QC Lab - Experiment 1: Preparation Test Solutions and Indicator

test solutions

TS

•A solution of a reagent in a specified strength, used in chemical analysis or testing

pH

- power of hydrogen

-developed by Soren Sorensen (danish scientist) = easier system for indicating the concentration of hydrogen ions

pH scale

acidic

0-6 = high concentration of H ions

- bronsted-lowry theory: proton donor

neutral

7 = equal concentration of H and Hydroxyl ions

basic/alkaline

7-14 = low concentration of H but high concentration of OH (hydroxyl ions)

- bronsted-lowry theory: proton acceptor

indicator

•A substance that changes color in response to a chemical change.

•complex organic compounds used:

✔️_ To determine the end points in neutralization process

ü_ To determine the hydrogen ion concentration

ü_ To indicate that the desired change in pH has been effected

•A drop of ? solution is added to titration in the beginning and the change of color signifies that the reaction is completed.

•The ? changes color when the reaction has reached the equivalence point or stoichiometric point

- will change color if pH is within pH scale

rules for indicators

•Use 3 drops of indicator test solution for a titration unless otherwise directed

•When a strong acid is titrated with a strong alkali, or a strong alkali with a strong acid, Methyl Orange, Methyl Red, or Phenolphthalein may be used

•When a weak acid is titrated with a strong alkali, use phenolphthalein

•When a weak alkali is titrated with a strong acid, use methyl red

•A weak alkali should never be titrated with a weak acid and vice versa, since there will not be a sharp end point.

•Presence of a color is more easily observable compared to a disappearance of a color, titrate to a color.

strong acid + strong base (vv)

(titrate) methy red, methyl orange, phenolphthalein

weak acid + strong base

Phenolphthalein

strong acid + weak base

methyl red

weak acid + weak base (vv)

never titrate because endpoint will not be sharp

colorless = colored (always)

malachite green

0.0-2.0

acid: yellow

base: green

methyl yellow

2.9-4.0

acid: red

base: yellow

bromophenol blue

3.0-4.6

acid: yellow

base: blue

methyl orange

3.2-4.4

acid: pink

base: yellow

bromocresol green

4.0-5.4

acid: yellow

base: blue

methyl red

4.2-6.2

acid: red

base: yellow

bromocresol purple

5.2-6.8

acid: yellow

base: purple

bromothymol blue

6.0-7.6

acid: yellow

base: blue

phenol red

6.8-8.2

acid: yellow

base: red

cresol red

7.2-8.8

acid: yellow

base: red

thymol blue

8.0-9.2

acid: yellow

base: blue

phenolphthalein

8.0-10 (basic medium)

acid: colorless

base: pink

thymolphthalein

9.3-10.5

acid: colorless

base: blue