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OCR chemistry > C5 > Flashcards

C5 Flashcards

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1
Q

What does it mean when a solution is more concentrated?

A

The more solute (the solid you’re dissolving) you dissolve in a given volume, the more crowded the molecules are and the more concentrated the solution.

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2
Q

How is concentration sometimes measured?

A

In grams per dm³

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3
Q

How do you find concentration with mass of solute and volume of solution?

A

Concentration = Mass of solute ÷ Volume of solution

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4
Q

How do you convert cm³ to dm³?

A

Divide by 1000

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5
Q

How do you convert grams per dm³ to moles per dm³?

A

Divide grams per dm³ by the relative formula mass of the solute

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6
Q

What is a standard solution?

A

Any solution that you know the concentration of.

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7
Q

What do titrations show us?

A

How much acid is needed to neutralise a given quantity of alkali, or vice versa

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8
Q

How do you perform titration?

A

The indicator changes colour when the alkali is neutralised - record the amount of acid needed, which is known as the titre.

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9
Q

What is the indicator often used in titration?

A

Phenolphthalein or methyl orange

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10
Q

Why is universal indicator not used in titration?

A

It changes colour gradually whereas you want a single colour change to be able to accurately measure the titre.

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11
Q

What are the colours of phenolphthalein and methyl orange in acids/alkalis?

A

Methyl orange - yellow in alkalis, red in acid

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12
Q

How do you calculate concentration with number of moles and volume of solution?

A

Concentration = Number of moles ÷ volume of solution

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13
Q

How do you convert moles per dm³ to grams per dm³?

A

Multiply moles per dm³ by the relative formula mass of the solute

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14
Q

What is molar volume?

A

The volume occupied by one mole of gas.

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15
Q

What is the common unit for molar volume?

A

mol/dm³

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16
Q

How do you calculate molar volume?

A

Gas volume ÷ number of moles

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17
Q

At room temperature, what is the molar volume of all gases?

A

24dm³/mol - one mole of any gass always occupies 24dm³ at room temperature and pressure.

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18
Q

What is yield?

A

The amount of product you get from a reaction.

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19
Q

What is percentage yield?

A

It tells you about the overall success of an experiment. It compares what you should get (theoretical yield) and what you get in practice (actual yield).

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20
Q

How do you calculate percentage yield?

A

(Actual yield ÷ Theoretical yield) x 100

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21
Q

What is the theoretical yield?

A

The mass of product you’d make if all the reactants were converted to products.

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22
Q

Why is it important to maintain a high percentage yield?

A

In industry it’s important in order to reduce waste and keep costs as low as possible.

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23
Q

What is atom economy?

A

The atom economy of a reaction tells you what percentage of the mass of the reactants was converted into a desired product.

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24
Q

How do you calculate atom economy?

A

(Total MR of desired products ÷ Total MR of all products) x 100

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25
Q

Why are reactions with low atom economies unsustainable?

A

Reactions with low atom economies use up resources very quickly. At the same time, they produce lots of waste that have to be somehow disposed.

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26
Q

Why are reactions with low atom economies expensive?

A

Raw materials can be expensive to buy and waste products can be expensive to remove and dispose of responsibly.

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27
Q

What is one way to resolve the problem of a reaction with low atom economy?

A

You can find a use for the waste products rather than just throwing them away. There’s often more than one way to make a product, so the trick is to find a way which produces useful “by-products”.

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28
Q

What factors need to be considered in industry?

A

Whether a reaction is reversible

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29
Q

What is rate of reaction?

A

How quickly a reaction happens - it can be observed either by how quickly the reactants are used or by how quickly the products are formed

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30
Q

How can you calculate rate of reaction?

A

Rate of reaction = Amount of reactant used or amount of product formed ÷ Time

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31
Q

How can you measure rate of reaction with precipitation?

A

This method works where mixing 2 clear solutions produces a precipitate. You mix the two together and put the flask on a piece of paper than has a mark on it. Observe the mark and measure how long it takes for it to be obscured.

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32
Q

What is the problem with measuring rate of reaction with precipitation?

A

The result is subjective - different people may not agree on when the mark is obscured

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33
Q

How can you measure rate of reaction with a change in mass?

A

You can measure the rate of a reaction that produces a gas using a mass balance. As the gas is released, the lost mass is easily measured on the balance. The quicker the reading drops, the quicker the reaction.

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34
Q

What can you do with the results from measuring rate of reaction with a change of mass?

A

You can plot a graph of change in mass against time

35
Q

How can you measure rate of reaction with the volume of gas given off?

A

This involves a gas syringe to measure the gas given off. The more gas given off during a set time interval, the faster the reaction.

36
Q

What can you do with the results from measuring rate of reaction with the volume of gas given off?

A

You can plot a graph of gas volume against time elapsed

37
Q

If you have a graph of amount of product formed against time, what is the gradient equal to?

A

The rate of reaction

38
Q

If you have a graph that is curved, how do you find the gradient?

A

To find the gradient at a certain point, you have to draw a tangent at that point. The rate at that point is the gradient of the tangent.

39
Q

What is the relationship between the rate of reaction and time?

A

1/time is proportional to rate

40
Q

What does the rate of a chemical reaction depend on?

A

The energy transferred during a collision.

41
Q

How does increasing temperature increase the rate of reaction?

A

Therefore, at higher temps there are more successful collisions.

42
Q

How does increasing concentration/pressure increase the rate of reaction?

A

In a gas, increasing pressure makes particles more crowded, making the frequency of collisions increase.

43
Q

How does increasing surface area increase the rate of reaction?

A

Particles with a higher surface area to volume ratio (meaning that more of it will be exposed compared to its overall volume) will have more area to work on, and so the frequency of collisions increases.

