Chemistry C2.3 : How much?
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- Created by: TillyF
- Created on: 25-02-17 12:15
What is the relative mass of both a proton and a neutron?
1
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Where is most of the mass in an atom?
In the nucleus, because the mass of the electrons is so tiny. The mass number is the total number of neutrons and protons.
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How can we calculate the number of neutrons?
Number of neutrons: mass number - atomic (proton) number
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What is an isotope?
Atoms of the same element with different numbers of neutrons. (proton number is always the same)
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What is common between isotopes?
The atomic (proton) number is the same but each isotope has a different mass.
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What makes an isotope radioactive?
The extra neutrons in the nucleus, can make the isotope unstable and therefore make it radioactive.
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Why do isotopes always have the same chemical properties?
Their reactions depend on their electronic structure, their atoms will have the same number of electrons/ protons but a different number of neutrons.
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What is relative atomic mass?
The ratio of the average mass of one atom of an element, to 1/12 of an atom of carbon-12
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The relative atomic mass is the same or similar to...
The mass number of its most common isotope
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What is atomic mass an average of?
The atomic mass is the average mass of an elements isotopes compared with the standard carbon-12 atom.
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How do we calculate the relative atomic mass of a compound? eg. H2O
Add the relative atomic masses of each compound are added together. H=1 O=16 so H2O = (1x2) + 16 = 18
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What is a mole?
A mole is a unit for relative atomic or formula mass expressed in grams
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How do we calculate the percentage of an element in a compound?
mass of element/ total mass of compound x 100
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What can the empirical formula find?
The ratio of elements in a compound
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How do we calculate the ratio of elements in a compound using the empirical formula?
1. Find the masses of the elements in the compound 2. look up the relative atomic mass values 3. divide the masses by the relative atomic mass 4. find the ratios by dividing by the smallest number in the ratio
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How do we calculate reacting masses? eg. 2HCL
A1 of H= 1 mass of H2 = (2x1) = 2g A1 of Cl = 35.5 Cl2 = (2x35.5) = 71g therefore, 2HCl = 73g
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How do we calculate percentage yield?
percentage yield = amount of product produced/ maximum amount of product possible x100%
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Why do very few chemical reactions have a yield of 100%?
- reaction may be reversible (as products form the react to re-form reactants again) -some reactants may give unexpected products -some product may be lost in handling or in the apparatus -reactants may be impure -product mixed with another
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Why is it important for companies to have a large percentage yield?
Making a product more efficiently, meaning making less waste. Lots of product made from reactants = higher profit for business if less energy/raw materials are wasted = more money if greater yield = better for environment as less product is wasted
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What is a reversible reaction?
When a reactions products can react together to make the original reactants again.
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Why do we add food additives?
- extend shelf life - improve taste - improve food appearance
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What is one way that we could identify food additives?
Using paper chromatography
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How does paper chromatography work?
It works because some compounds in a mixture dissolve better than others in particular solvents. Their solubility determines how far the substances travel across the paper.
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How can we identify food additives from paper chromatography?
Once the compounds in a food have been separated, they can be identifies and compare them with the results from known substances, tested using the same solvents at the same temperature.
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Advantages of instrumental methods?
-accurate -quick -enable small samples to be analysed
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Disadvantages of instrumental methods?
-can be expensive -takes special training to use -gives results that can often be interpreted only by comparison with data from known substances
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Eg. of instrumental method?
Gas chromatography
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How does gas chromatography help us identify elements/substances in a compounds?
Gas chromatography separates compounds that are easily vaporised. The separated compounds pass into a mass spectrometer, which identifies them from its peak pattern.
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Describe the process of gas chromatography?
-mixture vaporised -carrier gas moves the vapour through the coiled column -compounds in sample have different attraction to material in comlumn
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Carry on with previous question:
-compounds with the stronger attractions will take longer to get through column, they have a longer retention time. -the compounds with weak attraction in the material in the column leave first as they have shorter retention times
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What can we do to identify the compounds separated by gas chromatography?
-separated compounds recorded on mass spectrometer, they are then identified by comparing the peaks on the screen to the results of a known substance. (in the same conditions to compare retention times)
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What is a mass spectrometer?
-Piece of equipment attached to a gas chromatography machine that identifies unknown substances quickly and accurately (even small quantities)
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What else can a mass spectrometer identify?
The relative formula mass of a compound
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What is the molecular ion peak found on a mass spectrometer?
This is the last peak on the spectrometer screen that enables us to identify the relative formula mass of a substance: enabling us to identify the type of element in the mass spectrometer
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Other cards in this set
Card 2
Front
Where is most of the mass in an atom?
Back
In the nucleus, because the mass of the electrons is so tiny. The mass number is the total number of neutrons and protons.
Card 3
Front
How can we calculate the number of neutrons?
Back
Card 4
Front
What is an isotope?
Back
Card 5
Front
What is common between isotopes?
Back
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