The silver nitrate is a catalyst , a substance that makes the reaction go faster without participating in it. The sulfuric acid also might provide the acidic condition needed for this reaction. To determine the amount of alcohol in the expired air, the reacted mixture is compared to a vial of unreacted mixture in the photocell system, which produces an electric current that causes the needle in the meter to move from its resting place. The bonds of the three hydrogen atoms to the left carbon atom are not shown for clarity. The chemical bonds between the atoms are shared pairs of electrons.
Chemical bonds are much like springs.
They can bend and stretch. Molecules are constantly vibrating and these vibrations change when they absorb IR light. The changes in vibration include bending and stretching of various bonds. Each type of bond within a molecule absorbs IR at different wavelengths . The wavelength helps to identify it as ethanol and the amount of IR absorption tells you how much ethanol is there.