What if I have 50g water and I dissolve 5g of NaOH, will the solution have a total mass of 55g?
the masses add
Why should a chemistry problem be any different that a daily problem? If you have 10 lbs of apples and dump in 10 lbs of oranges, how many lbs of fruit will you have? 20?
No, the solution will not have a total mass of 55g. When you dissolve a solute (in this case, NaOH) in a solvent (in this case, water), the total mass of the solution may not simply be the sum of the masses of the solute and solvent.
To determine the total mass of the solution, you need to consider the fact that when NaOH dissolves in water, it dissociates into its constituent ions, sodium (Na+) and hydroxide (OH-) ions. Therefore, the actual mass of the solute in the solution is the sum of the masses of these ions.
To calculate the total mass of the solution, you should consider the molecular weight of NaOH. The molecular weight of NaOH is 22.99 g/mol for sodium, 15.999 g/mol for oxygen, and 1.008 g/mol for hydrogen. So the total molecular weight of NaOH would be:
Na: 1 × 22.99 g/mol = 22.99 g/mol
O: 1 × 15.999 g/mol = 15.999 g/mol
H: 1 × 1.008 g/mol = 1.008 g/mol
Adding these values together, we get:
22.99 g/mol + 15.999 g/mol + 1.008 g/mol = 40.997 g/mol
Now, we can calculate the total mass of NaOH in the solution:
5g of NaOH × (1 mol/40.997 g) = 0.122 mol
Since the molar ratio of NaOH to Na+ and OH- ions is 1:1, there would be 0.122 mol of both Na+ and OH- ions in the solution.
To determine the total mass of the solution, we need to consider the mass of the solvent as well. If we have 50g of water, its mass remains the same.
Therefore, the total mass of the solution would be:
Mass of water (solvent) + Mass of Na+ + Mass of OH-
= 50g (water) + (0.122 mol × 22.99 g/mol) (Na+) + (0.122 mol × 15.999 g/mol) (OH-)
Calculating the values:
50g + (2.804 g) (Na+) + (1.96 g) (OH-)
= 54.764 g
So, the total mass of the solution would be approximately 54.764g, not 55g.