Question 7

QUESTION 7 (Start on a new page.)

A hydrogen bromide solution, HBr(aq), reacts with water according to the following
balanced chemical equation:

The Ka value of HBr(aq) at 25 °C is 1 x 109.

7.1 Is hydrogen bromide a STRONG ACID or a WEAK ACID? Give a reason for
the answer. (2)

7.2 Write down the FORMULAE of the TWO bases in the above reaction. (2)

7.3 HBr(aq) reacts with Zn(OH)2(s) according to the following balanced equation:

An unknown quantity of Zn(OH)2(s) is reacted with 90 cm3 of HBr(aq) in a
flask. (Assume that the volume of the solution does not change during the

The EXCESS HBr(aq) is then neutralised by 16,5 cm3 of NaOH(aq) of
concentration 0,5 mol·dm-3. The balanced equation for the reaction is:

7.3.1 Calculate the pH of the HBr solution remaining in the flask AFTER
the reaction with Zn(OH)2(s). (7)

7.3.2 Calculate the mass of Zn(OH)2(s) INITIALLY present in the flask if
the initial concentration of HBr(aq) was 0,45 mol∙dm-3. (6)

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