Which solution has lowest freezing point?a.1% glucose b.1% sucrose c.1% starchd.1% urea

To determine which solution has the lowest freezing point among the options provided, we need to consider the concept of freezing point depression. This phenomenon occurs when a solute is added to a solvent, causing the freezing point of the solution to be lower than that of the pure solvent. The extent of freezing point depression depends on the number of solute particles in the solution, which is influenced by the solute's dissociation in solution.

Understanding Freezing Point Depression

The freezing point depression can be quantified using the formula:

ΔTf = i * Kf * m

• ΔTf = change in freezing point
• i = van 't Hoff factor (number of particles the solute dissociates into)
• Kf = freezing point depression constant of the solvent (for water, it's approximately 1.86 °C kg/mol)
• m = molality of the solution

Analyzing Each Option

Now, let's analyze each of the given solutions:

• 1% Glucose: Glucose does not dissociate in solution, so its van 't Hoff factor (i) is 1. This means that for every mole of glucose, there is one mole of particles.
• 1% Sucrose: Similar to glucose, sucrose also does not dissociate, giving it a van 't Hoff factor of 1. Thus, it behaves like glucose in terms of freezing point depression.
• 1% Starch: Starch is a large polysaccharide that does not dissolve well in water and does not dissociate into smaller particles. Therefore, it also has a van 't Hoff factor of 1, but its effect on freezing point depression is minimal due to its limited solubility.
• 1% Urea: Urea is a small molecule that also does not dissociate in solution, so its van 't Hoff factor is 1 as well. However, urea is more soluble than starch and can contribute more effectively to freezing point depression.

Comparing the Solutions

Since all the solutes have the same van 't Hoff factor of 1, the key factor that will determine the freezing point depression is the molality of the solutions. In this case, since all solutions are at the same concentration (1%), we can conclude that:

• Glucose and sucrose will have similar effects on freezing point depression.
• Starch will have the least effect due to its limited solubility.
• Urea, while also not dissociating, is more soluble and will have a more significant impact compared to starch.

Final Thoughts

Given these considerations, the solution with the lowest freezing point among the options is likely to be 1% urea, followed closely by glucose and sucrose, with starch having the least effect. This is primarily due to urea's higher solubility and its ability to contribute effectively to freezing point depression, despite all solutes having the same dissociation characteristics.