Please help me on this question below!

Question

A 1.025 g sample of an unknown alkaline earth metal bromide salt is dissolved in enough water to make a 25.00 mL solution. The osmotic pressure is found to be 12.16 atm at 25.0 degrees C. What is the molar mass of the alkali metal hydroxide base, and what is the name of the alkaline earth metal?

Answer 1

Use π = iMRT

π = osmotic pressure = 12.16 atm

i = van't Hoff factor = 3 because alkali metal bromide will be XBr₂ which has 3 particles

M = molarity = moles / liter = ?

R = gas constant = 0.0821 Latm/Kmol

T = temp in Kelvin = 298K

Solving for M we have...

M = π / (i)(R)(T)

M = 12.16 / (3)(0.0821)(298)

M = 0.1657 moles / liter

Since we have 25.00 mls, that's equal to 0.02500 L

Thus, moles of unknown = moles / 0.02500 L = 0.1657 mol/L and moles = 0.004142 moles

In your question you first state the unknown is an alkaline earth metal bromide salt. But later in the question you state it is a metal hydroxide salt, so not sure it if is XBr₂ or X(OH)₂

I'm going with XBr₂ (metal bromide salt)

molar mass of the salt = grams / moles

molar mass = 1.025 g / 0.004142 mols

molar mass of unknown metal salt = 247.5 g/mol

If the salt is XBr₂, then ...

mass of 2 Br is 2 x 79.9 = 159.8 and ...

mass of X = 247.5 - 159.8 = 87.7

Identity of X = STRONTIUM (Sr)