Water and Energy Changes

Question 1

What is filtration?

Answer 1

Water is sprayed onto layers of sand and gravel and as it trickles through, insoluble molecules are removed

Question 2

What is sedimentation?

Answer 2

A chemical is added to cause tiny solid particles to clump together

Question 3

What is chlorination and why is it good and bad?

Answer 3

Chlorine gas is injected into water. It kills harmful microbes but can react with harmless organic molecules to form toxic products like THM

Question 4

What is good and bad about adding fluorine to water?

Answer 4

It prevents tooth decay, but it causes learning difficulties and Alzheimers in the elderly

Question 5

What causes water hardness in temporary and permanent hard water?

Answer 5

Temporary - calcium and magnesium hydrogencarbonate

Permanent - calcium and magnesium sulphate, nitrate or chloride

Question 6

Why does reacting hard water with soap from scum?

Answer 6

sodium stearate+calcium ions__calcium stearate+precipitate(scum)+sodium ions

Question 7

When can soap lather?

Answer 7

When all calcium and magnesium ions have reacted

Question 8

Advantages of hard water?

Answer 8

• Good for bone development
• Tastes better
• Reduces heart disease

Question 9

Disadvantages of hard water?

Answer 9

• Forms scum with soap

- Temporary forms scale when boiled

Question 10

How can temporary hardness be removed?

Answer 10

Boiling the water, decomposing hydrogencarbonate ions to carbonate ions that react with ca/mg ions to form limescale. This removes the ca/mg ions from the water

Question 11

How can permanent hardness be removed?

Answer 11

• Adding sodium carbonate. This leaves soluble sodium ions and ca/mg carbonate that can be filtered out.
• Ion exchange column. Contains resins that replace ca/mg ions with sodium/hydrogen ions.

Question 12

How can resins be recharged with sodium ions?

Answer 12

Washing them with salt solution

Question 13

Why do water filters contain carbon and nanoparticles of silver?

Answer 13

To absorb impurities and kill microbes

Question 14

How is sea water desalinated?

Answer 14

Boiled and turned to steam, leaving salt behind, and then condensed to water.

Question 15

Advantages of softening water?

Answer 15

• Do not waste soap
• Do not get scum
• Do not get scale when heating water
• Better for industrial processes like dyeing

Question 16

Disadvantages of softening water?

Answer 16

• Expensive
• Hard water tastes better
• Sodium ions give high blood pressure

Question 17

How do you measure the energy released by burning a food or fuel?

Answer 17

Heat is captured by water and temperature rise calculated.

Question 18

What equation do you use to calculate the energy released by a food or fuel?

Answer 18

mass of water(g) X 4.2 X change in water temperature

Question 19

How do you convert calories to joules?

Answer 19

X 4.2

Question 20

Exothermic reaction?

Answer 20

More energy is released when new bonds are made than needed to break old bonds. The spare energy is released as heat.

Question 21

Endothermic reaction?

Answer 21

More energy is needed to break old bonds than is released when new bonds are made. The extra energy is taken from the surroundings.

Question 22

How do you calculate an energy change?

Answer 22

Add up number of each type of bond, multiply by bond energies and add answers together for reactants. Repeat for products. Reactants-products=energy change. If the answer is negative, the reaction is exothermic.

Question 23

Why is incomplete combustion less exothermic than complete?

Answer 23

It releases less energy

Question 24

How do you calculate a heat change of a fuel (kJ/mole)

Answer 24

1) mXcXt - convert to kJ
2) calculate mass of fuel used in reaction
3) calculate amount of fuel in moles
4) step1 / step3