Amount of substance

True, but what I meant was that you had supplied all the necessary formulas, so it's just a matter of substituting the numbers into them (though I suppose you have to know how to get the molar mass of H₂O from the individual masses supplied)

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You've essentially given the solution in your question EinsteinJr!  All you have to do is crunch the numbers (or am I missing something?).

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I didn't; I didn't gave the mass of 2L of water, nor the molar mass of water; I have just written down the formulas used to calculate this.

In order to calculate the amount of matter, you first have to determinate the mass m of 2L of water, using the first formula given, then you have to determinate the molar mass M of the water, and finally use the second formula to find the value of n.

You may be right; wait, I'll remove things in the wording...