1. Aim: How to determine if a solution is acidic, basic, or neutral

2. Acidic, Basic, and Neutral Solutions
Acidic solutions (acid in water (H2O)) have more H+ (H3O+) than OH-.
Basic solutions have more OH- than H+ (H3O+).
H2O (water alone) has the same number of H+ as OH- ions.

3. The pH concept
The pH scale is used to measure the hydrogen-ion concentration [H+].
pH = -log[H+]
Acidic solutions have a pH< 7, a neutral solution has a pH=7, and a basic solution has a pH>7.

4. Measuring pH
If [H+] is 1.0 x 10-4, pH is 4. The exponent gives you the pH of a solution.
At pH 4, [H+] = 1 x 10-4 M = M.
A solution with pH 3, [H+] = 1x 10-3 M = M
When the pH decreases by 1 unit the concentration of hydrogen ions increases by 10x.

5. Calculating pOH pOH measures the concentration of OH- ions.
pOH=-log[OH-]
pH + pOH = 14
pH = 14 – pOH
pOH= 14 – pH

6. pH Scale
(Basic)

7. Do Now What is the pH of 0.00001 molar HCl solution? 1 9 5 4
An acidic solution can have a pH of 7 10 3 14
An aqueous solution that has a hydrogen ion concentration of 1.0 x 10-8 mole per liter (M) has a pH of
6, which is basic
6, which is acidic
8, which is basic
8, which is acidic

8. pH Indicators
An indicator is a valuable tool for measuring pH because its acid form and base form have different colors in solution.

9. Methyl orange Red  pH 3.2 or less Yellow pH 4.4 or more
Orange pH 3.2 to 4.4

10. Bromthymol blue
Yellow pH 6.0 or less
Blue  pH 0f 7.6 or more

11. Phenolphthalein
Colorless  pH 8.2 or less
Pink  pH 9 or more

12. Litmus Turns blue litmus paper red for acidic solutions
Turns red litmus paper blue for basic solution

13. Bromcresol green
Yellow  pH 3.8 or less
Blue  pH 5.4 or more

14. Thymol blue
Yellow  pH 8.0 or less
Blue  pH 9.6 or more

15. Using more than one indicator
If you put bromcresol green in a solution and the solution turns blue, the pH is 5.4 or more.
If you put bromthymol blue in another test tube with the same solution and it turns yellow, it shows the pH is 6.0 or less.
Conclusion: the solution has a pH between 5.4 and 6.0

16. Question
A solution turns yellow with thymol blue and blue with bromthymol blue. What is the pH?
7.6-8

17. Question
If an aqueous solution turns blue litmus red, which relationship exists between the hydronium ion and the hydroxide ion concentration?
[H3O+] > [OH-]
[H3O+] < [OH-]
[H3O+] = [OH-]= 10-7
[H3O+] = [OH-]= 10-14

18. Summary pH below 7 Litmus  red Phelphthalein  clear
ACIDS
BASES
pH below 7
Litmus  red
Phelphthalein  clear
Bromthymol blue  yellow
Methyl orange  red
pH above 7
Litmus  blue
Phelphthalein  pink
Bromthymol blue  blue
Methyl orange  yellow