Chemistry - Acids and Bases: pH Indicators

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pH Indicators : pH Indicators

pH Paper : pH Paper pH 0 1 2 3 4 5 6 pH 7 8 9 10 11 12 13

Slide 5 : Desired Features of Sensors pH paper 1904 Detection limit Low deflection High sensitivity High selectivity Wide dynamic range Simple to use Cost-effective pH 0 1 2 3 4 5 6 pH 7 8 9 10 11 12 13

Slide 6 : Range and Color Changes of Some Common Acid-Base Indicators Indicators pH Scale 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Methyl orange red 3.1 – 4.4 yellow Methyl red red 4.4 6.2 yellow Bromthymol blue yellow 6.2 7.6 blue Neutral red red 6.8 8.0 yellow Phenolphthalein colorless 8.0 10.0 red colorless beyond 13.0 Bromthymol blue indicator would be used in titrating a strong acid with a strong base. Phenolpthalein indicator would be used in titrating a weak acid with a strong base. Methyl orange indicator would be used in titrating a strong acid with a weak base.

INDICATOR COLORS IN TITRATION : Indicator Acid color Transition color Base color Litmus Bromthymol blue STRONG ACID – STRONG BASE pH 2 3 4 5 6 7 8 9 10 11 12 INDICATOR COLORS IN TITRATION

INDICATOR COLORS IN TITRATION : INDICATOR COLORS IN TITRATION

Slide 11 : 1 2 3 4 5 6 7 8 9 10 11 12 Indicator Phenolphthalein Methyl Red Orange IV Colorless Pink Red Red Orange Yellow Orange Peach Yellow

Indicator Colors in Titration : Indicator Colors in Titration

Common pH Indicators : Common pH Indicators Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 520

Edible Acid-Base Indicators : Edible Acid-Base Indicators COLOR CHANGES AS A FUNCTION OF pH INDICATOR pH 2 3 4 5 6 7 8 9 10 11 12 RED APPLE SKIN BEETS BLUEBERRIES RED CABBAGE CHERRIES GRAPE JUICE RED ONION YELLOW ONION PEACH SKIN PEAR SKIN PLUM SKIN RADISH SKIN RHUBARB SKIN TOMATO TURNIP SKIN * *YELLOW at pH 12 and above

Phenolphthalein Indicator : Phenolphthalein Indicator Colorless = Acidic pH Pink = Basic pH H+

Slide 17 : (Colorless acid form, HIn) (Pink base form, In-)