4.3.2 - Laboratory Activity : Studying the reaction of alkali metals with water

Laboratory Activity 4.3.2: Studying the reaction of alkali metals with water

Aim: To study the reaction of alkali metals with water
Problem statement: How do lithium, sodium and potassium differ in reactivity with water?
Hypothesis: Reactivity increases for the reaction between alkali metals and water when going down Group 1
Variable:

	»	Fixed variable : Water
	»	Manipulated variable : Type of alkali metal
	»	Responding variable : Reactivity of the metal with water

Material: » Lithium » Sodium » Potassium » Phenolphthalein indicator » Water » Filter paper

Apparatus: » Test tube » Forceps » Water trough » Small knife

Procedure:

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1. The animation below shows the procedures and observation of the experiment. 2. A small piece of lithium is cut with a knife. Dry it with filter paper 3. The piece of lithium is placed on the water surface using a forceps. 4. The observation is recorded. 5. The solution formed in the basin is tested with a phenolphthalein indicator. 6. The experiment is repeated using sodium and potassium.

Results:

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Metal Observation Colour of solution produced when added with phenolphthalein indicator. Lithium Moves slowly on water surface. Burns with a red flame. Pink Sodium Move quickly on water surface. Burns with a bright yellow flame. Pink Potassium Moves vigorously on water surface. Burns a brilliant purple flame Pink

Discussion:

	►	Lithium, sodium and potassium react with water to produce an alkali and hydrogen gas. ○ $\mathrm{2Li(s)\; +}{\mathrm{2H}}_2\mathrm{O(l)}\to \mathrm{2LiOH(aq)\; +}{\mathrm{H}}_2\mathrm{(g)}$ ○ $\mathrm{2Na(s)\; +}{\mathrm{2H}}_2\mathrm{O(l)}\to \mathrm{2NaOH(aq)\; +}{\mathrm{H}}_2\mathrm{(g)}$ ○ $\mathrm{2K(s)\; +}{\mathrm{2H}}_2\mathrm{O(l)}\to \mathrm{2KOH(aq)\; +}{\mathrm{H}}_2\mathrm{(g)}$
	►	The reactivity of metals increases down Group 1.

Conclusion:

	►	All Group 1 metals react with water to form an alkali and hydrogen gas.
	►	The reactivity increases down the Group 1.
	►	The hypothesis is accepted.

↶ 4.3 Group 1 Elements

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