Question

. Citric acid, which can be obtained from lemon juice, has the molecular formula C6H8O7. A 0.250-g sample of citric acid dissolved in 25.0 mL of water requires 37.2 mL of 0.105 M NaOH for complete neutralization. What number of acidic hydrogens per molecule does citric acid have?

Answer 1

Answer:

3 acidic hydrogens per molecule of citric acid

Explanation:

In a sample of 37.2 mL(0.0372 L) of 0.105 mol/L of NaOH, will have:

n = 0.105x0.0372 = 0.0039 mol of NaOH

The dissociation of NaOH will give the same number of moles of Na⁺ and OH⁻.

The molar mass of citric acid is:

C: 12g/mol x 6 = 72 g/mol

H: 1g/mol x 8 = 8g/mol

O: 16 g/mol x 7 = 112 g/mol

192 g/mol

So, 0.250g of the acid has

n = mass/molar mass

n = 0.250/192

n = 0.0013 mol.

To be neutralized, it will be necessary 0.0039 mol of acidic hydrogens to react with the 0.0039 mol of OH⁻.

The dissociation reaction of one molecule of  the acid will give the stoichiometry:

1 mol of acid ----------------------- x mol of acidic hydrogens

0.0013 mol --------------------------- 0.0039

For a simple direct three rule:

0.0013x = 0.0039

x = 3 acidic hydrogens per molecule of citric acid.