Posted by **yvonne** on Saturday, November 29, 2008 at 10:21pm.

hellppp please i have a test on this on mondayy im so screwed

A solid mixture contains MgCl2 and NaCl. When 0.5000 g of this solid is dissolved in enough water to form 1.000 L of solution, the osmotic pressure at 25°C is observed to be 0.4010 atm. What is the mass percent of MgCl2 in the solid? (Assume ideal behavior for the solution.)

- Chemistry -
**GK**, Sunday, November 30, 2008 at 12:28am
Osmotic pressure is given by:

π = MRT

π = osmotic pressure in atm

Mi = moles of particles/liter <- unknown

R = 0.0821 L.atm/K.mol

T = 298 K

• Substitute and solve for Mi to moles of ions per liter.

• Divide M by 3 to get the overall molarity, M, in terms of MgCl2 formula units.

• Multiply M by the molar mass of MgCl2 to get grams / liter which is equal to grams/(1000mLs)

• Divide by 10 to get grams / 100 mLs = ___%

(NOTE: We assume the density of the solution is close to 1.00 g/mL, so that grams/100mLs is about the same as the mass % )

- Chemistry -
**GK**, Sunday, November 30, 2008 at 12:29am
Osmotic pressure is given by:

π = MRT

π = osmotic pressure in atm

Mi = moles of particles/liter <- unknown

R = 0.0821 L.atm/K.mol

T = 298 K

• Substitute and solve for Mi to moles of ions per liter.

• Divide Mi by 3 to get the overall molarity, M, in terms of MgCl2 formula units/L.

• Multiply M by the molar mass of MgCl2 to get grams / liter which is equal to grams/(1000mLs)

• Divide by 10 to get grams / 100 mLs = ___%

(NOTE: We assume the density of the solution is close to 1.00 g/mL, so that grams/100mLs is about the same as the mass % )

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