0.25 you divide 0.5 and 0.25 by 0.25.
This should get you a ratio. I.e. 2;1
So it’s be Ca Cl
                       2

Question 2

How do you calculate concentration (mass?

Answer 2

Mass of solute / volume of solution

Question 3

What does it mean if the experiment was in a non closed system?

Answer 3

Gas can escape

Question 4

What does it mean by a closed system?

Answer 4

Gases cannot escape and nothing new can be added or removed

Question 5

How do you calculate the mass of (Cl) to make 53.4g of Aluminium Chloride?

Answer 5

Write balanced equation
Calculate the rfm of Cl and Aluminium chloride
Then times the Rfm by the stoichiometry (71 x 3 for Cl) and (2x 133.5 for AlCl)
Then divided both answers by the answer you got from the reactant/product where you already know the mass (here we know there was 53.4 of AlCl so we divide both answers by the answer we got of AlCl)
213/ 267 (Cl) and 267/267 for AlCl
Then times both answers by the mass of the element/compound you already know so by 53.4

Question 6

How do you calculate the number of moles?

Answer 6

Mass / RFM

Question 7

How do you figure out the balanced equation using masses?

Answer 7

Calculate the number of moles of each element (mass/rfm)
Divide by the smallest answer
Find the simplest whole ratio

Question 8

What is the limiting reactant?

Answer 8

The reactant that determines the amount of product formed (every other reactants will be in excess)