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

Acidic, Basic, and Neutral Solutions Acidic solutions (acid in water (H 2 O)) have more H + (H 3 O + ) than OH -. Basic solutions have more OH - than H + (H 3 O + ). H 2 O (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.

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 M = M. A solution with pH 3, [H + ] = 1x M = 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 = 14 pH = 14 – pOH pOH= 14 – pH

pH Scale (Basi c)

Do Now An acidic solution can have a pH of An aqueous solution that has a hydrogen ion concentration of 1.0 x mole per liter (M) has a pH of 1.6, which is basic 2.6, which is acidic 3.8, which is basic 4.8, which is acidic What is the pH of molar HCl solution?

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  pH 3.2 or less Yellow  pH 4.4 or more Orange  pH 3.2 to 4.4

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

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

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

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

Thymol blue Yellow  pH 8.0 or less Blue  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.[H 3 O + ] > [OH - ] 2.[H 3 O + ] < [OH - ] 3.[H 3 O + ] = [OH - ]= [H 3 O + ] = [OH - ]=

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