BMSC 240 Final Exam Questions with
Verified Answers
Micropipette - ANSWER-A laboratory instrument used to measure, dispense, and
transfer very small amounts of liquid
Sub mL measurements
P1000 (1000-100uL)
P200 (200-20uL)
P20 (20-2uL)
P10 (10-0.5uL)
Concentrated solutions - ANSWER-Have a large amount of solute compared to
solvent
Weight/volume OR weight/weight OR volume/volume
1% = 1g/100mL
What is the % w/v, when 80mL of 2.0% solution is mixed with 50mL of 6.0% solution
- ANSWER-If most concentrated is 6% and least is 2%, the mixture will have to be
between them
2g/100mL x 80mL = 1.6g
6g/100mL x 50mL = 3g
4.6g/130mL = 3.5% m/v
10x TE is 0.1M Tris-Cl and 0.01M EDTA. It is commonly made from 1M Tris-Cl and
0.5M EDTA stock solution. How much EDTA is needed (mL) to make 500mL -
ANSWER-Only care about EDTA
C1V1 = C2V2
(0.5M)V1 = (0.01M)(500mL)
(0.5M)V1 = 5M•mL
V1 = 10mL
Acid - ANSWER-Proton donor
Increases concentration of protons when introduced to solution
Base - ANSWER-Proton acceptor
Decreases concentration of protons when introduced to solution
Water ~55mol/L - ANSWER-H2O —> H+ + OH-
10-14 —> 10-7 + 10-7
Strong acids & bases - ANSWER-Completely dissociate in solution
Buffers - ANSWER-Do NOT completely dissociate
Acid donates a proton to its conjugate base
,Uses weak acids & bases
Buffer neutralizes some of the acid (if basic) and base (is acidic)
Minimizes pH change
Only effective in +/- 1 pH from pKa
Math for mixing a buffer - ANSWER-Henderson hasselbalch
pH = pKa + log [base]/[acid]
pKa - intrinsic property
[ ] - concentration, change to make desired buffer
Ratio of [base] to [acid] - ANSWER-pH = pKa + log [b]/[a]
b=#,a=1
For base - # / total (b + a)
For acid - 1 / total (b + a)
Ratios give % of each acid & base
Comparing pH to pKa - ANSWER-If the pH is larger than the pKa, the buffer has
more base
If the pH is less than the pKa, the buffer has more acid
Dilutions - ANSWER-Making a solution less concentrated
1 in 10 = 1/10th —> 10% concentration
1 to 10 = 1/11th —> 9% concentration
The smaller the # diluted to, the more the difference in in/to matters
1 in 2 = 1/2 —> 50%
1 to 2 = 1/3 —> 33%
You are making a buffer at pH 7.3, pKa is 7.45. What is the % acid needed in the
buffer? - ANSWER-pH = pKa + log [base]/[acid]
7.3 = 7.45 + log [base]/[acid]
-0.15 = log [base]/[acid]
10^-0.15 = [base]/[acid]
= 0.7079
For acid —> 1 / (1 + 0.7079) = 59%
Isoelectric point - ANSWER-Point at which a compound is electrically neutral
PI = (pKa1 + pKa2) / 2
Ave of pKa of interest
Titration - ANSWER-A solution of known concentration is used to determine the
concentration of another solution
Can start outside the buffer region
pKa is the flat region in the graph
If 2 pKa values are within 1 +/- range of each other, flat region will overlap
Effectiveness of heat killing (sterilized) - ANSWER-Temp Time Conductance
Work together, inc one dec the others
,Autoclave - ANSWER-Piece of equipment used to sterilize with steam under
pressure and/or dry heat
Increased pressure = boiling point inc (121*C)
Steam filled chamber = more conductance
What will happen if you put a sealed container in an autoclave - ANSWER-The
container will implode - due to the difference of pressure inside/outside the container
Sterilize through filtration - ANSWER-When heat CANT be used (heat liable
compounds)
Liquid passes through filter - filter holes MUST be smaller then bacteria (0.2um)
Won't filter viruses (very small)
Basic microscope - ANSWER-Objective lens - bigger & more detail
Ocular lens - empty magnification - bigger, no more detail
Thickness of section - thinner = higher quality
Lighting - angle of light & brightness
Quality/cleanliness of lens
Staining - makes non visible visible - contrast
Resolution - ANSWER-R = 0.61(wavelength) / NA
NA = n sin theta
n = refractive index
