Doubts about Ksp, Solubility, Kb - Answered by João

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In summary, the solubility of a salt indicates the amount of the salt itself in aqueous state in a solution, not just its ions. The elements of the 2A family have moderate bases due to their low solubility in water, but they still dissociate quite strongly. Alkali metals are examples of bases that can dissociate 100%. In the context of the exercise, AgBr will precipitate first due to its smaller Kb value compared to AgCl, but eventually both salts will precipitate together.
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jaumzaum
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I'm having some doubts about Ksp, solubility, Kb...

1) If a salt has a solubility of 1g/L, it means that a) there is 1g of the salt itself in aqueous state in the solution or b) there is 1g of salt(aq) + salt ions in solution?

2) The elements of the 2A family makes moderate bases. That's because they are too little soluble in water. Anyway, if we DO NOT reach the saturation point, can we consider that all (or >95%) of the aqueous base is dissociated (I mean, do they have a great Kb)? For what other bases can we consider dissociation = 100%?

3) I was solving an exercise in where you had AgNO3, NaCl, NaBr. When mixing the solutions, it will form AgCl and AgBr, Ksp = 1.8.10^-10 and 5.10^-13
When I saw the resolution, the author says we have to see if AgCl will precipitate, as AgBr precipitates first. I didn't understand that well. Why will AgBr precipitate first than AgCl? I know AgBr has a smaller Kb, but don't both salts have to precipite together?

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João
 
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jaumzaum said:
If a salt has a solubility of 1g/L, it means that a) there is 1g of the salt itself in aqueous state in the solution or b) there is 1g of salt(aq) + salt ions in solution?

I don't understand the difference, please elaborate.

The elements of the 2A family makes moderate bases. That's because they are too little soluble in water. Anyway, if we DO NOT reach the saturation point, can we consider that all (or >95%) of the aqueous base is dissociated (I mean, do they have a great Kb)?

Yes, they are weakly soluble but quite strong. Not that they dissociate 100% (although that's a reasonable first level assumption).

For what other bases can we consider dissociation = 100%?

Alkali metals.

I was solving an exercise in where you had AgNO3, NaCl, NaBr. When mixing the solutions, it will form AgCl and AgBr, Ksp = 1.8.10^-10 and 5.10^-13
When I saw the resolution, the author says we have to see if AgCl will precipitate, as AgBr precipitates first. I didn't understand that well. Why will AgBr precipitate first than AgCl? I know AgBr has a smaller Kb, but don't both salts have to precipite together?

Salt starts to precipitate after its product of concentrations gets greater than the Ksp. In your example if we assume

[Br-]=[Cl-]=10-10

and

[Ag+]=10-2

it is easy to calculate

[Ag+][Cl-]=[Ag+][Br-]=10-12

so AgBr will already precipitate, but AgCl not yet.
 

Related to Doubts about Ksp, Solubility, Kb - Answered by João

1. What is Ksp and how is it related to solubility?

Ksp, or the solubility product constant, is a measure of the maximum amount of a substance that can be dissolved in a solvent at a given temperature. It is related to solubility because it tells us how much of a substance can dissolve in a solution before it reaches equilibrium and starts to precipitate.

2. How is Ksp calculated?

Ksp is calculated by multiplying the concentrations of the ions in a saturated solution. This can be done using the molar solubility (the amount of substance that dissolves in a liter of solution) or the solubility (the amount of substance that dissolves in a certain amount of solvent).

3. What is the difference between Ksp and Kb?

Ksp and Kb are both equilibrium constants, but they measure different types of equilibria. Ksp measures the equilibrium between a solid substance and its dissolved ions, while Kb measures the equilibrium between a weak acid and its conjugate base.

4. How does temperature affect Ksp?

The solubility of a substance generally increases with temperature, so as temperature increases, so does the value of Ksp. However, there are exceptions to this rule, such as in cases where the dissolution process is endothermic.

5. What are some factors that affect solubility?

The solubility of a substance can be affected by factors such as temperature, pressure, and the presence of other solutes. The nature of the solute and solvent, as well as any chemical reactions that may occur, can also impact solubility. Additionally, the pH of the solution can affect the solubility of certain substances, particularly acids and bases.

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