# A student dissolves the same number of moles of sulfuric acid and carbonic acid separately in equal volumes of water. Both solutions have the same concentration. Describe and explain the differences you would expect to observe in the pH values of the two solutions and in the rate at which each solution reacts with magnesium ribbon.

> Eduqas A-Level Chemistry — 3.9 Acid-base equilibria · Describe and explain · 5 marks

> Sulfuric acid is a strong acid. Carbonic acid is a weak acid.

## Mark scheme (5 marks)

1. Sulfuric acid has a lower pH than carbonic acid (at the same concentration)
2. Sulfuric acid fully / completely dissociates (ionises) in water, producing a high concentration of hydrogen ions
3. Carbonic acid only partially / incompletely dissociates (ionises), producing a lower concentration of hydrogen ions
4. Sulfuric acid reacts faster with magnesium ribbon than carbonic acid does
5. Because sulfuric acid has a higher concentration of hydrogen ions, giving a greater frequency of successful collisions with the magnesium

## Key terms

- [pH](https://www.gradenine.co.uk/glossary/ph)

## Related

- [Revision notes for Eduqas A-Level Chemistry](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-dissolves-the-same-number-c9e30f6b) · Published by Druglandscape Ltd.