R = 0.61(wavelength) / n sin theta
n sin theta also the aperture or focal length
How is resolution improved - ANSWER-Improved = smaller R value
R = (decreased)/(increased) —> will lower R
Dec wavelength
Inc refractive index (oil Emerson)
Inc angle
Overall magnification - ANSWER-objective lens x eyepiece lens
Inc magnification = dec field of view
To estimate size of things, need to know the size of the field of view
Spectrophotometry - ANSWER-An analytical method for identifying a substance by
its selective absorption of different wavelengths of light
Higher energy - shorter wavelength (blue)
Lower energy - higher wavelength (red)
Looks at BOTH absorbance & transmittance
Triprotic amino acids - ANSWER-7 amino acids - ionizable group on their side chain
- R group that can act as an acid/conjugate base pair
, 3rd pKa
Can buffer at additional pH region
Absorbance - ANSWER-the amount of light absorbed by a sample (the amount of
light that is blocked)
Transmittance - ANSWER-The amount of light passing through the sample
100% - fully transparent
0% - fully blocked
Can convert between absorbance & transmittance - ANSWER-Absorbance (A) = log
(1 / transmittance)
Transmittance (T) - is a decimal value
Log scale - values typically between 0-2
Standard curve - ANSWER-A series of known samples used to generate comparison
data for unknowns
Don't need to know all concentrations, can determine in betweens
Transmittance vs. Absorbance - ANSWER-100% T = 0 A
50% T = 0.3 A
10% T = 1 A
1% T = 2 A
Absorbance as logarithm
A student records in transmittance (67%) instead of absorbance, can absorbance be
found - ANSWER-Yes, can convert with A = log (1/T)
A = log (1/0.67)
A = 0.187
You were able to see your specimen using the 10x objective, but switching to 100x
you can't find it. You should - ANSWER-Adjust fine focus
Move stage around
Go back to 10x, make sure sample is in centre
100x needs oil
When should the spectrophotometer be re-zeroed - ANSWER-When ever the
controlled variable is changed (water vs ethanol)
Changing the wavelength
Changing the cuvette
Absorption spectrum pattern - ANSWER-Is unique to each compound
• can measure sample at multiple wavelengths to find optimum
The colour of light that is NOT absorbed is - ANSWER-The colour of appears
What wavelength should be used to measure a specific compound in an impure
mixture - ANSWER-A wavelength where only the specific compound is found
Verified Answers
Micropipette - ANSWER-A laboratory instrument used to measure, dispense, and
transfer very small amounts of liquid
Sub mL measurements
P1000 (1000-100uL)
P200 (200-20uL)
P20 (20-2uL)
P10 (10-0.5uL)
Concentrated solutions - ANSWER-Have a large amount of solute compared to
solvent
Weight/volume OR weight/weight OR volume/volume
1% = 1g/100mL
What is the % w/v, when 80mL of 2.0% solution is mixed with 50mL of 6.0% solution
- ANSWER-If most concentrated is 6% and least is 2%, the mixture will have to be
between them
2g/100mL x 80mL = 1.6g
6g/100mL x 50mL = 3g
4.6g/130mL = 3.5% m/v
10x TE is 0.1M Tris-Cl and 0.01M EDTA. It is commonly made from 1M Tris-Cl and
0.5M EDTA stock solution. How much EDTA is needed (mL) to make 500mL -
ANSWER-Only care about EDTA
C1V1 = C2V2
(0.5M)V1 = (0.01M)(500mL)
(0.5M)V1 = 5M•mL
V1 = 10mL
Acid - ANSWER-Proton donor
Increases concentration of protons when introduced to solution
Base - ANSWER-Proton acceptor
Decreases concentration of protons when introduced to solution
Water ~55mol/L - ANSWER-H2O —> H+ + OH-
10-14 —> 10-7 + 10-7
Strong acids & bases - ANSWER-Completely dissociate in solution
Buffers - ANSWER-Do NOT completely dissociate
Acid donates a proton to its conjugate base
,Uses weak acids & bases
Buffer neutralizes some of the acid (if basic) and base (is acidic)
Minimizes pH change
Only effective in +/- 1 pH from pKa
