P- Amounts =)

Question 1

State why it is important to fill the space below the tap in the burette before starting an accurate titration. (1)

Answer 1

Space will fill during titration/ titres added are too high.

Question 2

Suggest one reason why a 250 cm3 conical flask is preferred to a 250 cm3 beaker for a titration. (1)

Answer 2

↓ chance of losing liquid on swirling.

Question 3

During a titration, a chemist rinsed the inside of the conical flask with deionised water. The water used for rinsing remained in the conical flask.

Give one reason why this rinsing can improve the accuracy of the end-point. (1)

Answer 3

Returns reagent on the sides of the flask to the reaction mixture- ensure all reacts

Question 4

Explain why the water used for rinsing has no effect on the accuracy of the titre. (1)

Answer 4

X change no. of moles of reagents (water= one of the products)

Question 5

Suggest one reason why repeating a titration makes the value of the average titre more reliable. (1)

Answer 5

A single titration could be anomalous.

Question 6

State one hazard when using concentrated ethanoic acid and one safety precaution you would take to minimise this hazard. (1)

Answer 6

• corrosive
• eye protection/ gloves

Question 7

Suitable level of precision of relative formula mass?

Answer 7

Always round to 1 d.p. !!!

Question 8

A student rinsed the apparatus before starting an acid-base titration.
The volume of acid added from the burette was larger than expected.
What is the possible reason for this?

Answer 8

The burette was rinsed only with water.

Question 9

Suggest an appropriate safety precaution when using toxic chloroalkane gas. (2)

Answer 9

• fume cupboard
• avoid toxic vapour

Question 10

State the importance of percentage yield when choosing the method used to make a compound. (1)

Answer 10

get as much products as poss in a reaction

Question 11

State the importance of percentage atom economy when
choosing the method used to make a compound. (1)

Answer 11

• maximise mass of reactants –> desired
  product
• minimising amount of by-products

Question 12

Compound Solubility at 20 °C / g dm–3
barium hydroxide 38.9
calcium hydroxide 1.73

Suggest one reason why calcium hydroxide solution is not used in the titration of a 0.200 mol dm–3 solution of an acid. (1)

Answer 12

• dilution of acid needed /
• may react with CO2 in air

Question 13

The student rinses the burette with deionised water before filling with sodium hydroxide solution.
State and explain the effect, if any, that this rinsing will have on the value of the titre. (2)

Answer 13

• titre value increases
• NaOH would be more dilute

Question 14

The student uses a funnel to fill the burette with sulfuric acid before starting the titration. After filling, the student forgets to remove the funnel from the top of the
burette.
Suggest why this might affect the titre volume recorded. (1)

Answer 14

additional drops could have entered from funnel –> titre vol ↓

Question 15

State the reason for inverting the flask several times when making up a solution. (1)

Answer 15

to ensure the solution is homogenous.

Question 16

Titrating olive oil against bromine water.
A suitable target titre for the titration is 30.0cm3 of Br2 (aq).
Justify why a much smaller target titre would not be appropriate. (1)

Answer 16

smaller titre ↑ % uncertainty

Question 17

A sample of ethanoic acid is titrated with sodium hydroxide added from a burette.
Suggest how, using the same mass of ethanoic acid, the experiment could be
improved to reduce the percentage uncertainty. (2)

Answer 17

• ↓ conc of NaOH
• ↑ titre needed –> ↓ % uncertainty in titre

Question 18

Titration- adding NaOH to NH4Cl
Suggest a suitable piece of apparatus that could be used to measure out the sodium hydroxide solution.
Explain why this apparatus is more suitable than a pipette for this purpose. (2)

Answer 18

• burette
• ✔ deliver variable vols