# Saturated Solution Concentrations and Osmotic Pressure Calculations

• kateman
In summary, The conversation discusses three questions related to theoretical salts, reactions at a specific temperature, and osmotic pressure. The first question involves finding the millimolar concentration of a saturated solution of a theoretical salt with a given Ksp value. The second question deals with calculating the change in entropy for a reaction at a specific temperature using the change in enthalpy and free energy. The third question involves finding the osmotic pressure of a solution with a known concentration and volume. The conversation also includes a request for checking the correctness of the answers provided.
kateman
There are 3 questions below with my working and answers, could someone please check that I am right, even if you can only give approval or correction on just one question and nothing else - anything would be appreciated. Please forgive my not following the template, as I didn't think it would work with checking correct answers. Thanks for any responces!

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Q1: A theoretical salt (X2Y3) (with Ksp= 6.26 x 10 -15 ) is in a saturated solution. What is its millimolar concentration (mM) of X?

A1: Ksp= [X]2 [Y]3 = 6.26 x 10 -15

therefore concentration of Y = 3/2 concentration of X (or is it 2/3, iam not sure?)

therefore rewrite Y as [3/2 X]3

therefore Ksp= [X]2x 27/8 X3
= 27/8 [X]5

therefore, with rearranging, [M] = 1.131514468x10-3 mol/L
= 1.131514468 mM/L

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Q2: A reaction at temperature of 287K gives a change in enthaply of -7KJ and a free energy change of -10kJ, what is the change in entropy for this reaction (in J/K)?

A2: $$\Delta$$G = $$\Delta$$H - T$$\Delta$$S

with rearranging: $$\Delta$$S = $$\Delta$$H - $$\Delta$$G / T
=(-7 - -10)/287 = 0.010452961 J/K

That doesn't seem right to me.

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Q3: If a 0.5 L solution at a temperature of 294.75 K contains 13.7g of an unknown solute (with a molecular mass of 60.094g), what is its osmotic pressure in atmospheres?

A3: since moles (n) = concentration (c)/ volume (v) = mass (m)/ molecular weight (M)

then C = m/Mv = 13.7 / (60.094x0.5) = 0.455952341 mol/L

Now use the values of C, T and the gas constant (8.314 J/mol K) into the osmotic pressure formula P=CRT

P= 0.455952341x8.314x294.75 = 1117.334694 Pa (am I right to say that its in pascals, or is it in killapascals [Kpa]?)

atmospheres = 101.325 Kpa = 101325 Pa

osmotic pressure (in atmospheres) = 1117.334694/101325 = 0.011027236 atms

This is something iam really not sure about, the answer seems almost wrong to me but iam not sure where I would have gone wrong in my working, can someone please help? It would be very much appreciated!

Thank you!

You use too many significant digits every time.

First looks OK.

Second and third - approach seems correct (even if in the second your formula misses parantheses), but second opinion won't hurt.

Thank you Borek, and I agree, I'd still appreciate at least another person's opinion on my working.

## 1. What is a saturated solution?

A saturated solution is a solution in which the maximum amount of solute has been dissolved in a given amount of solvent at a specific temperature and pressure. This means that no more solute can be dissolved in the solution and any additional solute will remain undissolved at the bottom of the container.

## 2. How do you calculate the concentration of a saturated solution?

The concentration of a saturated solution can be calculated by dividing the amount of solute (in grams) by the volume of the solution (in liters). This will give you the concentration in units of grams per liter (g/L).

## 3. What is osmotic pressure?

Osmotic pressure is the pressure that must be applied to a solution to prevent the flow of solvent into the solution through a semipermeable membrane. It is a measure of the concentration of a solution and its ability to draw water into it.

## 4. How do you calculate osmotic pressure?

Osmotic pressure can be calculated using the equation π = iMRT, where π is the osmotic pressure, i is the van't Hoff factor (a measure of the number of particles in the solution), M is the molarity of the solution, R is the gas constant, and T is the temperature in Kelvin.

## 5. How does temperature affect osmotic pressure?

As temperature increases, the osmotic pressure of a solution also increases. This is because as temperature increases, the kinetic energy of the solvent molecules increases, causing them to move more rapidly and exert more pressure on the semipermeable membrane. Additionally, the solubility of many substances increases with temperature, leading to a higher concentration and therefore a higher osmotic pressure.

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