Indicators and pH
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Transcript of Indicators and pH
Indicators and pH
To learn about pH and how indicators
show a substance to be an acid or a base.
Objective:
Research:
Acid: solutions – high concentration of H3O
+ ions. Hydronium Base: solutions – high concentration of
OH- ions. Hydroxyl pH: percent of hydrogen – how acidic it
is.
pH scale: series of numbers 0-14. 7= neutral, 0-6 acid, 8-14 base.
Indicator: substance that shows a definite color change when mixed with acid or base.
Effect on Acids Effect on Bases
Blue litmus paper: pink ___ Red litmus paper: ___ blue Phenolphthalein: stays clear shocking pink Bromthymol blue: orange ___ Congo red: blue ___
• As the pH of a solution changes, the indicator shows a specific color change.
Procedure I – AcidAfter each step, record your
observations.
Drop a small drop of HCl onto blue litmus paper. Drop a small drop of HCl onto red litmus paper. Place a small amount of HCl into test tube A.
Add 1 drop of phenolphthalein. Rinse TT. Place a small amount of HCl into test tube A.
Add 2 drops of bromthymol blue. Rinse TT. Place a small amount of HCl into test tube A.
Add 1 drop of congo red. Rinse TT.
Procedure II – BaseAfter each step, record your
observations.
Drop a small drop of NaOH onto blue litmus paper.
Drop a small drop of NaOH onto red litmus paper.
Place a small amount of NaOH into test tube B.Add 1 drop of phenolphthalein. Rinse TT.
Place a small amount of NaOH into test tube B.Add 1 drop of bromthymol blue. Rinse TT.
Place a small amount of NaOH into test tube B.Add 1 drop of congo red. Rinse TT.
Reaction with Acid Base
Blue litmus paper
Red litmus paper
Phenolphthalein
Bromthymol blue
Congo red