This is explained in detail below !
Quantitative Prediction: -
The 2 Molar acid has twice the number of acid particles than the 1 Molar. This is cause would cause the particles of the 2M acid to have twice as much successive collisions as the 1M concentration of acid. This would therefore result to the rate of reaction doubling. (In this experiment, it is essential to keep the volume of the acid the same).
For example, 50 cm3 of 2M Hydrochloric Acid would contain the same number of acid particles as 100 cm3 of 1M Hydrochloric Acid despite the fact that the concentrations are different. Although in 100 cm3 the particles are further apart and the numbers of collisions would by reduced by this.
Also: -
Facts Theory
Diagram to show the collision theory
MAIN INVESTIGATION
Equipment: -
Diagram 2 (to show how to set up equipment)
Diagram 3 (of other equipment)
Method: -
- First, make sure of all the safety checks. Therefore, wear goggles. Then set up the experiment as shown in the Diagram 2 and 3.
- Measure out, 80 ml of Hydrochloric Acid (1M) and weigh 5 grams of Small Marble chips.
- Have the timer ready and add the Small Marble Chips simultaneously to the flask full of Hydrochloric Acid, shut the bung and start the clock.
- Every 5 seconds take a reading of the Gas Syringe and record the results.
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Repeat this experiment three times to ensure correct results and then repeat using different Hydrochloric Acid (2M, 3M, 4M). Mathematically calculate an average of the three experiments with the same Hydrochloric Acid concentration and plot on a line graph.
Safety: -
Making sure that the Acid does not drop or spill, or be exposed to the eyes. Wearing goggles can prevent this. Keeping a distance from the experiment when not taking results off the Gas syringe. Keeping Goggles on at all times when using the Hydrochloric Acid. Watching the Gas syringe when it gets to 100 ml because at this point the bung on the top of the conical flask will “pop” off because of the pressure in the flask.
Fair Test: -
The apparatus used in all the experiments is the same as is the amount of marble chips and the same volume of Hydrochloric Acid. This ensures a fair test. Having three tries at each experiment would show if one of the results were inaccurate. Keeping the same temperature throughout the experiment by putting the Hydrochloric Acid in a water bath helps keep the experiment fair (as mentioned earlier). Noticing that the Gas Syringe and the delivery tube is clean, no blockages and there is no water blocked in the Gas Syringe also helps. If there were water blocked in the Gas Syringe then this would make the leaver to the Gas Syringe stick and make the experiment inaccurate. Using petroleum jelly would solve the stickiness of the Gas syringe.
Variables kept constant: -
- Controlling the temperature by keeping the Acid in a water bath of cold water from the tap and this should keep the temperature of the Hydrochloric Acid constant. This is done to make the experiment fair and accurate to get precise results.
- Keeping the weight of the Marble chips the same every time to ensure getting accurate results.
- Hydrochloric Acid to be kept at the same volume for each experiment. This makes sure that the dissolving of the marble chips is accurate at the same volume at each stage of the experiment.
- To measure the time for the results in how much gas is given off to how long it takes to fill the Gas Syringe. This is to get the results and plot on a graph to show the accurate results
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To measure how long it takes to give off 100 cm3 of CO2 gas. To get the results on the table and on the graph.
Results for the main experiment: -
Volume of CO2 (g) produced (cm3) from the reaction between different concentrations of Hydrochloric Acid and small sized marble chips.
Volume of CO2 produced (cm3) Volume of CO2 produced (cm3)
Volume of CO2 produced (cm3) Volume of CO2 produced (cm3)
Interpretation of results
-
The volume of CO2 (g) produced (measured in cm3) increased with the increase of time (seconds)
- Rate of reaction was slowest with 1M HCl (aq)
The gradient/steepness of the graph was lowest i.e. least steep and took the longest time to produce the same volume of CO2.
- Rate of reaction was quickest with the 4M HCl (aq)
Gradient/Steepness of the graph is highest and it took the least length of time to produce the same volume of CO2.
- As the concentration of the HCl increases the rate of reaction is increased.
