Week 6 Flashcards
What are the two ways of diluting solutions ?
Simple Dilution
Serial dilution
What is a simple diluting solution?
A unit volume of a liquid material of interest is combined with an appropriate volume of a solvent liquid to achieve the desired concentration.
Example of a simple diluting solution?
1 litre of glucose solution mixed with 1l of water would give a solution half the concentration of the original glucose.
What is a series diluting solution?
A series of simple dilutions
The dilution factor is multiplied at each step
The dilution factor at any point in the series is the product of the individual dilution factors in each step up to it.
Errors can be made at each step! And these errors will multiple too!
Percent solutions: %(w/v)
The most common way of expressing a concentration in the Lab. = 1g in 100ml total volume = 1%
Percent solutions: %(v/v)
1ml of a substance in 100ml total solution = 1%
Percent solutions: %(w/w)
1g of a substance in 100g total = 1%
C1 x V1 = C2 x V2
C1 = Starting concentration
V1 = Starting volume
C2 = Final concentration
V2 = Final volume
Write an equation linking Mass, MW (molecular weight), Volume and Concentration
Mass = Conc x Vol x MW
Example question, calculating Mass.
250ml of 5M NaCl (MW 58.44 gmol-1) ?
MW = 58.44gmol-1 Concentration = 5M
Volume = 250ml/1000 = 0.25L
Mass = Conc x Vol x MW
5 x 0.25 x 58.44 = 73.05
Example question: What is the volume of Triton
50ml of 10% (v/v) Triton X-100 (supplied as a liquid at 100%)
Volume = 50ml
Concentration = 10ml (10%) of Triton X-100 per 100mL of solution
So, Volume of Triton = (Desired volume x Desired conc) / 100%
Vol of Triton = (50mL x 10) / 100 = 5mL
Example question: Calculating Mass
10ml of 1M DTT (MW 154.3 gmol-1)
Volume = 10ml/1000 = 0.01L Concentration = 1M MW = 154.3
Mass = Conc x Vol x MW
1M x 0.01L x 154.3 = 1.543g
Example question:
100ml of 500mM EDTA (MW 292.2 gmol-1)
Volume = 0.1L Concentration = 0.5M MW = 292.2
Mass = Vol x Conc x MW
0.1 x 0.5 x 292.2 = 14.61g
What is a line of best fit on a standard curve?
A straight line through data points on a scatter graph.
The best line has minimal distance between the line and the majority of data points. The line is an estimation of the linear equation that would best fit the data
Define interpolation?
Using known data to estimate the value of new data
What is Beer-Lambert law?
Absorbance and concentration have a linear relationship (A= ԑbC)
BUT as more light is absorbed by the sample, less light is transmitted and detected, so we need to adjust for this.
0 = 100%
5 = 0.001%
What do we need to think about when comparing methods?
- What was measured? (ie are the parameters directly comparable)
- What is practical in a lab setting?
- Is the difference significant
What is the P value to show whether a result is significant?
P = < 0.05
What does a small SD mean?
That most data points are close to the mean
What does the SD (standard deviation) tell us?
How much variability there is around the mean (for example, are the values clustered, or more evenly spaced)
Population SD
?
Measurements of all possible data points,
Less variability: than sample
Uses ‘n’
Sample SD?
Random sample of some of the population
Bigger SD than for SD.P as only representative
Uses ‘n-1’
What are the two different types of SD?
Population
Sample
When calculating the standard deviation for a data set, why is it necessary for the values for the differences to be squared?
it enables the negative values to be included in the calculation
