Question

The police often use a device called a Breathalyzer to test drivers suspected of being drunk. In one type of device, the breath of a driver suspected of driving under the influence of alcohol is bubbled through an orange solution containing potassium dichromate (K₂Cr₂O₇) and sulfuric acid (H₂SO₄). The alcohol in the driver's breath reacts with the dichromate ion to produce acetic acid (HC₂H₃O₂), which is colorless, and green chromium(III) sulfate [Cr₂(SO₄)₃]. The degree of color change from orange to green indicates the alcohol concentration in the breath sample, which is used to estimate blood alcohol concentration. The balanced overall equation for the Breathalyzer reaction is

3CH3CH2OH(g)+2K2Cr2O7(aq)+8H2SO4(aq)=3HC2H3O2+2Cr2(SO4)3(aq)+2K2SO4(aq)+11H2O(l)

a Classify each of the species in the Breathalyzer reaction as a strong electrolyte, weak electrolyte, or nonelectrolyte.

b Write the ionic and net ionic equations for the Breathalyzer reaction.    

c Determine the oxidation number of each element in the overall equation.

d One manufacturer of Breathalyzers specifies a potassium dichromate concentration of 0.025 percent weight per volume (0.025 g K₂Cr₂O₇ per 100 mL of solution). Express this concentration in terms of molarity.

e What volume of 0.014 M stock solution of K₂Cr₂O₇ would have to be diluted to 250 mL to make a solution of the specified concentration? (f) Using square-bracket notation, express the molarity of each ion in a K₂Cr₂O₇ solution of the specified concentration

Answer 1

Answer :

An oxidation reaction in breath analyzer,

3CH3CH2OH(g) +2K2Cr2O7(aq) + 8H2SO4(aq) --------> 3HC2H3O2+2Cr2(SO4)3(aq)+2K2SO4(aq)+11H2O(l)

Species involved in breath analyzer, Ethanol CH3CH2OH, Potassium dichromate K2Cr2O7, Sulphuric acid H2SO4.

a)

Ethanol CH3CH2OH is Non-electrolyte.

Potassium dichromate K2Cr2O7 and Sulphuric acid H2SO4 both are strong electrolytes.

3CH3CH2OH(g) +4K⁺ (aq) + 2 Cr2O7^2-(aq) + 16H⁺ + 8 SO4^2-(aq) =====>3HC2H3O2 + 4Cr³⁺ + 8 (SO₄)^2-(aq) + 4K⁺(aq) +11H2O(l)

4K⁺ & 8 SO4^2- cancells out mutually, then

3CH3CH2OH(g) + 2 Cr2O7^2-(aq) + 16H⁺ (aq) =====>3HC2H3O2 + 4Cr³⁺ + 11H2O(l).

is the net ionic equation.

c)

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d)