Practical 1- serial dilution and standard curve Flashcards
What is a solution?
homogenous mixture of 2 or more substances
What states can a mixture be?
Solid
Liquid
Gas
What is a stock solution?
concentrated solution of known concentration that needs to be diluted before you use it
What is wet chemistry?
working with liquids
What will often be done to a stock solution?
dilute it to a working stock solution which is less concentrated
What is the concentration of a substance?
How much of the solute is present per unit volume
What is a solute?
Something that has been dissolved into solvent
What are the common concentrations units?
Molarity (M)
Mass/volume
Normality (N)
What is molarity (M)?
molecules of a substance per unit volume or moles per litre (molar)
What are examples of Mass/ volume?
Milligrams
Litres
What is Normality (N) used for?
moles of active ions
usually for ionic solution to report ionic strength
What is dilution?
using a solvent (e.g. water) to decrease the concentration of a solution
What reasons might you dilute a concentrated stock solution?
when need low concentration solution difficult to accurately measure small mass/ volume
weigh large volume/ mass to make high concentration then dilute to what needed
What is a serial dilution?
we dilute a substance and then further dilute the product until we have a very dilute substance
What are the 2 options in the processes of serial dilution?
weigh large amount and get larger solution then need (lots of waste)
smaller volume to high concentration and dilute to needed
What can serial dilution be used to create?
a calibration curve
What is a calibration curve?
an analytical technique that allows
us to find the concentration of an unknown solution
What can you measure to form a calibration curve?
absorbance (colour) of solution
What does having the absorbance of solution allow for?
it means that we are able to plot known concentration against absorbance value
What can be added to the graph for serial dilution to find the equation line?
a line of best fit
What does re-arranging equation of the line allow us to calculate? (serial dilution practical)
unknown absorbance from an unknow concentration
What should the range in concentrations on the calibration curve do with the unknown sample?
included within the range
What is used to measure absorbance?
Using spectrophotometers
What is the optimum wavelength to measure crystal violet?
590nm
What symbol is used to represent the wavelength of electromagnetic radiation?
upside down Y (Lambda)
How much light does each molecule of crystal violet absorbed?
one unit
What does more crystal violet (CV) mean for adsorption?
greater adsorption
What is the formula for the Beer-Lambert law?
A= ElC
What do the letters in the Beer-Lambert formula mean?
A= absorbance
E= molar absorptivity or (extinction coefficient solution dependant)
l= path (1cm)
C= concentration (M)
What does the beer lambert law describe?
the relationship between the absorbance of a solution and its concentration (directly proportional)
What is the amount of light absorbed proportional to?
concentration
What do you have to make sure to do with the dilution factor?
keep it constant
What dies keeping the dilution factor constant allow for?
geometric progression of
the concentration in a logarithmic fashion
What is a standard curve?
analytical technique that allows us to determine the concentration of
substance
How do you produce a standard curve?
measuring several “standards” of known concentration to
produce an equation
What equipment is needed for the practical? (Crystal violet practical)
Four 100 mL Beakers
Six 250 mL Beakers
50 mL Graduated Cylinder
Glass Stirring rod
Grease Pencil
Cuvette
Spectrophotometer
10 mL Stock solution of Crystal violet (1.50 X 10-4 M) in water
2 unknown dilutions of the crystal violet stock solution
Kimwipes
What will the waste from the serial dilution practical be?
crystal violet solution
What is the problem with waste crystal violet solution?
very toxic to aquatic organisms
(especially bacteria)
What should not be done with waste crystal violet solution?
do not pour down sink instead put into waste bucket
What has to be done to crystal violet solution before being disposed of?
must be neutralised
What is step 1 of the procedure for serial dilution?
place crystal violet stock solution in 100ml beaker
What do you do once the crystal violet stock solution has been added to the beaker?
Dilute the crystal violet stock solution 1:9 with water
Why do you dilute the crystal violet stock solution?
provide you with a working stock solution
What will the working stock solution concentration be after the water has been added ratio 1:9?
1.50 X 10-5M
What step is done once you have your working stock soultion?
make 6 solutions of the dye using the serial dilation instructions
How many paper towels will you need and what should you do with them? (Crystal violet practical)
6 towels in a row
label solution towels (1,2,3)
250 ml beaker on each towel
What do you do to get your first solution (solution 1)? (serial dilution- crystal violet)
Use graduated cylinder
mix 40 mL working stock with 40mL deionized water into beaker 1
Once you’ve created solution how do you get further solutions 2,3,4,5,6?
Mix 40mL solution (1) with 40mL of deionized water into beaker 2
(repeat this adding the new solution into the next beaker)
What must you ensure when using the spectrophotometer?(crystal violet practical)
switched on and set to 590 nanometers
What must you do to blank the spectrophotometer?o
fill to the measurement line with blanking solution
Blank the instrument using the blue blank button
What must you do with the cuvette once filled with water? (Crystal violet practical)
Tip out the water from the cuvette and then place your least concentrated solution (i.e solution 6) in the same cuvette.
When you have put your least concentrated solution (solution 6) in the cuvette what do you do?
read absorbance on spectrophotometer
What must you do to ensure a good result from the spectrophotometer?
take multiple readings
When you have ensured a good result what must you do with the solution and cuvette?
tip them into the waste bin
What do you do to get the readings for all the solutions? (Crystal violet solution)
repeat using the cuvette with distilled water then the solution up to the most concentrated ensuring to get multiple results for each
Once you have gotten all your results from the solutions what do you do? (serial dilution)
Take the mean of your multiple readings to give one reading for each solution
and make a rough plot of absorbance (au) against the concentration (M)
What should the plotted line for absorbance against concentration go through?
the origin so both are at zero
How will Beers-Law affect the line plotted for absorbance against concentration?
should be fairly straight except for highest concentration
What data should be ignored? (Crystal violet graph)
any that falls out of linear region
What is the first step to determine the unknown concentration of 2 samples? (Crystal violet practical)
Measure each sample at 590nm
What does it mean if the unknown samples are outside linear range? (Crystal violet)
The absorbance is greater than the absorbance of your highest or lowest standard
If the absorbance is outside linear range what should you do?
dilute to inside your range (noting
down how much you diluted by) and re-measure the absorbance at 590 nm
How do you find out the concentration of the unknown solutions?(crystal violet)
use the standard curve with known absorbable reversing the equation of the line and then give answer in moles/litres
