Prior to their phaseout in the 1980s, chemicals containing lead were commonly ad

Question

Prior to their phaseout in the 1980s, chemicals containing lead were commonly added to gasoline as anti-knocking agents. A 8.907 g sample of one such additive containing only lead, carbon and hydrogen was burned in an oxygen rich environment. The products of the combustion were 9.695 g of CO2 and 4.961 g of H2O. The sum of the subscripts in the empirical formula of the lead additive is:

a. 26 b. 29 c. 30 d. 36

please explain if you can, got this question wrong on my exam, not sure if im going about it correctly

Explanation / Answer

tetraethyl lead was used as additive. (  (CH3CH2)4Pb. )

moles of co2 = 0.22

moles of h2o = 0.27,

in compound,

moles of c = 0.22

moles of h = .27 x 2 = 0.55 mol

it means for 2 atom of c, there is 5 atom of hydrogen

( it means c2h5 is the ratio)

oxydation state of lead = +2 and +4

for state = +4,

we need four anions, ie,

(CH3CH2)4 (4-)

Question - why is it not +2

try using +2 config.

you would guess (CH3CH2)2 Pb

but, then, see the molecular weight and weight of co2 and h2o formed

in the proposed wrong formula, there are 4 carbon atome, and 0.22 moles of co2 is formed.

hence amount of reactant needed will be 022/4 = 0.055 moles

find weight required for 0.055 moles of (  (CH3CH2)2Pb. )

the weight you calculate and weight given will not match ( you will find the weight is lesser in calculation. )

(  (CH3CH2)4Pb. ) has 8 c atom hence it has (.22/8) = 0.0275 moles of reactants

find weight of 0.0275 moles of reactants with formula of (  (CH3CH2)2Pb. ).

you will find that weights match.

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.