The aim on my investigation is to find the percentage of citric acid present in lemon squash by using a method of neutralisation, by a method of titration and volumetric analysis.
Aim:
The aim on my investigation is to find the percentage of citric acid present in lemon squash by using a method of neutralisation, by a method of titration and volumetric analysis. I will be using sodium hydroxide as an alkali, which will be neutralising the citric acid.
Background Knowledge:
Titration
Titration is a technique for investigating the volume of solutions that react together. One solution is placed in a burette and slowly added to a fixed volume of another solution, usually measured with a pipette, until the end point of the reaction is shown using an indicator.
Salts can be made by this method by repeating the titration between an acid and alkali using previously measured quantities without using the indicator.
Citric acid
Citric acid is the acid present in citrus fruits such as oranges and lemons. It is commonly used to add a 'tang' to fruit drinks and lemonades. Mixed with sodium hydrogencarbonate (commonly knows as bicarbonate of soda) and sugar, it becomes sherbet. Its chemical formula is H3 (C6H5O7). In this investigation I will be working out the percentage of this acid in lemon squash using titration
Hydrochloric acid
Hydrochloric acid is a mineral acid. The concentrated acid is a 35% by weight solution hydrogen chloride in water. It is a typical strong acid. It reacts with metals, alkalis and bases, carbonates and indicators in the same way that all strong acid do.
Manufacture of hydrochloric acid
Hydrogen chloride is made industrially by burning hydrogen in chlorine. It is also a valuable by- product of many processes in which chlorine is reacted with organic compounds.
Uses of hydrochloric acid
In the laboratory, concentrated hydrochloric acid will produce chlorine if added to potassium permanganate crystals.
Hydrochloric acid + oxygen atoms from chlorine + water
Potassium
Permanganate
2HCl (aq) + (O) Cl2 (g) + H2O (l)
One of its common industrial uses is to 'pickle' steel. Pickling is the process of dissolving rust from steel articles. The bodies of cars, cookers, and refrigerators are all pickled before painting.
Fe2O3 (s) + 6HCl (aq) 2FeCl3 (aq) + 3H2O
Sodium hydroxide, NaOH
Sodium hydroxide is a white solid which is very soluble in water. In the solid state it is deliquescent- becomes very wet if it is left in the air. It is a typical strong alkali and is used in the manufacture of soaps and aluminium.
Uses of sodium hydroxide
Chemicals -29%
Fibres -16%
Alumina -1%
Detergents -4%
Paper -5%
Neutralisation -5%
Other uses -40%
Sodium hydroxide is also called caustic soda because of its extremely corrosive nature
Phenolphthalein
Phenolphthalein is an indicator. It is colourless in acidic and neutral solutions and reddish pink in alkaline solutions. It is a common indicator in acid- alkali titration. As the difference can be easily spotted when the solutions is alkaline of acidic I will be using this an indicator in this investigation.
Acids and bases
Acids and Bases are two classes of chemical compounds that display generally opposite ...
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Detergents -4%
Paper -5%
Neutralisation -5%
Other uses -40%
Sodium hydroxide is also called caustic soda because of its extremely corrosive nature
Phenolphthalein
Phenolphthalein is an indicator. It is colourless in acidic and neutral solutions and reddish pink in alkaline solutions. It is a common indicator in acid- alkali titration. As the difference can be easily spotted when the solutions is alkaline of acidic I will be using this an indicator in this investigation.
Acids and bases
Acids and Bases are two classes of chemical compounds that display generally opposite characteristics. Acids taste sour, turn litmus (a pink dye derived from lichens) red, and often react with some metals to produce hydrogen gas. Bases taste bitter, turn litmus blue, and feel slippery. When aqueous (water) solutions of an acid and a base are combined, a neutralization reaction occurs. This reaction is characteristically very rapid and generally produces water and a salt.
Preliminary experiment:
This is a simple experiment, which I carried out before the actual investigation itself. My aim is to find the percentage of citric acid in lemon squash using titration as a method of neutralization. So to help my investigation I set up a simple investigation, to help understand titration as a topic on the whole.
