AS Chemistry - Investigate the effect of sodium carbonate on hard water
Chemistry Coursework
The aim of this experiment is to investigate the effect of sodium carbonate on hard water. To do this, a pipette and a burette are used to help give accurate readings, a conical flask will then be used to shake the mixture together and see if a permanent lather is formed.
Diagram of equipment to be used in the experiment:
A burette will be used to measure an amount of soap solution. It is a piece of equipment that can measure to an accuracy of 1/20cm³. An electronic balance (measuring to 3 decimal places) will be used to accurately measure the correct amount of sodium carbonate; a pipette will be used to measure exactly 25cm³ of water at 20oC, which will be added to the soap solution. This solution, together with the soap solution, water and sodium carbonate, will be put into a conical flask, corked and shaken. The conical flask will be shaken for precisely 10 seconds using a stopwatch. An accurate ruler will be used to measure the depth of lather formed that has remained for at least 10 seconds after shaking the conical flask, the lather should be at least 4mm in depth to categorise the lather as permanent.
However, not all the ions present in the above equation actually play a part in the reaction, the ions that do are:
The soap solution is used to find out the hardness of the water being tested. The equation below shows what happens when soap is added to water.
Again, not all the ions present in the above equation actually play a part in the reaction, the ions that do are:
It is important to make sure that all measurements and readings are precise, e.g. the weighing of the sodium carbonate and the cleanliness of the apparatus. Many of these key factors are variables. By using these variable one can ascertain different results. The results of the experiment will be affected by the changing the amount of sodium carbonate or the amount and/or source of the water will affect the results of the experiment, and most of all the cleanliness of the apparatus.
I predict that the graph will start high showing that a lot of the soap solution would be required to create the unbroken lather on the surface for ten seconds. Then when one gram of sodium carbonate is added, the amount of soap solution required to create a lather will be much less. In a previous experiment the amount of soap solution required to create the lather when no sodium carbonate was added was 7 cm3. The amount of soap solution required to create the lather when one gram of sodium carbonate was added however, was only five cm3. So the amount of solution required went down by 2cm3. I think that the amount of soap solution required to create the lather when two grams of sodium carbonate will go down less than before. So the amount of soap solution require could again go down by 2cm3. However, from other previous research I have found out that eventually the experiment will reach a point when there are no more calcium ions remaining in the water because the water has reached its maximum softness and no matter how much odium carbonate is added, the water will not become any softer. This implies that the graph will level off at the end.
Method:
. Fill a pipette with 25cm³ of water using a pipette filler.
2. Empty contents of pipette into a conical flask.
3. Add 0.5g of sodium carbonate to the conical flask containing water.
4. Put the cork in the conical flask and shake thoroughly to dissolve sodium carbonate (using a filter to remove any excess).
5. To titrate, fill a burette with soap solution to the zero mark. Dispense 1cm³ of soap solution into the conical flask.
6. Replace the cork in the flask and shake for 10 seconds; observe ...
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Method:
. Fill a pipette with 25cm³ of water using a pipette filler.
2. Empty contents of pipette into a conical flask.
3. Add 0.5g of sodium carbonate to the conical flask containing water.
4. Put the cork in the conical flask and shake thoroughly to dissolve sodium carbonate (using a filter to remove any excess).
5. To titrate, fill a burette with soap solution to the zero mark. Dispense 1cm³ of soap solution into the conical flask.
6. Replace the cork in the flask and shake for 10 seconds; observe if a permanent lather forms i.e. one that lasts more that 10 seconds.
7. Repeat steps 5 and 6 until a permanent lather is formed.
8. Note down the amount of soap used to form a permanent lather.
The experiment should be repeated a further nine times, using an extra 0.5g of sodium carbonate each time in step 3, i.e. the final experiment should contain 5g of sodium carbonate. However, each time an additional 0.5g of sodium carbonate is used, the experiment should be repeated so that clear results are obtained and any anomalies are easy to spot and eliminate from the final table of results. Altogether 18 results will be obtained; the average of the two results for the same quantity of sodium carbonate will be used in the final table of results.
The equation for the above experiment is as follows:
Safety:
. Care with wet glassware.
