Question #ebf5e

1 Answer
Simon Moore
May 15, 2017

See below.

Explanation:

If you titrate with sodium hydroxide solution, the reaction is:

#C_3H_5O(COOH)_3(aq) + 3 NaOH(aq) + Na_3C_3H_5O(COO)_3(aq) + 3 H_2O(i)#

Just as an example, lets say you had 100 ml of orange juice, which weighed 120 g. You titrated this against 0.1 M NaOH solution, and measured volume of titre as 20 ml.

First, work out how many moles of NaOH you used.

#M = n/V# where M is molarity, n is number of moles and V is volume in litres.

Therefore: #n = V.M = (20/1000)# x #0.1 = #0.002 moles

The equation tells you that 1 mole of citric acid reacts with 3 moles of NaOH, so you must have had (0.002/3) = 0.00067 moles of citric acid in your orange juice.

The molar mass of citric acid is 192.12 g, so 0.00067 moles is 192.12 x 0.00067 = 0.1287 g of citric acid.

The % of citric acid was therefore: #(0.1287/120).100 = 0.1073%#

Please note that, with the exception of the reaction equation and the molar mass, I just made these numbers up to illustrate the procedures - I can't recall how much citric acid is really in orange juice!

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