1. Acids Lesson 13 Indicators Theory

2. Indicators Indicators are organic chemicals with large complex formulas. They are weak acids where the acid and base forms have different colours.

3. Methyl Red

4. Look up Alizarin yellow on page 7 of your data package. It tells you that it changes from yellow to red as pH increases. This means that the acid form is yellow and the base form is red.

6. Transition Point=10.1+ 12.0 2 = 11.05

7. Alizarin Yellow HInd ⇄ H + +Ind - Acid form Base form yellowred The solution is yellow when the pH < 11.05 The solution is red when the pH > 11.05 At the transition point pH = 11.05, the yellow [HInd] = [Ind - ] red and the solution looks orange, which is a blend of yellow and red. Ka=[H + ][Ind - ] [HInd]

8. Alizarin Yellow HInd ⇄ H++Ind- Acid form Base form yellowred The solution is yellow when the pH < 11.05 The solution is red when the pH > 11.05 At the transition point pH = 11.05, the yellow [HInd] = [Ind - ] red and the solution looks orange, which is a blend of yellow and red. Ka=[H + ][Ind - ] [HInd] Ka=[H + ][Ind - ] [HInd]

9. Alizarin Yellow HInd ⇄ H++Ind- Acid form Base form yellowred The solution is yellow when the pH < 11.05 The solution is red when the pH > 11.05 At the transition point pH = 11.05, the yellow [HInd] = [Ind - ] red and the solution looks orange, which is a blend of yellow and red. Ka=[H + ][Ind - ] [HInd] Ka=[H + ][Ind - ]=[H + ]Only at the trans point [HInd]

10. Calculate the Ka for methyl orange. Transition point pH= (3.2 + 4.4)/2 = 3.8 [H + ]=10 -pH =10 -3.8 =1.58 x 10 -4 M Ka=[H + ]=2 x 10 -4 An indicator has a Ka = 1.0 x 10 -6, calculate the pH of the transition point. Ka=[H + ]=1.0 x 10 -6 M pH = -log[H + ]=-Log[1.0 x 10 -6 ] =6.00 The indicator is chlorophenol red because (5.2 + 6.8)/2 = 6.0

11. There are a few indicators that are diprotic and can change colours twice. You have one of those in this lab and it is called thymol blue. H 2 Ind ⇄ H + +HInd - HInd - ⇄ H + +Ind 2- pH 024678101214

12. There are a few indicators that are diprotic and can change colours twice. You have one of those in this lab and it is called thymol blue. H 2 Ind ⇄ H + +HInd - Red HInd - ⇄ H + +Ind 2- pH 024678101214

13. There are a few indicators that are diprotic and can change colours twice. You have one of those in this lab and it is called thymol blue. H 2 Ind ⇄ H + +HInd - Redblue HInd - ⇄ H + +Ind 2- Blue pH 024678101214

14. There are a few indicators that are diprotic and can change colours twice. You have one of those in this lab and it is called thymol blue. H 2 Ind ⇄ H + +HInd - Redblue HInd - ⇄ H + +Ind 2- BlueYellow pH 024678101214

15. There are a few indicators that are diprotic and can change colours twice. You have one of those in this lab and it is called thymol blue. H 2 Ind ⇄ H + +HInd - Redpurpleblue [H 2 Ind] = [HInd - ] HInd - ⇄ H + +Ind 2- BlueYellow pH 024678101214

16. There are a few indicators that are diprotic and can change colours twice. You have one of those in this lab and it is called thymol blue. H 2 Ind ⇄ H + +HInd - Redpurpleblue [H 2 Ind] = [HInd - ] HInd - ⇄ H + +Ind 2- BluegreenYellow [HInd - ] = [Ind 2- ] pH 024678101214