AQA C2 2.3 Atomic structure, analysis and quantitative chemistry
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- Chemistry
- Analysing substancesAtoms and compoundsCalculations, moles and yieldTesting and analysing substances
- GCSE
- AQA
- Created by: Rchilds
- Created on: 30-05-17 22:43
What do the numbers by the elements in the periodic table mean?
Top number = mass number which is the number of protons and neutrons. Bottom number = atomic number which is the number of protons
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What are the relative masses of protons, neutrons and electrons?
p=1, n=1, e=very small so practically 0
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What determines what type of element you have?
The number of protons/atomic number. e.g. carbon always has 6 protons, oxygen always has 8 protons etc
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What is an isotope?
Atoms of the same element so same number of protons but a different number of neutrons (same atomic number, different mass number)
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What is the relative atomic mass of an element (Ar)?
It compares the mass of atoms of the element with the Carbon-12 isotope. It is an average value for the isotopes of the element. These can be found in the periodic table
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What is the relative formula mass (Mr)
the sum of the relative atomic masses of the atoms in the numbers shown in the formula
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How much of a substance is equal to one mole?
The relative formula mass of a substance in grams would be one mole of the substance
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What is paper chromatography?
A dot of mixture is put at the bottom of filter paper, the paper is placed in a suitable solvent eg water. As the solvent soaks up the paper, it carries the mixture with it. Different components travel different distance and separate
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What types of substances can paper chromatography be used on?
Mixtures that are soluble
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Why must the reference line at the bottom of the filter paper be drawn in pencil? (the line that you place the dots along)
Because pencil isn't soluble so won't interfere in the experiment.
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Why do some substances travel further up the chromatography paper than others?
The more soluble a substance is, the higher it will travel
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What is GC-MS and what does it do?
Gas chromatography and mass spectrometry is a machine used to separate (GC) then identify components of mixtures (MS)
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What is gas chromatography?
gas chromatography allows the separation of a mixture of compounds, the time taken for a substance to travel through the column can be used to help identify the substance
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How does gas chromatography separate mixtures?
1. sample is dissolved in a solvent and injected into the column. 2. An unreactive gas (nitrogen) carries the sample through the column 3. Different substances travel at different speeds and so become separated
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What is retention time?
The time taken for a substance to travel through the column, it can be used to help identify the substance
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How can the output from gas chromatography help analyse a substance?
the number of peaks on the output of a gas chromatograph shows the number of compounds present, the position of the peaks on the output shows the retention time
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Why is using a mass spectrometer after gas chromatography good?
The mass spectrometer can be used to identify substances quickly and accurately, and in very small amounts. It can also provide the relative formula mass of the substances separated by gas chromatography
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What do the peaks on a mass spectrometer output graph tell you?
The molecular masses of each ion in the mixture e.g. carbon dioxide would have one peak for carbon, one for oxygen, one for carbon monoxide (CO) and one for carbon dioxide (CO2)
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How can you find the molecular mass of the substance put through a GC-MS?
The MOLECULAR ION PEAK (last peak on the right side of the output graph) Its relative mass is the relative formula mass of the substance being analysed
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How can you work out the percentage of an element in a compound?
Use the relative mass. % = relative mass of element ÷ the relative molecular mass of the compound
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What does conservation of mass mean?
The total mass of products at the end of the reaction is equal to the total mass of the reactants at the beginning
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What is an empirical formula?
The simplest ratios of elements in a compound - it gives the chemical formula of compound
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How can you find the empirical formula of a compound?
Find the mass of each individual element in the compound (using conservation of mass). Divide these by the relative masses from the periodic table (Ar). Use these answers to find the ratios of atoms, these tell you the small numbers in the compound.
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How can you work out the masses of compounds from balanced symbol equations?
work out the relative molecular mass of each compound in the equation. This gives you the right masses in grams. If you are not given these amounts you need to multiply or divide everything by the same amount until they match the masses.
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In reality, why don't you find the mass of reactants equals the mass of the products perfectly? Give 3 reasons.
(1) the reaction may not go to completion because it is reversible (2) some of the product may be lost when it is separated from the reaction mixture (3) some of the reactants may react in ways different from the expected reaction
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What is a yield?
The amount of product obtained from a chemical reaction
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What is the percentage yield?
The actual amount of product obtained (actual yield) ÷ the amount of product you should get in theory if the experiment was perfect (theoretical yield) x 100%
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What is a reversible reaction?
In some chemical reactions, the products of the reaction can react to produce the original reactants i.e. it naturally reacts backwards as well
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How do you represent a reversible reaction?
Instead of an arrow in the middle of an equation, you put 2 half arrows facing opposite directions on top of each other.
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Give an example of a reversible reaction
ammonium chloride ammonia + hydrogen chloride
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For some reactions, if you measure the mass of the reaction as it's taking place, it decreases. Why might this be?
A gas could be produced, conservation of mass still applies but the gas might escape making it look like mass is being lost.
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Other cards in this set
Card 2
Front
What are the relative masses of protons, neutrons and electrons?
Back
p=1, n=1, e=very small so practically 0
Card 3
Front
What determines what type of element you have?
Back
Card 4
Front
What is an isotope?
Back
Card 5
Front
What is the relative atomic mass of an element (Ar)?
Back
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