rp exam qs paper 1

Question 1

Another student is required to make up 250 cm3 of an aqueous solution that
contains a known mass of MHCO3. The student is provided with a sample bottle
containing the MHCO3.
Describe the method, including apparatus and practical details, that the student
should use to prepare the solution

Answer 1

1) Place beaker* on balance and zero
Transfer solid into beaker
Record mass
2) Add distilled water
Stir (with a glass rod) or swirl
Until all solid has dissolved
3) Transfer to volumetric flask
With washings
Make up to 250cm3
Shake

Question 2

Suggest how the students’ method, and the analysis of the results, could be
improved in order to determine a more accurate value for the enthalpy of
reaction.
Justify your suggestions.

Answer 2

1a Insulate the beaker or use a polystyrene cup or a
lid, To reduce heat loss
2a Record the temperature for a suitable time before
adding the metal, To establish an accurate initial temperature
3a Extrapolate the cooling back to the point of addition
3b To establish a (theoretical) maximum temperature

Question 3

The student uses this method to complete a titration.
* Rinse a burette with distilled water.
* Fill the burette with sodium hydroxide solution.
* Use a measuring cylinder to transfer 25 cm3 of the citric acid solution into a
conical flask.
* Add 5 cm3 of indicator.
* Slowly add the sodium hydroxide solution from the burette into the conical flask.
* Add the sodium hydroxide solution dropwise near the end point until the indicator
just changes colour.
* Repeat the titration to get concordant results.
The method used by the student includes three practical steps that will lead to an
inaccurate final result.
For each of these three steps
* identify the mistake
* explain why it is a mistake
* suggest how the mistake can be overcome.

Question 4

A student determines the enthalpy change for the reaction between
calcium carbonate and hydrochloric acid.
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)
The student follows this method:
* measure out 50 cm3 of 1.00 mol dm–3 aqueous hydrochloric acid using a measuring
cylinder and pour the acid into a 100 cm3 glass beaker
* weigh out 2.50 g of solid calcium carbonate on a watch glass and tip the solid into
the acid
* stir the mixture with a thermometer
* record the maximum temperature reached.
The student uses the data to determine a value for the enthalpy change.
Explain how the experimental method and use of apparatus can be improved to
provide more accurate data.
Describe how this data from the improved method can be used to determine an
accurate value for the temperature chang

Answer 4

a. Use a burette/pipette (instead of a measuring
cylinder)
1b. Use a polystyrene cup (instead of a beaker) /
insulate beaker
1c. Reweigh the watchglass after adding the solid
1d: Use powdered solid
Stage 2: Temperature Measurements
2a. Measure and record the initial temperature of
the solution for a few minutes before addition
2b. Measure and record the temperature after the
addition at regular intervals (eg each minute) for 8+
minutes/until a trend is observed
Stage 3: Temperature Determination
3a. Plot a graph of temperature against time
3b. Extrapolate to the point of addition