Courseworks

Acid/Base Investigation

The aim of the experiment is to find out which indigestion tablet is the best. We can do this by looking at how much alkali is put in after the tablet has been put in.Introduction:Hydrochloric Acid (HCl) is the solution of the colourless gas hydrogen chloride in water.Sodium Hydroxide (SHO) is a strong alkaline compound used in soap, etc; caustic soda.I think that when the naturalisation takes place the follow equation will take place:HCl + SHO + Tablet ==> NeutralisationPredictionMy prediction is that the one with the least base will be the best. The stronger the tablet, the less alkali we will have to put in afterwards and the weaker the tablet the more alkali we will have to put in afterwards.Theory of why it works:An acid is any of a class of substances that liberate hydrogen ions in water, are usually sour and corrosive, turn litmus red, and have a pH of less than 7.A base is an alkali. An alkali is any of a class of substances that liberate hydroxide ions in water, usually form caustic or corrosive solutions turn litmus blue and have a pH of more than 7, e.g. caustic soda.In this experiment we now that indigestion tablets neutralise acid in that is in the stomach and we also know that the experiment for neutralisation is titration.Some theory acids always contain H+ ions. These hydrogen ions are produced when an acid reacts with water:HCl (g) + water ==> H+ (aq) + Cl- (aq)Hydrogen ions can be measured on pH scale. If it’s an acid then the pH is always below a pH 7.Alkalis always contain OH- ions. They are the Hydroxides. The most commonly known Hydroxide is Sodium Hydroxide (SHO). Hydroxides have a pH of above 7.If the hydrogen ions and the hydroxide ions are put together, they form water (H2O). This is called neutralisation. The equation for this is below:H+ (aq) ions + OH- (aq) ions ==; H2OSafety:Safety will be a very important factor within our experiment; therefore steps to reduce any risks can be taken. Such steps include wearing goggles for the protection of our eyes because we will be working with acids, which are corrosive.We will wear an apron, because both the alkali and the acid are corrosive and they could react with our clothes (which they most likely won’t) or we could touch our clothes after we have spilt the substances and not wash our hands after and we would just eat without washing out hands and they could be dangerous in that way.We will also tie our hair back because our hair might get in the way while we are doing the experiment or it might fall in the experiment and it could ruin our results.Apparatus* Burette* Volumetric Flask* Conical Flask* Beaker* Indigestion Tablet* Clamp Stand* Funnel* Pipette* Distilled Water* Hydrochloric acid* Sodium hydroxide* Phenolphthalein* White piece of paper* Safety Goggles* ApronMethod1. Put a crushed tablet into a volumetric flask and then add acid to the tablet in the volumetric flask until it reads 250cm3.2. Wait until the tablet and acid forms a solution.3. Take out 25cm3 of the solution with a pipette and put it into a conical flask.4. Now add a few drops of Phenolphthalein to the solution.5. Put some of the alkali (Sodium Hydroxide) into the burette and record how much of the alkali you have put into the burette, with a funnel.6. Start to add the alkali to your solution, but only in a few drops at a time because if you put in too much, the solution won’t be neutralised and the pH will go over pH7.7. Add the alkali until it is a light pink colour.8. Write down the finishing point of the liquid (up to where the meniscus is) and calculate how much alkali has been used by subtracting the finishing point from the starting point.9. Repeat the steps from 1-8 another two times for the same tablet and do the experiment three times or more for each tablet you do, to get accurate results.10. Compare all the results by putting them in a table then transforming it into a graph. The tablet that has used the least amount of alkali is the best tablet as it had already neutralised most of the aid before the alkali was added.Fair test tableVariableChange or SameHow is it controlled/monitored?Effect on resultsTabletChangeWe will buy three different tablets and we will do different experiments for each tablet. We will also test the same tablet three times, to make sure we have accurate results.We will be able to compare all of the tablets that we have experimented with, as they will all be different in their own way.Amount of acid inputSameWe will use a volumetric flask to measure 250cm3. Then