Chemistry Calculations. Learning Intentions 1)How can we work out the formula mass of a chemical? 2)What is a mole? 3)How can we use formula mass and.

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Presentation transcript:

Chemistry Calculations

Learning Intentions 1)How can we work out the formula mass of a chemical? 2)What is a mole? 3)How can we use formula mass and moles to work out grams of a chemical?

Part 1: Formula Mass Each element has a Relative Atomic Mass Number e.g. Na = 23, O = 16 Task: Use your data book to find the Atomic Mass for: Ca, Cl, S, H, N, C, Ar

Formula Mass If we add up all the RAM nummbers present in a chemical we get the Formula Mass number Example: H 2 O = = 2 X X 16 2 X Hydrogen + 1 X Oxygen Mass Numbers = A formula mass of 18

Task: On your show me boards work out the formula mass of: 1)NaOH 2)HCl 3)O 2 4)HNO 3 5)H 2 SO 4 6)(NH 4 ) 3 PO 4

(NH 4 ) 3 PO 4 Solution: Split into 2 halves 2) PO 4 P = 31 X 1 O = 16 X 4 PO 4 = = a formula mass of 149 1) (NH 4 ) 3 N = 14 X 1 H = 1 X 4 NH 4 = 18 (NH 4 ) 3 = 18 X 3 = 54

Learning Intentions 1)How can we work out the formula mass of a chemical? 2)What is a mole? 3)How can we use formula mass and moles to work out grams of a chemical?

Part 2: The Mole Units of Measurement: We use units of measurement in life to give us an easier way to see large numbers. meter = 100 cm, liter = 1000 ml, kilogram = 1000 g The mole is a unit of measurement In chemistry we use it to tell us how many atoms or molecules there are

The Mole 1 mole of a chemical is equal to the Formula Mass in grams If I could weigh 6.02 X molecules of water it would weigh 18g Q) What is the formula mass of water? 18 Q) What is the relationship between the formula mass and 1 mole of a chemical?

Example I have 40g of NaOH The Formula Mass (FM) = 40 Therefore I have 1 mole NaOH FM = 40 1 mole = 40g 0.5 moles = 20g 0.25 moles = 10g etc

Learning Intentions 1)How can we work out the formula mass of a chemical? 2)What is a mole? 3)How can we use formula mass and moles to work out grams of a chemical?

Part 3: Mole Calculations M = n X FM (n) n = M/FM FM = M/n We can use moles and formula mass to work out mass of chemicals needed/used

Example If I have 9g of water, how many moles do I have? n = M/FM n = 9g/18 n = 0.5 What is the mass of 0.25 moles N 2 ? M = n X FM M = 0.25 X 28 M = 7g (n)

Task: 1) If I have 9g water how many moles do I have? 2) If I have 5g NaOH how many moles do I have? 3) If I have 0.5 moles O 2 how many grams do I have?

Learning Intentions 1)How can we work out the formula mass of a chemical? 2)What is a mole? 3)How can we use formula mass and moles to work out grams of a chemical?