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Chemistry Michael > C2.3 Quantatice Chemistry and Analysis > Flashcards

C2.3 Quantatice Chemistry and Analysis Flashcards

1
Q

What does the atomic mass represent?

A

The protons and neutrons

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2
Q

What does the atomic number represent?

A

The protons

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3
Q

How do you find the number of neutrons in an element?

A

Atomic mass - Atomic number

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4
Q

What is the relative mass of a proton?

A

1

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5
Q

What is the relative mass of a neutron?

A

1

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6
Q

What is the relative mass of an electron?

A

Very small 1/1836

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7
Q

What are isotopes?

A

Different atomic forms of the same element which have the same number of protons but a different number of neutrons

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8
Q

What’s changed from an element and its isotope?

A

It’s atomic mass, if the atomic number changes, it would be a different element

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9
Q

What is the relative atomic mass (Ar)?

A

A way of comparing the masses of atoms of different elements - the Ar is the same as the atomic mass

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10
Q

How is the relative atomic mass (Ar) measured?

A

How heavy atoms of an element are compared with the mass of an atom of carbon-12

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11
Q

What is the relative atomic mass of an element which has more than one stable isotope?

A

An average value of all the different isotopes is taken in to count

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12
Q

What is the relative formula mass (Mr)?

A

All the relative atomic masses of the atoms in a compound added together e.g. the Mr of Iron Oxide (Fe2O3) would be (2x56) + (3x16) = 160 (56=Ar of Fe) (16=Ar of O)

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13
Q

What is a mole?

A

The Ar or Mr of a substance in grams is one mole of that substance e.g. Fe has an Ar of 56, so one mole is 56g

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14
Q

What is the formula for finding the number of moles?

A

No. of moles = Mass in grams (of element /compound)
÷ Mr (of element/compound)

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15
Q

What is the formula for finding the mass of a substance when you know the moles?

A

Mass = Moles x Mr

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16
Q

What is percentage mass?

A

A way of saying what proportion of the mass of a compound is due to the atoms of a particular element

17
Q

What is the formula for finding the percentage yield of an element in a compound (%)?

A

Ar x No. of atoms (of that element) / Mr (of whole compound)

18
Q

What is the empirical formula?

A

The simplest possible whole number ratio of atoms of each element within that compound - sometimes the empirical formula is the same as the molecular of a compound e.g. MF of sodium hydroxide is NaOH, can’t be simplified so NaOH is the EF

19
Q

How do you find the empirical formula? (5 steps)

A
  1. List all the elements in the compound
  2. Underneath them, write their masses or percentages
  3. Divide the mass/percentage by the Ar of that particular element
  4. Take the values from step 3 and divide them by the smallest value from step 3 - this is the ratio of elements in the compound
  5. If you get values that are not whole numbers, multiply all values until you get the lowest whole No.
20
Q

How would you work out the mass of a product from a certain mass of reactant? (This is a prediction of the yield)

A
  1. Write out the balanced equation for the reaction
  2. Find the Mr of the reactant and the product that you’re interested in
  3. Now divide both Mr’s by the reactant’s Mr to get what 1g of reactant produces
  4. Now multiply both sides by the mass given in the Q
21
Q

How would you work out the mass of a reactant from a certain mass of product?

A
  1. Write out the balanced equation for the reaction
  2. Find the Mr of the reactant and the product that you’re interested in
  3. Now divide both Mr’s by the product’s Mr to get what 1g of reactant produces
  4. Now multiply both sides by the mass given in the Q
22
Q

What is percentage yield?

A

A comparison between the amount of product you expect to get and the amount of product you actually get

23
Q

What is the formula for working out percentage yield (%)?

A

(Actual yield (grams) /Predicted yield (grams)) x 100

24
Q

Why are percentage yields never 100%? (3)

A

If the reaction is reversible, some of the products will react to make reactants, product is lost when it is separated from its reactants e.g. when you filter a liquid, you’ll always lose a bit of liquid and also, unexpected reactions may be happening

25
Q

How can you make an industrial process sustainable?

A

Use reactions with high percentage yields, use reactions that don’t require much energy and use raw materials from renewable sources

26
Q

What is chemical analysis used for?

A

To identify the different additives in food

27
Q

What can paper chromatography be used for?

A

To find out what dyes are in a certain food colouring

28
Q

How do you carry out paper chromatography?

A
  1. extract the colour from the food by mixing it with a few drop of solvent (e.g. water, ethanol, salt water etc.)
  2. Put a spot of the solution on a pencil baseline on some filter paper (don’t use pen because it might dissolve and mess everything up)
  3. Put the sheet in a beaker with some solvent - keep the baseline above the solvent
  4. The solvent seeps up the paper, taking the dyes with it - different dyes form spots in different places
29
Q

In paper chromatography, what is the filter paper called with the separated spots?

A

A chromatogram

30
Q

What does the chromatogram tell you in paper chromatography?

A

What different dyes colouring contain, if two different colourings travel the same distance, they’re likely to be the same dye, it also tells you how many dyes a colouring contains

31
Q

What method allows you to identify different elements and compounds?

A

Instrumental methods

32
Q

What advantages are there to using instrumental methods over manual methods?

A

They are very sensitive and can detect tiny amounts of substances, they are very fast and can be automated (which saves time) and they are very accurate - machines don’t make mistakes like humans do

33
Q

Give an example of an instrumental method

A

Gas chromatography

34
Q

How is gas chromatography carried out?

A
  1. A gas is used to carry a mixture of substances through a column (tube) packed with a solid material
  2. The substances travel through the tube at different speeds so they’re separated
  3. The time each substance takes to reach the detector is called the retention time. It can be used to help identify substances
  4. The recorder draws a gas chromatogram
35
Q

What does the number of peaks on a GC chromatogram show?

A

The number of substances in the sample

36
Q

What can GC-MS be used for?

A

A mass spectrometer can identify substances leaving the column and can accurately detect very small quantities

37
Q

What does a mass spectrometer tell you?

A

It tells you the relative molecular mass of each substance, you can work out the Ar of the substances from the graph which is drawn - you just read of the x axis

Chemistry Michael (18 decks)

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