Quantitative Chemistry
- Created by: Kirsten Reading
- Created on: 22-04-13 19:09
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- Quantitative Chemistry
- Atomic Mass
- Protons + Neutrons = Mass Number
- Isotopes
- Same number of protons (atomic number)
- Different number of neutrons (mass number)
- Same element
- Different number of neutrons (mass number)
- Same number of protons (atomic number)
- Relative Formula Mass (Mr)
- = sum of all (Mr)s
- e.g. Mr for MgCl? = 95
- Moles
- Mr of substance in grams is known as one mole
- Number of moles = Mass in g of element ÷ Mr of element
- Percentage mass
- = (mass of element in compound ÷ total Mr of compound) x 100
- e.g. % mass of sodium in sodium carbonate
- (23x2 ÷ 106) x 100 = 43.4%
- Empirical Formula
- List all elements in compound
- Write amount in question
- Divide by Ar for that element (gives moles)
- Divide each by smallest number if moles
- Divide by Ar for that element (gives moles)
- Write amount in question
- List all elements in compound
- Mass of Reactants
- e.g. If we have 50g of CaCO3, how much CaO can we make?
- Work out the Mr values for the two compounds
- Mr of CaCO3 = 100
- Mr of CaO = 56
- Work out the Mr values for the two compounds
- e.g. If we have 50g of CaCO3, how much CaO can we make?
- Percentage Yield
- = (amount made ÷ predicted yield) x 100
- Never 100%
- Impurities
- Other reactants
- Difficult to separate
- Reversible reaction
- Reversible reactions
- Products of reaction can react to produce original products
- e.g. ammonium chloride ? ammonia + hydrogen chloride
- Analysing Substances
- Chromatography
- Paper
- Gas (GC-MS)
- Separates mixture of compounds
- Substances travel through tube at different speeds so become separated
- No. of peaks on gas chromatograph shows no. of different compounds present
- Position of peaks shows retention time for each substance
- Can be linked to mass spectronometer
- Sensitive
- Fast
- Accurate
- Mass Spectronomy
- Finds Mr of moelcule
- Chromatography
- Atomic Mass
- 100 g of CaCO3 would yield 56 g of CaO
- Mr of CaO = 56
- Mr of CaCO3 = 100
- Therefore, 50g of CaCO3 makes 28g of Cao
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