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Chemistry 1 > C5 > Flashcards

C5 Flashcards

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1
Q

What will one mole of any substance’s mass in grams be equal to?

A

The RFM of that substance

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2
Q

What is molar mass?

A

The mass of one mole

Measured in grams per mole

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3
Q

What is the formula for finding the number of moles?

A

RFM

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4
Q

What is the relative atomic mass?

A

It’s the average mass of an atom of the element compared to the mass of 1/12th of an atom of carbon-12

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5
Q

How do you use moles to work out masses in reactions?

A

Balance equation
Calculate moles
Find mole ratio

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6
Q

How do you calculate the percentage composition by mass of compounds?

A

RFM of everything

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7
Q

What is an empirical formula?

A

Smallest whole number ratio of atoms In a compound

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8
Q

How do you work out the empirical formula?

A

List elements
Write out experimental masses or percentages
Divide each mass or percentage by the RAM
Put in ratio
Simplify

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9
Q

What is concentration?

A

A measure of how crowded things are

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10
Q

What can concentration be measured in?

A

Moles per dm3

Grams per dm3

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11
Q

How do you work out concentration?

A

Volume

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12
Q

How do you convert moles into grams per dm3?

A

Mass = number of moles X RFM

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13
Q

How do you work out diluting something concentrated?

A

Work out ratio
Multiply by volume you want to end up with
Work out volume of water you’ll need to dilute
Volume of water = total volume - volume to dilute

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14
Q

How do you use sodium content to estimate the mass of salt?

A

Find ratio of sodium chloride RFM to sodiums RAM

Multiply by the amount of sodium

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15
Q

What is salt?

A

Sodium chloride

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16
Q

What are titrations used for?

A

Finding out concentrations

Find out exactly how much acid is needed to neutralise a quantity of alkali (or vice versa)

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17
Q

Describe titration

A

Use pipette to add some alkali to a conical flask and add 3 drops of indicator
Fill burette with acid (do below eye level for safety)
Use burette to add acid swilling after every addition - go slowly when the end point is nigh
Indicator changes colour when all the alkali has been neutralised (phenolphthalein is pink in alkalis but colourless in acids)
Record volume needed for neutralisation

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18
Q

What do you need to do in titration results wise?

A

Get several consistent reasons within point one of each other

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19
Q

Why do you use single indicators for titrations?

A

You want to see a sudden colour change at the end point e.g litmus or phenolphthalein

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20
Q

Describe universal indicator

A

Turns a variety of colours so can estimate the pH of a solution - each colour indicates a narrow range of pH values
Made from a mixture of different indicators

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21
Q

What do pH curves show?

A

PH against volume of acid or alkali added (titration)

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22
Q

Describe a pH curve

A

Very gradual change at beginning
Shoots up at endpoint of titration (near vertical line)
Stays constant

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23
Q

How would you calculate the concentration of you were given titration results?

A

Work out no of moles of the known substance you have
Use balanced equation to find ratio to find moles of the unknown substance
Work out concentration of unknown

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24
Q

What does the collection method depend upon?

A

The gas

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25
Q

What are the two different types of collection methods?

A

Gas syringe

Upturned measuring cylinder or burette

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26
Q

What is a mole?

A

Simply the name given to a certain number

When you get precisely this number of atoms or molecules they weigh the same as their RAM (or RFM)

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27
Q

Describe a gas syringe

A

Can use it to collect any gas
Give volumes accurate to the nearest cm3
If reaction too vigorous can blow plunger out the end

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28
Q

Describe an upturned measuring cylinder or burette

A

Use delivery tube to bubble has into an upside down measuring cylinder or gas jar filled with water
No good for collecting gases which dissolve in water (eg ammonia)
Upturned burette is more accurate (nearest 0.1cm3)

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29
Q

How do you measure the mass of gas produced in a reaction?

A

Do reaction on a gas scale and as gas is released the mass disappearing is easily measured
Very accurate

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30
Q

How much does one mole of gas occupy at room temperature and pressure (RTP)?

A

24dm3

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31
Q

How do you work out the volume of things at RTP?

A

Volume =moles X 24

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32
Q

When do reactions stop?

A

When one reactant is used up

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33
Q

What is the reactant that’s used up in a reaction called?

A

The limiting reactant

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34
Q

In a reaction how much product is formed?

A

Amount of product is directly proportional to the amount of limiting reactant

35
Q

On graphs what are faster rates of reaction shown as?

A

Steeper curves

36
Q

What is a reversible reaction?

A

A reversible reaction is one where the products of the reaction can themselves react to produce the original reactants

37
Q

What is equilibrium?

A

Where the forward reaction is going at exactly the same rate as the backward reaction
Both reactions are still happening but there’s no overall effect

38
Q

What is the only way that equilibrium will be reached?

A

Is the reaction takes place in a closed system (none of the reactants or products can escape)

39
Q

What happens as a reversible reaction goes on?

A

As the reactants react their concentration falls so the forward reaction will slow down
As more and more products are made their concentration rises so the backward reaction speeds up

40
Q

What does it mean if the equilibrium lies to the right?

A

Lots of products and not much reactants

41
Q

What does it mean if the equilibrium lies to the left?

A

Lots of the reactants but not much of the products

42
Q

What three things can change the position of the equilibrium?

A

Temperature
Pressure (only gas reactions)
Concentration

43
Q

What happens if you add a catalyst to an equilibrium reaction?

A

Catalysts speed up both forward and backward reactions by the same amount so it reaches equilibrium quicker but you end up with the same amount of product

44
Q

What does the equilibrium try to do if you change something?

A

Minimise the changes

45
Q

What happens if you decrease the temperature of an equilibrium?

