Hard water

Question 1

Hard water makes what?

Answer 1

Scum and scale

Question 2

What do you get with soft water but not hard, what do you get with hard?
Why do you not get with a lather with hard water?
So what needs to be done to get a decent lather, but…?

Answer 2

A nice lather with soap, scum.
The dissolved calcium and magnesium ions in the water react with the soap to form insoluble scum.
Use more soap, this is more expensive

Question 3

What happens when hard water is heated and where?

Answer 3

It forms scale (calcium carbonate) on the inside of pipes, boilers and kettles.

Question 4

What happens when pipes get badly scaled? why is this bad? What would happen eventually?

Answer 4

They reduce the efficiency of heating systems and may need replacing. The will block completely.

Question 5

What property of scale reduces the efficiency of a kettle?

What does this mean for the kettle?

Answer 5

It’s a thermal insulator.

It takes longer for the heating element to biol the water than a clean kettle so it’s less efficient

Question 6

What property of scale reduces the efficiency of a kettle?

What does this mean for the kettle?

Answer 6

It’s a thermal insulator.

It takes longer for the heating element to biol the water than a clean kettle so it’s less efficient

Question 7

What is hardness caused by?

Answer 7

Ca2+ and Mg2+ ions

Question 8

How does water become hard?

Answer 8

Rain falling on some types of rocks (limestone chalk, gypsum) can dissolve compounds like magnesium sulphate and calcium sulphate, both only a bit soluble.

Question 9

Why isn’t hard water bad for health? (2)

Answer 9

Ca2+ ions are good for healthy teeth and bones
It has been found that people living in hard water areas are at less risk of developing heart disease than people in soft water areas. This could be due to the minerals in the water.

Question 10

What needs removed to make hard water soft?

Answer 10

The dissolved Ca2+ and Mg2+ ions

Question 11

What are the two types of hardness?

Answer 11

Temporary and permanent

Question 12

What is temporary hardness caused by?

Answer 12

Hydrogencarbonate ion, HCO₃− in Ca(HCO₃)₂

Question 13

What is permanent hardness caused by?

Answer 13

Dissolved calcium sulphate (and others)

Question 14

How is temporary hardness removed?

Answer 14

By boiling water

Question 15

What happens when temporary hard water is heated?

Answer 15

The calcium hydrogencarbonate decomposes to form Calcium carbonate which is insoluble, water and CO2. The solid is the limescale in the kettle.

Question 16

What is the equation for the removal of temporary hardness? Word and symbol

Answer 16

Calcium hydrogen carbonate = Calcium carbonate + water + CO2

Ca(HCO₃)₂ (aq) = CaCO3 (s) + H2O (l) + CO2 (g)

Question 17

Why doesn’t the removal of temporary hardness work for permanent hardness?

Answer 17

Heating sulphate ions does nothing, they don’t decompose.

Question 18

How are both types of hardness softened?

How (why) does this soften the water?

Answer 18

By adding washing soda which is Na2CO3, sodium carbonate.
The added carbonate ions react with Mg2+ and Ca2+ ions to make an insoluble precipitate of calcium carbonate or magnesium carbonate. As the ions are no longer dissolved in the water it is not hard.

Question 19

How are both types of hardness removed?

Answer 19

By running the water through ion exchange columns

Question 20

What do ion exchange columns contain?

What do they do with these?

Answer 20

Lots of sodium ions or hydrogen ions

Exchange them for the calcium or magnesium ions in the water running through them.

Question 21

What is the equation for what happens in an ion exchange column?

Answer 21

Na2Resin (s) + Ca(2+) (aq) = CaResin (s) + 2Na+ (aq)

So the calcium ions dissolved in the water (aq) have been replaced with sodium ions, 2Na+ (aq)

Question 22

what do you use a titration reaction for?

Answer 22

Comparing the hardness of water.

Question 23

What is the method for a titration reaction? (8)

Answer 23

Fill a burette with 50 cm3 of soap solution
Add 50 cm3 of the first water sample into a flask
Use the burette to add 1cm3 of soap solution to the flask
Put a bun gin the flask and shake for 10 seconds
Repeat the previous 2 steps until a GOOD LASTING LATHER is formed, this is where bubbles cover the surface for at least 30 seconds
Record how much soap was needed to create a lasting lather
Repeat the steps with other water samples
Boil fresh samples of each type of water for ten minutes then repeat the experiment to see if it is permanent or temporary.

Question 24

If the volume of soap needed went down from 7 to 1 after boiling, what does that tell you about its hardness?
If it went down from 17 to 7 what would it mean?

Answer 24

It’s temporary

It contains half temporary hardness and half permanent

Question 25

What does water contain that we must remove? Why is one of them removed, what does it cause?

Answer 25

``` Poisonous salts (phosphates and nitrates) Harmful microbes - cause diseases such as cholera and dysentery. ```

Question 26

Where does most of our water come from? Where does this get its water from? What do government agencies do?

Answer 26

Reservoirs - companies build these were there is a good supply of clean water Water flows in from rivers and ground water Keep an eye on the pollution of reservoirs, rivers and ground water.

Question 27

Where does reservoir water go for treatment?

Answer 27

The treatment works

Question 28

What are the four stages of water treatment?

Answer 28

1. The water passes through a mesh screen to remove big bits like twigs 2. Chemicals are added to the water to make the microbes stick together and fall to the bottom 3. The water is filtered through gravel beds to remove all the solids 4. Water is chlorinated to kill and harmful microbes left

Question 29

What do people who aren't satisfied with water treatment buy? What do these do? What else do we buy to treat our water?

Answer 29

Filters containing carbon or silver to remove substances from their tap water. Carbon in the filters removes the chlorine taste and silver is supposed to kill bugs Water softeners which contain the ions exchange columns with ions exchange resins.

Question 30

How can totally pure uncontaminated water be produced? ... which is Why is this process not used for tap water? But where is this water used anyway?

Answer 30

Distillation - the boiling of water to make steam and then condensing the steam. It's too expensive as it requires a lot of energy to boil the water. In chemistry labs.

Question 31

Why is fluoride added to drinking water in some parts of the country? Why is chlorine added?

Answer 31

It helps to reduce tooth decay | To prevent disease

Question 32

Yet why has the use of chlorine in water been disputed?

Answer 32

It can react with other natural substances in water to produce toxic or poisonous by-products No consumer choice on whether it should be added

Question 33

What is the problem with fluoride in water? | What is the other concern?

Answer 33

In too higher doses it can cause cancer and bone problems so some people think it shouldn't be added. Whether it's right to mass medicate people if they can just chose fluoride tooth paste, but they can't chose if it's in their tap water

Question 34

What needs to be monitored then?

Answer 34

The levels of chemicals added to drinking water as too much fluoride (for example) could be harmful.

Question 35

Explain how scale forms on heating elements: (2 marks)

Answer 35

When heated calcium hydrogencarbonate decomposes | forming a scale of insoluble calcium carbonate