Acid Base Indicators

INDICATOR

pH RANGE

QUANTITY OF INDICATOR

PER 10 mL

ACID

ALKALINE

Thymol blue (A)*

1.2-2.8

1-2 drop of of 0.1% solution in aq.

Red

Yellow

Methyl orange (B)

3.1-4.4

1 drop of 0.1% solution in aq.

Red

Orange

Bromphenol blue (A)

3.0-4.6

1 drop of 0.1% solution in aq.

Yellow

Blue-Violet

Bromphenol green (A)

4.0-5.6

1 drop of 0.1% solution in aq.

Yellow

Blue

Methyl red (A)

4.4-6.2

1 drop of 0.1% solution in aq.

Red

Yellow

Bromcresol purple (A)

5.2-6.8

1 drop of 0.1% solution in aq.

Yellow

Purple

Bromthymol blue (A)

6.2-7.6

1 drop of 0.1% solution in aq.

Yellow

Blue

Phenol red (A)

6.4-8.0

1 drop of 0.1% solution in aq.

Yellow

Red

Neutral red (B)

6.8-8.0

1 drop of 0.1% solution in 70% alc.

Red

Yellow

Thymol blue (A)

8.0-9.6

1-5drops of 0.1% solution in aq.

Yellow

Blue

Phenolphthalein (A)

8.0-10.0

1-5 drops of 0.1% solution in 70% alc.

Colorless

Red

Thymolphthalein (A)

9.4-10.6

1drop of 0.1% solution in 90% alc

Colorless

Blue

A: Indicator of acid * For the acid range. B: Indicator of base For the alkaline range. Sodium salt.