Question #be783

For starters, you need a balanced chemical equation to go by.

#"Na"_ 2"SiO"_ (3(aq)) + 8"HF"_ ((aq)) -> "H"_ 2"SiF"_ (6(aq)) + 2"NaF"_ ((aq)) + 3"H"_ 2"O"_ ((l))#

Now, the balanced chemical equation tells you that for every #8# moles of hydrofluoric acid that the reaction consumes, you get #2# moles of sodium fluoride.

Since sodium silicate is said to be in excess, you know for a fact that all the moles of hydrofluoric acid present in your solution will actually take part in the reaction.

This means that the reaction will produce

#0.500 color(red)(cancel(color(black)("moles HF"))) * "2 moles NaF"/(8color(red)(cancel(color(black)("moles HF")))) = "0.125 moles NaF"#

To convert this to grams, use the molar mass of sodium fluoride

#0.125 color(red)(cancel(color(black)("moles NaF"))) * "41.988 g"/(1color(red)(cancel(color(black)("mole NaF")))) = color(darkgreen)(ul(color(black)("5.25 g")))#

The answer is rounded to three sig figs, the number of sig figs you have for the number of moles of hydrofluroic acid that take part in the reaction.