Laboratory Activity 7.1.2: Role of water to show properties of alkalis |
Problem statement: Does water needed to be present to enable a base to show its alkaline properties?
Hypothesis: Water must be present for a base to show its alkaline properties.
Variable:
» | Fixed variable : Type of base | |
» | Manipulated variable : Presence of water | |
» | Responding variable : Alkaline characteristics |
Material: » Dry calcium hydroxide » Calcium hydroxide solution » Ammonia solution » Litmus paper » Ammonia in trichloromethane |
Apparatus: » Test tube » Switch » Carbon electrodes » Connecting wires » Crocodile clip » Electric bulb » Beakers » Batteries |
► | The animation below shows the arrangement and results of the experiment.
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► | (A) Litmus paper test
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► | (B) Electrical conductivity test
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► | Without water, alkalis cannot exhibit alkaline characteristics as they cannot dissociate to form ions. | |||
► | In water, alkalis dissociate to form cations and OH-. | |||
► | OH- ions change red litmus to blue colour. | |||
► | Hydroxide ion, OH-, which is free to move in water allows electricity to pass through it. | |||
► | Ammonia that is dissolved in an organic solvent does not show its alkaline characteristics because ammonia exists in molecules form. | |||
► | In water, ammonia dissociate to form NH+ ions and OH- ions which is free to move.
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► | An alkali only shows its alkaline properties in the presence of water. | |
► | The hypothesis is accepted. |
⇲ For exercise(objective and subjective), download for free on Android OS. | ||
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