Lesson 6: RP: Water samples

Question 1

What are the steps of checking whether a water sample is pure or not?

Answer 1

1.) Check pH of water (place small amount of water - using pipiette - on universal indicator paper.
2.) Use a balance to weigh empty evaporating basin. Record mass.
3.) Fill evaporating basin with water sample (place on tripod/ gauze.)
4.) Gently heat water until all water has evaporated. Allow evaporatin basin to cool and weight it again.
5.) If mass of evaporating basin increased (from formation of crystals), the sample is impure. If mass remained the same, the sample is pure.

Question 2

What is the pH of pure water?

Answer 2

7

Question 3

If a water sample contains dissolved substances (ie is impure) when you re- weigh the mass of the evaporating basin after you evaporate water from it, what will happen?

Answer 3

• The mass of the evaporating basin would have increased (from when it was weighed at the beginning when it was empty.)
• Due to the mass of the dissolved solids/ crystals.

Question 4

How do you purify water by distillation? What are the steps?

Answer 4

1.) Set up conical flask (with water sample), on gauze and tripod, above bunsen burner. Connect delivery tube to test-tube in a beaker filled with ice.
2.) Gently heat water using bunsen burner, allowing the water to evaporate.
3.) Allow the water vapour to travel into delivery tube into test-tube.
4.) When water enters cold test-tube, the water vapour condenses into liquid water. This is distilled water.

Question 5

True or False

Distilled water is impure.

Answer 5

• False.
• Distilled water contains no dissolved substances, has a pH of 7 (it is pure water.)