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Chemistry > C2.3 > Flashcards

C2.3 Flashcards

1
Q

How do you work out the number of neutrons?

A

Mass number - atomic number

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2
Q

What actually is the atomic mass?

A

An average mass number of the isotopes

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3
Q

Why does chlorine have a relative atomic mass (Ar) or 35.5?

A

~ Because it is an average mass number of the isotopes

~ It does NOT mean that it has half a proton or neutron

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4
Q

What is the relative formula mass (Mr) of H2O?

A

1 x 2 + 16

2 + 16 = 18

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5
Q

The relative atomic mass (Ar) is the mass of what?

A

A particular atom compared to the 12C isotope

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6
Q

How do you work out the percentage by mass of an element in a compound?

A

Relative formula mass of the compound

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7
Q

What is the empirical formula?

A

The simplest whole number ratio of atoms of each element in a compound

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8
Q

What is the mass of a proton?

A

1

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9
Q

What is the mass of a neutron?

A

1

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10
Q

What is the mass of an electron?

A

Very small

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11
Q

What is the mass number made up of?

A

Protons + neutrons

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12
Q

What is one mole of a element?

A

The relative atomic mass in grams

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13
Q

How can elements and compounds be detected?

A

Using instrumental methods as they’re accurate, sensitive, rapid and are useful when the sample is very small

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14
Q

What can chemical analysis be used to identify?

A

Additives in food

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15
Q

How can artificial colours be detected and identified?

A

Paper chromatography

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16
Q

What does gas chromatography do?

A

Allows the separation of a mixture of compounds

17
Q

Why may the mass of a product change in a reaction?

A

~ 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

18
Q

What is the yield?

A

The amount of a product obtained

19
Q

What is an example of a reversible reaction?

A

Ammonium chloride ~ ammonia + hydrogen chloride

20
Q

What is the retention time?

A

The time taken for a substance to travel through the column

21
Q

What is used as the solvent in paper chromatography?

A

Water or ethanol

22
Q

What do the ink spots (solute) tell you?

A

How many chemicals are in the substance

23
Q

Why is the baseline on paper chromatography marked with a pencil?

A

So it doesn’t run up with the ink and dissolve in the solvent

24
Q

What are some reasons why gas chromatography is better than paper chromatography?

A

More accurate, sensitive and rapid

25
Q

What does the filter paper do in paper chromatography?

A

Detects the chemicals and gives a reading of how many chemicals there are

26
Q

What is the process of paper chromatography?

A

~ 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

27
Q

Why do the different samples separate out?

A

~ Some dissolve really easily in the solvent and move up quickly
~ Some don’t dissolve as well and move up slowly

28
Q

How does gas chromatography work?

A

~ 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

29
Q

What does the molecular ion peak give you?

A

The relative formula mass of the compound

30
Q

Why is a mass spectrometer useful?

A

It can identify chemicals quickly, accurately and can detect small amounts

31
Q

What do the number of peaks show on the output data from gas chromatography?

A

The number of different compounds

32
Q

Where is the molecular ion peak found?

A

The peak on a mass spectrometer which is furthest on the right

33
Q

What is one mole of a compound?

A

The relative formula mass in grams

34
Q

A compound contains 1 mole of carbon, 2 moles of hydrogen and 1 mole of oxygen.
What is the empirical formula?

A

CH2O

35
Q

Why may the percentage yield after a reaction be lower than expected?

A

~ 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

36
Q

How do you work out the % yield?

A

Amount produced
——————– X 100
Maximum amount possible

37
Q

What are solvents used for?

A

Dissolving substances that can’t dissolve in water

Chemistry (20 decks)

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