3.2 Quantitative Chemistry

Question 1

What is the mass of one mole of a substance equal to?

Answer 1

It’s formula mass in grams e.g.
Iron has a formula mass of 56

Therefore one mole of iron weights 56g

Question 2

What does one mole mean in terms of number of atoms?

Answer 2

Number of atoms is the same

1 mole of iron = 6.02x10^23 atoms

1 mole of hydrogen = 6.02x10^23 atoms

But as the atoms are different masses, one mole of each atom weighs a different amount

Question 3

What is the equation for moles?

Answer 3

Moles = Mass / MR

Question 4

What is the number of atoms in 1 mole called?

Answer 4

Avogadro’s constant

Question 5

What is the limiting reactant?

Answer 5

In a chemical reaction you use one in excess to ensure all of the other is used up

Limiting reactant is the reactant that is completely used up

The amount of product is limited by how much of that reactant there is e.g.

2Mg + O2 -> 2MgO

But if I only have 14Mg and 20 O2, Mg would be the limiting reactant

14Mg + 20O2 - > 14MgO + 13O2

You can see that oxygen was used in excess to make all of the magnesium react

Question 6

What is concentration measured in?

Answer 6

Mass per volume

g/dm^3

dm^3 is just chemistry talk for litre

Question 7

What is the equation for conentration?

Answer 7

Concentration = Mass / Volume