How does normality compare to molarity for monoprotic and polyprotic acids?

Verified step by step guidance

1. Understand the definitions: Molarity (M) is the number of moles of solute per liter of solution, while Normality (N) is the number of equivalents of solute per liter of solution.
2. For monoprotic acids, each mole of acid provides one mole of hydrogen ions (H⁺). Therefore, the normality is equal to the molarity (N = M) because one equivalent of acid is the same as one mole of acid.
3. For polyprotic acids, each mole of acid can provide more than one mole of hydrogen ions. For example, sulfuric acid (H₂SO₄) is diprotic, meaning it can donate two hydrogen ions per molecule.
4. Calculate the normality for polyprotic acids by multiplying the molarity by the number of hydrogen ions the acid can donate. For example, if the molarity of H₂SO₄ is M, then its normality is 2M because it can donate two H⁺ ions.
5. Summarize: Normality accounts for the number of reactive species (like H⁺ ions) in a solution, making it particularly useful for titration calculations, while molarity simply measures the concentration of the solute.

Key Concepts

Normality

Normality is a measure of concentration equivalent to the number of equivalents of solute per liter of solution. It is particularly useful in acid-base reactions, where it accounts for the reactive capacity of an acid or base. For monoprotic acids, normality is equal to molarity, as they donate one proton per molecule. However, for polyprotic acids, normality can be greater than molarity, reflecting the total number of protons that can be donated.

Molarity

Molarity is defined as the number of moles of solute per liter of solution. It is a fundamental unit of concentration used in chemistry to express the amount of a substance in a given volume. Molarity does not account for the reactivity of the solute, making it less informative than normality in acid-base chemistry, especially for polyprotic acids, which can release multiple protons.

Monoprotic vs. Polyprotic Acids

Monoprotic acids are acids that can donate only one proton (H+) per molecule, such as hydrochloric acid (HCl). In contrast, polyprotic acids can donate more than one proton; for example, sulfuric acid (H2SO4) can donate two protons. This distinction is crucial when calculating normality, as polyprotic acids require consideration of all possible protons released, leading to a higher normality compared to their molarity.