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 is more dangerous than coal pieces because it cannot be confined to a certain area, leaving it more venerable too combustion resulting in a danger for human safety.
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?
‘Alko’ will cure acid indigestion faster than ‘Neutro’ as the name suggests it is the more powerful Alkali, this strength is needed for the neutralization of acid indigestion.
You could test this by having 2 beakers filled with the stomach acid (same amounts) and then add a single serving of either the tablet or the powder to one of the beakers, stir for the same duration then test the ph value with indicator paper, the mixture with the ‘Alko’ tablet should be more natural (closer to ph 7, purple) then the mixture with the powder.
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.
Catalyst B is better because its O2 production is always higher and (faster) or the same as catalyst A.
c. Explain why both experiments were done at the same temperature
This is done so temperature does not affect one more than the other, fair test.
d. Explain why both sets of figures stop at 18 cm3 of oxygen
This is the limit of how much O2 each catalyst can produce.
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?
Experiment 2
b. Which experiment produced the greatest final volume of gas?
c. Experiment 2
d. Which experiment used the most concentrated acid?
Experiment 3
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?
b. A substance that increases the rate (speed) of a reaction.
c. Draw a diagram of suitable apparatus that you would use to carry out this experiment.
Collect gas over water.
d. Name the gas that is formed.
Soot
e. Write a balanced chemical equation for the decomposition of hydrogen peroxide.
2H2O2 (aq) ----- 02 (g) + 2H2O (l)
f. Plot a graph of the volume of gas against time.
g. What happen to the concentration of hydrogen peroxide as the reaction proceeds?
It levels out at around 65 seconds.
h. What chemicals are present in the flask after 90 seconds?
Copper
i. What mass of copper (II) oxide would be left in the flask at the end of the reacting?
2 grams
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.
Reactions are taking place.
c. Draw two graphs on the same set of axes to show how the total loss of mass changes with time for each sample.
d. On the same grid sketch the graph you would expect to obtain if the experiment was repeated with 10g of powdered calcium carbonate
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