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DSEE 🇹🇿 NECTA ✓ Official NECTA answers

Chemistry · Paper 2A · 2024

2 questions

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Questions (2)

Section A

1. 0 marks

An acidic compound with a coded chemical formula HX is useful for small scale industries; therefore, it has to be identified and its exact concentration must be known. A beaker labeled C contains a solution prepared by dissolving 0.9125 g of HX in 100 cm3 of solution. You are also provided with a standard solution in a beaker labeled D prepared by dissolving 1.00 g of NaOH in 250 cm3 of solution and methyl orange as an indicator. Perform the activities listed in the procedure in order to identify the concentration of HX. Procedure: (i) Pipette 20 cm3 or 25 cm3 of solution D and transfer it into a titrating flask. Add three drops of methyl orange indicator in the titrating flask. (ii) Titrate this mixture with solution C until a permanent colour change is observed. (iii) Repeat procedures (i) - (ii) for three times.

((a)(i) Present your results in an appropriate table of results. 4 mk
(b) Calculate the average titre volume of C. 3 mk
(c) With state symbols included, write a balanced chemical equation for the reaction between solutions contained in bottles labeled C and solution D. 3 mk
(d) Calculate the concentration of NaOH in solution D in moles per dm3. 4 mk
(e) Identify element X in compound HX. 3 mk
(f) Write a balanced chemical equation representing the reaction which will occur when X is reacted with water. 2 mk

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