Chemistry C3 2.2 Removing hardness.

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What type of water does not contain salts that produce scum or scale?
Soft water.
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How can hard water be softened?
By removing the salts that produce scum and scale.
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What type of water is softened by heating?
Temporary hard water, but permanent hard water is not.
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What happens when temporary hard water is heated?
The hydrogencarbonate ions in temporary hard water decompose, the carbonate ions formed react with Ca^(2+)(aq) and Mg(2+)(aq) making precipitates.
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How can both types of hard water be softened?
By adding washing soda or by using an ion-exchange resin to remove calcium and magnesium ions.
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Does soft water contain dissolved substances?
Yes, but it does not contain dissolved salts that react with soap to produce scum, and it does not produce scale when heated.
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How can hard water be made soft?
By removing the dissolved calcium and magnesium ions that react with soap.
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Are all types of hard water affected by heating?
No, only temporary hard water.
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Why is temporary hard water affected by heating/boiling?
When temporary hard water is heated the calcium and magnesium compounds form insoluble scale and this removes them from the water.
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Why is permanent hard water unaffected by heating/boiling?
It does not produce scale when heated.
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What is meant by 'temporary hard water'?
Water that is softened by heating or boiling and forms a scale when heated.
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What does temporary hard water contain?
Hydrogencarbonate ions, HCO_3(aq).
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What do the hydrogen carbonate ions in temporary hard water decompose to produce when heated?
Carbonate ions, water and carbon dioxide.
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What is the chemical reaction that occurs when temporary hard water is heated and hydrogencarbonate ions decompose using chemical symbols?
2HCO_3^-(aq) to CO_3^(2-)(aq) +H_(2)O(l) + CO_2(g).
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When temporary hard water is softened by heating, what is produced when the carbonate ions react with calcium ions and magnesium ions in the water?
Precipitates of calcium carbonate and magnesium carbonate that are deposited as scale.
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What is the balanced equation, including state symbols, for the reaction of calcium ions with carbonate ions when temporary hard water is softened by heating?
Ca^(2+)(aq) + CO_3^(2-)(aq) to CaCO_3(s).
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What will any method that removes dissolved calcium and magnesium ions from hard water do?
Soften the water.
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How is precipitating out the ions that cause hardness in either type of hard water done?
By adding washing soda, which is sodium carbonate, the sodium reacts with calcium ions and magnesium ions in the water to form solid calcium carbonate and magnesium carbonate that cannot react with soap.
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How is an ion-exchange column packed with a resin containing sodium or hydrogen ions used to soften either type of hard water?
When hard water is passed through the resin, calcium and magnesium ions become attached to the resin and sodium or hydrogen ions take their place in the water. Sodium ions and hydrogen ions do not react with soap.
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How does an ion-exchange resin soften hard water?
Ion-exchange resin removes the calcium and magnesium ions from hard water and replaces them (exchanges them) for sodium ions or hydrogen ions (that do not react with soap).
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Other cards in this set

Card 2

Front

How can hard water be softened?

Back

By removing the salts that produce scum and scale.

Card 3

Front

What type of water is softened by heating?

Back

Preview of the front of card 3

Card 4

Front

What happens when temporary hard water is heated?

Back

Preview of the front of card 4

Card 5

Front

How can both types of hard water be softened?

Back

Preview of the front of card 5
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