# Osmotic Pressure and Equilibrium constant

1. Oct 28, 2013

### WK95

1. The problem statement, all variables and given/known data
An aqueous solution contains 0.84 g/L of an organic detergent. The osmotic pressure of this solution is 54.4 torr, at 25°C. What is the molar mass (in g/mol) of this detergent?

2. Relevant equations
$pi=MRT$
$R=0.08206L*atm/(mol*K)$

3. The attempt at a solution
$pi=MRT$
$M=pi/(RT)$
$M=(54.4 torr * 1 atm/760 torr)/(0.08206L*atm/(mol*K))(298.15 K)$
This is wrong but I;m not sure why and how to get the right asnwer.

1. The problem statement, all variables and given/known data
What is the equilibrium constant expression for the following reaction:

PtCl42−(aq)↔Pt2+(aq) + 4Cl−(aq)

Choose from the list below and enter the letters alphabetical order. (e.g. For an equilibrium constant of [Cl-]4eq[Pt2+]eq enter AH.)

A) [Pt2+]eq E) [Cl-]-1eq I) [PtCl42-]4eq
B) [Cl-]eq F) [PtCl42-]-1eq J) [Pt2+]-4eq
C) [PtCl42-]eq G) [Pt2+]4eq K) [Cl-]-4eq
D) [Pt2+]-1eq H) [Cl-]4eq L) [PtCl42-]-4eq

2. Relevant equations

3. The attempt at a solution

2. Oct 30, 2013

### Saitama

It's quite difficult to follow what you have done here.

For the first part, please define the variables used.

For the second part, use the subscript and superscript tags or LaTeX to format your working.

3. Oct 30, 2013

### Staff: Mentor

The osmotic pressure satisfies the same equation as the ideal gas law. In your problem solution, you need to use the density of the detergent.

$$ρ=\frac{p_iM}{RT}$$

You need to solve for M.