AH Biology - Unit 1 - KA1(b) - Liquids and Solutions

What are the two important types of dilution?

The two important types of dilution are:

• Linear dilution

• Serial/Log Dilutions

What is a linear dilution?

A linear dilution is a type of dilution where a series of dilutions differ by an equal interval. For example, 0.1, 0.2, and 0.3.

What is a serial/log dilution?

A serial/log dilution is a type of dilution where the series of dilutions differ by a constant proportion. For example, 1, 0.1, and 0.01.

How is a standard curve produced?

A standard curve is produced by plotting measured values for known concentration to produce a line or a curve. This line or curve can then be used to determine the concentration of an unknown concentration.

What are buffers?

Buffers are chemicals whose pH changes very little when acids or alkalis are added to them.

Why are buffers added to reaction mixtures?

Buffers are added to reaction mixtures to keep the pH of the reaction mixture constant throughout the chemical reaction.

What is a colorimeter?

A colorimeter is a piece of equipment used to measure absorbance or transmission of a solution.

How does a colorimeter work?

A colorimeter works by:?

• Light passes through a coloured filter and the cuvette containing the solution.

• Some of the light is absorbed as it passes through the solution.

• The rest of the light passes through and is recorded by a sensor.

• From this, the proportion of the total light that has reached the sensor can be calculated.

What must be done to the colorimeter?

The colorimeter must be calibrated with a suitable blank between readings as a baseline.

What is absorbance in the context of colorimetry, and what is it used to determine?

Absorbance is how much light has been absorbed and not reached the sensor. This can then be used to determine the concentration of a coloured solution.

What is percentage transmission, and what is it used to determine?

Percentage transmission is how much light has reached the sensor, and is used to determine turbidity in cell suspensions.