Rates of reactions: questions

1.    There is a danger in coalmines that coal dust may catch fire and start an explosion.  Explain why coal dust is more dangerous than pieces of coal.

Coal dust can explode when ignited.

2.    ‘Alko’ indigestion tablets and ‘Neutro’ indigestion powder are both alkalis. Which do you think will act faster to cure acid indigestion?  Describe how you could test the two remedies in the laboratory with a bench acid to see whether you are right?

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3.    Catalysts A and B both catalyse the decomposition of hydrogen peroxide.  The following figures were obtained at 20°C for the volume of oxygen formed against the time since the start of the reaction.

Time (in minutes	0	5	10	15	20	25	30	35
Volume of oxygen with catalyst A (in cm3)	0	4	8	12	16	17	18	18
Volume of oxygen with catalyst B (in cm3)	0	5	10	15	16.5	18	18	18

a.    Plot  a graph to show both sets of results

b.    Say which is the better catalyst, A or B.

Although both catalysts rise to the same amount eventually, catalyst B is better and the volume of oxygen increases faster.

c.    Explain why both experiments were done at the same temperature

To keep it a fair test, also both catalyst may work differently at different temperatures.

d.    Explain why both sets of figures stop at 18 cm³ of oxygen

Because there is no energy left in the catalyst

e.    Add a line to your graph to show the shape of the graph you would obtain for the uncatalysed reaction.

4.    The graph below shows the results of three experiments involving the reaction of magnesium and dilute hydrochloric acid

a.    Which experiment has the fastest rate at the start?

1

b.    Which experiment produced the greatest final volume of gas?

2

c.    Which experiment used the most concentrated acid?

1

5.    Copper (II) oxide catalyses the decomposition of hydrogen peroxide.  0.5 g of the copper oxide was added to a flask containing 100 ml of hydrogen peroxide.  A gas was released.  It was collected and its volume noted every 10 seconds.  The table below shows the results:

Time (in seconds)	0	10	20	30	40	50	60	70	80	90
Volume (in ml)	0	18	30	40	48	53	57	58	58	58

a.    What is a catalyst?

A substance which speeds up the rate of reaction but does not affect the chemical process.

b.    Draw a diagram of suitable apparatus that you would use to carry out this experiment.

c.    Name the gas that is formed.

Oxygen + (water)

d.    Write a balanced chemical equation for the decomposition of hydrogen peroxide.

H2O2 ---> H2 + O2

e.    Plot a graph of the volume of gas against time.

f.     What happen to the concentration of hydrogen peroxide as the reaction proceeds?

The concentration decreases

g.    What chemicals are present in the flask after 90 seconds?

Copper oxide and hydrogen peroxide

h.    What mass of copper (II) oxide would be left in the flask at the end of the reacting?

0.5g

i.      Sketch on your graph the curve that might be obtained when:

i)             1.0 g of copper (II) oxide is used (red line)

ii)            0.5 g of copper (II) oxide is used in a hydrogen peroxide solution of a lower concentration (anything below blue line)

6.    The equation for the reaction between calcium carbonate and hydrochloric acid is

            CaCO₃  (s)   +    2 HCl (aq)  ¾®  CaCl₂ (aq)    +   H₂ O (l)   +   CO₂  (g)

Two different 10.0 g samples of calcium carbonate were reacted at 25 C with excess hydrochloric acid for a period of 6 minutes.  One of the samples was in the form of large lumps and the other consisted of small lumps.

	Mass of flask and contents (in g)
Time (min)	Large lumps	small lumps
0	112.4	111.6
0.5	111.6	109.2
1	111.1	108.3
2	110.2	107.4
3	109.6	107.2
4	109.1	107.2
5	108.7	107.2
6	108.5	107.2

a.    Draw a diagram of apparatus which would be suitable for carrying out this experiment.

b.    Explain why the mass of each flask and contents decreases.

The mass decreases because the hydrochloric acid displaces the calcium carbonate to form calcium chloride.

c.    Draw two graphs on the same set of axes to show how the total loss of mass changes with time for each sample.

Total loss for red (small) = 3.9g

Total loss for blue (large) = 2g

d.    On the same grid sketch the graph you would expect to obtain if the experiment was repeated with 10g of powdered calcium carbonate

Advantages vs Disadvantages in producing alcohol by fermentation and in industry.

Fermentation


Advantages:

• Raw material is renewable
• Does not create harmful gasses
• Little energy required

Disadvantages:

• Rate of reaction is slower
• Multiple stages
• More workers required to run process

Industrial

Advantages:

• Reaction is only one stage
• Much faster and more efficient

Disadvantages:

• It is not renewable
• Creates harmful gases
• More energy needed to produce

3.4 - I can recall the products of complete and incomplete combustion of alkanes.

1. Saturated hydrocarbons are called _____.
2. Small chain _____ are used as fuels.
3. The reaction is called _____.
4. The word equation for this chemical reaction is: fuel (_____) + _____ --> _____ + _____ + ENERGY (heart, light, sound)
5. If there is insufficient oxygen then the word equation is: fuel (_____) + _____ --> _____ + _____ + ENERGY (heart, light, sound)
6. The problem with this reaction is that _____ is produced. This gas is _____ to the human body (see objective 5.11)
7. Where can you find incomplete combustion?
8. What is used to reduce the harmful products from incomplete combustion?
9. During incomplete combustion a smoky flame is often seen, explain this observation.
10. Describe the two chemical tests for water.
11. Describe the chemical test for carbon dioxide gas.
12. Describe the physical test for water.
Extension. Write a balanced equation (with state symbols) for the combustion of propane gas:

3.2 & 3.3 - I can recall the general formula and displayed formula of Alkanes.

2. What is the general formula for Alkanes?
3. Describe and explain the boiling point.

Alkanes:


Methane (1 carbons), Ethane (2), Propane (3), Butane (4), Pentane (5

Annual Chemistry Exam 2011 Targets

• Read the question carefully (physical state, not value).
• Learn the observations of the reactions (potassium bromide + chlorine).
• Read the question carefully (word equation NOT symbol equation).
• Describe, in terms of electrons, when sodium reacts with oxygen.
• Protons in isotopes.
• Colour change in test for water.
• Outline how fractional distillation works.

5.13 - I can describe catalytic cracking of long-chain hydrocarbons.

a. What is cracking?


b. Why does it need to be carried out?


c. What is a catalyst?


d. What catalyst is used in this experiment?


e. What allows the liquid paraffin to break down into short-chain hydrocarbons?


d. Which important safety aspects should be carried out?


e. Why are the first bubbles not collected?


f. Why is the gas collected under water?

5.12 - I can recall the problems associated with the fractional distillation of crude oil.

a. When crude oil undergoes ________ ________ there are too many ________ chain hydrocarbons (eg ________) produced and not enough ________ chain hydrocarbons (eg ________).
b. To solve these problems the ________ chain hydrocarbons undergo a chemical reaction called ________. (see objective 5.13)