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Advanced Higher Unit 3

Advanced Higher Unit 3. Elemental microanalysis. Elemental Microanalysis. Elemental microanalysis (or combustion analysis) is used to determine the masses of the elements in a sample of an organic compound in order to calculate its empirical formula.

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Advanced Higher Unit 3

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  1. Advanced Higher Unit 3 Elemental microanalysis

  2. Elemental Microanalysis • Elemental microanalysis (or combustion analysis) is used to determine the masses of the elements in a sample of an organic compound in order to calculate its empirical formula. • The carbon, hydrogen and nitrogen contents are measured using an instrument known as a CHN analyser.

  3. The Process Step 1 - An accurate mass of sample (~2 mg) is weighed out. Step 2 - Sample is then placed in a sealed oxygen atmosphere and combusted at ~1000 °C. Step 3 - CO2, H2O and NxOy are produced and passed through a CHN analyzer (a different but similar analyzer is used for S) Step 4 - Other elements, except oxygen, are determined by alternative methods. Step 5 - Samples are analysed in dup;icates to give more reliable results.Results are calculated and expressed as a percentage, by mass. Now watch the RSC video on ‘Elemental Microanalysis’

  4. ¸ Element Mass RAM Moles Whole number by Present present ratio smallest ¸ C 72 12 6 6 6 1 =6 ¸ H 12 1 12 12 12 1 =12 ¸ O 16 16 1 1 1 1 =1 Empirical Formula Calculations Calculate the empirical mass of a compound that contains 72 % carbon, 12 % hydrogen, and 16 % oxygen Empirical Formula isC6H12O

  5. Calculate the empirical formula of the following two examples a) C = 73.17 % H = 7.32 % O = 19.51 % b) C = 69.77 % H = 11.63 % O = 18.60 % C5H6O C5H10O

  6. A sample of an organic compound with a mass of 1.224g was completely burned in oxygen and found to produce 2.340g of CO2 and 1.433g of H2O. Calculate the empirical formula of the organic compound. Mass of carbon = 12.0/44.0 x 2.340 = 0.638g Mass of hydrogen = 2.0/18.0 x 1.433 = 0.159g Mass of oxygen = 1.224 – (0.638 + 0.159) =0.427g

  7. Empirical formula = C2H6O

  8. Exercise • Now try the exercise on page 3 of your Unit 3(d) notes.

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