Question

In aviation gasoline of 100 octane number, 1.0 Ml of tetraethyl lead (TEL), ${\left( {{C_2}{H_5}} \right)_4}Pb$ of density 1.615g/mL per litre is added to the product .TEL is prepared as follow:
$4{C_2}{H_5}Cl + 4Na\left( {Pb} \right) \to {\left( {{C_2}{H_5}} \right)_4}Pb + 4Nacl + 3Pb$
Calculate the amount of ${C_2}{H_5}Cl$ required to make enough TEL for 1.0L of gasoline.
A. 0.645g
B. 1.29g
C. 1.935g
D. 2.58g

Answer 1

We will start by finding the weight of TEL from the density. Here, we use the concept of stoichiometry which is the quantitative relationship between the number of moles of various products and reactants in a chemical reaction.

Complete step by step answer: As we know, the molecular weight of TEL, i.e. tetraethyl lead is 323 g/mol. Given,
Density of the tetraethyl lead = 1.615g/ml
Volume of the tetraethyl lead = 1.0ml
By using the below formula,
$Density = \dfrac{{mass}}{{volume}}$
$moles = \dfrac{{given{\text{ }}mass}}{{molecular{\text{ }}mass}}$

The weight of the 1.0 ml of tetraethyl lead = Density ×Volume
$1.0 \times 1.615 = 1.615g$
The weight of tetraethyl lead needed per litre of gasoline = 1.615g
The molecular mass of tetraethyl lead=4×mass of ethyl + mass of lead
$4 \times 29 + 207 = 323{\text{ }}g/mol$
Moles of tetraethyl lead is calculated as:
$\dfrac{{1.615}}{{323}} = 0.005mol$

According to the reaction, 1 mol of tetraethyl lead required =$4 \times 0.005{\text{ mole of ethyl chloride}}$
That is equal to 0.02mol of ethyl chloride.

So the weight of ethyl chloride = no of mole × molecular mass of ethyl chloride
$0.02 \times 64.5 = 1.29g$
So, the correct answer is “Option B”.

Additional Information: Tetraethyl lead is an organometallic compound of lead. It is a fuel additive and used as an anti-knock agent is gasoline and jet fuel. It ensures the petrol is burned smoothly and slowly which prevents knocking and also gives a higher octane rating.

Note: Molarity is the term which is used to express the concentration. Also, Density can be mathematically defined as molarity/molality. Molarity and density are related to each other as
- Both are affected by the number of moles, i.e. amount of the particle
- Both are affected by the mass of the molecules
- Both are affected by volume
- External Temperature also affects both properties.