2.2 Removing Hardness Flashcards Preview

GCSE Chemistry 3.2 Water > 2.2 Removing Hardness > Flashcards

Flashcards in 2.2 Removing Hardness Deck (13)
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1
Q

How can we make hard water soft?

A

Remove the calcium and magnesium ions

2
Q

How is temporary hard water softened?

A

Boil the water so the ions form insoluble scale and are no longer in the water

3
Q

What happens to the hydrogencarbonate ions when temporary hard water is softened?

A

The hydrogencarbonate ions decompose when heated to form carbonate ions, water and carbon dioxide. The carbonate ions react with calcium ions and magnesium ions in the water to produce precipitates of calcium and magnesium carbonate that are deposited as scale

4
Q

Write a balanced equation for the reaction of calcium ions with carbonate ions

A

Ca(2+) (aq) + CO3(2-) (aq) –> CaCO3 (s)

5
Q

Write a balanced equation for the decomposition of hydrogencarbonate ions

A

2HCO3(-) (aq) –> CO3(2-) (aq) + H2O (l) + CO2 (g)

6
Q

What does soft water not contain?

A

Dissolved salts that react with soap to form scum or scale when it’s heated

7
Q

What can be added to hard water to precipitate out the calcium and magnesium ions?

A

Washing soda/sodium carbonate

8
Q

How does washing powder remove hardness of water?

A

The sodium carbonate reacts with calcium and magnesium ions in the water to form solid calcium carbonate and magnesium carbonate that cannot react with soap

9
Q

What is the machine called that softens hard water?

A

Ion exchange column

10
Q

What does the ion exchange column contain?

A

A resin containing sodium or hydrogen ions

11
Q

What happens when hard water is passed through the resin?

A

Calcium and magnesium ions become attached to the resin and the sodium or hydrogen ions take their place in the water

12
Q

Name a disadvantage of boiling temporary hard water to remove hardness

A

It is expensive so not suitable for large scale

13
Q

Name an advantage of using washing powder to remove hardness of water

A

It is much cheaper using washing crystals