Are you able to answer this Secondary Chemistry Tuition Question? (Part 2)

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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.

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……………………………………………………………………………………………………………

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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

 

1. to stop Mg reacting with air (or oxygen)/to stop side reactions/to stop air getting in

 

1. low temperature/the cold(ness)/it is cold/it is –60 °C

 

33. 33.7kJ (3s.f.)

 

1. Mg excess, Mol of Mg = 0.25, Mol of CO₂ = 0.0957

 

1. Bond forming > bond breaking

 

8. a. Oxidant: potassium chlorate

Reductant: phosphorus

Explanation: phosphorus – gain oxygen; potassium chlorate – lost oxygen

 

1. P₂O₅ (s) + H₂O (g) à 2 HPO₃ (aq)

 

1. Efferverence; blue litmus turns red

 

 

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