# Ksp, saturated solutions and precipitation (Ionic Equilibria)

• Ashu2912
In summary, the conversation discusses the concept of precipitates and their relation to the Ksp values. It is established that the solid undissolved solute in contact with the solution is considered as the precipitate. It is also mentioned that there is a difference between saturated solutions and solutions at equilibrium, with the former potentially containing precipitates. The conversation further explains that when the ionic product is greater than the Ksp value, precipitation occurs. However, there is a moment before the precipitate appears due to an initial energy barrier that needs to be overcome.
Ashu2912
(1) What is a precipitate exactly? While determining the Ksp values, we say that there in a dynamic equilibrium between the solid undissolved solute in contact with the solution and the ions in solution. Is this solid undissolved solute the 'precipitate'?
(2) Is there any difference between such solutions and a saturated solution?? If yes, then what? And if not, does this mean that saturated solutions contain precipitate?
(3) We say that when ionic product > Ksp, the equilibrium is disturbed and the reaction proceeds in the backward direction and precipitation occurs. But isn't there a precipitate (undissolved solid solute) at the above equilibrium? Then why this 'other' precipitation?

Yes, solid is a precipitate.

If you mix two solutions containing ions that form a weakly soluble salt, as loin gas their ionic product is below Ksp nothing happens. Then moment the ionic product raises up to Ksp, precipitate appears. When you mix two concentrated solutions quickly, as every reaction has a finite speed, there is a short moment when ionic product is above Ksp and there is no precipitate yet - but it will usually appear very fast. There is a kind of initial energy barrier (google for nucleation) that has to be overcomed, so it may happen that supersaturated solution can be quite stable - but it is stable only in kinetic terms, not thermodynamically.

## 1. What is Ksp and how is it calculated?

Ksp, or the solubility product constant, is a measure of the maximum amount of a substance that can dissolve in a solvent at a given temperature. It is calculated by multiplying the concentrations of the ions in a saturated solution raised to the power of their coefficients in the balanced chemical equation.

## 2. How does a solution become saturated?

A solution becomes saturated when the maximum amount of solute has been dissolved in the solvent at a given temperature. This can happen by adding more solute to a solution that is already saturated, or by slowly adding solute to a solvent until it reaches its maximum solubility.

## 3. What is the relationship between Ksp and solubility?

Ksp and solubility are directly related. The higher the value of Ksp, the more soluble the substance is in the solvent. This means that a substance with a higher Ksp will have a higher solubility, and vice versa.

## 4. What happens when a solution is supersaturated?

When a solution is supersaturated, it contains more dissolved solute than it can normally hold at a given temperature. This can happen when a solution is heated and then cooled, causing the solute to remain in the solution even though it would normally precipitate out. Supersaturated solutions are unstable and can quickly revert back to a saturated state by adding a seed crystal or stirring.

## 5. How does precipitation occur in a saturated solution?

Precipitation occurs in a saturated solution when the concentration of solute ions exceeds the solubility product constant (Ksp). This causes the excess ions to come together and form a solid (precipitate) that settles out of the solution. The amount of precipitate formed depends on the concentration of the ions and the Ksp value for the specific substance.

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