Question

A 10.00 mL sample of pineapple juice was titrated with 0.100 M sodium hydroxide solution. The average volume of NaOH required to reach the endpoint was 12.8 mL.

a. Calculate the number of moles of sodium hydroxide required to reach the endpoint.

b. Using the mole ratio(number of moles of citric acid divided by the number of moles of sodium hydroxide) for the neutralization reaction , determine the number of moles of citric acid in 10 mL of pineapple juice

c. Multiply the number of moles of citric acid by its molar mass to calculate the mass of citric acid in 10.0 mL of the juice.

d. The concentration of acid in juices is usually expressed in grams of acid per 100 mL of juice. What is the concentration of citric acid in pineapple juice?

Answer 1

a.

number of moles = moalrity * volume in L

= 0.100 mole/ L * 12.8/1000

= 1.28 *10^-3 mole NaOH

B

The balance reaction is as follows;

.

H3C6H5O7 (aq) +3NaOH (aq) ---> Na3C6H5O7 (aq) + 3H2O (l)

from balanced equation

3 moles of NaOH react with 1 mole of H3C6H5O7

0.000128 moles of NaOH react with = 1*0.000128/3  

= 4.27*10^-4 moles of H3C6H5O7

c.

amount in g = number of moles * molar mass

= 4.27*10^-4 moles of H3C6H5O7 *192.124 g/mol

=0.081972906 g

=0.0820 g

d.

10 ml juice contains 0.0820 g citric acid

Therefore 100 ml juice will contain= 0.0820 g/10 ml* 100 ml

= 0.82 g in 100 ml