Summary
This video explains how to test water purity using pH indicators and evaporation to detect dissolved solids. It then details the process of water purification through distillation, where water is boiled, vaporized, and condensed to remove impurities, resulting in pure, distilled water with a neutral pH. The practical is highlighted as essential for students.
Key Insights
Evaporate water in a basin to detect dissolved solids by mass change.
Even if the pH is 7, the water might still contain dissolved solids. To test for these, weigh an empty evaporating basin, record its mass, fill it with the water sample, and gently heat it with a Bunsen burner until all the water has evaporated. Allow the basin to cool, then weigh it again. If the mass has increased, it indicates the presence of dissolved solids that formed crystals, proving the water is not pure.
Condensed vapor in the cold test tube yields pure, distilled water.
As the water vapor travels along the delivery tube and enters the cold test tube, it condenses back into liquid water. This collected liquid is distilled water, which is pure, contains no dissolved solids, and has a neutral pH of 7.
Sections
Assessing Water Purity
Potable water is safe to drink but not necessarily pure water.
Potable water is defined as water that is safe to drink. However, it is important to understand that potable water is not the same as pure water. Pure water contains no dissolved solids and has a neutral pH of 7.
Test water pH using universal indicator paper to check for acidity or alkalinity.
To begin analyzing a water sample for purity, check its pH. Pure water has a pH of 7. This can be tested by placing a small amount of water onto universal indicator paper. If the paper does not turn green, indicating a pH of 7, the water is impure because it contains dissolved acid or alkali.
Evaporate water in a basin to detect dissolved solids by mass change.
Even if the pH is 7, the water might still contain dissolved solids. To test for these, weigh an empty evaporating basin, record its mass, fill it with the water sample, and gently heat it with a Bunsen burner until all the water has evaporated. Allow the basin to cool, then weigh it again. If the mass has increased, it indicates the presence of dissolved solids that formed crystals, proving the water is not pure.
A neutral pH and no detected solids suggest purity, but dissolved gases are not tested.
If the pH is 7 and the mass of the evaporating basin does not increase after evaporation, the water sample is considered pure within the scope of this practical, as it contains no dissolved solids. However, it's noted that such water may still contain dissolved gases, which are not investigated in this required practical.
Purifying Water by Distillation
Distillation purifies water by boiling, vaporizing, and condensing the liquid.
To purify a sample of water, distillation is used. Set up an apparatus with a conical flask containing the water sample, heated gently by a Bunsen burner over a tripod and gauze. A delivery tube directs the resulting water vapor (steam) into a test tube placed in an ice-water bath.
Condensed vapor in the cold test tube yields pure, distilled water.
As the water vapor travels along the delivery tube and enters the cold test tube, it condenses back into liquid water. This collected liquid is distilled water, which is pure, contains no dissolved solids, and has a neutral pH of 7.
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