A, the mixture of bromoethane and a small amount of ethanol is added with water to remove ethanol, and the principle of adding carbon tetrachloride to bromowater to extract bromine is the extraction principle, so A is correct;

B, the conical flask containing the solution to be tested is not dry after cleaning, which does not affect the amount of solute in the solution to be tested and the volume of standard solution, so B is correct;

The primary battery composed of dilute H2SO4 at C, Z-C, when proper H2O2 is added to the solution, the potential of oxidation electrode rises R, so it can improve the discharge efficiency of the battery, so C is correct;

M, amino acids will not appear purple roses when they meet biuret reagent, but protein can make biuret reagent change color, so M is wrong.

So choose m.