10g of nacl were added to 10ml of water. he resulting solution was diluted to be a final volume of 250ml.
Calculate the molarity of the solution.
My calculation
10g/58g/mol = 0.173M
0.173M/025L =0.689M
Given the density of the solution is 0.9864g/ml. Calculate the molality of the solution. The right answer 0.7233m/kg
Who helps
In scientific calculations, it is important to know how accurate you'd like your answers. If you see a number like 0.9864g/ml, it means 4 significant figures are expected, so you have to carry your calculations to at least 5 significant digits, and then round off to 4 for the final answer.
Except for the number of significant digits, your calculation of molarity is correct.
Molality is defined as the ratio of the number of moles of solute to the mass of solvent.
For this problem, we need to find the mass of solvent (mass of solute is known, 10 g). Since the final volume is known (250 ml), so is the density (0.9864), the mass of the solution is therefore
m(solution) = 250*0.9864=246.60 g
Next calculate 10 g of NaCl is equivalent to how many moles (M), using accurate atomic masses.
The molality is then
M mol /(1000 g/kg /(246.6 g - m g)
The molality is then
M mol /(1000 g/kg /( m -10 g)
To calculate the molarity of the solution, we need to first find the number of moles of NaCl in 10g of the compound. The molar mass of NaCl is 58 g/mol.
Number of moles = Mass / Molar mass
Number of moles = 10g / 58 g/mol ≈ 0.1724 mol
Next, we need to find the volume of the solution after dilution. Since the initial volume was 10ml and the final volume is 250ml, the volume of water added during dilution is:
Volume of water = Final volume - Initial volume
Volume of water = 250ml - 10ml = 240ml
Now, we can calculate the molarity of the solution:
Molarity = Number of moles / Volume of solution in liters
Molarity = 0.1724 mol / 0.25 L ≈ 0.689 mol/L
So, your calculation for the molarity of the solution is correct at 0.689M.
To calculate the molality of the solution, we need to consider the mass of the solvent (water) rather than the volume. Molality is defined as the number of moles of solute per kilogram of solvent.
First, let's calculate the mass of water in the solution:
Mass of water = Volume of water × Density of water
Mass of water = 240ml × 0.9864 g/ml ≈ 236.736g
Since we know the molar mass of water is 18 g/mol, we can calculate the number of moles of water:
Moles of water = Mass of water / Molar mass of water
Moles of water = 236.736g / 18 g/mol ≈ 13.152 mol
Now we can calculate the molality of the solution:
Molality = Number of moles of solute / Mass of solvent in kg
Molality = 0.1724 mol / (236.736g / 1000) kg ≈ 0.729 mol/kg
The correct answer for the molality of the solution is approximately 0.729 mol/kg, not 0.7233 mol/kg.