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C5 - Quantitative analysis > C5 > Flashcards

C5 Flashcards

1
Q

Formula for hydrochloric acid

A

HCl

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2
Q

Formula of ethanoic acid

A

CH3COOH

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3
Q

Formula of carbon dioxide

A

CO2

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4
Q

Hydrogen

A

H2

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5
Q

Water

A

H2O

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6
Q

Formula of sodium chloride

A

NaCl

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7
Q

Formula of potassium chloride

A

KCl

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8
Q

Formula of ammonia

A

2NH3

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9
Q

Formula for calcium carbonate

A

CaCO3

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10
Q

Formula for Sulphuric Acid

A

H2SO4

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11
Q

Formula for nitric acid

A

HNO3

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12
Q

Formula for sodium hydroxide

A

NaOH

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13
Q

Formula for potassium hydroxide

A

KOH

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14
Q

Formula for magnesium carbonate

A

MgCO3

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15
Q

Formula for sodium sulphate

A

Na2SO4

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16
Q

Formula for potassium sulphate

A

K2SO4

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17
Q

Magnesium sulphate

A

MgSO4

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18
Q

Barium sulphate

A

BaSO4

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19
Q

Lead(II) nitrate

A

Pb(NO3)2

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20
Q

Lead iodide

A

PbI2

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21
Q

Potassium iodide

A

KI

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22
Q

Potassium nitrate

A

KNO3

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23
Q

Relationship between moles, mass and molar mass

A

Moles = mass/ molar mass

24
Q

What is relative atomic mass

A

Average mass of an atom when compared to the mass of 1/12th of a carbon-12 atom.

25
Q

How do you work out the percentage composition?

A

Substance% = substance mass/total mass * 100

26
Q

How do you work out the empirical formula for 0.72g of Mg and 0.48g of Oxygen

A 
Write the molar mass -> 
Mg = 24 , O = 16
Divide mass by molar mass to get moles ->
Mg moles = 0.72/24 = 0.03
O moles = 0.48/16 = 0.03
Divide by smallest number ->
Gives 1 of each atom ->
MgO
27
Q

How do you convert cm^3 into dm^3

A

Divide by 1000

28
Q

What is the relationship between concentration, moles and volume?

A 
Moles = Concentration * Volume
M = CV
29
Q

Formula for diluting solutions

A

Volume of water to add = (starting concentration/target concentration -1) * starting volume

30
Q

How do you calculate the amount of sodium in salt and why may this conversion be inaccurate?

A

1g of salt * 39.3 = 0.393g in 1g of sodium chloride
Sodium ions can come from other sources of food.
Like in monosodium glutamate- this contains sodium ions

31
Q

What would a pH curve for an acid being added to an alkali look like?

A

Go from a high pH of 14 to a low one of 1. (Vice versa)

32
Q

Why do you need several consistent titre readings in a titration?

A

Because you will be able to avoid having anomalous results.

You will have a more accurate average with more precision.

33
Q

Describe how phenolphthalein changes in alkali solutions when it becomes acidic

A

Pink in alkali solutions

Colourless in acidic solutions

34
Q

Describe the colours of litmus in acidic and alkali solutions

A

Blue in alkali solutions

Red in acidic solutions

35
Q

How is universal indicator (mixed) different from single ones?

A

Contains several different indicators
Changes over a range of different pH values
Continuous colour change

36
Q

Explain why an acid-base titration should use a single indicator rather than a mixed indicator

A

Because it gives a sudden change between pink and colourless which tells us what the end point is

37
Q

Describe an experimental method to measure the volume of gas produced in a reaction given appropriate details about the reaction.

A

Use a gas syringe to measure the amount of gas as the reaction goes on, plunger is pushed out gradually.
Use upward displacement: upturned cylinder of water in placed in a trough of water.
Air pressure keeps water inside
Delivery tube goes into cylinder
As gas fills, the water is pushed out. Gas can be measured.
Can measure the difference in masses to see how much gas has been released.

38
Q

How do you calculate the volume of gas ?

A

Amount of gas = volume of gas at RTP / molar volume at RTP

1.2dm^3 of CO2 contains -> 1.2/24 = 0.05 moles

39
Q

Describe the graph for volume of gas produced over a set time period

A

Gas produced increases at a decreasing rate

It starts off with a steep gradient but gradually becomes less steep and levels off eventually

40
Q

What happens when a reversible reaction is at equilibrium?

