Question

3. Hydrofluoric acid, HF, cannot be stored in glass bottles because compounds such as silicates in the glass are attacked by HF as seen in the following example with Naz SiO3 Na2SiO3(s) + 8HF(1) H2SiF6(aq) + 2NaF(aq) + 3H2O(1) a. How many grams of Naz SiO3 dissolve when 225 mL of 0.1256 M H2Sifo is produced? b. How many grams of H2SiFo form when 35.00 mL of 2.78 M HF reacts by this reaction?

Answer 1

a)

lets calculate the mol of H2SiF6

volume , V = 2.25*10^2 mL

= 0.225 L

use:

number of mol,

n = Molarity * Volume

= 0.1256*0.225

= 2.826*10^-2 mol

According to balanced equation

mol of Na2SiO3 reacted = (1/1)* moles of H2SiF6

= (1/1)*2.826*10^-2

= 2.826*10^-2 mol

This is number of moles of Na2SiO3

Molar mass of Na2SiO3,

MM = 2*MM(Na) + 1*MM(Si) + 3*MM(O)

= 2*22.99 + 1*28.09 + 3*16.0

= 122.07 g/mol

use:

mass of Na2SiO3,

m = number of mol * molar mass

= 2.826*10^-2 mol * 1.221*10^2 g/mol

= 3.45 g

Answer: 3.45 g

b)

lets calculate the mol of HF

volume , V = 35 mL

= 3.5*10^-2 L

use:

number of mol,

n = Molarity * Volume

= 2.78*3.5*10^-2

= 9.73*10^-2 mol

According to balanced equation

mol of H2SiF6 reacted = (1/8)* moles of HF

= (1/8)*9.73*10^-2

= 1.216*10^-2 mol

This is number of moles of H2SiF6

Molar mass of H2SiF6,

MM = 2*MM(H) + 1*MM(Si) + 6*MM(F)

= 2*1.008 + 1*28.09 + 6*19.0

= 144.106 g/mol

use:

mass of H2SiF6,

m = number of mol * molar mass

= 1.216*10^-2 mol * 1.441*10^2 g/mol

= 1.753 g

Answer: 1.75 g