A solution is made up by dissolving 14.8 g Na2CO3 · 10 H2O in 110.5 g of water. What is the molality of Na2CO3 in this solution?
moles Na2CO3.10H2O = grams/molar mass.
Solve for moles.
Then m = moles/kg solvent
solve for m.
Step 1 - molar mass Na2CO3 = 106 g/mol
Step 2 - molar mass Na2CO3 *10 H2O = 106 + ( 18 x 10) = 286 g/mol
Step 3 - moles Na2CO3*10H2O = 14.8 / 286 = 0.0517
Step 4 - moles water = 10 x 0.0517 = 0.517
Step 5 - mass water = 18 x 0.517 = 9.31 g
Step 6 - Total mass water = 110 + 9.31 = 119.31 g
Step 7 - m = 0.0517 / 0.11931 Kg = 0.433
To find the molality of Na2CO3 in the solution, we need to first calculate the moles of Na2CO3 and the mass of water.
1. Calculate the moles of Na2CO3:
The molar mass of Na2CO3 · 10 H2O can be calculated by summing the molar masses of the individual elements:
Na = 22.99 g/mol × 2 = 45.98 g/mol
C = 12.01 g/mol
O = 16.00 g/mol × 3 = 48.00 g/mol
H = 1.01 g/mol × 2 × 10 (since there are 10 water molecules) = 20.20 g/mol
Adding these up, we get:
45.98 g/mol + 12.01 g/mol + 48.00 g/mol + 20.20 g/mol = 126.19 g/mol
To calculate the moles of Na2CO3, divide the mass given (14.8 g) by the molar mass calculated:
moles = mass / molar mass = 14.8 g / 126.19 g/mol
2. Calculate the mass of water:
The mass of water in the solution is given as 110.5 g.
3. Calculate the molality:
Molality (m) is defined as the moles of solute per kilogram of solvent.
First, convert the mass of water to kilograms by dividing by 1000:
mass of water (kg) = 110.5 g / 1000 = 0.1105 kg
Now, we can calculate the molality:
molality (m) = moles of Na2CO3 / mass of water (kg)
Substituting the values we calculated:
molality (m) = (14.8 g / 126.19 g/mol) / 0.1105 kg
Calculating this expression will give you the molality of Na2CO3 in the solution.