#### Answer

0.61 grams

#### Work Step by Step

For each mole of Na2SiO3, you need 8 moles of HF. Therefore, if we have 0.800g of HF then we need to convert this to moles.
H is 1 g/mol
F is 19 g/mol
20 g/mol.
Then we have 0.8g * (1 mole/20g) = 0.04 moles HF
We need 8 moles HF for every mole of Na2SiO3 so 0.04/8 = 0.005 moles Na2SiO3.
The molar mass of Na2SiO3 is:
Na is 23, 23*2 = 46
Si is 28
O is 16, 3*16 = 48
46+28+48 = 122 g/mol
0.005 moles * 122g/mol = 0.61 grams