applied science - unit 19 b part 3- chemistry -Determine empirical and molecular formulae- distinction level
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Course
Unit 19 - Practical Chemical Analysis
Institution
PEARSON (PEARSON)
this cover unit 19B part 3 .
it up to distinction level
Section 3: Determine empirical and molecular formulae from percentage elemental composition data and mass spectra.
Section 3: Determine empirical and molecular formulae from percentage elemental composition
data and mass spectra.
Introduction:
how to calculate empirical formula
firstly, you convert % to grams.
secondly you divide the grams by the AR of the element to find the mole.
thirdly, divided the moles of each element by the smallest mole.
Fourthly, multiply if needed to make it a whole number.
Describe the molecular ion peak on a mass spectrum
A scientist will use a technique called mass spectrometry if they want to study a molecule. In mass
spectrometry, the molecules are bombarded with special particles that give it a positive charge. This
charged molecule is then called a molecular ion. The molecular ion peak is the highest peak in the
graph.
explain how this can be used to work out molecular formula from empirical formula
you can obtain the molecular formula by dividing empirical formular from the molecular ion peak
molecular ion peak/ MR of empirical formula = molecular formula
Compound P
Percentage Elemental Composition:
Carbon: 92.3% Hydrogen: 7.7%
Empirical Formula calculation:
Step 1
92.3% = 92.3g
7.7% = 7.7g
Step 2
92. = 7.69
7.7/1 = 7.7
Step 3
7.69/7.69 = 1
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