chapter 11 chemical changes

Question 1

what are the 3 reactions of acids

Answer 1

1. acid + alkali -> salt + water (neutralisation)
2. acid + metal -> salt + hydrogen
3. acid + carbonate -> salt + water + carbon dioxide

Question 2

what are the 3 tests?

Answer 2

1. Test for hydrogen
   • Insert a lighted splint into a test tube
   • Result: the lighted split will extinguish with a ‘pop’ sound
   • Describe: hydrogen is a colourless and odourless gas
   2. Test for carbon dioxide
      • Bubble gas produced through lime water (calcium hydroxide)
      • Result: a white precipitate is formed with lime water
      • Describe: carbon dioxide is a colourless and odourless gas
   3. Iodine test
      • Starch present: changes from brown to blue-black
      • Starch absent: remains brown

Question 3

what are the ways to prevent rusting?

Answer 3

Ways to prevent rusting:
1. Painting
2. Oiling
3. Galvanising (coating iron with zinc, more reactive with oxygen than iron)
4. Drying

Question 4

what are the 3 types of chemical changes?

Answer 4

1. combustion
   carbon + oxygen -> carbon dioxide
2. thermal decomposition
   calcium carbonate (heat)-> calcium oxide + carbon dioxide
3. oxidation
   glucose + oxygen -> carbon dioxide + water

Question 5

what are the properties of acids?

Answer 5

Acids (pH<7)
• Have a sour taste
• Dangerous as some acids may burn the skin (corrosive)
• Turn blue litmus paper red
• Reacts with alkalis, metals and carbonates
• Examples: hydrochloric acid, sulfuric acid, nitric acid

Question 6

what are properties of alkalis?

Answer 6

Alkalis (pH>7)
• Have a bitter taste
• Have a soapy feel
• Dangerous as some alkalis may burn the skin (corrosive)
• Turn red litmus paper blue
• reacts with acids in neutralisation reactions
• Examples: sodium hydroxide, calcium hydroxide, potassium hydroxide, aqueous ammonia

Question 7

difference between aerobic and anaerobic respiration?

Answer 7

Aerobic respiration Anaerobic respiration
Releases large amounts of energy Releases small amounts of energy
Occurs in the presence of oxygen Occurs in the absence of oxygen
Carbon dioxide and water are produced as waste products Only lactic acid is produced as waste product

Question 8

similarity between aerobic and anaerobic respiration

Answer 8

Both anaerobic and aerobic respiration involve the breakdown of glucose to release energy

Question 9

word equation for aerobic respiration

Answer 9

glucose + oxygen -> carbon dioxide + water
release a large amt of energy

Question 10

word equation for anaerobic respiration

Answer 10

glucose -> lactic acid
release a small amt of energy