What is the osmolarity of the following solutions? a. 0.35 M KBr b. 0.15 M glucose + 0.05 M K₂SO₄

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1. Identify the dissociation of solutes in the solution. For KBr, it dissociates into K⁺ and Br⁻ ions. For K₂SO₄, it dissociates into 2 K⁺ ions and 1 SO₄²⁻ ion. Glucose does not dissociate.
2. Calculate the osmolarity for each solution. Osmolarity is the sum of the molarities of all particles in solution.
3. For 0.35 M KBr, since it dissociates into 2 ions (K⁺ and Br⁻), the osmolarity is 0.35 M * 2.
4. For the mixture of 0.15 M glucose and 0.05 M K₂SO₄, calculate the contribution of each component. Glucose contributes 0.15 M to the osmolarity as it does not dissociate. K₂SO₄ contributes 0.05 M * 3 (since it dissociates into 3 ions: 2 K⁺ and 1 SO₄²⁻).
5. Add the contributions from glucose and K₂SO₄ to find the total osmolarity of the solution.

Key Concepts

Osmolarity

Osmolarity is a measure of the total concentration of solute particles in a solution. It is expressed in osmoles per liter (osmol/L) and accounts for all particles, including ions and molecules. For ionic compounds, osmolarity is calculated by considering the dissociation of the compound into its constituent ions.

Dissociation of Ionic Compounds

Ionic compounds, such as KBr and K₂SO₄, dissociate into their respective ions when dissolved in water. For example, KBr dissociates into K⁺ and Br⁻ ions, while K₂SO₄ dissociates into 2 K⁺ and SO₄²⁻ ions. This dissociation increases the number of particles in solution, which is crucial for calculating osmolarity.

Calculating Osmolarity

To calculate the osmolarity of a solution, multiply the molarity of each solute by the number of particles it produces upon dissociation. For instance, a 0.35 M KBr solution has an osmolarity of 0.35 M × 2 = 0.70 osmol/L, while a 0.15 M glucose solution remains 0.15 M (non-dissociating), and a 0.05 M K₂SO₄ solution has an osmolarity of 0.05 M × 3 = 0.15 osmol/L, leading to a total osmolarity for the mixture.