Liquids And Solutions

Question 1

Benefit of solutions

Answer 1

Solutions allow you to transfer parts for sampling and can be diluted so you can better analyse

Question 2

What are standard flasks and solutions used for

Answer 2

A standard flask is used where you need to make up a specific volume of solution.
Also used to make up standard solutions

Question 3

What is a standard solution

Answer 3

When there is a known concentration of the solution

Question 4

How to make standard solution

Answer 4

Dissolve sample in clean beaker 
Empty into flask
Rinse beaker with solvent and add washings to flask
Fill to graduation mark
Always read the base of meniscus

Question 5

Possible apparatus

Answer 5

Standard flasks and solutions
Pipettes
Micropipettes
Burettes

Question 6

Benefit of micropipettes

Answer 6

Disposable tip means can cut down contamination risk when taking samples

Question 7

When are burettes used

Answer 7

Titrations

Setting volumes for dilution

Question 8

What is linear dilution series and what could it be used for

Answer 8

Range of solutions that differ by an equal interval for example 0.1,0.2,0.3ml (small range)
Each concentration should be made individually so any measurement errors only affect the one concentration

It could be used to measure enzyme activity against substrate concentration

Question 9

What is log/serial dilution series and what could it be used for

Answer 9

Consists of a range of dilution that differ by constant proportion for example 100, 10, 1, 0.1, 0.001 ml
Use if range is much larger than linear
Errors are compounded in later dilutions as each conc depends on the previous dilution

Often used in direct count methods for cells

Question 10

What are colorimeter used for and how do they work

Answer 10

Used to measure the concentration of a pigment in a solution, the turbid of liquid or density of cells in a culture.
Records how much light is absorbed, so concentration can be determined
E.G. The density of a cell culture growing in a liquid broth

Question 11

How does standard curve for determining an unknown work

Answer 11

Standard curve is made by plotting the absorbency readings for a series of unknown concentrations. Once the standard curve has been produced it can be used as a reference for samples of unknown concentrations of the same substance or culture. The concentration of the unknown can be estimated through interpolation .

Question 12

What is a buffer and how does it work

Answer 12

A buffer is a solution which sets the pH and then resists change to that pH.
A lot of biological systems only work in a particular pH range and within that range there will be an optimum.