WAEC Chemistry 2021 Objective — Question 31
Question 31 of 50 from the West African Examinations Council (WAEC) Chemistry 2021 Objective paper, with the correct answer and a full explanation.
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31. Student X titrated 25cm³ of Na2CO3 with 0.1mol dm⁻³ HCl, using methyl orange as indicator. Student Y carried out the same exercise but used phenolphthalein as indicator. Which of the following statements about the titration is true?
- A. Hydrogen chloride gas was released in the reactions in both titrations
- B. The titre values obtained from the titrations are equal
- C. The titre value obtained by X is twice that of YCorrect
- D. The titre value obtained by Y is twice that of X
Explanation
With methyl orange, the reaction goes to completion (Na2CO3+2HCl→2NaCl+H2O+CO2); with phenolphthalein, it stops at the bicarbonate stage (Na2CO3+HCl→NaCl+NaHCO3), needing half the acid — so X's titre is twice Y's.
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