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Ch.10 Acids and Bases
Chapter 10, Problem 91

What are the molarity and the normality of a solution made by dissolving 25 g of citric acid (triprotic,C₆H₅O₇H₃) in enough water to make 800 mL of solution?

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1
Calculate the molar mass of citric acid (C₆H₈O₇) by adding the atomic masses of all atoms in the formula.
Convert the mass of citric acid (25 g) to moles using the molar mass calculated in the previous step.
Convert the volume of the solution from milliliters to liters by dividing 800 mL by 1000.
Calculate the molarity of the solution by dividing the number of moles of citric acid by the volume of the solution in liters.
Determine the normality of the solution by multiplying the molarity by the number of acidic protons (3) in citric acid, since it is triprotic.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molarity

Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. It is calculated using the formula M = moles of solute / liters of solution. In this case, to find the molarity of citric acid, one must first convert the mass of citric acid into moles using its molar mass, then divide by the volume of the solution in liters.
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Normality

Normality is another measure of concentration that reflects the number of equivalents of a solute per liter of solution. For acids, normality is particularly relevant as it accounts for the number of protons (H⁺ ions) that can be donated. Since citric acid is triprotic, it can donate three protons, meaning its normality will be three times its molarity when calculating the solution's concentration.
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Equivalents Concept 2

Triprotic Acid

A triprotic acid is an acid that can donate three protons (H⁺ ions) per molecule in a reaction. Citric acid (C₆H₅O₇H₃) is an example of a triprotic acid, which means that when calculating its normality, one must consider the total number of protons available for reaction. This characteristic is essential for determining the solution's acidity and its behavior in chemical reactions.
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