C2.3 Flashcards
How do you work out the number of neutrons?
Mass number - atomic number
What actually is the atomic mass?
An average mass number of the isotopes
Why does chlorine have a relative atomic mass (Ar) or 35.5?
~ Because it is an average mass number of the isotopes
~ It does NOT mean that it has half a proton or neutron
What is the relative formula mass (Mr) of H2O?
1 x 2 + 16
2 + 16 = 18
The relative atomic mass (Ar) is the mass of what?
A particular atom compared to the 12C isotope
How do you work out the percentage by mass of an element in a compound?
Relative formula mass of the compound
What is the empirical formula?
The simplest whole number ratio of atoms of each element in a compound
What is the mass of a proton?
1
What is the mass of a neutron?
1
What is the mass of an electron?
Very small
What is the mass number made up of?
Protons + neutrons
What is one mole of a element?
The relative atomic mass in grams
How can elements and compounds be detected?
Using instrumental methods as they’re accurate, sensitive, rapid and are useful when the sample is very small
What can chemical analysis be used to identify?
Additives in food
How can artificial colours be detected and identified?
Paper chromatography
What does gas chromatography do?
Allows the separation of a mixture of compounds
Why may the mass of a product change in a reaction?
~ The reaction may not go to completion as it’s reversible
~ Some of the product may be lost when it’s separated from the reaction mixture
~ Some of the reactants may react in ways different from the expected reaction
What is the yield?
The amount of a product obtained
What is an example of a reversible reaction?
Ammonium chloride ~ ammonia + hydrogen chloride
What is the retention time?
The time taken for a substance to travel through the column
What is used as the solvent in paper chromatography?
Water or ethanol
What do the ink spots (solute) tell you?
How many chemicals are in the substance
Why is the baseline on paper chromatography marked with a pencil?
So it doesn’t run up with the ink and dissolve in the solvent
What are some reasons why gas chromatography is better than paper chromatography?
More accurate, sensitive and rapid
What does the filter paper do in paper chromatography?
Detects the chemicals and gives a reading of how many chemicals there are
What is the process of paper chromatography?
~ Pencil line put on filter paper
~ Spots of samples are put on the line
~ Put into a beaker of solvent ensuring that the sample is not put in the solvent
~ Lid is put on beaker to prevent evaporation
~ Wait for solvent to soak up paper, dissolve samples and separate them out
Why do the different samples separate out?
~ Some dissolve really easily in the solvent and move up quickly
~ Some don’t dissolve as well and move up slowly
How does gas chromatography work?
~ Sample is vaporised and passed through a column
~ The chemicals are carried through the column at different speeds and they separate
~ A detector detects the different chemicals and shows them as a peak on a chart
What does the molecular ion peak give you?
The relative formula mass of the compound
Why is a mass spectrometer useful?
It can identify chemicals quickly, accurately and can detect small amounts
What do the number of peaks show on the output data from gas chromatography?
The number of different compounds
Where is the molecular ion peak found?
The peak on a mass spectrometer which is furthest on the right
What is one mole of a compound?
The relative formula mass in grams
A compound contains 1 mole of carbon, 2 moles of hydrogen and 1 mole of oxygen.
What is the empirical formula?
CH2O
Why may the percentage yield after a reaction be lower than expected?
~ Some product may be lost when separated from the reaction mixture
~ Reaction might be reversible
~ Reactants may react in ways which are different to what is expected
How do you work out the % yield?
Amount produced
——————– X 100
Maximum amount possible
What are solvents used for?
Dissolving substances that can’t dissolve in water
