Question

2. Using the same method, answer the same questions for mixing 30 g of hydrogen fluoride and 30 g of glass (which is made of silicon dioxide) with focus on determining the percent yield of silicon tetrafluoride (and water). Silicon tetrafluoride is found in volcanic plumes and has some limited use in microelectronics.

HF(g) + SiO2(s) → SiF4(g) + H2O(l)

a) Write a balanced chemical equation for the equation above.
b) From your balanced chemical equation, what is the molar ratio between the reactants and products?
c) What is the stoichiometric amount of moles of SiF4 that can be formed when 30 grams of HF and 30 grams of SiO2 are reacted?
d) What is the theoretical amount (in grams) of nitric acid that can be formed when 30 grams of HF and 30 grams of SiO2 are reacted?
e) What is the percent yield of Silicon tetrafluoride?
f) How much of the excess reagent remains?

Answer 1

a)  

b) Molar ratio is the ratio between the amounts in moles of any two compounds involved in the chemical reaction.

NHF : NSiF4 = 4:1

NSiO2 : NH2O = 1:2

c) For this we need to find limiting reagent. NHF = 1.5 mol and NSiO2 = 0.5

4 mol HF requires 1 mol of SiO2

  So 1.5 mol HF will require 0.375 mol of SiO2

So HF is limiting reagent as it will be exhausted before SiO2

moles of SiF4 = 0.375 mol

e) We need to find both theoretical yield and actual yield to calculate percent yield.

Actual yield of SiF4 = 0.375 mol = 39 g of SiF4

Theoretical yield of SiF4  is the maximum amount of SiF4 that can be formed.

So thoretical yield will be when 0.5 mol SiO2 will react with SiF4 to produce 0.5 mol of SiF4

Theoretical yield = 0.5 mol = 52 g of SiF4

% yield = actual yield / theoretical yield *100

= 39/52 *100 = 75%

f) excess amount of reagent = (0.5 - 0.375) mol of SiO2

= 0.125 mol of SiO2     

How is nitric acid formed in this reaction?

n