Wednesday, 7 January 2015

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

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

» Test tube
» Forceps
» Water trough
» Small knife

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.

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

Lithium, sodium and potassium react with water to produce an alkali and hydrogen gas.
2Li(s) + 2H2O(l) 2LiOH(aq) + H2(g)
2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)
2K(s) + 2H2O(l) 2KOH(aq) + H2(g)

The reactivity of metals increases down Group 1.

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.

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  1. What is the operational definition for the reactivity of Group 1 elements?

  2. What is inferens from the observation