Other alkaline solutions
5 marks · HardThe following table shows two acids and their reactions in water.
| Acid | Equation in water |
|---|---|
| Acid A | |
| Acid B |
For Acid A, explain what the presence of H^+ ions in solution tells you about the nature of the solution.
For Acid B, how many moles of H^+ ions are formed from 1 mole of HB_2?
Both Acid A and Acid B are added separately to water to make solutions.
Describe in terms of ions what occurs in each solution and which property they share.
Explain, using one example from above, what is meant by the 'replaceable hydrogen' in acids.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) The solution is acidic / contains H^+ ions.
(b) 2
(c) Both acids dissociate in water to produce hydrogen ions (H^+); both solutions contain H^+ as a common ion, which makes them acidic.
(d) Replaceable hydrogen in an acid is the hydrogen atom that can be lost as a H^+ ion. Example: In HB_2, both hydrogen atoms are replaced to form 2H^+.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States the solution is acidic because of H^+ ion presence.
A1 (b) · 1 mark · States 2 moles of H^+ are formed per mole of HB_2.
M1 (c) · 1 mark · Describes that both acids dissociate to form H^+ ions in water.
B2 (c) · 1 mark · States a shared property: both solutions are acidic because of H^+ ions.
M2 (d) · 1 mark · Explains replaceable hydrogen with reference to an example from the acids given (e.g., HB_2).
Worked solution
a) The solution is acidic because it contains hydrogen ions (H^+).
b) HB_2 dissociates to give 2 moles of H^+ ions per mole.
c) In both cases, the acid dissociates in water to form H^+ ions in solution. Both Acid A and Acid B make the solution acidic by providing H^+.
d) Replaceable hydrogen means the hydrogen atoms in the acid that are released as H^+ ions. For HB_2, both H atoms are replaceable, as shown by the two H^+ ions in the equation.