Question

A student is given 2.19 g of an unknown acid, which can be either oxalic acid, H2C2O4, or citric acid, H3C6H5O7. To determine which acid she has, she titrates the unknown acid with 0.560 M NaOH. The equivalence point is reached when 61.0 mL are added. Answer the following questions to determine the identity of the unknown acid. How many moles of NaOH are consumed

Answer 1

Answer:

The unknown acid is citric acid.

There is 0.0342 moles of NaOH consumed.

Explanation:

Step 1: Data given

Mass of the unknown acid = 2.19 gram

Titrating with 0.560 M of NaOH

The equivalence point is reached when 61.0 mL are added

Molar mass of oxalic acid = 90.03 g/mol

Molar mass of citric acid = 192.12 g/mol

Step 2: The balanced equations for both acids

The reaction between oxalic acid and NaOH is:

H2C2O4 + 2NaOH → Na2C2O4 + 2H2O

The reaction between citric acid and NaOH is:

H3C6H5O7 +3NaOH → Na3C6H5O7 + 3 H2O

Step 3: Calculate the number of moles of the acid

Moles = mass / Molar mass

In case of oxalic acid: 2.19 grams / 90.03 g/mol = 0.0243 moles

In case of citric acid: 2.19 grams /192.12 g/mol = 0.0114 moles

Step 4: Calculate number of moles of NaOH

The mole of NaOH required for titration;

number of moles  = Molar mass * volume = (0.560 M * 0.061 L) = 0.03416 mol

Step 5: Calculate which acid

For each mole of oxalic 2 moles of NaOH is required, for 0.0243 mol citric acid 0.0243 *2= 0.0486 mol NaOH is required. This is more than the number of moles consumed.

For each mole of citric acid 3 moles of NaOH is required, for 0.0114 mol citric acid 0.0114 * 3= 0.0342 mol NaOH is required. This is the number of moles NaOH used for the titration.

The unknown acid is citric acid. There is 0.0342 moles of NaOH consumed.