4.3 and 4.4 – Determine the turning point of one or more indicator(s).

TURNING POINT

The pH at which an indicator changes color is called its turning point

It is a gradual change from one color to another

Ex:1 2 3 4 5 6 7 8 9 10 11 12 13 14

Turning PointpH 3 – 4.4

What are the turning points for the indicators below?

Which indicator would be best to identify the pH 2.5 solution?

You have a solution with a pH of 2.5 You are given 3 different indicators.

pH

Indicator #1 Yellow Orange Red

Indicator #2 Yel

lowBrown

Violet

Indicator #3 Colorless Fuchsia

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Indicator #2Because its turning point is around 2.5

As mentioned earlier, one indicator may not give a precise value for

the solution, therefore, often a mix of indicators is used to help identify

the pH value.

Two indicators & their colour changes are shown below.

pH ScaleIndicator

1 2 3 4 5 6 7 8 9 10 11 12 13 14Methyl

Red Red Orange Yellow

If a mixture of these indicators were placed in a solution with a pH of 8, what colour would it turn? Green

Bromothymol Blue

Yellow Green

Blue

If a mixture of these indicators were placed in a solution with a pH of 5, what colour would it turn?

Orange - Yellow

pH ScaleIndicator

1 2 3 4 5 6 7 8 9 10 11 12 13 14#1 Colorless Pink

You mix all three indicators together. You add a drop of pH 8. What colour would it turn?

Green - Blue

#2 Yellow Green Blue

#3 Red Purple Blue

Three indicators & their colour changes are shown below.

pH ScaleIndicator

1 2 3 4 5 6 7 8 9 10 11 12 13 14#1 Colorless Pink

You have a unknown pH solution. It turns pink in indicator #1. It turns blue in indicator #2. What color would it turn in indicator #3?

Blue

#2 Yellow Green Blue

#3 Red Purple Blue

Three indicators & their colour changes are shown below.

pH ScaleIndicator

1 2 3 4 5 6 7 8 9 10 11 12 13 14#1 Colorless Pink

If these indicators were mixed together, what colours would they turn?

#2 Yellow Green Blue

Two indicators & their colour changes are shown below.

#1 & #2 Yellow Green Purple

pH ScaleIndicator

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Worksheet #8

References:

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