The breathalyzer test utilizes the reaction between the dichromate ion and ethanol to produce acetic acid. Balanced equation for this process is given below. How much acetic acid can be produced from a mixture containing an excess of dichromate ion and 1.37 × 10−1 g of ethanol?

16H+ + 2Cr2O72− + 3CH3CH2OH → 3CH3COOH + 4Cr3+ + 11H2O

0.15g

Explanation:

Given parameters:

Mass of ethanol  = 1.37 x 10⁻¹g  = 0.137g

Unknown:

Mass of acetic acid produced  = ?

Solution:

The reaction equation is given by;

     16H⁺    +     2Cr₂O₇²⁻   + 3CH₃CH₂OH  → 3CH₃COOH + 4Cr³⁺  + 11H₂O

The equation above is balanced.

Now we solve from the known to the unknown i.e from the mass of ethanol to that of acetic acid.

     First find the number of moles of ethanol;

                           number of moles  =

               molar mass of CH₃CH₂OH = 12 + 3(1) + 12 + 2(1) + 16 + 1  = 56g/mol

                            number of moles  =   = 0.0025moles

From the balanced reaction equation;

        3 mole of CH₃CH₂OH  produces 3 moles of CH₃COOH

      0.0025mole of CH₃CH₂OH will produce 0.0025mole of CH₃COOH

Mass of CH₃COOH = number of moles x molar mass

                molar mass of CH₃COOH = 12 + 3(1) + 12 + 2(16) + 1  = 60g/mol

 Mass  = 0.0025 x 60  = 0.15g