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30019- Molecules to Materials: deconstructing the environment > Practical 1- serial dilution and standard curve > Flashcards

Practical 1- serial dilution and standard curve Flashcards

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Organic Chemistry 101 flashcards
1
Q

What is a solution?

A

homogenous mixture of 2 or more substances

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2
Q

What states can a mixture be?

A

Solid
Liquid
Gas

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3
Q

What is a stock solution?

A

concentrated solution of known concentration that needs to be diluted before you use it

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4
Q

What is wet chemistry?

A

working with liquids

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5
Q

What will often be done to a stock solution?

A

dilute it to a working stock solution which is less concentrated

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6
Q

What is the concentration of a substance?

A

How much of the solute is present per unit volume

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7
Q

What is a solute?

A

Something that has been dissolved into solvent

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8
Q

What are the common concentrations units?

A

Molarity (M)
Mass/volume
Normality (N)

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9
Q

What is molarity (M)?

A

molecules of a substance per unit volume or moles per litre (molar)

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10
Q

What are examples of Mass/ volume?

A

Milligrams
Litres

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11
Q

What is Normality (N) used for?

A

moles of active ions
usually for ionic solution to report ionic strength

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12
Q

What is dilution?

A

using a solvent (e.g. water) to decrease the concentration of a solution

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13
Q

What reasons might you dilute a concentrated stock solution?

A

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

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14
Q

What is a serial dilution?

A

we dilute a substance and then further dilute the product until we have a very dilute substance

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15
Q

What are the 2 options in the processes of serial dilution?

A

weigh large amount and get larger solution then need (lots of waste)
smaller volume to high concentration and dilute to needed

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16
Q

What can serial dilution be used to create?

A

a calibration curve

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17
Q

What is a calibration curve?

A

an analytical technique that allows
us to find the concentration of an unknown solution

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18
Q

What can you measure to form a calibration curve?

A

absorbance (colour) of solution

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19
Q

What does having the absorbance of solution allow for?

A

it means that we are able to plot known concentration against absorbance value

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20
Q

What can be added to the graph for serial dilution to find the equation line?

A

a line of best fit

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21
Q

What does re-arranging equation of the line allow us to calculate? (serial dilution practical)

A

unknown absorbance from an unknow concentration

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22
Q

What should the range in concentrations on the calibration curve do with the unknown sample?

A

included within the range

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23
Q

What is used to measure absorbance?

A

Using spectrophotometers

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24
Q

What is the optimum wavelength to measure crystal violet?

A

590nm

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25
Q

What symbol is used to represent the wavelength of electromagnetic radiation?

A

upside down Y (Lambda)

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26
Q

How much light does each molecule of crystal violet absorbed?

A

one unit

27
Q

What does more crystal violet (CV) mean for adsorption?

A

greater adsorption

28
Q

What is the formula for the Beer-Lambert law?

A

A= ElC

29
Q

What do the letters in the Beer-Lambert formula mean?

A

A= absorbance
E= molar absorptivity or (extinction coefficient solution dependant)
l= path (1cm)
C= concentration (M)

30
Q

What does the beer lambert law describe?

A

the relationship between the absorbance of a solution and its concentration (directly proportional)

31
Q

What is the amount of light absorbed proportional to?

A

concentration

32
Q

What do you have to make sure to do with the dilution factor?

A

keep it constant

33
Q

What dies keeping the dilution factor constant allow for?

A

geometric progression of
the concentration in a logarithmic fashion

34
Q

What is a standard curve?

A

analytical technique that allows us to determine the concentration of
substance

35
Q

How do you produce a standard curve?

A

measuring several “standards” of known concentration to
produce an equation

36
Q

What equipment is needed for the practical? (Crystal violet practical)

A

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

37
Q

What will the waste from the serial dilution practical be?

A

crystal violet solution

38
Q

What is the problem with waste crystal violet solution?

A

very toxic to aquatic organisms
(especially bacteria)

39
Q

What should not be done with waste crystal violet solution?

A

do not pour down sink instead put into waste bucket

40
Q

What has to be done to crystal violet solution before being disposed of?

A

must be neutralised

41
Q

What is step 1 of the procedure for serial dilution?

A

place crystal violet stock solution in 100ml beaker

42
Q

What do you do once the crystal violet stock solution has been added to the beaker?

A

Dilute the crystal violet stock solution 1:9 with water

43
Q

Why do you dilute the crystal violet stock solution?

A

provide you with a working stock solution

44
Q

What will the working stock solution concentration be after the water has been added ratio 1:9?

A

1.50 X 10-5M

45
Q

What step is done once you have your working stock soultion?

A

make 6 solutions of the dye using the serial dilation instructions

46
Q

How many paper towels will you need and what should you do with them? (Crystal violet practical)

A

6 towels in a row
label solution towels (1,2,3)
250 ml beaker on each towel

46
Q

What do you do to get your first solution (solution 1)? (serial dilution- crystal violet)

A

Use graduated cylinder
mix 40 mL working stock with 40mL deionized water into beaker 1

47
Q

Once you’ve created solution how do you get further solutions 2,3,4,5,6?

A

Mix 40mL solution (1) with 40mL of deionized water into beaker 2
(repeat this adding the new solution into the next beaker)

48
Q

What must you ensure when using the spectrophotometer?(crystal violet practical)

A

switched on and set to 590 nanometers

49
Q

What must you do to blank the spectrophotometer?o

A

fill to the measurement line with blanking solution
Blank the instrument using the blue blank button

50
Q

What must you do with the cuvette once filled with water? (Crystal violet practical)

A

Tip out the water from the cuvette and then place your least concentrated solution (i.e solution 6) in the same cuvette.

51
Q

When you have put your least concentrated solution (solution 6) in the cuvette what do you do?

A

read absorbance on spectrophotometer

52
Q

What must you do to ensure a good result from the spectrophotometer?

A

take multiple readings

53
Q

When you have ensured a good result what must you do with the solution and cuvette?

A

tip them into the waste bin

54
Q

What do you do to get the readings for all the solutions? (Crystal violet solution)

A

repeat using the cuvette with distilled water then the solution up to the most concentrated ensuring to get multiple results for each

55
Q

Once you have gotten all your results from the solutions what do you do? (serial dilution)

A

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)

56
Q

What should the plotted line for absorbance against concentration go through?

A

the origin so both are at zero

57
Q

How will Beers-Law affect the line plotted for absorbance against concentration?

A

should be fairly straight except for highest concentration

58
Q

What data should be ignored? (Crystal violet graph)

A

any that falls out of linear region

59
Q

What is the first step to determine the unknown concentration of 2 samples? (Crystal violet practical)

A

Measure each sample at 590nm

60
Q

What does it mean if the unknown samples are outside linear range? (Crystal violet)

A

The absorbance is greater than the absorbance of your highest or lowest standard

61
Q

If the absorbance is outside linear range what should you do?

A

dilute to inside your range (noting
down how much you diluted by) and re-measure the absorbance at 590 nm

62
Q

How do you find out the concentration of the unknown solutions?(crystal violet)

A

use the standard curve with known absorbable reversing the equation of the line and then give answer in moles/litres

63
Q
A

30019- Molecules to Materials: deconstructing the environment (29 decks)

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