Question

Determine the number of moles of Na2CO3 required to react with 0.01516 mol HCl.

1 Na2CO3(aq) + 2 HCl(aq) → 2 NaCl(aq) + 1 CO2(g) + 1 H2O(l)

Answer 1

You're just using the coefficients to relate the two, HCl and Na2CO3. you can use a ratio

Answer 2

Simply use molar ratios since it takes 2 HCl to react with 1 Na2CO3 you will only need half the mols of Na2CO3 to react with a given amount of HCl. Simply take your mols and divide by two.