1.21 m
The balanced reaction is
2 HCl + Na2CO3 ==> CO2 + H2O + 2 NaCl
which indicates that for every mole of CO2 produced, 2 moles of HCl are required. So let's determine how many moles of CO2 were produced, starting with the atomic weights of carbon and oxygen.
Atomic weight carbon = 12.0107
Atomic weight oxygen = 15.999
Molar mass CO2 = 12.0107 + 2 * 15.999 = 44.0087 g/mol
Moles CO2 = 15.1 g / 44.0087 g/mol = 0.343113975 moles
Because of the balanced equation, we know we needed twice as many moles of HCl, so
0.343113975 mol * 2 = 0.68622795 mol
And since molarity is defined as moles per liter, just divide the number of moles by the number of liters, so:
0.68622795 mol / 0.567 l = 1.210278572 mol/l
Since we only have 3 significant figures in our data, round to 3 figures, giving 1.21 m
