Read GCSE Chemistry C2 Calculations Revision text version

Reacting amounts This is used to calculate how much product can be produced or reactant is needed in a reaction. Step 1. Write the mass of the substance you are given above that substance and put a `?' above the substance you are trying to find the mass of. Step 2. Write the formula mass of each of the two substances you are interested in underneath each one. (don't forget to multiply by the number in front of the formula) Step 3. Make an equation and solve. Eg Find the mass of ethene needed to produce 10 tonnes of ethanol. C2H4 + Step 1. H2O C2H5OH

10 T ?T C2H4 + H2O C2H5OH Step 2. 28 46 Step 2. Formula mass C2H4 = (12 x 2) + (4 x 1) = 28 C2H5OH = (2 x 12) + (6 x 1) + (1 x 16) = 46 Step 3. 10T = ?T = 10T x 46 = 16.4 Tonnes 28 46 28

How much CO2 is released from 20g of CaCO3? CaO + CO2 CaCO3 How much carbon would be needed to make 8.8g of CO2? C+O CO2 How much AlO3 is needed to make 4.5kg of Al? 2AlO3 4Al + 3O2

Percentage Yield - This is used to calculate the percentage of a product actually produced compared to the amount you would expect to be produced based on the amount of reactants you started with. The first part of the calculation is the same as &quot;reacting amounts&quot;. Step 1. Write the mass of the reactant you are given above that substance and put a `?' above the substance you are trying to find the yield of. Step 2. Write the formula mass of each of the two substances you are interested in underneath each one (don't forget to multiply by the number in front of the formula). Step 3. Make an equation and solve. This gives you your theoretical yield ­ the maximum yield you could obtain. Step 4. Divide the yield (mass) of the product you are given by the theoretical yield and multiply by 100. Eg 12tonnes of ethanol is produced from 30 tonnes of ethane work out the percentage yield. C2H4 + Step 1. H2O C2H5OH

30T ?T C2H4 + H2O C2H5OH Step 2. 28 46 Step 2. Formula mass C2H4 = (12 x 2) + (4 x 1) = 28 C2H5OH = (2 x 12) + (6 x 1) + (1 x 16) = 46 Step 3. 30T = ?T = 30T x 46 = 49.3Tonnes 28 46 28 Step 4. 12T x 100 = 24.3% 49.3

Find the % yield if 10g CO2 is released from 20g of CaCO3? CaCO3 CaO + CO2

Find the % yield if 5g of CO2 is produced from 5g of C? C+O CO2

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GCSE Chemistry C2 Calculations Revision

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