Question

The US DOT-11 Tank rail car is used for transporting liquids on railways. The EPA mandates that ethanol be mixed with gasoline: currently pump gas is 90% gasoline and 10% ethanol. One common use of the tank car is to transport ethanol to oil refineries to be mixed with gasoline. The DOT-111 tank car holds 34500 US gallons. Assume that the temperature of the ethanol is 20 C. If a DOT-111 tank car is full of ethanol,

1. How many kilograms of ethanol are in the DOT-111 tank car?

2. How many moles of ethanol are in the DOT-111 tank car?

3. How many hydrogen atoms are in the ethanol in the DOT-111 tank car?

Answer 1

Ans. Total mass of fuel = 34500 US gallons

                                    = 34500 x 3.78541 L                                    ; [1 US gallon = 3.78541 L]

                                    = 130596.71 L

#1. Amount of ethanol in tank = 10 % of total fuel

                                                            = 10 % of 130596.71 L

                                                            = 13059.671 L

Now,

            Mass of ethanol = Volume x Density at 20.0⁰C

                                                = 13059.671 L x (0.7893 kg L^-1)

                                                = 10308.0 kg

#2. Moles of ethanol = Mass of ethanol in grams / Molar mass of ethanol

                                    = (10308.0 x 10³ g) / (46.069 g/mol)

                                    = 223751.33 moles

#3. Molecular formula of ethanol = C₂H₅O_H

Stoichiometry: 1 ethanol molecule has 6 H-atoms. Or, 1 mol ethanol has 6 mol H-atoms.

So,

Moles of H-atoms in ethanol = (6 mol H-atom / 1 mol ethanol) x 223751.33 mol ethanol

                                                            = 1342507.977 mol

Now,

No. of H-atoms = Moles of H-atom x Avogadro number

                        = 1342507.977 mol x (6.022 x 10²³ atoms/ mol)

                        = 8.085 x 10²⁸ atoms