2. Be careful when attaching the pipette to the pipette filler as holding the pipette below the bulge could result in injury.
3. Use a pipette filler so that one does not have to suck up the water in the mouth, which could cause fatality.
4. Keep soap solution away from fire as it is flammable.
5. Eye protection will be worn so no harmful substances can enter ones eyes.
6. Be careful with sharp edges.
The theory behind all this is that the sodium carbonate will remove all the calcium ions as calcium carbonate and therefore will have softened the water. However, there is a limit of the amount of sodium carbonate one can add because when all of the calcium ions have been removed the water cannot be softened any more and therefore the sodium carbonate will not make a difference.
The ionic equation below, which has been proven to work, shows that the sodium carbonate will soften the water and prove that the theory is reliable and works.
To make sure that the experiment is producing reliable results, very precise measuring instruments will be used during the course of the experiment. A burette will be used to measure the amount of soap solution. It is a piece of equipment that can measure to an accuracy of 1/20cm³. An electronic balance will be used to accurately measure the correct amount of sodium carbonate, the balance has a wind shield to make sure that no breeze will affect the mass of the sodium carbonate measured, as well as this the balance is correct to three decimal places; a pipette will be used to measure exactly 25cm³ of water, which will be added to the soap solution. The conical flask, containing the soap solution, water and sodium carbonate, will be shaken for precisely 10 seconds using an accurate stopwatch to make sure that there is not too much or too little time spent shaking the conical flask that could affect the results, the stopwatch being used will be correct to one hundredth of a second. An accurate ruler will be used to measure the depth of lather formed that has remained for at least 10 seconds after shaking the conical flask, the lather should be at least 4mm in depth to categorise the lather as permanent.
To make sure the experiment is a fair test, certain procedures must be carried out. Firstly, every time new amounts of water are taken, they must be from the same source and of the same amount as it is a controlled amount each time. Secondly, the soap solution should be from the same bottle each time more amounts of it are added. Once again, this applies to the sodium carbonate, which must also be pure. The amount of sodium carbonate is varied and as a result the amount of soap solution used varies. The time taken to shake the solution should be a fixed time of 10 seconds using a stopwatch in order to produce accurate results. The laboratory used to carry out the experiment should be kept at exactly the same temperature all the time; this temperature should be "room temperature" (21ºC). The control, to which all results are compared, is varied and the differing results are analysed in a table of results.
Much preliminary work has been done to help make a prediction. The preliminary work was as follows:
. Fill a pipette with 25cm³ of water using a pipette filler.
2. Empty contents of pipette into a conical flask.
3. Add 0.5g of sodium carbonate to the conical flask containing water.
4. Put the cork in the conical flask and shake thoroughly to dissolve sodium carbonate (using a filter to remove any excess).
5. To titrate, fill a burette with soap solution to the zero mark. Dispense 1cm³ of soap solution into the conical flask.
6. Replace the cork in the flask and shake for 10 seconds; observe if a permanent lather forms i.e. one that lasts more that 10 seconds.
7. Repeat steps 5 and 6 until a permanent lather is formed.
8. Note down the amount of soap used to form a permanent lather.
The experiment is repeated using 2g of sodium carbonate. The results are as follows:
Mass of sodium carbonate (g)
Source of Water
Volume of soap for a permanent lather cm3
0.000
London region water
7
0.500
London region water
3
2.000
London region water
The results above show that the more sodium carbonate used, the softer the water becomes. We can see this because when no sodium carbonate is used the amount of soap needed to make a permanent lather is 7cm3, then when 0.50g of sodium carbonate is used less than half the amount of soap is needed to make a lather and when 2.00g is used only 1 cm3 is required to form a permanent lather.
. Care with wet glassware.
2. Be careful when attaching the pipette to the pipette filler as holding the pipette below the bulge could result in injury.
