What the bubbles showed
The same reaction takes place in all three tubes — magnesium reacts with the acid and sets hydrogen gas free.
magnesium + hydrogen chloride → magnesium chloride + hydrogen
Mg + 2HCl → MgCl2 + H2
The observation
Where more HCl acid was added — that is, where the HCl was more concentrated — the gas bubbles are seen to come off faster.
| Tube | Volume of HCl acid | Rate of bubbling |
|---|---|---|
| 1 | 2.5 ml | Slowest |
| 2 | 5.0 ml | Middling |
| 3 | 7.5 ml | Fastest |
The conclusion
As the concentration of the HCl increases, the rate of reaction increases.