Chemistry 104 Laboratory
	This Week
Answer Keys Gen Chem Lab Periodic Table	· pKa of an Acid-Base Indicator · Quiz 3: Expt 1
	Next Week
	Expt 5: pH Titration
	Notes for Today
	Goal: Find Ka of an Indicator Ka = [H^+][In^-]/[HIn] Strategy Make a solution of indicator at pH where both HIn, In^- are present Measure [In^-] from absorbance measurements at λ where only In^-absorbs A = εIn-b[In^-] Beer’s Law [HIn] = Cindicator - [In^-] [H^+] using pH meter How do you measure εIn-? · Make solution of just In^-. For the indicator shown below, how? · εIn- = A/ b[In^-] · What λ do you use? Phosphate Buffer Chemistry KH2PO4 contains two ions K^+ is a spectator ion H2PO4^- can react with H^+ or OH^- With H^+ : H3PO4 forms With OH^-: HPO4^2- forms Add enough H^+ to KH2PO4 to create mixture of H3PO4 and H2PO4^- Weak acid + weak base now present Name for this mixture? How will mixture respond to addition of acid or base? Add enough OH^- to KH2PO4 to create mixture of H2PO4^-and HPO4^2- Weak acid + weak base How will mixture respond to addition of acid or base? Safety Goggles required Exercise caution with glass pipets