As the concentration of the HCl was increased from the 1M to the 2M to the 3M to the 4M the Steepness/gradient increased i.e. it took gradually shorter length of time to produce the same volume of CO2 (g)
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Volume of CO2 produced is the same for 4M, 3M, and 2M HCl.
All three concentrations of HCl (4M, 3M, 2M) produced 100 cm3 of CO2 (g) (this is the maximum volume of CO2 (g) that could be accommodated by the Gas syringe).
- Rate of reaction increased with increase of time particularly for 1M HCl.
Steepness/gradient of the graph is increased with the increase of time for each concentration. This is particularly obvious on the 1M HCl where the rate is slow to begin with but increases as time increases.
Mathematically doubling the concentration of Hydrochloric Acid, to see if the rate of reaction doubles: -
- Table to show rate of reaction for each concentration between 5-10 seconds
Calculation shows that the rate of reaction increases when the concentration is increased.
This supports the first prediction (i.e. prediction 1). The scientific evidence for this has already been discussed. The higher the concentration the greater chance the particles have in colliding. This therefore would result in the increase of the rate of reaction.
When the concentration is doubled, the rate is doubled. This is stated in prediction 2. Calculations will show if this is true.
1M 2M HCl Rate increased from 0.4 cm3/second to 3.4 cm3/second. Rate actually increased at a rate of 8.5
Calculated as follows 3.4 this would
- equal to
2M 4M HCl Rate increased from 3.4 cm3/second to 5.8 cm3/second. Rate increased at a rate of 1.7
Calculated as follows 5.8 this would
3.4 equal to
Changing the concentration from 2M to 4M is doubling the concentration; this does approximately result in doubling of rate. However analysing changes in concentration from 1M to 2M, although the concentration does double the rate goes up by a factor of 8.5 i.e. more than doubles. This could be contributed to errors (see evaluation “P10"). From this information, it is not possible to say that prediction 2 is correct or incorrect. Further experiments e.g. comparison of rate after doubling other concentrations are needed to prove this theory (for example 2M to 6M, 4M to 8M etc).
Conclusions: -
Concentration of HCl effects the rate of reaction of HCl with Calcium Carbonate. As concentration increases rate will increase (to a limit).
Scientific evidence for this is based on the collision theory (see predictions “P3").
Experimental evidence is provided by the results, for some reactions the relationship between concentration and rate of reaction is linear i.e. if concentration is increased by a factor the rate increases by the same factor ** (sometimes called first order). It is not clear if this is true for this reaction until further investigation is carried out. The limit occurs because there is only a certain mass of CaCO3 available to react.
Evaluation: -
Sources of Error
The accuracy of the experiment
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Keeping the variables constant e.g. concentration of Hydrochloric Acid (see Variables “P6")
- Preliminary experiment was relevant and useful because it determined the chip size.
Accurate graph
Line had a line of best fit
Far out Results: -
There were two results outside of the 1M line and this was probably due to Human error.
Further investigations: -
- Look at actual mathematical relationship in further detail between Hydrochloric acid and the rate of reaction by using different concentrations.
E.g. 0.25M & 0.5M
0.5M & 1M
- Look at actual mathematical relationship between mass of CaCO3 and rate of reaction.
(1 and 2 would allow rate of reaction to be formulated)
- Look at the effect of the factors on rate e.g. surface area of chips
or the addition of catalysts.
Appendix for the main experiment: -
Volume of CO2 (g) produced (cm3) from the reaction between different concentrations of Hydrochloric Acid and small sized marble chips.
Volume of CO2 produced (cm3) Volume of CO2 produced (cm3)
Volume of CO2 produced (cm3) Volume of CO2 produced (cm3)
This is another way to show the results given but the Bar Graph would be complicated to look at. The Line Graph would be easier to retrieve data from Time against concentration.
References: -
- Philip Mattews, Advanced Chemistry I (Physical and Industrial)
Published by Cambridge University 1992
- Michael Lewis & Guy Waller, Thinking Chemistry
Published by Oxford University Press
- RoseMarie Gallagher, Paul Ingram & Peter Whitehead, Co-ordinated Science Chemistry
Published by Oxford University Press