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Science 3 > Chemistry b > Flashcards

Chemistry b Flashcards

0
Q

How is ‘a mole’ significant in chemistry ?

A

When you have that precise number of carbon-12 atoms it will weigh 12g. It works for every element (Ar) or compound (Mr)

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1
Q

What is ‘a mole’ ?

A

It is the name given to the number:

602,300,000,000,000,000,000,000

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2
Q

What is concentration ?

A

A measure of how crowded things are

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3
Q

What is concentration measured in ?

A

Moles per dm^3
(^3 = cubed)
Or Grams per dm^3

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4
Q

What are titrations ?

A

They allow you to find out exactly how much acid is needed to neutralise a quantity of alkali

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5
Q

What indicators are used in titrations ?

A
  • Phenolphthalein - alkali=pink acid=colourless

* Methyl Orange - alkalis=yellow acid=red

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6
Q

Why is universal indicator not used ?

A

It changes colour gradually, but we need definite colour change.

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7
Q

Explain the process of a titration experiment

A

Put some alkali in a flask with indicator. Gradually add the acid a bit at a time using the burette. The indicator will change as it becomes neutralised. Record the amount of acid used using the marks along the burette.

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8
Q

1 dm^3 is equal to what ?

A

1000cm^3 or a litre

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9
Q

See revision guide for titration calculations

A

Page 88

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10
Q

How can you measure energy transfer ?

A

By taking the temperature at the start and at the end of the reaction. The difference gives us the amount of energy transferred

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11
Q

What is biggest problem with energy measurements ?

A

Some of the energy will be loft to the surroundings

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12
Q

How can you reduce heat lost to the surroundings when measuring heat exchange ?

A
  • Insulate the equipment holding the liquid

* Put a lid on to reduce heat loss through evaporation

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13
Q

What is an exothermic reaction ?

A

A reaction which GIVES OUT energy to the surroundings, usually in the form of heat and shown by a RISE in temperature

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14
Q

What is an endothermic reaction ?

A

A reaction which TAKES IN energy from the surroundings, usually in the form of heat and shown by a FALL in temperature

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15
Q

What happens during a chemical reaction ?

A

Old bonds are broken and new bonds are formed

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16
Q

Is breaking bonds an endothermic reaction ?

A

Yes. Energy must be supplied to break existing bonds, so energy is TAKEN IN by the surroundings.

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17
Q

If energy is released to form bonds, what type of reaction is it ?

A

Exothermic

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18
Q

If the reaction is endothermic overall, what does this tell us ?

A

The energy required to break old bonds is greater than the energy released when new bonds are formed.

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19
Q

What is calorimetry ?

A

Different fuels have different amounts of energy. To measure the amount of energy released when a fuel is burnt, you can simply use the flame to heat up water. This is known as calorimetry

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20
Q

What equation will tell you the energy transferred by different fuels ?

A

Energy transferred = mass of water x specific heat capacity of water x temperature change

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21
Q

What is the unit energy change is recorded in ?

A

Joules

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22
Q

Why is the energy transfer figure usually lower than the real energy transferred ?

A

Because a lot of energy is wasted heating the container or the air around the container

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23
Q

What does the difference of heights between the reactants and the products represent on an energy level diagram ?

A

The energy change

24
Q

What sign is given to an endothermic reaction - positive or negative ?

A

Positive - the products appear higher than the reactants on the graph so are at a higher energy

26
Q

How does a catalyst affect activation energy ?

A

It provides a different pathway for a reaction that has a lower activation energy. This speeds up the reaction

27
Q

Do catalysts affect the energy transferred ?

A

No. The overall energy is the distance between reactants and products, so catalysts only have an effect on the height of the activation energy

29
Q

What is activation energy ?

A

The minimum energy needed by reacting particles to break their bonds

30
Q

What useful product is formed when you react hydrogen with oxygen ?

A

It is an exothermic reaction so energy is released

31
Q

What are the two ways hydrogen can be used as a fuel ?

A

By burning it in an engine

Using it in a fuel cell

32
Q

How is hydrogen used in engines ?

A

It can be burnt in oxygen as the fuel in combustion engines. It produces water which is clean unlike fossil fuels which release emissions

33
Q

What are the disadvantages of using hydrogen in combustion engines ?

A
  • A special, expensive engine is needed
  • Energy from another source is needed to make the hydrogen
  • hydrogen is very explosive
34
Q

What is a fuel cell ?

A

An electrical cell that is supplied with fuel and oxygen and uses energy from the reaction between them to generate electricity

35
Q

Why are fuel cells better than batteries ?

A

They don’t run down or need recharging, they will produce electricity as long as fuel is supplied

36
Q

Why are vehicle manufacturers developing fuel cell technology ?

A

They can be used instead of petrol/Diesel engines. The only by products are water and heat which are safe unlike greenhouse gases.

37
Q

What are the disadvantages of using fuel cells ?

A
  • Hydrogen takes up much more space than liquid fuels
  • Hydrogen is explosive so hard to store
  • The hydrogen comes from hydrocarbons or from the electrolysis of water so use electricity
38
Q

What is one method of testing for positive ions ?

A

Flame tests

39
Q

What ion turns a flame crimson ?

A

Lithium

40
Q

What ion turns a flame yellow ?

A

Sodium

41
Q

What ion turns a flame lilac ?

A

Potassium

42
Q

What ion turns a flame red (brick red) ?

A

Calcium

43
Q

What ion turns a flame green ?

A

Barium

44
Q

How do you do a flame test of a compound ?

A

First make sure a wire loop is really clean by dipping it in hydrochloride acid and then wash it with distilled water. Dip the loop in the compound and then place it in the flame

45
Q

What happens when you add sodium hydroxide solution to most metal ions ?

A

A precipitate forms because the metal hydroxides are insoluble

46
Q

How do precipitates forming help us to find positive ions ?

A

Some of the hydroxides have a characteristic colour and can therefore be identified

47
Q

What colour precipitate is formed with calcium ?

A

White

48
Q

What colour precipitate is formed with copper (II) ?

A

Blue

49
Q

What colour precipitate is formed with iron (II) ?

A

Green

50
Q

What colour precipitate is formed with iron (III) ?

A

Brown

51
Q

What colour precipitate is formed with aluminium ?

A

It is white at first but then dissolves to form a colourless solution

52
Q

What colour precipitate does magnesium form ?

A

White

53
Q

What is the first thing you do when finding negative ions ?

A

Check for CO2 which would mean carbonates are present

54
Q

How do you test for carbonates ?

A

Add an acid to the substance. This will create CO2 bubbles if it is a carbonate. To make sure they are CO2 bubbles, pass them through limewater. If the limewater is cloudy then it is carbon dioxide

55
Q

What are halides ?

A

Chloride, bromide and iodide

56
Q

How do you test for halides ?

A

Add dilute nitric acid and then silver nitrate solution, this will form precipitates

57
Q

What colour precipitate is formed by chloride ?

A

White

58
Q

What colour precipitate is formed by bromide ?

A

Cream

59
Q

What colour precipitate is formed by iodide ?

A

Yellow

60
Q

How do you test for sulphate ions ?

A

Add dilute hydrochloric acid followed by barium chloride solution. If a white precipitate forms it is sulphate

Science 3 (6 decks)

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