Question

How many moles of HF are required to dissolve 6.9 moles of sodium dilicate in this reaction?

Answer 1

To answer this question we are to write down the reaction and to put the coefficients:
2HF+Na2SiO3=2NaF+H2SiO3
So we can see that the amount of HF is two times more than Na2SiO3.
If we have 6.9 moles of sodium silicate the amount of HF is: 6.9 /2=3,45 moles