A

Rate of forward reaction is equal to the rate of the backwards reaction
Concentration of the reactants and products do not change.

41
Q

What happens when the concentration of a substance is decreased in a reversible reaction?

A

Position of equilibrium moves to its side. More of that product will be made.

42
Q

Why may a reversible reaction reach equilibrium?

A

Initially the rate of the forward reaction will decrease as these substances are used up.
This means the rate of the backwards reaction begins to increase as more product increases on its side. (more concentration)
They then react increasingly quickly until the rate of the forward reaction equals the rate of the backwards reaction.

43
Q

Why is a closed system important?

A

Because all the reactants stay in the solution, if they escaped then equilibrium would never be reached.

44
Q

What happens when pressure is increased and decreased?

A

Only using gases
Increased - position of equilibrium moves to the side of fewer moles
Decrease - moves to the side with more moles

45
Q

What happens when temperature is increased?

A

Position of equilibrium moves to the direction of the endothermic reaction - move to the left if right is an exothermic reaction

46
Q

What is the second stage of the contact process? Symbol equation?

A

Sulphur dioxide + oxygen ->

47
Q

What are the conditions needed in the contact process?

A

Vanadium oxide catalyst (V2O5) - increases ROR but does not change position of equilibrium
Temperature of 450 degrees centigrade - compromise as a lower temperature would produce more product as second stage is an exothermic process, although the rate of reaction would be too slow. So it gives a reasonable ROR without decreasing the yield too much.
Atmospheric pressure as the positions of equilibrium is already far to the right -> extra costs to increase pressure is not worth the small yield increase

48
Q

What is the difference between the ionisation of strong and weak acids?

A

Weak acid - party ionises in water and produces less H+ ions (produces an equilibrium mixture)
Strong acids - completely ionises in water and produces more H+ ions.

49
Q

Explain why the pH of a weak acid is much higher than the pH of a strong acid of the same concentration.

A

Because acid strength is a measure of how ionised an an acid is in the solution. The stronger it is, the more ionised it is.
The concentration is the amount of moles of acid which are dissolved in 1dm^3 of solution

50
Q

Explain why ethanoic acid reacts slower than hydrochloric acid of the same concentration

A

Because ethanoic acid has less H+ ions so there is a lower collision frequency between the reactant particles.
Hydrochloric acid has a higher concentration of H+ ions so a greater collision frequency.

51
Q

Explain why ethanoic acid is less conductive than hydrochloric acid of the same concentration

A

Ethanoic acid has a lower concentration of H+ ions to carry the charge through it than there is in hydrochloric acid.

52
Q

Explain, in terms of collisions between ions, why most precipitation reactions are extremely fast.

A

Because the collision frequency between ions in solution is very large. High change that different ions will collide with each other - hence the precipitate forms as soon as 2 suitable solutions are mixed together.

53
Q

Describe the experiment for testing for ions using barium chloride

A

Tests for sulphate ions
Acidify test solution with some hydrochloric acid
Add barium chloride
If sulphate ions are present -> white precipitate of barium sulphate forms

54
Q

Describe the experiment for testing for ions using lead nitrate

A 
Tests for Halide ions
Acidify with few drops of nitric acid
Add lead nitrate
White precipitate - chloride ions present
Cream precipitate - barium ions present 
Yellow precipitate - iodide ions present
55
Q

Construct word equations for simple precipitation reactions e.g. for the reaction between solutions of barium chloride and sodium sulfate

A

Barium chloride(aq) + sodium sulphate(aq) -> barium sulphate(s) + sodium sulphate(aq)

56
Q

Construct an ionic equation for reaction between lead nitrate and sodium chloride. Explain what spectator ions are here.

A

Pb2+(aq) + 2Cl-(aq) -> PbCl2(s)

Na+ and NO-3 ions are spectators because they do not take part in the reaction but form other products - sodium nitrate.

57
Q

Describe the stages involved in the preparation of a dry sample of an insoluble compound by precipitation given the names of the reactants:

A

Lead nitrate is added to potassium iodide to form a precipitate of lead iodide
Mixture is filtered to separate it from the potassium nitrate using a filter funnel and filter paper.
Lead iodide is washed with water on filter paper, then dried in a warm oven.

C5 - Quantitative analysis (1 decks)

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