ap chem actual percentage of hydrogen peroxide lab

what is hydrogen peroxide

an environmentally friendly alternative to chlorine for water purification and wastewater treatment

why does H₂O₂ need to be regularly checked

hydrogen peroxide can decompose in the presence of heat, light, or other catalysts

purpose of the lab

finding the actual percentage of hydrogen peroxide in the solution using redox titration with potassium permanganate.

redox titration summary

if a solution contains a substance that can be oxidized (hydrogen peroxide), than the concentration of that substance can be analyzed by titrating it with a standard solution of a strong oxidizing agent (potassium permanganate)

who is the oxidizing agent

potassium permanganate, gains electrons (reduced) when it takes electrons from hydrogen peroxide, which is (oxidized)

half reaction of hydrogen peroxide to oxygen gas

(add hydrogens to balance, and then electrons)

H₂O₂ (aq) —> O₂ (g) + 2H⁺(aq) + 2e^-

0 = 2 + (-2)

half reaction of permanganate ion reduced from 7+ in MnO₄^- to 2+ in Mn²⁺

(add water to balance oxygens, then hydrogens to balance, and then electrons)

MnO₄^- (aq) + 8H⁺ (aq) + 5e^- —> Mn²⁺ (aq) + 4H₂O (l)

7 + (-8)

-1 + 8 + (-5) = 2 + 0

BALANCED net ionic equation (after multiplying first by 5, and second by 2); simplify H⁺

5H₂O₂ (aq) + 2MnO₄^- (aq) + 6H⁺ (aq) —> 2Mn²⁺ (aq) + 5O₂ (g) + 8H₂O (l)

0 + -2 + 6 = 4 + 0 + 0

how many electrons in total are transferred in the balanced equation

10e^- are transferred

experiment overview

standard dark purple KMnO₄ is added from a buret into the H₂O₂ solution, reacting and fading until all H₂O₂ is consumed.

endpoint: reached when the last drop of KMnO₄ retains its color, causing the solution to turn light pink

H₂O₂ is the limiting reactant

Lab Procedure

• Prep Buret: Obtain ~75 mL KMnO4 (record exact M). Rinse and fill a 50-mL buret to 0 line, clear tip air bubbles, and record initial buret volume.

• Prep Flask: Mass an empty Erlenmeyer flask. Add 1 mL H2O2 and record mass of flask + peroxide. Add ~25 mL distilled H2O and 5 mL 6M H2SO4, then swirl.

• Titrate: Place flask over white paper under buret. Titrate while swirling until a persistent light pink color appears. Record final buret volume.

• Repeat: Clean flask and repeat for at least 2 trials (3 if endpoint is missed). Clean lab station when finished.