use a pipette to use only 25cm3 of that solution.Each of the time we do this experiment; this will have no effect on the results because it is the same every time.Amount of Alkali inputChangeIt will be controlled by the burette as it controls the amount of drops that are going to be put in.It will neutralise the acid and the tablet according to how strong the tablet is.Type of acidSameWe will use the same type of acid each time by checking that the same concentration is used every time.Each of the time we do this experiment; this will have no effect on the results because it is the same every time.Type of AlkaliSameWe will use the same type of alkali each time by checking that the same concentration is used every time.Each of the time we do this experiment; this will have no effect on the results because it is the same every time.Same amount of tablet each timeChangeWe will measure the tablet each time with the same or the same type of scales and also in the same units.This will have an effect in one way and in the other way it won’t. It will have an effect because all of the tablets are different and it won’t have an effect because the weight of the tablet doesn’t matter as there will be the same amount of acid + tablet each time.ResultsBoots peppermintRennieSettlers windezeVolume of Alkali in cm3Concentration usedVolume of Alkali in cm3Concentration usedVolume of Alkali in cm3Concentration used19.80.19.30.122.30.117.10.19.50.122.60.1170.18.60.122.80.116.30.19.10.122.60.1130.18.60.122.50.1160.18.60.122.40.1160.111.50.1160.111.50.1Average: 22.5333333317.20.111.80.1220.111.60.113.20.522.40.112.90.522.20.1Average: 10.0112.90.523.30.1Average: 12.923.90.115.80.122.760.515.60.115.80.1Average: 22.76160.116.80.116.60.116.50.1Average: 17.8714285730.54.60.54.90.54.80.5Average: 4.766666667AnalysisMy resultsTabletMass of TabletAlkali input in cm3Start in cm3End in cm3Concentration usedRennie1.39.30.09.30.1Peppermint1.019.80.019.80.1Peppermint1.03.00.03.00.5Peppermint1.04.60.04.60.5Peppermint1.04.90.04.90.5Class ResultsBoots peppermintRennieSettlers windezeVolume of Alkali in cm3Concentration usedVolume of Alkali in cm3Concentration usedVolume of Alkali in cm3Concentration used19.80.19.30.122.30.117.10.19.50.122.60.1170.18.60.122.80.116.30.19.10.122.60.1130.18.60.122.50.1160.18.60.122.40.1160.111.50.1160.111.50.1Average: 22.5333333317.20.111.80.113.20.5220.111.60.112.90.522.40.1Average: 10.0112.90.522.20.122.760.5Average: 12.923.30.1Average: 22.7623.90.115.80.115.60.115.80.1160.116.80.116.60.116.50.1Average: 17.8714285730.54.60.54.90.54.80.5Average: 4.766666667The next few paragraphs show the moles of each of the tablets and also with the different concentrations.The calculation for the number of moles is:Moles of Alkali = x = amount of alkali25cm3 of the mixture = x/1000 * 0.1 moldm-3 = y moles250cm3 of the mixture = y * 10 = z molesStarting amount of acid = 250/1000 * (the concentration) = v molesTo find out how much reacted with the tablet = V – Z = R Moles (the acid used)The number of moles in each tablet.Tablet: PeppermintConcentration: 0.1Calculation:X = 17.87142857/1000 * 0.1 = 0.00178142Z = 0.00178142 * 10 = 0.0178142V = 250/1000 * 0.1 0.025R = 0.025 – 0.0178142 = 0.0071858 MolesNumber of moles = 0.0071858 MolesTablet: PeppermintConcentration: 0.5Calculation:X = 4.766666667/1000 * 0.1 = 0.0004766666667Z = 0.000466666667 * 10 = 0.004766666667V = 250/1000 * 0.5 = 0.125R = 0.125 – 0.004766666667 = 0.120233333 MolesNumber of moles = 0.120233333 MolesTablet: RennieConcentration: 0.1Calculation:X = 10.1 * 0.1 = 0.00101Z = 0.00101 * 10 = 0.0101V = 250/1000 * 0.1 = 0.025R = 0.25 – 0.0101 = 0.2399 MolesNumber of Moles = 0.2399 MolesTablet: RennieConcentration: 0.5Calculation:X = 22.76/1000 * 0.1 = 0.002276Z = 0.002276 * 10 = 0.02276V = 250/1000 * 0.5 = 0.125R = 0.125 – 0.02276 = 0.10224Number of Moles = 0.10224Tablet: SettlersConcentration: 0.1Calculation:X = 22.53333333/1000 * 0.1 = 0.002253333333Z = 0.002253333333 * 10 = 0.022533333V = 250/1000 * 0.1 = 0.125R = 0.025 – 0.022533333 = 0.2246667 MolesNumber of Moles = 0.2246667 MolesTablet: SettlersConcentration: 0.5Calculation:X = 13/1000 * 0.1 = 0.0013Z = 0.0013 * 10 = 0.013V = 250/1000 * 0.5 = 0.125R = 0.125 – 0.013 = 0.112 MolesNumber of Moles = 0.112 MolesThe results that I have chosen to use are my class results. I am using these because in my group we weren’t able to collect enough results to compare them with each other, as some of our experiments went wrong. We added too much alkali and the solution went over the neutralisation point.When