2013
YEAR 12 PRACTICAL
ASSESSMENT TEST
Chemistry
THE ACIDIC ENVIRONMENT
NAME: ___________________________
TIME ALLOWED:
60 minutes
TOTAL MARKS: 40
GENERAL INSTRUCTIONS:

Attempt all questions at each of three stations.

Answer all questions in the spaces provided.

Please leave all equipment as you found it before moving onto the next station.

You will require a calculator for this assessment task.

A periodic table is attached to this test.

You are allowed 30 minutes for station 1 and 15 minutes each for stations 2 and 3.
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(Working space only – this will not be marked)
STATION 1 TITRATION (20 marks)
AIM: To use a titration technique to determine the concentration of a solution of hydrochloric acid.
MATERIALS PROVIDED:
 A standard solution of 0.100 mol L-1 sodium carbonate.
 A solution of hydrochloric acid of unknown concentration.
 A dropper bottle containing methyl orange indicator.
 Glassware - burette, conical flask, funnel, pipette and beakers.
 Additional materials - wash bottle (containing distilled water), clamp, tile and pipette filler.
INSTRUCTIONS:
 Collect no more than 120 mL of the known concentration of sodium carbonate solution in the
beaker labelled base.
 Collect no more than 120 mL of the unknown concentration of hydrochloric acid solution in the
beaker labelled acid.
 Your base should be placed into your conical flask and your acid into your burette.
 You should perform at least three titrations (that is, one rough and two accurate titrations) using
the apparatus provided and record each titre in the table in Question 2.
 Your titration technique will be assessed. Show one end point colour to your teacher.
 When you have finished, rinse all glassware and return all equipment to the appropriate place.
 Complete the additional questions on your answer sheet. All working should be shown.
1. Write a balanced equation for the reaction.
(2 marks)
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2. Perform three titrations to complete the information in the following table. Use this
information to calculate the concentration of the hydrochloric acid solution.
Rough
First titration
Second titration
(mL)
(mL)
(mL)
Final
reading =
First
reading =
(6 marks)
Remember: show
one end point to
your teacher.
Titre =
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3. Justify the use of this method of volumetric analysis.
(2 marks)
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TECHNIQUE MARK (teacher use only): ________________
(10 marks)
STATION 2 ESTERS (10 marks)
1. Examine the model of a molecule of an ester at this station.
(a) Draw a structural diagram of this molecule.
(2 marks)
(b) Name this ester molecule. _________________________________________
(1 mark)
(c) Name the two reactants that would be used to prepare this ester.
(2 marks)
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2. Examine the reflux apparatus set up by your teacher.
List one obvious aspect of this set-up which represents a poor technique and give a reason
why this technique is incorrect.
(2 marks)
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3. A student collected the following information about three chemicals.
Compound
1-hexanol
pentanoic acid
1-propyl ethanoate
Molecular mass (g mol-1)
102.2
102.1
102.1
Boiling point (°C)
157.5
185.5
101.6
(a) Explain the difference between the boiling points of all three substances.
(2 marks)
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(b) In answering part (a) suggest why it is important that the molecular mass of chemicals
are similar when investigating the reasons for differing boiling points.
(1 mark)
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STATION 3 ATOMIC ABSORPTION SPECTROMETRY (10 marks)
A scientist prepared five 100 mL standard lead ion solutions by adding nitric acid to each sample and filtering
the solution. After filtration, each solution was analysed using atomic absorption spectrometry. The results of
this analysis are shown below.
Pb2+ Concentration (mgL-1)
Absorbance
2.0
0.31
4.0
0.59
6.0
0.92
8.0
1.20
10.0
1.49
(a) Produce a calibration graph on the grid below by plotting a line of best fit for the five standard
lead ion solutions and label both axes.
(4 marks)
AAS Calibration Graph for Pb2+
(b) (i) A sample of soil weighing 0.50 g was found to be contaminated with lead.
The soil sample was analysed using the same method shown in (a).
(1 mark)
Unknown soil sample absorbance = 1.3
Use the graph to determine the lead ion concentration for this soil sample. ___________________
(ii) Comment on the validity of your answer to (i). _________________________________________
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(2 marks)
(c) Calculate the percentage by weight of lead ions in the soil.
(2 marks)
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(d) The soil comes from an old industrial site. Suggest a possible cause of this contamination.
(1 mark)
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End of Test