C2 Calculations and analysis
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Calculate the relative formula mass (Mr) of Calcium hydroxide - Ca(OH)2
40 + (16 + 1) x 2 = 74
Calculate the percentage by mass of calcium in calcium hydroxide
(40 ÷ 74) x 100 = 54%
Calculate the mass of calcium in 30g of calcium hydroxide
(54 ÷ 100) x 30 = 16g
A sample of calcium compound contains 0.8g of calcium, 0.64g of oxygen and 0.04g of hydrogen, find its empirical formula.
Mass ÷ Mr Ca – 0.8 O – 0.64 H – 0.04 40 = 0.02 16 = 0.04 1 = 0.04 Divide by the smallest Ca – 0.02 O – 0.04 H – 0.04 0.02 = 1 0.02 = 2 0.02 = 2 = CaO2H2
Calculate how much Iron could be made from 320g of Iron oxide Fe2O3 + 3CO → 2Fe + 3CO2
Moles of Fe2O3 = 320 ÷ 160 = Mass ÷ Mr = 2 Moles Ratio of Fe2O3 1 : Fe 2 Moles of Fe = Moles of Fe2O3 x 2 = 4 Moles Mass of Fe = Moles of Fe x Mr of Fe = 4 x 56 = 224g
What is the formula for percentage yield?
(Actual Yield ÷ Theoretical yield) x 100
Give 3 reasons why the yield is not 100%.
Reversible reaction Product can be lost when separated Other reactions occur
What is the percentage yield if a reaction only produces 20g when in theory it produces 40g.
% yield = (20 ÷ 40) x 100 = 50%
Give 3 reasons why instrumental methods are useful.
Sensitive/ Accurate Fast Only needs samples that are small
What method can be used to analysis food additives?
Paper Chromatography
What is separated in gas chromatography?
Mixture of compounds
In the column, what can be used to help identify the substance?
The retention time
What can a mass spectrometer be used for?
Gives the relative formula mass
What is shown by the molecular ion peak?
Relative formula mass of substance