3. Use a pipette filler so that one does not have to suck up the water in the mouth, which could cause fatality.
4. Keep soap solution away from fire as it is flammable.
5. Eye protection will be worn so no harmful substances can enter ones eyes.
6. Be careful with sharp edges.
Amount of Water used
(cm3)
Sodium carbonate
(Na2CO3)
(g)
Volume of soap used
Average
(cm3)
Try 1
(cm3)
Try 2
(cm3)
Try 3
(cm3)
25.0
0.000
6.00
6.50
6.50
6.33
25.0
0.500
4.50
4.50
5.00
4.67
25.0
.000
4.00
4.00
3.50
3.83
25.0
.500
3.00
3.00
3.00
3.00
25.0
2.000
2.00
2.00
3.00
2.33
25.0
2.500
2.00
2.50
2.00
2.17
25.0
3.000
.50
.50
.50
.50
25.0
3.500
.00
.50
.50
.33
25.0
4.000
.50
.00
.00
.17
25.0
4.500
.00
.50
.00
.17
25.0
5.000
.50
.50
.50
.50
By looking at the results it appears that the more sodium carbonate added, the less soap solution is required to form a permanent lather. On the table of results above and the graph below it shows the amount of soap solution required to create the lather when no sodium carbonate was added to the water was 6.33cm3. However, when one grams of sodium carbonate were added, the amount of soap solution required to make a lather fell to 3.83. The drop in the amount of soap solution required to create a lather between 0 grams of sodium carbonate and 0.5 grams was 1.66cm3 and the drop between 0.5 grams and 1 gram was only 0.84cm3. This pattern of the drop in the amount of soap solution required when more and more sodium carbonate was added continued throughout the entire experiment, as predicted, except for the last result which went up a small amount. This resulted in the graph showing a curve, which was also as predicted. From this it is noticeable that the more sodium carbonate added the less effective it becomes each time.
The reason the water gets softer in the first place is because the calcium ions in the water react with the sodium carbonate. When this happens calcium carbonate is formed:
This means that the calcium ions become tied up with the carbonate, which means that they cannot react with anything else. The reason that this reaction means less soap solution is required to create a lather is because the calcium ions dissolved in the water can also react with the water to create calcium stearate also known as 'scum':
When the calcium ion is present in calcium carbonate it cannot react with the stearate to create scum. So as more and more sodium carbonate is added it reacts with more and more calcium ions. As more and more calcium ions become tied up with the carbonate, the less there are to react with the stearate. As the amount of the calcium ions become fewer and fewer, there is less collision between them and the stearate. This means that the more and more stearate ions cause the lather before they come into contact with the calcium ions. This results in the amount of soap solution required dropping by less and less as the amount of sodium carbonate goes up and up.
Analysis Gidon Mahalla
The procedure went well, however, the only problem was that we had to weigh the sodium carbonate out separately every time and this took some time. This made the experiment very stop-start as once we had tested one solution we had to wait for the other one to be weighed. To help overcome this problem one person weighed and the other person performed the tests. However, the weighing was much quicker and the testing could not keep up with the weighing. If this problem had improved we would have had a lot more time to obtain a greater amount of results and therefore obtain more accurate results.
The results from the experiment were good, they almost exactly matched the prediction I had made. There were no anomalous results that stand too far out of line, however, there were a couple of results which did not quite fit in the line of best fit, but did not ruin the trend of the other results. These results have been circled on the graph. A reason why the results are anomalous is that the amount of sodium carbonate was too little as more soap was required to create a lather.
I do not feel that the results give an accurate enough set of results. This is because more repeats could have been carried out than just three times. Another reason is that the experiment was split up into two parts, the first time I used an accurate stopwatch and the second time I used a wall clock. The experiment could also have been carried on further to see how the results would have become after much more sodium carbonate was added.
To improve this experiment we could have used a thermometer to make sure the temperature was the same each time. Another way of making sure the temperature was the same both times is to take all the water necessary for the whole experiment and store it in large container at exactly the same temperature for the whole course of the experiment and in the gap between both halves of the experiment. To improve the accuracy of the timing we could have used a stopwatch both times. To make sure the water had not been contaminated from the ring main system we could have taken the water from a place before it had been put in to the ring main system to give a true reading of the hardness of water in London.
To extend the work to support my conclusion two different experiments could be carried out. Firstly, we could try the experiment with different temperatures of water to see what affect the change in temperature had on my results. Secondly, different samples of water can be taken from different areas. For example, samples could be taken from all over the country or even the world. This would show us the different hardness's of water across the globe.
Analysis
Evaluation Gidon Mahalla
