THE UNITED REPUBLIC OF TANZANIA
PRESIDENT’S OFFICE REGIONAL ADMINISTRATION AND LOCAL GOVERMENT
IRINGA DISTRICT COUNCIL
FORM IV PRE-MOCK EXAMINATION MAY 2021
032 CHEMISTRY 2A
TIME; 2:30HOURS (ACTUAL PRACTICAL A)
INSTRUCTIONS:
- This paper consists of two questions.
- Answer all questions.
- Qualitative Analysis Guidance Pamphlets may be used after a thorough check by the supervisor.
- Each question carries 25 marks
- Cellular phones and any authorised materials are not allowed in the examination room.
- Write your Examination number on every page of your answer booklet(s)
- You may use the following constant:
Atomic masses:
H=1, C=12, O=16, K=39, S=32
1litre=1dm3=1000cm3
- You are provided with the following solutions:
U: 0.05M sulphuric acid solution.
T: Containing 1.4g of metal hydroxide (YOH) dissolved in 250cm3 of the solution.
M.O: Methyl orange.
Procedures:
- Put solution U into the burette, pipette 25cm3 or 20cm3 of solution T into titration flask. Put two to three drops of methyl orange into the titration flask. Titrate solution U from the burette against solution T in the titration flask until colour change is observed. Note the burette readings. Repeat the procedures to obtain three more readings in a tabular form.
QUESTIONS:
- (i)…………cm3 of T required ………….cm3 of U for complete reaction.
(ii)The colour change at end point was from…………………to …………………….
- (i)Write a balanced chemical and ionic equation for the reaction between solution U and T.
(ii)State a reason to why methyl orange indicator is used.
(iii)State which solution is titrant and analyate?
- Calculate the concentration of solution T in,
(i) mol/dm3 (ii) g/dm3
- Calculate
(i) The molar mass of metal hydroxide YOH
(ii) The atomic mass of Y
(iii) Name element Y
- Mention two application of volumetric analysis in medicine.
- You are provided with the following:
A: Containing 1M sodium thiosulphate (Na2S2O4)
B: Containing 0.1M Nitric acid (HNO3)
C: Distilled water,
Piece of paper
Stop-watch
Procedures
- Using measuring cylinder measure 5cm3 of solution A and put 100cm3 beaker.
- Measure 5cm3 of solution B and put into 100cm3beaker containing solution A and immediately start the stop- watch.
- Swirl the contents in the 100cm3 beaker and put the beaker on the top of mark X on piece of the ‘paper. Watch the mixture from the above and observe changes.
- Switch off the stop –watch when the mark X disappears.
- Record the time taken for the later X to disappear.
- Repeat procedures (i) to (v) using the data shown in Table 1.
Table1
- Using measuring cylinder measure 5cm3 of solution A and put 100cm3 beaker.
Experiment | Volume of B cm3 | Volume of A cm3 | Volume of Distilled water cm3 | Time (s) |
1 | 5 | 5 | 0 | |
2 | 5 | 4 | 1 | |
3 | 5 | 3 | 2 | |
4 | 5 | 2 | 3 |
QUESTIONS.
- What is the aim of the whole experiment?
- Complete Table1
- With state symbols, write the balanced chemical for the reaction between A and B.
- Which the substance was produced during the reaction which obscured letter X?
- Why did the cross X disappear?
- Write two main allotropes and two uses of the product which obscured the cross X
- Plot the graph of volume of A ( Na2S2O3) solution against time (s)