MIDTERM 2 pH Indicators

Question 1

Purpose of pH indicators

Answer 1

To identify unknown organisms/ to characterize the behavior of organisms based on the production of acidic/alkaline products ( or the removal of acidic or alkaline substrates from a medium )

Question 2

Where are most pH indicators derived from?

Answer 2

originally derived from plants for use as dyes

Question 3

how does a pH indicator work?

Answer 3

1. They change in color with a change in pH

2. change color when they bind hydrogen or hydroxyl ions in solution

Question 4

How to know which pH indicator to use?

Answer 4

Each of the dyes used as a pH indicator has a defined pH range in which it may be used

Question 5

True or false: more pH indicators are used to detect acid production than alkali production

Answer 5

True

Question 6

Common feature of most pH indicators?

Answer 6

the color change from the starting color is not visually indentifiable until some percentage of the dye ( at least 10%) has changed its state of protonation

Question 7

Problem with pH indicators?

Answer 7

In between two distinct color states, the color continues to change with the change in pH but the incremental color changes are not sufficiently distinct to indentify as a specific color.

Question 8

How to interpret phenol red pH indicator

Answer 8

1. Phenol red changes from red–>yellow

2. It goes from several shades of reddish yellow or yellowish red that are difficult to interpret.

Question 9

What is Standard diagnostic procedure?

Answer 9

A reaction is not designated as positive until all the dye has completed the color change and any intermediate color is designated as a negative result

Question 10

What allows pH indicators to be sensitive to small amounts of acid or alkali production and the pH range of these indicators to be around 2 pH unit?

Answer 10

Most dyes are intensely colored, the concentration of the dye used is usually small and the amount of acid or alkali that is required to complete the color change is small as well

Question 11

Methly Red statistics? Low pH color, Transition pH range, and high pH color

Answer 11

1. low pH color = Red
2. Transition pH range = 4.4-6.2
3. High pH color = yellow

Question 12

Bromothymol Blue statistics? Low pH color, Transition pH range, and high pH color

Answer 12

1. low pH color = yellow
2. Transition pH range = 6.0-7.6
3. High pH color = blue

Question 13

Phenol Red statistics? Low pH color, Transition pH range, and high pH color

Answer 13

1. low pH color = yellow
2. Transition pH range = 6.8-8.4
3. High pH color = red

Question 14

Neutral Red statistics? Low pH color, Transition pH range, and high pH color

Answer 14

1. low pH color = red
2. Transition pH range = 6.8-8.0
3. High pH color = yellow