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'The Molecular Formula of Succinic Acid'.

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'The Molecular Formula of Succinic Acid' The aim of this experiment is to determine the molecular formula of a sample of anhydrous succinic acid. Succinic acid is a diprotic, which means it donates two protons per molecule. Succinic acid can be completely neutralised by sodium hydroxide. The indicator most suitable for this experiment is phenolphthalein, it is colourless in acids and pink in alkalises. The half way stage is about pH 9.3, this is when it will either change from colourless to a very pale pink or from pink to colourless. To determine the relative formula mass of succinic acid I am going to do a titration against sodium hydroxide. The equation for the reaction is given below. To make the equation easier to read, HOOC(CH2)nCOOH will be condensed to H2A because of the two hydrogen atoms at either end. H2A+2NaOH --> Na2A+2H2O (CV) H2A = 1 (CV) NaOH 2 I am going to use the NaOH as 0.1M because I don't want it too concentrated, so therefore I am going to use H2A as 0.05M because of the ratio 2:1. In the formula of succinic acid below n is a whole number between 1 and 4. So therefore first I need to calculate the relative molecular mass of succinic acid. HOOC(CH2)nCOOH H = 1 O = 16 C = 12 Mr when n = 1 1+16+16+12 (12+2) ...read more.


This will also ensure that the jet space of the burette is full of sodium hydroxide as it counts towards the measurement. I will then remove the drop remaining on the tip of the burette as this may affect results. Next I need to clean out a conical flask; I do this by again rinsing with distilled water. I will also need to swill out a 25cm3 pipette, again using distilled water. After this is completed I have to shake the volumetric flask of succinic acid, I do this by turning it upside down and shaking the contents, returning it upright, repeating this ten times, I must do this each time before I use the acid. After that I will use the 25cm3 pipette with a pipette filler to suck up some succinic acid. I will fill it up over the 25cm3 mark and then drain it out under gravity into a beaker, making sure the tip does not touch the liquid as it will not run out as good. Next I need to again shake the succinic acid. I will then fill the pipette up again to the 25.0cm3 mark, making sure the meniscus of the acid touches the 25.0cm3 mark. I will then transfer this to the conical flask. I will then add 4 drops of phenolphthalein indicator to the acid, which will turn the solution pink. ...read more.


It is important that only a few drops of indicator are added because excess indicator will result in a different volume of solution to be added from a burette before the required colour change is obtained. Now to combine all the errors worked out so I can get the total percentage of errors of the whole experiment. 0.04 + 2 + 2 + 0.2 + 0.15 = 4.39% From combining all the error rates I estimate the overall error rate for the experiment to be �4.39%. To make this clearer I will turn the percentage into a measurement: 25.2 x 4.39 = 1.10628cm3 Therefore the observed result was 25.2cm3 � 1.12cm3. 100 From my hypothetical results I am going to use the mean titre of 25.2cm3 of sodium hydroxide and the 25cm3 of succinic acid to work out the relative formula mass of succinic acid. (Concentration x Volume) NaOH = 2 (CV) NaOH = 2 = 0.1 x 25.2 (Concentration x Volume) H2A 1 (CV) H2A 1 2 x 25 x C H2A = 0.0504 Number of moles = Concentration x Volume n = 0.0504 x 250 n = 0.0126 1000 1000 Number of moles = mass taken 0.0126 = 1.32 Mr = 1.32 Mr Mr 0.0126 Mr = 104.7619046 Mr = 104.8 Looking back at the relative molecular mass of succinic acid I can see that when the Mr is 104, n = 1. Skill 1 - Planning Charlotte Nellist Page 1 ...read more.

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