In K2CO3 + 2HCl yields 2KCl + H2O + CO2, to calculate how many milliliters of 6.0 M HCl would be needed do I do this:


6 moles/L X 1L/1000ml. = 6moles X the molecular mass of HCl

I explained in your other post. You know the concentration of HCl in moles/liter. You don't need the molecular mass (molecular weight) of HCl unless you want to know the mass of HCl that you use. The problem doesn't require this.

Use "unit analysis" (dimensional analysis) to figure out what to do.

Concentration given:

\frac {moles}{\cancel {liter}} \,\times\, \cancel {liters} = moles

Molecular weight given:

\cancel {grams} \,\div\, \frac {\cancel {grams}}{mole} = moles

\cancel {moles} \,\times\, \frac {grams}{\cancel {mole}} = grams