Question

Citric acid (C6H8O7) is an important intermediate in the Krebs cycle and a triprotic acid. What is the normality of a solution made by weighing 128 g of citric acid into a volumetric flask and diluting it to 2 L with water

Answer 1

2.67 N

Step-by-step explanation:

The normality equation looks like this:

Normality = Molarity (M) x Number of Equivalents

In this formula, the number of equivalents represents how many moles of the acidic species exist in the molecule. In other words, how many hydrogen atoms are in citric acid? This value would be 8 equivalents (as denoted by the subscript).

So, to find the normality, you need to (1) convert grams C₆H₈O₇ to moles (via molar mass), then (2) calculate the molarity (via molarity equation using moles and volume), and then (3) calculate normality (via normality equation using molarity and # of eq.).

(Step 1)

Molar Mass (C₆H₈O₇): 6(12.011 g/mol) + 8(1.008 g/mol) + 7 (15.998 g/mol)

Molar Mass (C₆H₈O₇): 192.116 g/mol

128 g C₆H₈O₇ 1 mole
---------------------- x ---------------------- = 0.666 moles C₆H₈O₇
192.116 g

(Step 2)

Molarity = moles / volume (L)

Molarity = 0.666 moles C₆H₈O₇ / 2 L H₂O

Molarity = 0.333 M

(Step 3)

C₆H₈O₇ -----> 8 hydrogen atoms

Normality = molarity x number of equivalents

Normality = 0.333 M x 8

Normality = 2.67 N