Aim: How to determine if a solution is acidic,

basic, or neutral

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.

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.

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 = 0.0001 M.•A solution with pH 3, [H+] = 1x 10-3 M = 0.001 M•When the pH decreases by 1 unit the concentration of

hydrogen ions increases by 10x.

Calculating pOH

•pOH measures the concentration of OH- ions.

•pOH=-log[OH-]

pH + pOH = 14pH = 14 – pOHpOH= 14 – pH

pH Scale

(Basic)

Do Now

• An acidic solution can have a pH of1. 72. 103. 34. 14• An aqueous solution that has a hydrogen ion

concentration of 1.0 x 10-8 mole per liter (M) has a

pH of1. 6, which is basic2. 6, which is acidic3. 8, which is basic4. 8, which is acidic

• What is the pH of 0.00001 molar HCl solution?

1. 12. 93. 54. 4

pH Indicators

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

Methyl orange

•Red in a solution with pH 3.2 or less• Yellow in a solution with

pH 4.4 or more•Orange in a solution

between pH 3.2 and 4.4

Bromthymol blue

•Yellow in a solution with pH 6.0 or less•Blue in a solution with pH 0f 7.6 or more

Phenolphthalein

•Colorless in a solution with pH 8.2 or less•Pink in a solution with pH 9 or more

Litmus• Turns blue litmus paper red for acidic solutions• Turns red litmus paper blue for basic solution

Bromcresol green

•Yellow in a solution with pH 3.8 or less•Blue in a solution with pH 5.4 or more

Thymol blue

•Yellow in a solution with pH 8.0 or less•Blue in a solution with pH 9.6 or more

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

Question

•A solution turns yellow with thymol blue and blue with bromthymol blue. What is the pH?

Question

• If an aqueous solution turns blue litmus red, which relationship exists between the hydronium ion and the hydroxide ion concentration?

1. [H3O+] > [OH-]2. [H3O+] < [OH-]3. [H3O+] = [OH-]= 10-7

4. [H3O+] = [OH-]= 10-14