if a student mixes 250 grams of Na2O with 300 grams of H2O how many grams of NaOH ?

Answer 1

This is a limiting reagent problem (LR) and I work these the long way.
Na2O + H2O ==> 2NaOH
mols Na2O = grams/molar mass = ?
mols H2O = grams/molar mass

Using the coefficients in the balanced equation convert mols Na2O to mols NaOH.
Do the same for mols H2O to mols NaOH.
It is likely that the two values will not be the same which means one of them is not right; the correct value in LR problems is ALWAYS the smaller value and the reagent responsible for that number is the LR.

Using the smaller value, convert mols to grams. grams NaOH = mols NaOH x molar mass NaOH. If I punched in the right numbers on my calculator I think the answer is approx 160 grams. I think a more interesting question would have been to calculate the M NaOH solution.