Chemistry Paper 3 Last Minute Cram

Front 1

Front (Term)

Back 1

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Front 2

Safety precautions if working with an oxidising chemical?

Back 2

Keep away from flammable materials

Front 3

What is a danger of working with:

• dil. acids

• dil. alkalis

Back 3

Both irritants

Front 4

Draw the heating in a crucible apparatus for calculating the amount of water of crystallisation in a hydrated salt.

Back 4

Back (Definition)

Front 5

What reactions do we use heating in a crucible for?

Back 5

• working out the amount of water of crystallisation

• mass gain when Mg reacts with O2

• mass loss in various thermal decomposition reactions

Front 6

When using a gas syringe to measure the volume of a gas, always note down the temperature and pressure (as this affects gas volume)

Back 6

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Front 7

Front (Term)

Back 7

Back (Definition)

Front 8

When diluting a solution - why is it better to use a volumetric pipette than a measuring cylinder?

Back 8

It has a smaller uncertainty.

Front 9

Never put hot solutions into a volumetric flask. Why?

Back 9

• the heat could cause the flask to expand -> the volume measured would then be incorrect

Front 10

How to make sure the volume of distilled water that is added to a volumetric pipette to dilute a solution is accurate.

Back 10

Use a dropping pipette for the last few drops

Front 11

Invert several times to ensure a uniform solution.

Back 11

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Front 12

In experiments, before you start, wash out each piece of equipment with the solution to be used in it.

Why is this important?

Back 12

•If not rinsed out:

1) could be residual water which diluted the acid/alkali leading to a larger titre

2) could be a substance in that reacts with the acid/alkali leading to a larger titre

Front 13

Touch surface of alkali with pipette - to ensure correct amount is added.

Back 13

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Front 14

Make sure the jet space in the burette is filled with acid.

Back 14

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Front 15

Add a few drops of indicator.

Indicators are weak acids -> too much will affect the titration result

Back 15

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Front 16

Phenolphthalein colour?

Back 16

Alkali -> pink

Acid -> colourless

Front 17

Titrations

Add acid drop wise at end point.

Back 17

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Front 18

Titrations

Repeats titration until at least 2 concordant results (within 0.1cm^3)

Back 18

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Front 19

You can add distilled water to the conical flask during titration to wash the sides of the flask.

Explain why this is ok?

Back 19

Won’t affect the titration

• doesn’t change the number of moles of acid

• doesn’t react with the reagents

Front 20

Manganate titrations are self indicating.

Back 20

Back (Definition)

Front 21

What colour is the Mn2+ ion?

Back 21

Colourless

Front 22

Describe what the solution is like that is needed in order to find out how much iron is in iron tablets?

Back 22

• grind up the tablets

• make up to the solution to 100cm^3 with dil. H2SO4

• stopper the volumetric flask and invert

Front 23

Only use dilute sulfuric acid for manganate titrations.

Back 23

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Front 24

What will be the bad thing that happens if you use insufficient volumes of H2SO4 (or use a weak acid) in manganate titrations?

Back 24

(remember the role of the H2SO4 is to supply the 8H+ ions)

• the solution will not acidic enough

• MnO2 will be produced (instead of Mn2+)

• MnO2 is a brown ppt -> masks the colour change -> leads to a greater volume of manganate being used

Front 25

How to reduce uncertainties in measuring mass?

Back 25

• Use a balance that measures to more decimal places

• Use a larger mass

Front 26

How can you ensure a more accurate measurement of mass added?

Back 26

• weigh before and after addition and then calculating the difference will ensure a more accurate measurement of the mass added

Front 27

Errors in flame calorimetry?(these are just the ones you forgot)

Back 27

• Evaporation of fuel after weighing the spirit burner

• measurements not made under standard conditions - H2O is a gas

Front 28

Flame calorimetry diagram?

(Remember the lid)

Back 28

Back (Definition)

Front 29

When describing how to do an enthalpy change reaction.

Always add the solution first to the polystyrene cup

Then add the solid on the 4th minute

Back 29

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Front 30

When describing how to do an enthalpy change reaction.

Always add the solution first to the polystyrene cup

Then add the solid on the 4th minute

Back 30

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Front 31

Enthalpy change

Make sure to stir the solution constantly (before 4 minutes and after)

Why is this important?

Back 31

All the solution at the same temperature

Front 32

Enthalpy change

How do you know if a reaction is exothermic?

Back 32

The temperature will increase

+ve ΔT

Front 33

Enthalpy change

How do you know if a reaction is exothermic?

Back 33

The temperature will increase

+ve ΔT

Front 34

Enthalpy change

How do you know if a reaction is endothermic?

Back 34

The temperature of the solution will decrease