[Arthr2shedsJacksn]

Hi, thanks for helping! 

Okay, when a reaction occurs in aqueous solutions, the chemical system is equivalent to that of water.
The reactants given are CuSO_4(aq) (0.300 M) + 2 NaOH_(aq) (0.600 M,) and the volume of each solution is 50.0 mL.

Why is the volume of water assumed to be 100.0 mL? (this is what the teacher says)

Wouldn't for CuSO_4(aq), the concentration of water be 1.000 - 0.300 = 0.700 M? and the concentration of water in NaOH_(aq) be 1.000 - 0.600 = 0.400 M? Thus, shouldn't the volume of water be assumed as (0.700 M)(50.0 mL) + (0.400 M)(50.0 ml) = 55 mL? (this is what I say)

Am I making a massive error?


Thanks for helping!!

[Borek]

Wouldn't for CuSO_4(aq), the concentration of water be 1.000 - 0.300 = 0.700 M?

Why do you think sum of concentrations must be 1? What is pure water concentration? (Hint: concentration is number of moles per liter).

[Arthr2shedsJacksn]

I am confused.

I understand that concentration equals to moles per litre, so the sum of concentrations needn't be 1.000. Misconception erased, thank you.
I don't actually understand what an aqueous solution is! According to Wikipedia, for aqueous solutions reacting, "solution concentration is given in terms of the form of the solute prior to it dissolving." Does that mean that there is no water in the aqueous solution, and water comes from somewhere else... is the concentration provided for the aqueous solution just the same regardless of whether it were (aq), (s) or (l)?

I am thoroughly confused.

Is volume of water related at all with the concentrations of the reactants? or just their volumes?

[Borek]

It just means that listing concentration you neglect possible reactions taking place during dissolution. 1M H₂SO₄ contains traces of H₂SO₄, a lot of HSO₄^- and some SO₄^2- (not to mention H⁺) - but nonetheless you call it 1M H₂SO₄.