## 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
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:

 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:

 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.
 ○ $2Li\left(s\right) +{\mathrm{2H}}_{2}O\left(l\right)\to 2LiOH\left(aq\right) +{H}_{2}\left(g\right)$ ○ $2Na\left(s\right) +{\mathrm{2H}}_{2}O\left(l\right)\to 2NaOH\left(aq\right) +{H}_{2}\left(g\right)$ ○ $2K\left(s\right) +{\mathrm{2H}}_{2}O\left(l\right)\to 2KOH\left(aq\right) +{H}_{2}\left(g\right)$

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.