A reverse osmosis unit is used to obtain drinkable water from a source that contains 0.530 g NaCl per liter. What is the minimum pressure (in torr) that must be applied across the semipermeable membrane to obtain water? Assume room temperature or about 298 K. (Don′t forget the van′t Hoff factor!)

I'm not really sure what to do with this question. I know for osmotic pressure, the equation is iMRT, but I don't know what exactly to do.

This should get you started.

You know M NaCl = grams/molar mass and that's in 1 L so that is the molarity.
i = van't Hoff factor = 2 for NaCl
R is 0.08206
T = 298.
solve for pi (in atm) and convert to torr..

To solve this problem, we will use the van't Hoff factor and the osmotic pressure equation to find the minimum pressure required.

Step 1: Calculate the osmotic pressure
The osmotic pressure (π) can be calculated using the formula: π = iMRT
Where:
- π is the osmotic pressure
- 'i' is the van't Hoff factor
- 'M' is the molarity (moles of solute per liter of solution)
- 'R' is the ideal gas constant (0.0821 L·atm/mol·K)
- 'T' is the temperature in Kelvin

Step 2: Calculate the molarity
To calculate the molarity (M), we need to convert the given concentration into moles of NaCl per liter of solution.

Given: Concentration of NaCl = 0.530 g/L

First, convert grams of NaCl to moles:
Molar mass of NaCl = atomic mass of Na + atomic mass of Cl
= 22.99 g/mol + 35.45 g/mol
= 58.44 g/mol

Number of moles of NaCl = mass of NaCl / molar mass of NaCl
= 0.530 g / 58.44 g/mol

Now, convert moles of NaCl to molarity:
Molarity (M) = moles of NaCl / volume of solution (in L)

Step 3: Calculate the van't Hoff factor (i)
The van't Hoff factor takes into account the dissociation of solute particles in solution. For NaCl, the van't Hoff factor is 2 because it dissociates into two ions (Na+ and Cl-) in the water.

Step 4: Calculate the osmotic pressure
Using the given values and the osmotic pressure equation:
π = iMRT

Substitute the values:
π = 2 (van't Hoff factor) * M (molarity) * R (ideal gas constant) * T (temperature in K)
= 2 * M * 0.0821 L·atm/mol·K * 298 K

Step 5: Convert to torr
The osmotic pressure is typically expressed in units of atmospheres (atm). However, in this question, we need to convert it to torr.

Since 1 atm = 760 torr, we can convert the pressure from atm to torr by multiplying by 760.

Finally, you will have the value for the minimum pressure required in torr.