Calculate the molarity and the molality of an NH3 solution made up of 30 g of NH3 in 70 g of water. The density of the solution is 0.982 g/ml.
Molar Mass of NH3 = 17.04 g
I think I got the answer. Can some please check it.
Molarity = 17.3 mol/L = 17.3 M
Molality = 25.1 mol/kg = 25.1 m
I confirmed 25.1 m but not 17.3 M.
moles NH3 = 30/17.04 = ??
volume = mass/density = 70/0.982 = xx and that divided by 1000 to convert to L = zz.
Then M = ??moles/zzL
20.1
20.1
The solution of 30% (w/w) NH3, i.e. 30 g NH3 + 70 g H2O = 100 g.
with d = 0.982 g/ml -> 100 g solution = 101.8 ml; and molality = 30 g (NH3)/17 (g/mol) = 1.76 mol of NH3 in 100 g (or 101.8 ml) solution; So Cm = 1.76 (mol)*1000 (ml)/101.8 (ml) = 17.3 mol/L
why are we multiplying by 1000
To calculate the molarity and molality of the NH3 solution, we first need to determine the number of moles of NH3 and the mass of water in the solution.
1. Calculate the number of moles of NH3:
To find the number of moles, we divide the mass of NH3 by its molar mass:
Number of moles of NH3 = mass of NH3 / molar mass of NH3
Given:
Mass of NH3 = 30 g
Molar mass of NH3 = 17.04 g/mol
Number of moles of NH3 = 30 g / 17.04 g/mol
2. Calculate the mass of water in the solution:
Given:
Mass of water = 70 g
3. Calculate the volume of the solution:
To find the volume of the solution, we divide the mass of the solution by its density:
Volume of solution = mass of solution / density of solution
Given:
Mass of solution = mass of NH3 + mass of water = 30 g + 70 g = 100 g
Density of solution = 0.982 g/mL
Volume of solution = 100 g / 0.982 g/mL
4. Calculate the molarity:
Molarity is defined as the number of moles of solute (NH3) per liter of solution.
Molarity (M) = moles of solute / volume of solution (in liters)
Given:
Number of moles of NH3 = calculated in step 1
Volume of solution = calculated in step 3 / 1000 (to convert mL to liters)
Molarity = moles of NH3 / volume of solution (in liters)
5. Calculate the molality:
Molality is defined as the number of moles of solute (NH3) per kilogram of solvent (water).
Molality (m) = moles of solute / mass of solvent (in kilograms)
Given:
Number of moles of NH3 = calculated in step 1
Mass of water = calculated in step 2 / 1000 (to convert grams to kilograms)
Molality = moles of NH3 / mass of water (in kilograms)
Now, substitute the calculated values into the respective formulas to find the molarity and molality.