← Back to papers
DSEE 🇹🇿 NECTA ✓ Official NECTA answers

Chemistry · Paper 2A · 2021

7 questions

📖 View PDF ⬇
🎯 Quiz from this
💰 Sit full exam 200 TZS

3-hour timed simulation · auto-graded · counts toward ranking

Pay & start exam →
Questions (7)

Section A

1. 0 marks

Experimental Data Time, t for X Volume of Volume of Volume of 1/time Exp. to disappear B1 (cm3) water (cm3) B2 (cm3) (s-1) (s) 1 30 0 10 2 25 5 10 3 20 10 10 4 15 15 10 5 10 20 10 6 5 25 10 After the experiment, answer the following questions: (a) Write a balanced chemical equation for the reaction which took place during the experiment. (b) (i) Plot a graph of volume of B1 (cm3 ) against 1/time (s-1 ). (ii) Interpret the graph. (iii) What does 1/time represent? (iv) If temperature was to be the factor affecting the rate of reaction, how would the two relate? (v) Draw a conclusion about this experiment

(a)(i)) What was the colour change observed during this titration experiment? 1 mk
(a(i)) What was the colour change observed during this titration experiment? 0 mk
(a) Write a balanced chemical equation for the reaction which took place during the experiment. 0 mk
(a(ii)) What was the volume of the pipette used? 0 mk
(b(i)) Plot a graph of volume of B1 (cm3 ) against 1/time (s-1 ). 0 mk
(a(iii) Calculate the average volume of solution X1 that was used to neutralize solution X2. 0 mk
(b(ii)) Interpret the graph. 0 mk
(a)(ii) Calculate the average volume of solution X1 that was used to neutralize solution X2. 1 mk
(b)) Write a balanced chemical equation between X2 and X1 with all state symbols and the corresponding ionic equation. 1 mk
(b) Write a balanced chemical equation between X2 and X1 with all state symbols and the corresponding ionic equation. 0 mk
(b(iii) What does 1/time represent? 0 mk
(c)(i)) Calculate the concentration of the following: 1 mk
(b(iv)) If temperature was to be the factor affecting the rate of reaction, how would the two relate? 0 mk
(b(v)) Draw a conclusion about this experiment 0 mk
(c)(ii) Solution X1 in g/dm3 . 1 mk

Upgrade to see model answers.

2. 0 marks

Sample J is a simple salt containing one cation and one anion. Carefully, carry out qualitative analysis experiment to identify the ions present in the salt based on the following tests: (a) Appearance of the sample. (b) Action of heat on the sample. (c) The sample dissolved in the water. (d) Action of potassium iodide on the solution of the sample then warm. (e) Action of a freshly prepared iron (II) sulphate on the solution of the sample followed by concentrated sulphuric acid (i) Prepare a relevant Table showing the qualitative analysis results. (ii) Write a balanced chemical equation (with state symbols) for the reaction that took place in experimental test (b)

(none) The question describes an experiment to investigate the rate of reaction between sodium thiosulphate and hydrochloric acid by measuring the time taken for the 'X' mark to disappear. Students are expected to perform the experiment and record data as per the provided table (which is not fully provided in the text). The subsequent questions would likely involve data analysis, calculation of reaction rates, and discussion of factors affecting reaction rates. 15 mk
(a) Appearance of the sample. 0 mk
(b(i)) Plot a graph of volume of B1 (cm3 ) against 1/time (s-1 ). 0 mk
(b) Action of heat on the sample. 0 mk
(b(ii)) Interpret the graph. 0 mk
(c) The sample dissolved in the water. 0 mk
(d) Action of potassium iodide on the solution of the sample then warm. 0 mk
(b(iii) What does 1/time represent? 0 mk
(b(iv)) If temperature was to be the factor affecting the rate of reaction, how would the two relate? 0 mk
(e) Action of a freshly prepared iron (II) sulphate on the solution of the sample followed by concentrated sulphuric acid 0 mk
(b(v)) Draw a conclusion about this experiment 0 mk
(i) Prepare a relevant Table showing the qualitative analysis results. 0 mk
(ii) Write a balanced chemical equation (with state symbols) for the reaction that took place in experimental test (b) 0 mk

Upgrade to see model answers.

3. 0 marks

Sample J is a simple salt containing one cation and one anion. Carefully, carry out qualitative analysis experiment to identify the ions present in the salt based on the following tests: (a) Appearance of the sample. (b) Action of heat on the sample. Page 3 of 4

(a) Appearance of the sample. 0 mk
(b) Action of heat on the sample. 0 mk

Upgrade to see model answers.

💡 Unlock all answers & explanations
Premium · 3000 TZS/mo