I looked at the table in which my class results are, I could see that for all three of the tablets and the different concentrations as well, the neutralisation points were very close. When the concentration was 0.1, the settlers tablet the results were actually within the number and they were only 0.1cm3 away from each other. But the best tablet was the Rennie because it had used the lowest amount of alkali each time even though the results had been spread out into two numbers. The one in this experiment that was second best was the peppermint tablet. But the problem with this tablet was that the results weren’t reliable because they were spread out over a large amount of numbers, even though some of the volumes of the alkalis were the same.In the 0.5 concentrations, the peppermint tablet was the best to use. Then came the settlers and last of all came the Rennie. But I think that these results are not reliable because there are many more results taken down in the 0.1 concentrations than in the 0.5 concentrations. Also because they are only done by one pair of people in each of the tablets and they were done many times by those pairs.Many of our results didn’t fit the pattern. There are two reasons for this. One of them is that we used different alkalis that had different concentrations. The other reason is that there were lots of people in the class and each one of the groups did the experiment in their own way and everybody didn’t do it in the same order.I think that we should have been given a little bit more time to complete the experiment, so we could have got more results and more people could have got on to doing all of the tablets instead of just one or two of the tablets. We would have been able to work with our own results. The results don’t prove our point as well because two different types of concentrations have been used both of them have come out with different views to the other one.EvaluationVariablesChange or sameWhat happened, did you control this successfully?Use scientific theory to explain what effect this might have on you resultsTabletChangeWe controlled this successfully as we used different tablets to experiment with, to see which one was stronger.It is obvious that each tablet cannot have the same results, so because they are different we will be able to compare them to see which one is best.Amount of acid inputSameWe controlled this successfully as the amount we put in each time had already been measured for us, so all we had to do was make sure the meniscus was in line of where it had to be.It didn’t have any effect on the results because we used the same amount of acid each time.Amount of alkali inputChangeThis was controlled successfully, by a burette. It made sure that the amount of drops that were needed was put in. But there wasn’t a set amount of liquid that needed to be in there. But we went over the neutralisation point a few times as we put in too much.The effect it will have on our results is that the substance will turn pink in the end, which means it is neutral.Type of acidSameWe controlled this successfully because we used the same type of acid each time. The acid was called Hydrochloric acid.This will have no effect on our results because there is only one type on cid being used.Type of alkaliSameWe controlled this successfully because we used the same type of alkali each time. The alkali was Sodium Hydroxide.This will also have no effect on our results because there is also only one type of alkali that is being used but some people also used an alkali with a different concentration to the others.Same amount of indigestion tablet used each timeChangeWe controlled this successfully because we measured each tablet with the same, or same type of weighing scales and also in the same units.This will have an effect on the results because each of the three tablets have different strengths but the weight of the tablet won’t have that much of an effect because we put in the same amount of acid + tablet each time.If I were to do this experiment and this piece of coursework again, then I would make sure that I used only one type of concentration, made sure that I collected more results so I would only be able to use my results so they would be reliable, and I would also do things more accurately, like make sure that all of the tablet had gone into the conical flask after I had crushed it and that most of it had not just stuck to the side of the crusher or the bowl that I was crushing it in.

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