Question

Liquid silicon tetrachloride reacts violently with liquid water to product solid silicon dioxide and aqueous hydrochloric acid.

Write a balanced equation for this reaction.

If 76.5 g of water is mixed with 275 g of silicon tetrachloride and the reaction goes to completion, how many grams of silicon dioxide can be produced?

[97.3 g SiO2]

How many grams of the nonlimiting (excess) reagent remain unreacted when the reaction is over?

[18.2 g H2O]

If the percent yield for the reaction was 85.0 %, how many grams of silicon dioxide were formed?

[82.7 g SiO2]

Answer 1

atomic weights (g/mole): SI= 28, Cl= 35.5, H= 1, O= 16

molar masses ( g/mole): SICl4= 1*atomic weight of SI+4* atomic weight of Cl = 1*28+4*35.5 =170

H2O= 2*1+16= 16, The balanced reaction is

SiCl4(l) + 2 H2O(l) 4 HCl(aq) + SiO2(s)

The stoichionetry suggests 1 mole of SICl4 reacts with 2 mole of H2O. Theoretical moles ratio of SiCl4: H2O= 1 :2

moles =mass/molar mass

actual moles : SiCl4= 275/170 =1.62, H2O= 76.5/18=4.25

Actual moles ratio of SiCl4: H2O= 1.62: 4.25 or 1.62/1.62 : 4.25/1.62= 1: 2.62

so excess is H2O. all the SiCl4 reacts. hence 1 mole of SiCl4 from the reaction gives 1 mole of SiO2

1.62 moles of SiCl4 gives hence 1.62 moles of SIO2, molar mass of SiO2= 28+2*16= 60 g/mole

mass of SiO2 formed= 1.62*60= 97.2 gm

As per the reaction, 1 mole of SiO2 requires 2 moles of H2O

1.62 moles of SiO2 requires 2*1.62= 3.24 moles of H2O

water remaining = water supplied- water consumed= 4.25-3.24= 1.01 moles

mass of H2O, the excess reactant remaining = 1.01*18= 18.2 gm

theoretcial SiO2 formed = 97.2 gm

% yiled= 85%, actual yiled= theoretical yiled*85/100= 97.2*0.85 = 82.62 gm