44
Q

What is a catalyst?

A

A substance which increases the rate of a reaction without being chemically changed or used up.

45
Q

How do catalysts work?

A

They decrease the amount of activation energy needed for a reaction to occur.

46
Q

How do catalysts decrease the amount of activation energy needed?

A

They provide an alternative reaction pathway that has a lower activation energy.

47
Q

What are biological catalysts?

A

Enzymes - they catalyse the chemical reactions in living cells. They affect processes such as respiration, photosynthesis and protein synthesis.

48
Q

What is a reversible reaction? ⇌

A

A reaction where the products can react with each other to produce the original reactants.

49
Q

What is the relationship between concentrations in a reversible reaction?

A

As reactants react, their concentrations fall - so the forward reaction will slow down. As more products are made and their concentrations rise, the backward reaction speeds up.

50
Q

What is equilibrium?

A

It is when the forward reaction occurs at the same rate as the backward reaction in a reversible reaction. It ca only occur in a closed system.

51
Q

What happens to the concentrations of reactants and products when equilibrium is achieved?

A

They have reached a balance and don’t change.

52
Q

What is a “closed system”?

A

A closed system means that no products or reactants can escape.

53
Q

When a reaction is at equilibrium, are the reactants and products always equal?

A

No

54
Q

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

A

This means that there is “lots of products and not much of the reactants” (the concentration of products > the concentration of reactants)

55
Q

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

A

This means that there is “lots of the reactants but not much of the products” (the concentration of reactants > the concentration of products)

56
Q

What three things change the position of equilibrium?

A

Concentration

57
Q

What is Le Chatelier’s principle?

A

If there’s a change in concentration, pressure or temperature in a reversible reaction, the equilibrium position will move to counteract the change.

58
Q

How does the equilibrium position change if temperature changes?

A

If you increase the temperature, the equilibrium will move in the endothermic direction to absorb the extra heat.

59
Q

How does the equilibrium position change if pressure changes?

A

If you decrease the pressure, the equilibrium will move towards the sides that has more moles of gas to increase pressure.

60
Q

How does the equilibrium position change if concentration increases?

A

If you increase the concentration of the products, the equilibrium will move to the left to use up the products (making more reactants).

61
Q

How does the equilibrium position change if concentration decreases?

A

If you decrease the concentration of the products the equilibrium will move to the right to use up the reactants (making more products).

62
Q

How can changing equilibrium have applications in industry?

A

You can increase yield by changing the conditions to shift the equilibrium to the right (towards the products).

63
Q

If carbonate ions are present, a white precipitate of barium carbonate will be produced.

A

What should happen if a carbonate is present when you add barium chloride to the solution?

64
Q

The mixture should fizz, as a result of the carbonate reacting with the acid to produce carbon dioxide gas.

A

What should happen if a carbonate is present when you add hydrochloric acid to the solution, after adding barium chloride?

65
Q

A colourless solution containing Ba²⁺ ions.

A

What is the product of barium carbonate reacting with hydrochloric acid?

66
Q

The same way you test for carbonates - you add barium chloride and then dilute hydrochloric acid.

A

How can you test for sulfate ions?

67
Q

If carbonate ions are present, a white precipitate of barium sulfate will be produced.

A

What should happen if sulfate ions are present when you add barium chloride to the solution?

68
Q

Barium sulfate will not react with hydrochloric acid, which proves that you’ve got sulfate ions and not carbonate ions.

A

Why do you add hydrochloric acid when testing for sulfate ions?

69
Q

Produces a crimson red flame

A

How does Lithium react in a flame?

70
Q

Produces a yellow flame

A

How does Sodium react in a flame?

71
Q

Produces a lilac flame

A

How does Potassium react in a flame?

72
Q

Produces a brick red flame

A

How does Calcium react in a flame?

73
Q

Produces a blue-green flame

A

How does Copper react in a flame?

74
Q

Dip the wire loop into a sample of the metal compound and put the loop into the flame.

A

How do you perform a flame test for metal?

75
Q

You add a few drops of sodium hydroxide to a solution of the mystery compound. If a hydroxide precipitate forms, you can use its colour to tell which metal ion is present.

A

How can you test some metal ions with sodium hydroxide?

76
Q

Ca²⁺ + 2OH⁻ → Ca(OH)₂

A

What colour precipitate does Calcium, Ca²⁺ produce when reacted with Sodium Hydroxide? What is the Ionic Equation?

77
Q

Cu²⁺ + 2OH⁻ → Cu(OH)₂

A

What colour precipitate does Copper, Cu²⁺ produce when reacted with Sodium Hydroxide? What is the Ionic Equation?

78
Q

Fe²⁺ + 2OH⁻ → Fe(OH)₂

A

What colour precipitate does Iron(II), Fe²⁺ produce when reacted with Sodium Hydroxide? What is the Ionic Equation?

79
Q

Fe³⁺ + 3OH⁻ → Fe(OH)₃

A

What colour precipitate does Iron(III), Fe³⁺ produce when reacted with Sodium Hydroxide? What is the Ionic Equation?

80
Q

Then: Zn(OH)₂ + 2OH⁻ → ZN(OH)₄²⁻

A

What colour precipitate does Zinc, Zn²⁺ produce when reacted with Sodium Hydroxide? What is the Ionic Equation?

81
Q

A method which involves using machines rather than a person doing chemical tests manually.

A

What is an instrumental method?

82
Q

They are very accurate - they don’t involve human error.

A

What are the advantages of instrumental methods?

83
Q

Mass spectrometry - technique which can find the relative molecular mass of a mystery compound

A

What are some examples of instrumental methods?

OCR chemistry (6 decks)

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