The aim of this preliminary experiment was to calculate how much hydrochloric acid (HCl) is needed to neutralize sodium hydroxide (NaOH), of a concentration of 0.1 moles.
I used the necessary apparatus and then carefully I pipetted 25cm3 of hydrochloric acid into a conical flask and added four drops phenolphthalein indicator. I then funneled 50 cm3 of NaOH into the burette and when I was set up I released the NaOH slowly drop by drop into the flask, which contained HCl, until I noticed a change in colour, (the phenolphthalein indicator is pink in acid and clear when neutral). I carefully read the reading on the burette and carried out the test three times, and then I made an average reading; this was 23.5 cm3. I then used this to calculate the value of HCl. The calculation is as below:
Volume of NaOH= 25cm3
Volume of HCl= 23.5cm3
Concentration of NaOH= 0.1mols
Concentration of HCl=? Moles
NaOH + HCl NaCl + H2O
mole of NaOH = 1 mole of HCl
Therefore 1000cm3 of NaOH= 0.1mols
23.5cm3 of NaOH=?
23.5cm3 x 0.1mols = 1mole of HCl
1000cm3
According to the equation, 1 mole of NaOH= 1 mole of HCl
Therefore:
23.5cm3 x 0.1mols x 1 = 1mole of HCl
1000cm3 x 1
25cm3 of HCl = 23.5 cm3 x 0.1moles
1000cm3 x 1
000cm3 x 23.5cm3 x 0.1moles x 1
1000cm3 x 1 x 25cm3
= 23.5cm3 x 0.1
25
=0.094moles
From this I learnt that 1 mole of an acid is required to neutralise 1 mole of an alkali. I also learnt how to do the experiment; this gave me a chance to get some experience with the apparatus. This also gave me a chance to know of the safety precautions and variables of the experiment, for me to receive an accurate set of results.
Apparatus:
The apparatus that I will be using to do my experiment are
) Phenolphthalein- this is the indicator I will be using to find out when the acid has neutralised.
2) Burette- this is like a drip, it will slowly pour the NaOH into the conical flask.
3) Pipette- I will need exactly 25cm3 on acid and so I will use this the measure this as it is more accurate than pouring it straight into the flask.
4) Pipette filler- I will fill the pipette with this, it is like a sucker on the top of the pipette.
5) Conical flask- this is where the reaction will be occurring; the acid will mix with the alkali.
6) Lemon squash- this is the acid solution that I am going to neutralise.
7) Sodium hydroxide- this is the alkali I am going to use to neutralise the acid.
8) Clamp stand- the burette is too long to stand upright on is own and so I am going to use the clamp stand as a support for the burette.
9) Beakers- will store the acid and alkali until I need them.
0) White tile- this will make it easier to see the change in colour of the solution.
1) Distilled water- this will be needed to rinse the beakers and other apparatus.
2) Safety glasses- will be needed to stop any splashes of the acid or the alkali getting to my eyes.
3) Funnel- the top of the burette if narrow and so to make it easier to pour the alkali into the burette the funnel will be used, this will also reduce the likeliness that the alkali will spill or overflow.
Above I have listed all the apparatus, which includes the safety apparatus that I will be using.
Diagram:
Method:
The apparatus required to perform this experiment is listed earlier. If I use the apparatus properly, I can accurately find out how much sodium hydroxide is needed to neutralise 25cm3 of citric acid from lemon squash, and then using this to work out the percentage of citric acid in lemon squash. To do this I will perform the following stages.
) Firstly, I will set up the apparatus as I have shown in the diagram.
2) I will then place a funnel on the top of the burette and check that the tap is off and then pour the 50cm3 of acid into the burette
3) I will pour the acid until the lower meniscus reaches the '0' mark as accurately as possible. If too much is poured I will have to open the tap and let some of the alkali pour out and then try again.
4) Using the pipette filler, I will fill the pipette with 25cm3 of sodium hydroxide; and I have to make sure no air traps in the pipette by making sure the tip of the pipette stays in the middle of the solution of sodium hydroxide.