A

The equilibrium will try to move and increase it by moving in the exothermic direction

46
Q

What will happen if you raise the temperature of an equilibrium?

A

Will try to move and decrease it by moving in the endothermic direction

47
Q

What happens if you increase the pressure of an equilibrium?

A

Equilibrium tries to reduce it by moving in the direction where there are fewer miles of gas

48
Q

What happens if you decrease the pressure of an equilibrium?

A

The equilibrium tries to increase it by moving in the direction where there are more moles of gas

49
Q

What happens if you increase the concentration of the reactants in an equilibrium?

A

It tries to decrease it by moving to the right and making more product

50
Q

What happens If you increase the concentration of product in an equilibrium?

A

It will try and decrease it by shifting to the left and making more reactants

51
Q

What is the contact process used to make?

A

Sulfuric acid

52
Q

What are the three stages of the contact process?

A

Make sulfur dioxide by burning sulfur in air
Oxidise the sulfur dioxide (with catalyst) to make sulfur trioxide
Make sulfuric acid out of the sulfur trioxide

53
Q

What are the equations for the first stage of the contact process?

A

Sulfur + oxygen -> sulfur dioxide

S + O2 -> SO2

54
Q

What are the equations for the second stage of the contact process?

A

Sulfur dioxide + oxygen

->

55
Q

What are the equations for stage three of the contact process?

A

Sulfur trioxide + water -> sulfuric acid

SO3 + H2O -> H2SO4

56
Q

What is special about stage 2 in the contact process?

A

It’s reversible so the conditions can be controlled to get a higher yield

57
Q

What temperature do they use in stage two of the contact process?

A

Oxidising sulfur dioxide to form Sulfur trioxide is exothermic
But reducing the temperature slows the reaction down despite creating high yield
So a compromise of 450 degrees C is used to get quite a high yield quickly

58
Q

What pressure do they use in stage two of the contact process?

A

Two moles of product to three reactant so increasing the pressure increases yield
But it’s expensive and not necessary as equilibrium is already on the right
So 1 atmospheric pressure is used

59
Q

What catalyst is used in stage two of the contact process?

A

Vanadium pentoxide catalyst

Increases rate of reaction but doesn’t change equilibrium position

60
Q

What do acids do?

A

They ionise and produce hydrogen ions

Produce protons in water (hydrogen ions)

61
Q

What does it mean if an acid is strong?

A

It ionises completely in water so loads of hydrogen ions are released

62
Q

What does it mean if an acid is weak?

A

It doesn’t fully ionise in water and only small numbers of hydrogen ions are released - it’s a reversible reaction with the equilibrium lying on the left

63
Q

Give 3 examples of strong acids

A

Sulfuric acid
Hydrochloric acid
Nitric acid

64
Q

Give 3 examples of weak acid

A

Ethanoic acid
Citric acid
Carbonic acid

65
Q

What is the pH?

A

A measure of the concentration of hydrogen ions in the solution - can be measured with a pH meter or universal indicator paper

66
Q

What does acid strength tell you?

A

What proportion of the acid molecules ionise in water - number of molecules that produce hydrogen ions

67
Q

What is concentration telling you?

A

How many moles of acid there are in a litre of water - total number of dissolved acid molecules

68
Q

Which type of acid is a better electrical conductor?

A

Strong acids

69
Q

Why are strong acids better electrical conductors than weak acids?

A

Higher concentration of ions which carry the can the

70
Q

What does electrolysis of hydrochloric acid (strong) or ethanoic acid (weak) produce?

A

Hydrogen gas

71
Q

Which type of acid reacts faster?

A

Strong acids

72
Q

Why does a weak acid react slower than a strong acid?

A

Equilibrium causes a drip feed kind of reaction so the hydrogen ions are released more slowly (as more ions removed equilibrium shifts so more are supplied)
But in strong acid all the hydrogen a already there waiting to react - high collision frequency

73
Q

Despite strong acids reacting faster than weak acids what is true if their concentrations are the same in the beginning?

A

The will produce the same amount of product the weak acid will just take longer to get there

74
Q

Describe precipitation reactions

A

Involve two solutions reacting to make an insoluble substance - precipitate
Most involve ions - to react need to collide so they must be in solutions
Usually extremely quick because of high collision frequency between the ions

75
Q

How can you tell if something’s a precipitation reaction by looking at the equation?

A

It will be two solutions (aq) reacting to make a solid (s)

76
Q

What are spectator ions?

A

Ones which don’t change during a reaction - eg if they were dissolved in solution before and are still dissolved in solution after

77
Q

What is an ionic equation?

A

Concentrates on the precipitate and ignores the spectator ions

78
Q

How do you use precipitation reactions to identify mystery substances?

A

The colour of the precipitate can tell you what ions are present

79
Q

How do you test for sulfate ions?

A

Add dilute hydrochloric acid followed by barium chloride to the compound you have if it makes a white precipitate it’s a sulfate

80
Q

How do you test for chloride, bromide or iodide ions?

A

Add dilute nitric acid followed by lead nitrate to the original compound
Chloride = white
Bromide = cream
Iodide = yellow

81
Q

What can you use precipitation reactions to make?

A

Insoluble salts

82
Q

What’s important about the ions needed to make an insoluble salt?

A

They must be in solution so they can collide and form a precipitate

83
Q

Describe the process of making insoluble salts

A

Combine solutions to make precipitate
Put folded filter paper into a filter funnel over a conical flask and pour contents into it - make sure all the product from the beaker goes in
Rinse filter paper contents with distilled water to make sure all soluble salts washed away
Scrape what’s left onto fresh filter paper and leave to dry

Chemistry 1 (4 decks)

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