- You are provided with:
- Sodium hydroxide labelled solution A
- 128M hydrochloric acid labelled solution B
- Carboxylic acid labelled solution C
You are required to: - Standardize solution D with solution B
Determine the: - Reaction ratio between sodium hydroxide, solution A and the carboxylic acid, solution C
- Concentration of solution C in moles per litre.
Procedure1
Pipette 25 cm3 of solution A into a 250 cm3 beaker. Add distilled water to make up to 150 cm3. Label this solution D.
Fill the burette with solution B. Pipette 25cm3 of solution D into a 250cm3 conical flask. Add 2 dropsofphenolphthalein indicator and titrate with solution B. Record your results in table 1. Repeat the titration two more times and complete the table
I.
II.
III.
Final burette reading
Initial burette reading
Volume of solution B used (cm3)
- Determine the average volume of solution B (1mark
- Calculate the concentration in moles per litre of sodium hydroxide in:
Solution D (2marks)
Solution A (1mark)
Procedure 2
Using a clean burette, place 16cm3 of solution C into a 100 ml plastic beaker. Take the initial temperature of the solution and record it in table 2. Using a clean measuring cylinder, measure 4cm3 of solution A and add it to solution C in the 100ml beaker. Stir the mixture immediately with the thermometer and record in table 2 the maximum (final) temperature reached. Repeat the experiment with the other sets of volumes of C and Ain table 2 and complete it.
(Rinse the thermometer and the beaker with distilled water after each experiment. It is assumed that the initial temperatures for solution A and C are equal at room temperature.)
Volume of solution C (cm3)
16
12
8
6
4
2
Volume of solution A (cm3)
4
8
12
14
16
18
Final temperature (0C)
Initial temperature (0C)
Change in temperature, ∆T (0C)
- On the grid provided, plot a graph of ∆T (vertical axis) against the volume of sodium hydroxide, solution A ( 3marks)
- From the graph, determine the volume of sodium hydroxide, solution A required to neutralize the carboxylic acid (1mark)
- Calculate the volume of carboxylic acid, solution C used for neutralization (1mark)
Calculate the- Ratio between the volumes of solutions A and C (1mark)
- Concentration in moles per litre of the carboxylic acid, solution C.
(Assume that the volume ratio is the same as the mole ratio) (2marks)
- You are provided with solid E. Carry out the tests below and record your observations and inferences in the spaces provided.
Place all the solid E in a boiling tube, add 10cm3of distilled water and shake.
OBSERVATION
INFERENCE
- To about 1cm3 of the solution, add 2M sodium hydroxide drop wise until in excess
OBSERVATION
INFERENCE
- Place 1cm3 of the solution in a test-tube and add 2 to3 drops of 2M sulphuric (VI) acid.
OBSERVATION
INFERENCE
- To about 1cm3 of the solution, add 4-5 drops of 2M lead (II) nitrate solution and warm.
OBSERVATION
INFERENCE
- You are provided with solid F. Carry out the tests below and record your observations and inferences in the spaces provided.
Place all of solid F into a boiling tube. Add 10cm3 of distilled water and shake well. Use 2cm3 portions of the mixture for the following reactions
OBSERVATION
INFERENCE
- Test the PH of first portion using the universal indicator paper.
OBSERVATION
INFERENCE
- To the second portion, add three drops of bromine water.
OBSERVATION
INFERENCE
- To the third portion, add 2 drops of acidified potassium manganate (VII) and shake well
OBSERVATION
INFERENCE
- To the fourth portion, add all the sodium hydrogen carbonate provided.
OBSERVATION
INFERENCE
MARKING SCHEME
PROCEDURE I
Table . . . . .. (5 marks) Expected average titre = 32.6cm³
- Complete table . . . . . . (1 mark)
Conditions- 3 titrations done . . . . . .(1 mark)
- 2 titrations done . . . . . . (½ mark)
- 1 titration done . . . . . . . 0 mark
Penalties
Penalise ½ mark only ONCE for any of the following- Wrong arithmetic / subtraction
- Inverted table
- Unrealistic burette readings and titre values i.e. burette readings beyond 50cm³, unless explained or titre values less than 1cm³ or in hundreds.
- Use of decimal . . . . . (1 mark)
(Tied to 1st and 2nd row only)
Conditions- Accept 1 or 2 decimal places used consistently, otherwise penalise fully.
