Required Practical: Reactivity of Metals with Acids

Purpose of Practical

This practical investigates how different metals react with dilute acids, specifically hydrochloric acid. The main aims are to:

• Test the reactivity of various metals by observing their reactions with acid.
• Observe the production of hydrogen gas as a sign of reaction.
• Compare the rates at which different metals react with acids.

By comparing how quickly hydrogen gas is produced, you can rank metals in order of reactivity.

Materials and Setup

• Samples of different metals such as magnesium (Mg), zinc (Zn), iron (Fe), and copper (Cu).
• Dilute hydrochloric acid (usually around 1 mol/dm³ concentration).
• Test tubes or small reaction vessels.
• Delivery tube connected to a gas syringe or an inverted measuring cylinder in a water bath to collect hydrogen gas.
• Water bath or trough filled with water for gas collection.

The setup allows the hydrogen gas produced to be safely collected and measured, either by volume or by timing the reaction.

Method

1. Place a small piece of metal into a test tube.
2. Add a fixed volume of dilute hydrochloric acid to the metal.
3. Immediately connect the test tube to a gas collection system (gas syringe or inverted measuring cylinder in water).
4. Measure the volume of hydrogen gas produced over a set time or measure how long it takes to produce a certain volume of gas.
5. Record observations such as bubbling rate and volume of gas collected.
6. Repeat the procedure for each metal under the same conditions for a fair comparison.

Ensure all measurements are as accurate as possible and conditions (acid concentration, temperature, metal size) are kept constant.

Observations and Results

When a metal reacts with hydrochloric acid, hydrogen gas is produced. The rate of reaction can be observed by:

• The speed and amount of bubbles produced from the metal surface.
• The volume of hydrogen gas collected over time.

More reactive metals produce hydrogen faster and in greater volumes within the same time frame. For example, magnesium reacts vigorously, zinc reacts moderately, iron reacts slowly, and copper often shows no reaction.

From these observations, metals can be ordered by reactivity:

Magnesium > Zinc > Iron > Copper (no reaction)

This order matches the known reactivity series of metals and helps predict how metals behave in acid reactions.

For instance, if magnesium produces 40 cm³ of hydrogen in 1 minute, and zinc produces 20 cm³ in the same time, magnesium is more reactive.

Safety and Precautions

• Always wear safety goggles and gloves to protect against acid splashes.
• Handle dilute hydrochloric acid carefully; avoid skin and eye contact.
• Use small pieces of metal to control the reaction rate and avoid excessive gas production.
• Carry out the experiment in a well-ventilated area to avoid build-up of hydrogen gas.
• Keep flames or sparks away, as hydrogen is highly flammable.

Example: Calculating Rate of Hydrogen Gas Production

If 30 cm³ of hydrogen gas is collected in 90 seconds when zinc reacts with hydrochloric acid, the rate of hydrogen production is:

Rate = volume of gas / time = $\frac{30 \text{ cm}^3}{90 \text{ s}} = 0.33 \text{ cm}^3/\text{s}$

This rate can be compared with other metals to determine which reacts faster.