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A Level > Paper 3 corrections > Flashcards

Paper 3 corrections Flashcards

1
Q

why is free radical substitution a poor method for producing a high yield of chloromethane?

A

Because further substitution occurs

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2
Q

Why are C-C bonds the same length in benzene?

A

The pi bonds are delocalised

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3
Q

How can the concentration of bromine be monitored?

A

Measure the reduction of colour of bromine

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4
Q

Why is excess used for 0 order?

A

The concentration of HCOOH would be constant

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5
Q

What is the name for the reaction of metals with carboxylic acids?

A

Redox

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6
Q

When are they optical isomers and when are they cis/trans isomerism?

A

Optical = chiral centre

Cis / trans = anything that isn’t octahedral and bidentate ligands

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7
Q

Why would an excess of something be used?

A

So all the product is formed

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8
Q

How is pH measured?

A

With a pH probe on a data logger

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9
Q

How do you go from gdm-3 to moldm-3?

A

Divide by the molar mass of the compound

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10
Q

Why are salts more soluble than carboxylic acids?

A

Because they are ionic and are attracted to polar H2O molecules

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11
Q

If theres an impure compound, what would its TLC look like?

A

Two different spots on each place, not just one in the middle

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12
Q

Purification of an organic LIQUID

A
  • Add impure liquid to a separating funnel
  • If < 1 gcm-3 it is less dense than water so is on the top layer
  • If > 1 gcm-3 it is more dense than water so is on the bottom layer
  • If unknown density then the layer that increases with added distilled water is the water layer
  • Run out layers into separate beakers
  • Add drying agent of anhydrous CaCl2 to remove water
  • Filter into round bottomed flask
  • Redistill at boiling point of the organic liquid
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13
Q

What is the first step of purifying organic solvents?

A

Cool and filter under reduced pressure

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14
Q

How do you work out the percentage of a component in a mixture from gas chromatography?

A

You do the area under the peak of that compound / total area under the peaks

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15
Q

How do you plot a calibration curve for gas chromatography?

A

Plot graph of area against concentration for known concentrations of the compound and then compare the values

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16
Q

Which moles do you use which dividing the Q value to get the enthalpy change?

A

The limiting reagent so the one that isn’t in excess or the one with the least amount of moles

17
Q

What’s the test for ammonium ions?

A

Add NaOH and warm gently

Turns damp red litmus paper blue

18
Q

How do fuel cells work and what do they need?

A

The fuel reacts with oxygen to produce electrical energy

They need a constant supply of fuel an O2

19
Q

Is the fuel oxidised or reduced?

A

Oxidised - loses electrons

20
Q

When testing for halide ions, what do you add?

A

AgNO3 and then NH3

21
Q

What happens to the ppts when NH3 is added to the white/cream/yellow of halide ions?

A

Chlorine - white is soluble in dilute NH3
Bromine - cream is soluble in CONC NH3
Iodine - yellow is insoluble in NH3

22
Q

What are the limitations of calorimetry?

A

Heat loss to surroundings
Non standard conditions
Contents of calorimeter may evaporate

23
Q

What is there to watch out for when working out the enthalpy change from a calorimeter?

A

If there are two solutions then the m (mass) is them added together
If the reaction is exothermic then dont forget the minus sign

24
Q

What is the enthalpy change of neutralisation for strong acids and alkalis?

A

-57 kJmol-1 because they fully ionise in solution

25
Q

What is the ionic equation for the enthalpy change of neutralisation?

A

H+ + OH- —> H2O

26
Q

What is the enthalpy change of neutralisation for weak acids and alkalis?

A

Less exothermic than -57 kJmol-1

27
Q

What is the reaction at the negative terminal of a hydrogen fuel cell?

A

H2 + 2OH- ——-> 2H2O + 2e-

loses electrons

28
Q

What is the reaction at the positive terminal of fuel cells?

A

1/2O2 + H2O + 2e- ——-> 2OH-

Gains electrons

29
Q

How does a hydrogen fuel cell work?

A

The hydrogen reacts with the OH- ions to form water and release electrons, which are gained by the oxygen which reacts with the water to form more OH- ions. This cycle repeats with an H2O waste product

30
Q

What is the overall equation of a hydrogen fuel cell?

A

H2 + 1/2 O2 ——-> H2O

A Level (25 decks)

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