Metals and dilute acids
The acids in common use in the laboratory are hydrochloric (HCl) acid, nitric (HNO3) acid and sulphuric (H2SO4) acid.
Activity 16.6
Put 10 ml of dilute hydrochloric (HCl) acid solution into each of several test tubes. Into each tube drop a piece of magnesium (Mg), aluminium (Al), zinc (Zn), copper (Cu) or iron (Fe) whose surface has been well cleaned, and observe. Compare the rate at which gas bubbles are given off.
| Metal | Rate at which gas bubbles appear |
|---|---|
| Magnesium (Mg), aluminium (Al), zinc (Zn) | given off rapidly |
| Iron (Fe) | given off slowly |
| Copper (Cu) | none given off |
What is happening?
The corresponding metal chloride is formed and hydrogen gas is given off. The bubbling is itself the evidence that the reaction is taking place.
HCl — gas or acid?
As a gas, HCl is called hydrogen chloride. When hydrogen chloride gas is dissolved in water it is called hydrochloric acid.
That no bubbles appear in the copper tube is the most important observation here — it fixes copper's place in the activity series.