Investigating the Rate of Reaction From the Concentration of Hydrochloric Acid On Calcium Carbonate.

4) Concentration: The higher the concentration the quicker the reaction.

The lower the concentration the slower the reaction.

A higher concentration of a substance means there are more particles in the same volume of space so there are more collisions, this increases the rate of reaction.

A reaction takes place when two particles collide together. They need to have enough kinetic energy to break the bonds of the reactant molecule; this requires the reaction to take place at a certain temperature, and we often heat reactions for them to occur. The rate of reaction is the number of collisions during a certain amount of time; this is why the reaction rate is also known as the Collision Theory. With a larger surface area of the reactants there are more particles and so more collisions. With a higher temperature the particles move with more kinetic energy and move further faster increasing the number of collisions and with a higher concentration there are more particles in one area and so more collisions.

PLAN:

Equation: CaCO3 (s) + 2HCl › CO2 (g) + CaCl2 (aq) + H2O (l)

For this experiment I will be using dilute hydrochloric acid and calcium carbonate. Calcium carbonate is marble; I will be using the marble in small chips. I will use four concentrations of acid, 0.5 moles per dm3, 1 m/dm3, 1.5 m/dm3 and 2m/dm3. The reaction will be recorded by measuring the volume of carbon dioxide given off in a stated amount of time (1 min.).

FAIR TEST:

For the results to be reliable we must make this a fair test and so there must be only one variable and everything else constant.

Constants:

- Size, small, and mass, 1g, of CaCO3.

- Volume of HCl, 20cm3.

- Temperature, 20oC (room temperature)

- Time of experiment, 1 min.

- Equipment

Variable:

- Concentration of HCl

SAFETY:

Safety must always be considered for any experiment, especially when there are dangerous substances being used. In this experiment we are using Hydrochloric acid, which is corrosive, even more so at its higher concentration.

- Wear safety goggles

- Work on a clear and large work-surface

- Take care at all times, especially with the acid and glass equipment.

METHOD:

Apparatus:

- conical flask

- rubber bung

- delivery tube

- plastic tub

- water, to fill plastic tub

- measuring cylinder

- calcium carbonate, small chips

- hydrochloric acid, varying concentrations

- stopwatch

The apparatus was set up as above. To keep the measuring cylinder full of water so we gain an accurate result you must fill it up and keep your finger over the end as you tip it up and place it in the tub of water. There must be no water allowed to escape and air let in so that it is a fair test.

20ml of HCl was placed in the conical flask followed by 1g of small marble chips. The rubber bung must be placed on immediately after and the stopwatch started. The bubbles from the delivery tube will then be collected in the measuring cylinder. After 1 minute stop and take a reading of the volume of carbon dioxide. Repeat the experiment for the other concentrations of HCl. Once all the results are gathered repeat the whole experiment to check for continuous results and be sure there are no anomalous results.

After the first time we did this experiment the reaction happened too fast and there was too much CO2 being produced in 1 minute for 1 measuring cylinder to take. We could have used more measuring cylinders but some CO2 would be lost in the change over so we increased the size of the chips to medium, as the surface area affects the rate of a reaction, this controlled the experiment a great deal.

PREDICTION:

I predict that with a higher concentration of acid the reaction will be faster and more carbon dioxide will be collected. It may be that there will be quadruple the volume of CO2 for 2 m/dm3 of concentration to that of 1 m/dm3 because there is twice the number of moles in the same volume and as volume is 3-D the result will be squared. This would mean that there are more molecules of acid available in a shorter space to collide with the surface of the calcium carbonate.

OBSERVATIONS:

When the CaCO3 was added to the HCl there was effervescence on the surface of the chips, it was quite violent for the concentration of 2 moles but calmed down by 0.5 moles of concentration. From the equation I know this gas was CO2. As the reaction went on the size of the chips decreased as they were being reacted away.

RESULTS:

Concentration of HCl

(moles)

Volume of CO2 after 1 min.

(cm3)

st experiment

2nd experiment

Average

0.5

2

2

2

4

4.5

4.25

.5

8

7

7.5

2

6

6

6

ANALYSIS:

These results show us that there is a definite affect of the concentration of hydrochloric acid on the rate of the reaction between it and calcium carbonate. For each 0.5 mole increase in concentration of the acid there was a doubling in the amount of gas produced, an increase in the rate of reaction. The first sets of results were better as they were exact. These results do fit my prediction of a higher concentration producing more gas. This has happened because, with a higher concentration, there are more acid particles in the same volume and so therefore more particles that can collide with the calcium carbonate so more reactions are happening at the same time.

EVALUATION:

These results are quite reliable, the first experiment was perfect because the results were exact but there were some questionable results in the second, they were only marginally out and you could still clearly see the pattern. Because these results were only marginally out it proves that these results were reliable and that is why the results were averaged out. As the first experiment proves this was a good method just good care needs to be taken when doing the experiment. The hardest part of the experiment to keep fair was making sure that no air got into the measuring cylinder when it was turned upside down to collect the gas, it may be best to use a sealed syringe to collect the gas in future experiments. The range of the results I took was good enough to show me exactly what I needed to know, I would predict that this pattern would continue for a larger range of results, I could try this as another investigation, to find how far the pattern goes. I could also investigate the effect of surface area, temperature and the use of a catalyst on the rate of a reaction for more investigations, I could compare the different affects they have against each other and perhaps what environments they would be useful to use in.

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Laura Hill Page 1 of 5