1. Learning Objectives
Aiming for 4: Define one mole in terms of Mr and Ar.
Aiming for 6: Calculate the number of moles of substance from given information.
Aiming for 8: Rearrange the mole formula to find the weight of a substance in grams.

2. Does anyone know what the mole is?
No, not the animal!

3. Definition – Copy into your book!
Mole: A unit of amount of substance — one mole of a substance is the relative formula mass of that substance in grams.

4. More about the mole…
Watch the video to learn more about the mole…

5. This picture shows us moles of different compounds – they’re like groups of atoms that are big enough for us to see…

6. The Mole – For example Iron (Fe) has an Ar of 56.
One mole of iron weighs exactly 56 g.
Nitrogen gas (N2) has an Mr of 2 × 14 = 28.
: What will one mole weigh?
: One mole of N2 weighs exactly 28 g.

7. Rearranging Formulae
You can convert between moles and grams using this formula:
Complete the sheet: Fill in the empty formula triangle, using the equation above and the abbreviations given below, and then complete the general equations and the definition. Stick into book when done.
Abbreviations for the Formula Triangle
Number of moles = n
Mass in grams (of element/compound) = m
Mr (of element/compound) = Mr

8. Example Questions
Use the sheet you completed to answer the following questions:
How many moles are there in 42 g of carbon?
How much would 0.8 moles of sulfuric acid (H2SO4) weigh in grams?
The Ar of carbon is 12, so the number of moles in 42 g of carbon is:
The Mr of sulfuric acid is (2 × 1) (4 × 16) = 98. Rearrange the formula to find mass (multiply both sides by Mr): mass = moles × Mr = 0.8 × 98 = 78.4 g. So 0.8 moles of sulfuric acid would weigh 78.4 g

9. Answers – Worksheet (Q1-3)
a. 9 b. 31 c. 65 d. 63.5
a. 16 × 2 = 32 b = c (3 × 16) = 63 d (3 × 16) = 100
a. Ar of K = 39, moles = mass ÷ Ar = 19.5 ÷ 39 = 0.5 moles b. Mr of NaCl =  = 58.5 moles = mass ÷ Mr = 23.4 ÷ 58.5 = 0.4 moles c. Mr of SO2 = 32 + (2 × 16) = 64 moles = mass ÷ Mr = 76.8 ÷ 64 = 1.2 moles d. Mr of CuSO4 = (4 × 16) = 159.5 moles = mass ÷ Mr = 31.9 ÷ 159.5 = 0.2 moles

10. Answers – Worksheet (Q4)
a. Ar of Ni = 59 mass = moles × Ar = 0.8 × 59 = 47.2 g b. Mr of MgO = = 40 mass = moles × Mr = 0.5 × 40 = 20 g c. Mr of NH3 = 14 + (3 × 1) = 17 mass = moles × Mr = 1.6 × 17 = 27.2 g d. Mr Ca(OH)2 = 40 + (2 × (16 + 1)) = 74 mass = moles × Mr = 1.4 × 74 = 103.6 g