- If 2d.p used, the second decimal place must be '0' or '5', otherwise penalise fully.
- Accept inconsistency in the use of zeros as the initial burette reading e.g. 0, 0.0 or 0.00.
- Accuracy . . . . . . .(1 mark
Compare the candidate's correct titre values with the school value and tick (ü) the chosen value if it earns a mark and award as follows:- If at least one titre value is within ± 0.1 of SV . . . . . (1 mark)
- If at least one titre value is within ± 0.2 of S.V. . . . . .(½ mark)
- If none is within ± 0.2 of S.V. . . . . . . (0 mark)
NOTE- The school value must be written above the table.
- If there was wrong arithmetic or no subtraction, then work out the correct value and compare the correctly worked out value with the S.V and award accordingly.
- If no school value is given or cannot be worked out from the teachers' values as per the principles of averaging then; sample from all the candidates; correct average titre values.
- Principles of averaging . . . . . .(1 mark)
(/V1 + V2 + V3)/3 = correct answer
If answer has decimals rounding off should be to 2 decimals otherwise penalise for rounding to 1 decimal.
Values averaged must be consistent within ± 0.2 of each other.- 3 consistent titrations done and averaged . . . . . 1 mark
- 3 titration done but only 2 are consistent and averaged . . . .1 mark
- Only 2 titrations done, are consistent and averaged . . . . 1 mark
- 3 consistent titrations done but only 2 are averaged . . . .. 0 mark
- 3 inconsistent titrations done and averaged . . . . . 0 mark
NOTE.- The mark for principles of averaging is awarded after marking the working and answer for calculating the average volume of solution C.
- Penalise ½ mark if no working is shown but correct answer is given.
- Penalise fully if no working shown but answer given in wrong or wrong working done and correct answer given
- Accept rounding off or trancation of answer to at least 2 decimal places, otherwise penalise ½ mark for rounding off to less than 2 decimal places, unless the answer works out exactaly to a whole number or to 1 decimal place.
- Final accuracy . . . . . . .(1 mark)
Compare the candidates' correct averaged titre with the school value used in III and award as follows.- If within ± 0.1 of school value . . . . . .1 mark
- If within ± 0.2 of school value . . . . . .1 mark
- If not within ± 0.2 of S.V. . . . . . . . . . 0 mark
NB
If wrong principles of averaging is used by the candidate, then pick the correct values ( if any), average and award accordingly.
CALCULATIONS- Mol of B in av= (0.128 x 32.6)/1000 =0.0042 molP1/2
Mol of NaOH in D =0.0042 molP1/2
Molarity = (0.0042 x 1000)/ 25P1/2 =0.1669 MP1/2
Conditions and penalties.
Accept correct answer for ½ mark if working is not shown
Penalise fully for any strange figure used in the working
Answer to be to atleast 4 decimal places, otherwise penalise ½ mark for rounding off to less than 4dp, unless it works out exactly to lesser number of decimal places.
Answer should be as expected, otherwise penalise ½ mark for wrong arithmetic.
Units may not be shown, but if shown must be correct, otherwise penalise ½ mark for wrong units. - Mol of NaOH of D in 150 = (150 X 0.0042)/25 = 0.0252 molP1/2
25 cm3of A contain 0.0252 mol
Molarity = (1000 x 0.0252)/25 = 1.0008 MP1/2
Conditions and penalties.
Penalise ½ mark for wrong transfer of answer b(I), otherwise penalise fully for any strange figure used.
Apply all the conditions and penalties in b(I) above.
- Mol of B in av= (0.128 x 32.6)/1000 =0.0042 molP1/2
PROCEDURE 2
- Complete table . . . . . . . (2 mark)
- Complete table with 6 readings . . . . . 2 marks
- Incomplete table with 4 - 5 readings . . . . . . .1 mark
- Incomplete table with less than 4 readings . . . . . . . 0 mark
Penalties
Penalise ½ mark for unrealistic initial temperature reading i.e. if reading is below 10°C or above 40° C
- Decimal . . . . . . . (1 mark)
(Subject to atleast 2 readings.
