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What is the relative mass of the proton ? 1
What is the relative mass of the neutron ? 0
What is the relative mass of the electron ? 1/1800 or 1/2000 or very small
What is the mass number ? The total number of protons and neutrons in an atom
What is the atomic number ? The number of protons in an atom
What is an isotope ? Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element.
Give a definition for the relative atomic mass of an element The relative atomic mass of an element (Ar) compares the mass of atoms of the element with the 12C isotope. It is an average value for the isotopes of the element.
Give a definition for the relative formula mass of a compound The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of the atoms in the compound
What is one mole of a substance ? The relative formula mass of a substance, in grams.
Elements and compounds can be detected and identified using instrumental methods. List the advantages of using instrumental methods. Instrumental methods are 1. accurate, 2. sensitive 3. rapid 4. are particularly useful when the amount of a sample is very small.
What type of chemical analysis can be used to identify additives in foods. Artificial colours can be detected and identified by paper chromatography
Why do you use pencil and not pen to draw the base line in paper chromatography it might dissolve in the solvent and make it difficult to interpret results. ***do not say it would effect the result***
Suggest why it is important to be able to identify the colour additives in food. To check if safe to eat
Describe how gas chromatography works. Different substances, carried by a gas, travel through a column packed with a solid material at different speeds, so that they become separated. The time taken for a substance to travel through the column can be used to help identify the substance
What is the output of the gas chromatography column linked to ? the output from the gas chromatography column can be linked to a mass spectrometer, which can be used to identify the substances leaving the end of the column
What do the number of peaks on the output of the gas chromatograph tells us ? the number of peaks on the output of a gas chromatograph shows the number of compounds present
What is the retention time ? The time taken for a substance to reach the detector
What part of the mass spectrometer graph gives the molecular mass of a substance ? The molecular mass is given by the molecular ion peak.
Why do different compounds separate in a gas chromatography column? Different substances travel at different speeds
In what part is the mixture separated ? The column
Why is helium used as a carrier gas in chromatography? It is inert (uncreative)
When a blood sample is taken from an athlete the sample is often split into two portions. Each portion is tested at a different laboratory. To avoid bias
Even though no atoms are gained or lost in a chemical reaction, it is not always possible to obtain the calculated amount of a product , give 3 reasons why ? aka : why is the actual yield always less than the theoretical yield ? 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.
What is the amount of product obtained in a chemical reaction called ? The amount of a product obtained is known as the yield.
What formula is used to calculate the % yield ? actual yield / theoretical yield x 100
What is the symbol for a reversible reaction?
Give an example of a reversible reaction ?
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