Redox Titration OF bleach Due Today: 1. Redox Titration of Bleach Pre-Lab 2. Copper Reduction Formal Lab Report Homework: 1. Redox Titration Short Report 2. Gravimetric Analysis of Phosphorus Pre-Lab Redox Titration OF bleach

Objective Determine the weight percent of sodium hypochlorite (NaOCl) in bleach via redox titration.

Key Terms Oxidation-Reduction (Redox) Reaction: Follow the transfer of electrons Matched reaction – you cannot have one without the other

Key Terms Titration – process of reacting a solution of unknown concentration with a solution of a known concentration until the reaction is JUST complete All reactants are limiting

Key Terms Equivalence Point – equal quantities of opposite solutions exist For acid/base titrations: Moles of acid = Moles of base For redox titrations, you must you the reaction equation to determine moles

Procedure Notes Preparation of KIO3 Solution: Use 250 mL volumetric flask Be precise!

Procedure Notes Standardization of (Na2S2O3): Rinse the buret with DI water and Na2S2O3 before you titrate PIPETE KIO3 solution DO NOT PIPET FROM VOLUMETRIC FLASK!! IMMEDIATELY titrate after KI is added

Procedure Notes During the Titration: Look for light yellow color Add starch Blue/Black Titrate until clear 1-5 drops 3 good trials Molarities within 5% of average

Procedure Notes Titration of Bleach During the Titration: Weigh 2.000g of bleach During the Titration: Immediately titrate when you add KI Look for light yellow color

Procedure Notes Add starch Titrate until clear 3 good trials Blue/Black Titrate until clear 1-5 drops 3 good trials Molarities within 5% of average RECORD THE REPORTED MASS NaOCl FROM THE BLEACH BOTTLE!!!!!!!

Waste Solutions can go down the drain

Risk assessment Sodium Hypochlorite (Bleach) Danger Skin Irritant Respiratory Irritant

calculations Molarity of KIO3 Solution: Moles KIO3 used in titration:

calculations Mass Percent: Moles of Na2S2O3 used in titration: You will need to use stoichiometry HINT look for a relationship between the two equations on page 44 Mass Percent:

Redox Equation Example 𝐶𝑢𝑆𝑂 4 𝑎𝑞 +𝑍𝑛 𝑠 → 𝑍𝑛𝑆𝑂 4 𝑎𝑞 +𝐶𝑢(𝑠) 1. Make sure your equation is balanced 𝐶𝑢𝑆𝑂 4 𝑎𝑞 +𝑍𝑛 𝑠 → 𝑍𝑛𝑆𝑂 4 𝑎𝑞 +𝐶𝑢(𝑠)

Redox equation example 2. Assign Oxidation Numbers 𝐶𝑢𝑆𝑂 4 𝑎𝑞 +𝑍𝑛 𝑠 → 𝑍𝑛𝑆𝑂 4 𝑎𝑞 +𝐶𝑢(𝑠) Cu : +2 S : +4 O : -8 Zn: 0 Cu: 0 Zn : +2

Redox equation example 3. Determine which species is oxidized and reduced 𝐶𝑢𝑆𝑂 4 𝑎𝑞 +𝑍𝑛 𝑠 → 𝑍𝑛𝑆𝑂 4 𝑎𝑞 +𝐶𝑢(𝑠) Cu : +2 S : +4 O : -8 Zn: 0 Cu: 0 Zn : +2 Zn: 0→+2 loss of electrons Zinc is oxidized and is the reducing agent Cu: +2→0 gain electrons Copper is reduced and is the oxidizing agent