Chemistry C2.3

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What are the bottom and top numbers of an element on the periodic table and what do they mean?
Bottom = atomic number and it is the no. protons in an atom. Top = mass number that is the no. protons + no. neutrons
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What are the relative masses of Protons, Electrons and Neutrons respectively?
1, almost nothing, 1
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What are isotopes?
They are different atomic forms of the same element, which have the same no. Protons but different no. neutrons.
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What does Ar represent?
Ar = relative atomic mass which is a way of comparing the masses of atoms of different elements, it is usually the mass number of the element.
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Why is the carbon-12 isotope important when discussing Ar?
Because carbon-12 has an Ar of exactly 12 by definition, every element is compared to that.
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What happens when there is more than 1 stable isotope?
The relative atomic mass is the average of all the different isotopes and the abundance of each one.
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What is Mr?
it is relative formula mass which is the sum of all the relative formula masses in a compound.
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What is a mole? How is it calculated?
A mole is the relative mass of a substance in grams. No. Moles = Mass in g (of substance) / Mr (of substance).
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How do you calculate the percentage mass? What does it mean?
(Ar (of element) * no. atoms of that element) / Mr (of whole compound). It shows what proportion of the mass of a compound is due to atoms of one element.
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What shows the simplest possible whole number ratio of atoms of each element within the compound?
The empirical formula. It can quite often be the same as the molecular formula.
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What are the first three steps of finding the empirical formula?
1. List all the elements in the compound. 2. Underneath them, write their masses or percentages. 3. Divide each mass or percentage by the Ar of that element.
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What are the last 2 steps of the empirical formula?
4. Divide each number by the smallest result of step 3, this is your ratio. 5. If they are not whole numbers, multiply so that you get the lowest whole number ratio.
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How would you find the mass of a product?
1. Writ the balanced equation of the reaction. 2. Find the Mr of the reactant and product. 3. Divide both by the Mr of the reactant, to find what 1g of reactant would produce, then multiply by the amount of reactant.
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How would you find the mass of a reactant?
Same as product, except reverse what you divide and multiply by.
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What is the percentage yield?
It is a comparison between the amount of product you expect to get and the amount of product you actually get.
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How do you calculate the percentage yield?
(actual yield (grams) / predicted yield (grams)) * 100.
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Why are percentage yields never 100%, name 3 examples?
1. If the reaction id reversible it means that some of the product is not fully converted to product because the reaction goes both ways. 2. Product is lost when its sperated from the reactants e.g filtering and residue is left. 3.UnexpectedReactions
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What can be done to make industrial processes sustainable?
Use reactions with high percentage yields. Use reactions that don't require much energy, so less fuel burned etc. Use raw materials from renewable sources, never run out.
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What is chemical analysis used for?
Identifying different additives present in foods.
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How do you use paper chromotography?
Extract colour from a food sample by placing it with a few drops of solvent. Put a spot of the coloured solution on a pencil baseline on some filter paper (not pen, it dissolves). Put the sheet in a beaker w/ some solvent, baseline above the solvent.
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How do you use paper chromotography (Final Step).
The solvent seeps up the paper, taking the dyes with it. Different dyes form spots in different places.
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What does a chromatogram give you information about?
What dyes different colourings contain, each dye moves and if two move to the same place, they are likely to be the same. How many dyes a colouring contains, 4 spots means AT LEAST 4 dyes, not exactly 4. Dyes may have traveled similar distances.
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What are instrumental methods, why are they better than analysing substances manually?
it means using machines. They are very sensitive - they can detect even the tiniest amounts if substances. they are very fast and can be automated. They are very accurate.
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Name a commonly used instrumental method. How does it work (First 2 steps)?
Gas chromatography. A gas is used to carry a mixture of substances through a column (tube packed with solid material. the substances travel through the column at different speeds, they are separated.
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How does gas chromatography work (final 2 steps)?
the time each substance takes to reach the detector is called the retention time. It can be used to help identify the substance. Finally, the recorder draws a gas chromatogram.
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How do you tell how many substances there were from a gas chromatogram?
The number of peaks.
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What can the gas chromatography column be linked to? What can it do? How would you read this on its graphs?
A mass spectrometer. It can accurately identify the substances leaving the column and the relative molecular mass of each one. To find the relative molecular mass you just the read the value of the molecular ion peak.
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Other cards in this set

Card 2

Front

What are the relative masses of Protons, Electrons and Neutrons respectively?

Back

1, almost nothing, 1

Card 3

Front

What are isotopes?

Back

Preview of the front of card 3

Card 4

Front

What does Ar represent?

Back

Preview of the front of card 4

Card 5

Front

Why is the carbon-12 isotope important when discussing Ar?

Back

Preview of the front of card 5
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