Lab

Question 1

solution

Answer 1

a random mixture of a soluble or ionizable molecule, the solute, in a liquid solvent
- solvent in living cells is always water, so the solutions in cells are said to be aqueous

Question 2

solute

Answer 2

each molecule has a unique degree of solubility in water, and this is a temperature-dependent phenomenon
- solubility increases with temperature

Question 3

suspension

Answer 3

a mixture of insoluble particles in a suspending fluid, in which the particles will eventually settle out due to gravity if allowed to stand for a sufficient time
- rate of this sedimentation or precipitation depends on the particle density

Question 4

methods of expressing concentration

Answer 4

• moles: one mole is the formula weight, in grams, of a molecule dissolved in one liter of water at standard temperature and pressure
• mass per unit volume: such as mg/L or µg/µL
• percentage: w/v is the number of parts of solute in 100 parts of the solvent or medium (ie. w/v 10% aqueous DMSO solution means 10 parts of DMSO in 100 total parts of water)

Question 5

dilution

Answer 5

adding water or some other fluid to a solution of known concentration, usually called the stock solution
-results in a reduction in concentration of the solution, because the solute molecules are now distributed in a larger volume of fluid

Question 6

making dilutions equation

Answer 6

C1V1 = C2V2

Where, C1 is the initial concentration;

            V1 is the initial volume;

            C2 is the desired final concentration;

            V2 is the final total volume.

• units used do not matter, as long as they are the same for C1 and C2 and the same for V1 and V2

Question 7

Beer-Lambert Law

Answer 7

A = kLC

Where, A is the absorbance;

            k is a wavelength-dependent molar absorptivity coefficient with units of M(^-1)cm(^-1);

            L is the length of the light path in cm;

            C is the concentration of the absorbing solution in moles/liter

-absorbance has no units, as the units on the right side of the equation cancel each other

Question 8

intensity, I

Answer 8

energy of the radiation per unit area per unit time
- used to measure the “amount” of electromagnetic radiation impinging on a solution

Question 9

percent transmittance, %T

Answer 9

%T = 100 It / I0
the intensity of the light falling on the sample, I0, and the light transmitted through the sample, It

Question 10

absorbance of a sample

Answer 10

A = log (100 / %T)
A = 2.000 - log (%T)
- absorbance of a sample exhibiting a percent transmittance of 100 (a completely transparent sample) will thus be 0
-each increment of increase in absorbance is equivalent to a ten times reduction in transmittance (t a sample that absorbs 10 % of the light will have A = 1; so a 1% transmittance corresponds to A = 2, and a 0.1% transmittance to A = 3, etc)

Question 11

Novaspec III+

Answer 11

allows the recording of absorbance, transmittance or concentration over the wavelength range 325 – 1100 nm