1.1 Liquids and Solutions

Question 1

Linear dilutions

Answer 1

Dilutions in a linear dilution series differ by an equal interval, for example 0.1, 0.2, 0.3 etc.

Question 2

Log dilutions

Answer 2

Dilutions differ by a constant proportion, for example 10-1, 10-2, 10-3 etc.

Question 3

Standard curve to determine unknown

Answer 3

Plotting measured values for known concentrations to produce a line or curve, allows the concentration of an unknown to be determined from the standard curve.

Question 4

Buffers to control pH

Answer 4

Addition of acid or alkali has very small effects on the pH of a buffer, allowing the pH of a reaction mixture to be kept constant.

Question 5

Colorimeters

Answer 5

Used to quantify concentration and turbidity. Before use they need to be calibrated with an appropriate blank sample to provide a baseline reading.
absorbance of solution can be used to determine concentration of a coloured solution using suitable wavelength filters.
Percentage transmission can be used to determine turbidity, such as cells in suspension.

Question 6

How colorimeters work?

Answer 6

Light is split into its component colours and filtered so there is one wavelength of light. This is then passed through the sample solution where a dector picks up how much light has been absorbed by the sample or transmitted.

Question 7

What are colorimeters used for?

Answer 7

Finding the density of a cell culture growing in a liquid broth.

Quantifying the result of an ELISA demonstration.