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Gravimetric analysis

Gravimetric analysis. Using changes in mass to analyse composition Done by strongly heating the substance and measuring the loss of mass due to water loss. Percentage Composition. To calculate the percentage composition of a substance you use the formula: %age = mass x /mass total x 100

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Gravimetric analysis

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  1. Gravimetric analysis • Using changes in mass to analyse composition • Done by strongly heating the substance and measuring the loss of mass due to water loss 12 Chemistry 2.3 gravimetric analysis CR 07

  2. Percentage Composition • To calculate the percentage • composition of a substance • you use the formula: • %age = mass x/mass total x 100 • ‘x ‘ can be an element, fat, water, sugar….anything 12 Chemistry 2.3 gravimetric analysis CR 07

  3. Food example • In a 100g pot of yoghurt 45g is water – • what is the %age water in yoghurt? • %age water • = mass water/mass yoghurt x 100 • =45/100 x 100 = 45% water 12 Chemistry 2.3 gravimetric analysis CR 07

  4. Chemistry example • What percentage water is there in CuSO4.5H2O? • %(H2O) • = M(H2O) /M(CuSO4.5H2O)x 100 • =90/249.55x100 • =36% 12 Chemistry 2.3 gravimetric analysis CR 07

  5. The process • To find the % composition of each element in a compound use the following steps…. • Use the formula to find the number of moles of each element. • Use the molar masses to find the mass of each element 12 Chemistry 2.3 gravimetric analysis CR 07

  6. Write the mass of each element as a fraction of the total mass of one mole of the substance, then multiply by 100 to give %age. • CHECK (add up %ages – they should add to 100) 12 Chemistry 2.3 gravimetric analysis CR 07

  7. CuSO4.5H2O • n(Cu) = 1, n(S) = 1, n(O) = 4 + 5 = 9, n(H) = 5 x 2 = 10 • From periodic table: • m(Cu) =63.55g • m(S) = 32g • m(O) = 64g (16 x 4) • m(H) = 10g • m(O) = 80g (16 x 5) • total mass = 249.55g 12 Chemistry 2.3 gravimetric analysis CR 07

  8. 3. % Cu = 63.55/249.55 x100 • = 25.5% • % S = 32/249.55 x100 • = 12.8% • % O = 144/249.55 x100 • = 57.7% • % H = 10/249.55 x100 • = 4% 12 Chemistry 2.3 gravimetric analysis CR 07

  9. Check: • 25.5+12.8+57.7+4 = 100 • *always check answers 12 Chemistry 2.3 gravimetric analysis CR 07

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