Transcript Solutions and Solution Stoichiometry

Detection of Ethanol
Detection of Ethanol
• DUI
– Saliva (coupled enzyme assay) [“On-Site”]
– Breathylizer
• BAC via breath
–
–
–
–
“Breathalyzer” (visible spec)
“Intoxilyzer 5000” (infrared spec)
“Alco-Sensor” (fuel cell)
“Alcohawk” (solid-oxide conductor)
– Urine
– Blood (directly)
• Chromic acid oxidative method
• Synergistic action with other drugs
• Poisoning (ethanol and methanol)
Oxidative method of ethanol
determination involves color change
C2H5OH + K2Cr2O7 + H2SO4→ CH3COOH + Cr2(SO4)3 + H2O + K2SO4
orange
green
Our Tasks:
1. Use the above reaction to help us determine an unknown ethanol
concentration.
2. Use the above reaction to help us explore limiting reagents.
Determination of Unknown
Concentration of Ethanol in Blood
• Beer’s Law: A = bc
• The absorbance of a solution is linearly
proportional to it’s concentration.
• We can make a calibration curve, do a
linear fit, and solve for the unknown
Task 1: Determination of Unknown
Concentration of Ethanol in Blood
% Alcohol vs Absorbance at 440 nm
0.4
0.35
Absorbance
0.3
Series1
0.25
Linear (Series1)
y = -0.4691x + 0.3602
R2 = 0.9972
0.2
0.15
0.1
0
0.05
0.1
0.15
0.2
% Alcohol (w /v)
0.25
0.3
0.35
0.4
Task 2: Investigate the
stoichiometry of the reaction
C2H5OH + K2Cr2O7 + H2SO4→ CH3COOH + Cr2(SO4)3 + H2O + K2SO4
Task 3: If 0.2 mL of an ethanol solution is mixed with 20.0 mL of a solution
prepared by dissolving 50 mg of K2Cr2O7 in 100 mL of deionized water and
diluting to 200 mL with concentrated sulfuric acid, what molarity must the
ethanol be to completely consume all of the potassium dichromate?
In order to answer the above question, we need to learn about
balancing reactions and reaction stoichiometry!