THE UNITED REPUBLIC OF TANZANIA
PRESIDENT’S OFFICE
REGIONAL ADMINISTRATION AND LOCAL GOVERNMENT
FORM FOUR MD-TERM TEST
CHEMISTRY 2A
TIME: 2:30HOURS
AUGUST 2023
INSTRUCTIONS:
- This paper consists of two (2) questions paper
- Answer all questions and each question carries 25 marks
- Cellular phones and any unauthorized materials are not allowed in the assessment room.
- Write your examination number at the top of every page of your answer sheet.
- The following constant may be used
·
Atomic masses H=1, C=12, 0=16, Na=23, S=32, Mg=24
1. Solution JOH was used to standardize
the ethanedioic acid (COOH)2 2H2O solution during the class experiments. You are required to
determine the unknown element in an alkali if an acid solution was prepared by
dissolving 1.575 g in 250cm3 of distilled water.
Procedures
i. Pour
approximately 5cm3 of both the solution given into separate 100cm3
beakers. Use a blue litmus paper strip only to identify an alkali and
acid solution. Label an acidic solution as C and an alkali as D.
ii. Titrate an
acidic solution C against an alkaline D using P.O.P as an indicator.
iii. Repeat step
(ii) to obtain three more accurate readings and record your results in a tabular
form.
Questions
A. (i)
How did you identify an acidic and alkaline solution using a blue litmus paper?
(ii) What will
happen to the solution if blue litmus will be replaced by a red litmus paper
strip?
(iii) Would you
expect the same results if a blue litmus paper is dipped in distilled water as in
solution C?
(iv) Why do you think
MO may not work as P.O.P. indicators in this experiment?
B. (i) What was the color change of the
solution when the required drops of P.O.P indicator were added into solution D.
(ii) What was
the tit volume of acid used?
C. Write
a balanced chemical equation for the reaction between C and D.
D. Showing all of your necessary steps
clearly, identify the unknown element in an alkali, containing 2.8g in 500cm3
of solution
2. You are provided with the following
Solution JJ – 2M Sulphuric acid solution
5 pieces of 1cm long Magnesium ribbon, measuring cylinder, distilled water, measuring cylinder, stopwatch, water and 100ml beaker.
Procedures.
(i) Measures 25cm3 of
solution JJ using a measuring cylinder and pour into 100cm3 beaker,
put 1 piece of magnesium ribbon into a beaker contained solution JJ immediately
start the stopwatch, swirl the mixture in the beaker twice and observe the
reaction taking place in the beaker and stop the stopwatch as soon as the metal
disappear and record the time taken. Discard the mixture from the beaker.
(ii) Measure 20cm3 of
solution JJ and put up with 5cm3 of distilled water in the same
measuring cylinder and then pour into the beaker and swirl the mixture twice.
Record the time taken for the disappearance of Magnesium ribbon.
(iii) Repeat the procedure by changing
the volume of solution JJ by 15cm3 , 10cm3 and 5cm3 in
every experiment top with distilled water in the same measure cylinder to make
the total volume of solution JJ and distilled water to be 25cm3 as
shown in the tale below
|
Experiment |
Volume
of JJ(cm3 ) |
Volume
of distilled water cm3 |
Time
taken for Mg ribbon to disappear |
Rate
of reaction |
Concentration
of solution JJ |
|
1 |
25 |
0 |
|
|
|
|
2 |
20 |
5 |
|
|
|
|
3 |
15 |
10 |
|
|
|
|
4 |
10 |
15 |
|
|
|
|
5 |
5 |
20 |
|
|
|
Questions
(a) Fill the table above
(b) What is the aim of this experiment?
(c) What would happen to the experiment
when copper turnings are used instead of Mg ribbon
(d) With the aid of state symbols write
a balanced chemical equation for the reaction between solution JJ and magnesium
ribbon
(e) Plot the graph of volume of JJ against
the rate of reaction
(f) What can you conclude from the
graph?
.jfif)
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