Question

3(b). Give a reason for each of the following laboratory practices: (i) the first jar of hydrogen gas collected during its preparation is discarded; (ii) the conical flask is not rinsed with the solution to be put in it during titration.

Accepted Answer

(i) The first jar contains air, an impurity, mixed in with the gas.
(ii) Rinsing the flask with the solution would leave extra solute behind, causing an unintended increase in the amount/concentration of that solution eventually placed in the flask, giving an inaccurate titre.

WAEC Chemistry 2021 Theory — Question 17

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