1. Indicators And Titration

2. Indicators Usually organic acid or base whose color is sensitive to pH Indicator is weak acid or base In basic solution, indicator produces H+ ions that combine with OH- to make water, leaving indicator in the form In- In acid solution, indicator takes up H+ and is in the form HIn

3. Indicators The reaction of the indicator with OH- or H+ takes place over a range of [H+] (pH) Transition interval Different indicators have different transition intervals (se Table 16-6)

4. Titration Used to determine the concentration of an unknown solution (volumetric analysis) Controlled addition and measurement of volume of a solution of known concentration to a measured volume of unknown Uses indicators to tell the “end point”

5. Steps in Solving Titration Problems Start with balanced equation for neutralization reaction Determine the moles of the known solution used in the titration Determine the moles of unknown solution used during the titration Determine the molarity of the unknown

6. Sample Problem 16-6 In a titration, 27.4 mL of 0.0154 M Ba(OH) 2 is added to 20.0 mL sample of HCl solution. What is the molarity of the acid? Step 1: Balanced chemical equation: 2HCl + Ba(OH) 2  2H 2 O + BaCl 2

7. Sample Problem 16-6 Step 2: Determine the moles of the known solution: 0.0154 mole x 0.0274 L = 4.2196 x 10 -4 1 Lmole Ba(OH) 2

8. Sample Problem 16-6 Step 3: Determine the moles of the unknown: 4.2196 x 10 -4 mole Ba(OH) 2 x 2 mole HCl = 1 mole Ba(OH) 2 8.4392 x 10 -4 mole HCl

9. Sample Problem 16-6 Step 4: Determine the molarity of the unknown: 8.4392 x 10 -4 mole = 4.2196 x 10 -2 M HCl 0.020 L Concentration is 4.22 x 10 -2 M HCl

10. Now it’s your turn! Read p 497-503 Do Practice Problems 1-2 p 503