Must be consistently recorded as whole numbers or to one decimal place of '0' or '5', otherwise penalise fully. - Accuracy . . . . . .(1 mark)
Compare the candidate final temperature reading at vol of C = 16 with the school value. Award 1 mark if within ± 2°C of the S.V, otherwise penalise fully.
NB Place a tick ( P) on the candidates initial temperature reading if credited. - Trend . . . . . . .(2 mark)
Award the first 1/2 mark if temperature rise
Award the second ½ mark for temperature either being constant at higher then steadily followed by drop. - Graph . . . . . . 3 marks
- Labelling of axes . . . . . ½ marks
Award ½ mark if both axes are labelled correctly.
Conditions.- Penalise fully for inverted axes
- Penalise fully if only ONE axis is labelled
- Penalise fully for wrong units used, otherwise ignore if units are not shown.
- Scale . . . . . . . ½ mark
The area covered by the actual plots should be atleast half of the grid provided on both axes
The scale chosen must be able to accommodate all the points whether plotted or not.
Scale interval must be uniformly caliberated on both axes.
NOTE:- Penalise fully if any of the above conditions is not met.
- Award for correct scale even if the axes are inverted.
- Plotting . . . . . . 1 mark
- if 5-6 points correctly plotted . . . . . 1 mark
- If 3-4 points correctly plotted . . . . . .½ mark
- If less than 5 points correctly plotted . . . 0 mark
NOTE:- Mark all the plots on the graph by placing a tick (P) if correct or a cross (×) if wrong.
- Accept correct plots even if the axes are inverted and award accordingly.
- If scale interval are inconsistent, credit only correct plots (if any) within the first correct scale interval and treat all the others as wrong.
- Line/shape . . . . . .(1 mark)
Accept two straight lines and each extrapolated to meet on extrapolation for 1 mark.
Showing DT correctly on the graph . . . . .½ mark
Correct value of DT stated . . . . . . . . . . . .½ mark- Vol of C + volA = 20 cm3 P1/2
Vol of C = 20 – 10 = 10 cm3P1/2
Conditions
Penalise ½ mark for wrong transfer of average titre of answer B(ii) otherwise penalise fully for any strange figure.- ratio = 1:1P1
molarity of A = 1.008 MP1
Ratio 1:1
Molarity of C = 1.008 MP1
- ratio = 1:1P1
- Vol of C + volA = 20 cm3 P1/2
- You are provided with solid E. Carry out the tests below and record your observations and inferences in the spaces provided. Place all the solid E in a boiling tube, add 10cm3 of distilled water and shake well until all the solid dissolves.
OBSERVATION
INFERENCE
Solid dissolves to form a colourless solution
Soluble salt
Cu2+ Fe2+ Fe2+ absent
To about 1cm3 of the solution, add 2M sodium hydroxide drop wise until in excess
OBSERVATION
INFERENCE
White precipitate, insoluble in excess,
Ca2+ ,Mg2+ present
- Place 1cm3 of the solution in a test-tube and add 2 to3 drops of 2M sulphuric (VI) acid.
OBSERVATION
INFERENCE
White precipitate
Ca2+present
- To about 1cm3 of the solution, add 4-5 drops of 2M lead (II) nitrate solution and warm
OBSERVATION
INFERENCE
White precipitate, dissolves on warming
Reject: dissolves in excess
Cl- present.
Place all of solid F into a boiling tube. Add 10cm3 of distilled water and shake well. Use 2cm3 portions of the mixture for the following reactions.
OBSERVATION
INFERENCE
Solid dissolves to form a colourless solution
Polar substance
Test the first portion with universal indicator papers.
OBSERVATION
INFERENCE
PH = 4 or 5
Weakly Acidic substance.
OBSERVATION
INFERENCE
Yellow colour of bromine water persists
P1absent
- To about 1cm3 of the solution, add 4-5 drops of 2M lead (II) nitrate solution and warm
- To the second portion, add three drops of bromine water.
OBSERVATION
INFERENCE
Yellow colour of bromine water persists
P1absent
- To the third portion, add 2 drops of acidified potassium manganate (VII) and shake well
OBSERVATION
INFERENCE
Purple colour of acidified potassium manganate (VII) persists
, P1/2R-OH P1/2absent
To the fourth portion, add a little solid G, sodium hydrogen carbonate.
OBSERVATION
INFERENCE
Bubbles/effervescence
R-COOH
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