09 May Are you able to answer this Secondary Chemistry Tuition Question? (Part 2)
Miracle Learning Centre (O Level Chemistry Tuition/ IP Chemistry Tuition)
Are you able to answer this Secondary Chemistry Tuition Question?
7 . Several small pieces of magnesium are placed on a block of solid carbon dioxide.
The solid carbon dioxide is at a temperature of -60 °C. The magnesium is ignited and another block of solid carbon dioxide is immediately placed on top.
A vigorous reaction is observed.
2Mg + CO2 → 2MgO + C
(a) Suggest what could be seen as the reaction proceeds to completion.
...........................................................................................................................
......................................................................................................................
(b) Why is another block of solid carbon dioxide placed above the burning magnesium?
......................................................................................................................
(c) State one factor in the experiment which slows down the reaction.
......................................................................................................................
(d) When 2 moles of magnesium react with one mole of carbon dioxide, 810 kJ of energy are released.
Calculate the energy released when 2.0 g of magnesium reacts completely with carbon dioxide.
Energy released........................................ kJ
(e) In a second experiment 6.0 g of magnesium and 4.4 g of carbon dioxide are used. Which solid, magnesium or carbon dioxide is in excess? Show your working.
(f) Explain, in terms of the energy changes taking place in both bond-making and bondbreaking, why the reaction is exothermic.
...........................................................................................................................
...........................................................................................................................
......................................................................................................................
8 . The head of a safety match contains potassium chlorate and antimony sulfide. The side of the matchbox contains red phosphorus.
When a match is struck on the side of the box, the friction produces enough heat to light the match.
(a) The equation for this reaction is shown.
5KCl O3 + 6P → 5KCl + 3P2O5
potassium chlorate phosphorus(V) oxide
Which is the oxidant and which is the reductant in this reaction?
Explain your answer.
oxidant ..............................................................................................................
reductant ...........................................................................................................
explanation ........................................................................................................
.......................................................................................................................
(b) Phosphorus(V) oxide, P2O5, absorbs water from the air to form meta-phosphoric acid, HPO3.
(i) Write a balanced chemical equation, with state symbols, for this reaction.
............................................................................................................
(ii) On addition of more water, phosphoric acid is formed. Phosphoric acid has typical acidic properties. What would you observe when aqueous phosphoric acid is added to
aqueous sodium carbonate, ....................................................................
blue litmus paper? .............................................................................
Miracle Learning Centre (O Level Chemistry Tuition/ IP Chemistry Tuition)
Did you answer the Secondary Chemistry Tuition Question correctly?
7.a. • carbon dioxide disappears or vaporises
ALLOW: carbon dioxide melts/carbon dioxide block decreases in size/hole in block gets deeper
- black powder/black solid formed/black smuts/black fumes/sooty
ALLOW: black gas/black smoke
- white powder/white solid formed/white fumes
ALLOW: white gas
- bright light/flame
- to stop Mg reacting with air (or oxygen)/to stop side reactions/to stop air getting in
- low temperature/the cold(ness)/it is cold/it is –60 °C
- 33.7kJ (3s.f.)
- Mg excess, Mol of Mg = 0.25, Mol of CO2 = 0.0957
- Bond forming > bond breaking
- a. Oxidant: potassium chlorate
Reductant: phosphorus
Explanation: phosphorus – gain oxygen; potassium chlorate – lost oxygen
- P2O5 (s) + H2O (g) à 2 HPO3 (aq)
- Efferverence; blue litmus turns red
Learn from our Chemistry Tuition Question and Answer.
Miracle Learning Centre Call 6463 8756 or sms 8128 8342/9839 9908.
(Specialist in Science and Maths) for Primary, Secondary and JC levels.
Miracle Learning Centre specialises in Physics tuition, Chemistry tuition, Maths tuition and Science tuition Classes.