5) I will then pour it into the 250cm3 conical flask
6) I will then pour 3-4 drops of phenolphthalein indicator into the flask. This will make the solution turn pink.
7) I will place a white tile underneath the flask. This will aid me in finding any colour changes that may be hard to see.
8) Finally I will open the burette tap, and allow the acid to drop into the solution. The left arm will control the tap, and with my right I will shake the flask. When there is a definite colour change I will close the tap and read the reading on the burette.
I will repeat it about three times and make the average out of the three.
Hypothesis:
The sodium hydroxide will neutralise the citric acid from lemon squash, giving a salt (sodium citrate) and water. By analysing my formulas I can predict that
0.1 Mole of citric acid will neutralise 1 mole of sodium hydroxide.
The solution of lemon squash that I am going to use is 100% citric acid concentration. And the volume is 25cm3. The acid will be diluted to 250cm3, by adding water, in other words the citric acid was diluted x10 more than water.
I can predict this because
Percentage of citric acid = 25cm3 x 100%
250cm3
= 10%
Safety:
During my investigation I will make sure that:
) I have my safety glasses on at all times, so that any spilled solutions and chemical do not damage my eyes.
2) That all the chemicals and apparatus are kept well away from the edge of the table to prevent any breaking or spilling.
3) I will make sure that I handle my apparatus very carefully so then I avoid breaking any thing, this would disrupt the investigation.
Fair test:
I have to keep my experiment in the same condition throughout so that it is a fair test, so that no external factors will affect the experiment. Some factors affecting the investigation are listed below:
) I will make sure that the same volumes of citric (50cm3) and sodium hydroxide (25cm3) are used. If this isn't done the results would be affected and the calculation would be inaccurate.
2) Every time I fill the burette to the lower of the 0cm3 mark, I will make sure it doesn't go up and down, and therefore not affect the readings.
3) Also, the number of drops of phenolphthalein indicator will not change the colour of the indicator.
Variables
In this investigation, I don't have any variables that I can change, because I am going to perform only investigation, and repeat the same thing three times, so that I can obtain accurate results.
Calculations:
When I have got the volume of citric acid required to neutralise 25cm3 of sodium, hydroxide by performing my investigation. I will have to calculating the percentage of citric acid in lemon squash using the following calculations.
Citric acid = 25cm3
Sodium hydroxide=?
H3 (C6H5O7) + 2NaOH Na2H (C6H5O7) + 2H2O
Number mole= concentration x volume
= 0.1 x ?
1000
= y number of sodium hydroxide moles.
Therefore
The number of citric acid moles required are
0.5 x y number of NaOH molecules
Number of moles= mass .
Molecular mass
Mass= number of moles x molecular mass
Molecular mass of citric acid= H2 (C6H5O7)
= 3[(12X6) + (1X5) + (16X7)]
= 3 + 189
= 192g
Mass= Number of citric acid moles x 192g
=Mass of citric acid in g
% Of citric acid in lemon squash= mass of citric acid x100
25cm3
Doing this I will be able to workout the percentage of citric acid in lemon squash.
Results:
The results to my investigation will be recorded on a table like the one below.
Titration number.
Trial
Accurate 1
Accurate 2
Accurate 3
Final burette reading (cm3)
Initial burette reading (cm3)
0
0
0
0
Volume of NaOH added (cm3)
If I have more time I will make more columns to include more readings. I will carry out a rough titration to see roughly where the colour will begin to change. So then next time when I perform the accurate readings I would know where I would have to slow down. And where it changes colour, I will record it on the table. In this way the results would be more accurate.
Measurements:
During the investigation I will be taking a few measurements,
The volume of sodium hydroxide will be measured in cm3; this is a volume.
And the volume of citric acid will also be measured in cm3.
Predicted graph:
Below is a graph on my predicted results, it is a straight line this show that the results are accurate.
Rajesh Patel, 0175 Page 1 of 12
Chemistry coursework
Finding the percentage of citric acid in lemon squash
Skill P: Planning skill