Types Of Reactions

Question 1

3 different types of reactions

Answer 1

• Decomposition of a compound
• Synthesis reaction
• Extraction of metals from their ores

Question 2

Heating Mercury (II) oxide

Answer 2

• Spatula of orange mercury (II) oxide powder heated in test tube over Bunsen burner in fume cupboard
• Powder changes: orange ➡️ red ➡️ black
• Tiny silver droplets mercury form on sides of test tube
• Colourless odourless gas released: oxygen
  ENDOTHERMIC + DECOMPOSITION

Question 3

We test for Oxygen by:

Answer 3

Holding a glowing wood splint in the mouth of the test tube: Oxygen gas will reignite a glowing wooden splint

Question 4

Electrolysis of copper (II) chloride

Answer 4

• When current is switched on: electrical energy converted to chemical energy at electrodes
• Copper (II) chloride is decomposed: copper metal at cathode (- electrode)
• Chlorine gas at anode (+ electrode)
  ENDOTHERMIC + DECOMPOSITION

Question 5

Heating of copper (II) carbonate

Answer 5

• Spatula of turquoise copper (II) carbonate powder heated in test tube above Bunsen burner
• Powder changes: turquoise ➡️ black
• Colourless odourless gas released - carbon dioxide
  ENDOTHERMIC + DECOMPOSITION

Question 6

We test for carbon dioxide:

Answer 6

By bubbling it through clear limewater: carbon dioxide will turn clear limewater milky

Question 7

Heating of ammonium carbonate

Answer 7

• Spatula of white ammonium carbonate powder heated in test tube over Bunsen burner
• 3 different products formed:
  Gas with pungent smell = ammonia (turns moist red litmus paper blue)
  Odourless carbon dioxide gas (turns clear limewater milky)
  Colourless odourless steam is formed
  ENDOTHERMIC + DECOMPOSITION

Question 8

Application: limestone cycle

Answer 8

• Calcium carbonate/limestone heated to produce calcium oxide
• Calcium oxide/unslaked lime reacts with water: calcium hydroxide/slaked lime
• Calcium hydroxide used to prepare clear limewater
• Calcium hydroxide reacts with carbon dioxide: calcium carbonate is formed

Question 9

Endothermic reactions

Answer 9

• Energy is needed or absorbed from surroundings & endothermic reactions take place
• Without constant supply of energy reaction would not take place
• These reactions feel cold because they absorb heat from environment

Question 10

Synthesis reaction

Answer 10

• Spatula of grey-black iron fillings & yellow sulphur mixed together in test tube
• Test tube heated over Bunsen burner until red glow is observed
• Red glow keeps spreading even after flame is removed: great deal of heat energy released
• Small amount of yellow sulphur vapour given off
• Test tube cooled: black solid iron (II) sulphide formed is removed

Question 11

Extraction of metals from their ore

Answer 11

Some minerals can be found in their natural form, many have to be chemically/physically extracted from rocks (core) in Earth

Question 12

Mining provides

Answer 12

• Employment for many South Africans
• Generating revenue for the country

Question 13

Extracting lead from lead oxide

Answer 13

• Lead oxide orange powder
• Blowpipe is used to direct sharp, hot flame onto mixture
  Observation: lead oxide and carbon react together. After a while, bright droplet of metal forms which solidifies as it cools. This metal is lead
  Conclusion: carbon combines with oxygen in the lead oxide and forms carbon dioxide leaving lead metal as product

Question 14

Extraction of other metals from their metal-ores

Answer 14

In nature many metals occur in their ores as oxides: these metals can be extracted from their ores by using carbon (which is a reducing agent)