A solution is made up of 150g of disodium phosphate. Na2HPO4.7H20,dissolved in 2500g of water. what is the molality of the solution?
1) 0.107m
2)0.224m
3)2.365m
4)2.679
Molality=molessolute/kgwater=(150/molemass)/2.5
so count up the atomic mass of the disodium phosphate.
To find the molality of the solution, you need to use the formula:
Molality (m) = moles of solute / mass of solvent in kg
First, let's calculate the moles of disodium phosphate (Na2HPO4.7H20) in the solution:
Step 1: Calculate the molar mass of disodium phosphate:
Na2HPO4: 2(Na) + 1(H) + 1(P) + 4(O) = 22.99(2) + 1.01 + 30.97 + 16(4) = 141.96 g/mol
Step 2: Calculate the molar mass of water (H2O):
H2O: 2(H) + 16(O) = 2(1.01) + 16 = 18.02 g/mol
Since there are 7 water molecules in one mole of disodium phosphate, we multiply the molar mass of water by 7:
7(H2O) = 7(18.02) = 126.14 g/mol
The total molar mass of disodium phosphate. Na2HPO4.7H20 is the sum of the molar masses of Na2HPO4 and 7(H2O):
141.96 + 126.14 = 268.10 g/mol
Step 3: Calculate the moles of disodium phosphate:
moles = mass / molar mass
moles = 150 g / 268.10 g/mol = 0.56 mol
Next, we need to convert the mass of water to kg, as molality is defined in terms of kg:
mass of water = 2500 g
mass of water in kg = 2500 g / 1000 = 2.5 kg
Now, we can calculate the molality:
Molality = moles of solute / mass of solvent in kg
Molality = 0.56 mol / 2.5 kg = 0.224 m
Therefore, the molality of the solution is 0.224 m.
The correct answer is 2) 0.224 m.