The molar ratios in the reaction are 1:1::1:2, so one Mole (Na2CrO4, produces two moles, (NaNO3).
Using the equation: moles = mass(g) /Mr
1. Calculate the Mr of Na2CrO4
from the periodic table,
Na x 2 = 23 x 2 = 46
Cr x 1 = 52 x 1 = 52
O x 4 = 16 x 4 = 64
46 + 52 + 64 = 162.
moles (na2CrO4) = 253 g / 162 = 1.56 moles.
moles(NaNO3) = 1.56 x 2 = 3.12 moles.
The answer is 3.12 moles.
Hope this helps!
Correct me if I'm wrong.
(Some of this was due to help from Yahoo!)