Chemistry CE MC

In a titration experiment, which of the following apparatus should be rinsed with the solution it is about to contain?
(1) burette (2) pipette (3) conical flask

Ans: (1) burette and (2) pipette. It is because the remaing solution in the burette and the pipette will change the concentration, namely, molarity of the titrant and the titre respectively. On the other hand, although the concentration of titre in the conical flask has changed, the no. of mole of the titre has not changed. However, the conical flask must be rinsed with deionized water before titration.

An aqueous solution of a compound reacts with dilute HCl to give a gas. This aqueous solution does NOT give a precipitate with NaOH. Which could the compound be?
(1) sodium sulphite (2) iron(II)sulphate (3) ammonium carbonate

Ans: (1) sodium sulphite (3) ammonium carbonate. Since increase in the acidity of sulphite solution and carbonate solution will drive chemical equilibrums to produce more gas, namely, SO2 and CO2. Moreover, Na and NH4+ will NOT give a precipitate with NaOH but FeSO4 will give ppt.