Consider the reaction

CaSO4(s)rightleftharpoons Ca^2+(aq)+ SO_4^2-(aq)
At 25 C the equilibrium constant is Kc = 2.4 \times 10^-5 for this reaction.

If excess CaSO4(s) is mixed with water at 25C to produce a saturated solution of CaSO4, what are the equilibrium concentration of Ca^2+?

......CaSO4(s) ==>Ca^2+(aq) + SO4^2-(aq)

I.....solid........0............0
C.....solid........x............x
E.....solid........x............x

Substitute the E line of the ICE chart into Ksp expression and solve for x = (Ca^2+) = (SO4^2-).

I got 4.9*10^-3 M. Thanks and

If the resulting solution has a volume of 1.9L , what is the minimum mass of CaSO4 (s) needed to achieve equilibrium?

To find the equilibrium concentration of Ca^2+ in the saturated solution of CaSO4, we need to use the equilibrium constant (Kc) and the initial concentration of CaSO4.

Given:
Reaction: CaSO4(s) ⇌ Ca^2+(aq) + SO4^2-(aq)
Equilibrium constant: Kc = 2.4 × 10^-5
Temperature: 25°C

First, we need to understand that the reaction CaSO4 ⇌ Ca^2+ + SO4^2- is not balanced in terms of moles of reactants and products. This means that we cannot directly use the concentrations or molar ratios of the species in the reaction to determine equilibrium concentrations.

However, since we are dealing with a saturated solution, we can assume that the concentration of CaSO4 remains constant at a maximum value (saturation) after equilibrium is established. In other words, we can treat the concentration of CaSO4(s) as a constant.

Let's assume the initial concentration of CaSO4 is [CaSO4]. Since it is in excess, we can consider it to be very large compared to the concentration of Ca^2+ and SO4^2- at equilibrium.

At equilibrium, the concentrations of Ca^2+ and SO4^2- will both be x (assuming the formation of 1 mole of each ion from 1 mole of CaSO4).

The equilibrium expression for this reaction is:
Kc = [Ca^2+][SO4^2-] / [CaSO4]

Now, substituting the given values, and keeping in mind that the concentration of solid CaSO4 remains constant:
2.4 × 10^-5 = x * x / [CaSO4]

Since [CaSO4] is a constant, we can rewrite the equation as:
2.4 × 10^-5 = k * x^2

Now, solve this equation to find the equilibrium concentration of Ca^2+ (x). Rearrange the equation to isolate x:
x^2 = (2.4 × 10^-5) / [CaSO4]
x = sqrt((2.4 × 10^-5) / [CaSO4])

Since the concentration of CaSO4(s) is very large (in excess), we can treat it as infinite, simplifying the equation to:
x = sqrt(2.4 × 10^-5)

Evaluate the expression to find the equilibrium concentration of Ca^2+.