Math for mixing a buffer - ANSWER-Henderson hasselbalch
pH = pKa + log [base]/[acid]
pKa - intrinsic property
[ ] - concentration, change to make desired buffer
Ratio of [base] to [acid] - ANSWER-pH = pKa + log [b]/[a]
b=#,a=1
For base - # / total (b + a)
For acid - 1 / total (b + a)
Ratios give % of each acid & base
Comparing pH to pKa - ANSWER-If the pH is larger than the pKa, the buffer has
more base
If the pH is less than the pKa, the buffer has more acid
Dilutions - ANSWER-Making a solution less concentrated
1 in 10 = 1/10th —> 10% concentration
1 to 10 = 1/11th —> 9% concentration
The smaller the # diluted to, the more the difference in in/to matters
1 in 2 = 1/2 —> 50%
1 to 2 = 1/3 —> 33%
You are making a buffer at pH 7.3, pKa is 7.45. What is the % acid needed in the
buffer? - ANSWER-pH = pKa + log [base]/[acid]
7.3 = 7.45 + log [base]/[acid]
-0.15 = log [base]/[acid]
10^-0.15 = [base]/[acid]
= 0.7079
For acid —> 1 / (1 + 0.7079) = 59%
Isoelectric point - ANSWER-Point at which a compound is electrically neutral
PI = (pKa1 + pKa2) / 2
Ave of pKa of interest
Titration - ANSWER-A solution of known concentration is used to determine the
concentration of another solution
Can start outside the buffer region
pKa is the flat region in the graph
If 2 pKa values are within 1 +/- range of each other, flat region will overlap
Effectiveness of heat killing (sterilized) - ANSWER-Temp Time Conductance
Work together, inc one dec the others
,Autoclave - ANSWER-Piece of equipment used to sterilize with steam under
pressure and/or dry heat
Increased pressure = boiling point inc (121*C)
Steam filled chamber = more conductance
What will happen if you put a sealed container in an autoclave - ANSWER-The
container will implode - due to the difference of pressure inside/outside the container
Sterilize through filtration - ANSWER-When heat CANT be used (heat liable
compounds)
Liquid passes through filter - filter holes MUST be smaller then bacteria (0.2um)
Won't filter viruses (very small)
Basic microscope - ANSWER-Objective lens - bigger & more detail
Ocular lens - empty magnification - bigger, no more detail
Thickness of section - thinner = higher quality
Lighting - angle of light & brightness
Quality/cleanliness of lens
Staining - makes non visible visible - contrast
Resolution - ANSWER-R = 0.61(wavelength) / NA
NA = n sin theta
n = refractive index
R = 0.61(wavelength) / n sin theta
n sin theta also the aperture or focal length
How is resolution improved - ANSWER-Improved = smaller R value
R = (decreased)/(increased) —> will lower R
Dec wavelength
Inc refractive index (oil Emerson)
Inc angle
Overall magnification - ANSWER-objective lens x eyepiece lens
Inc magnification = dec field of view
To estimate size of things, need to know the size of the field of view
Spectrophotometry - ANSWER-An analytical method for identifying a substance by
its selective absorption of different wavelengths of light
Higher energy - shorter wavelength (blue)
Lower energy - higher wavelength (red)
Looks at BOTH absorbance & transmittance
Triprotic amino acids - ANSWER-7 amino acids - ionizable group on their side chain
- R group that can act as an acid/conjugate base pair
, 3rd pKa
Can buffer at additional pH region
Absorbance - ANSWER-the amount of light absorbed by a sample (the amount of
light that is blocked)
Transmittance - ANSWER-The amount of light passing through the sample
100% - fully transparent
0% - fully blocked
Can convert between absorbance & transmittance - ANSWER-Absorbance (A) = log
(1 / transmittance)
Transmittance (T) - is a decimal value
Log scale - values typically between 0-2
Standard curve - ANSWER-A series of known samples used to generate comparison
data for unknowns
Don't need to know all concentrations, can determine in betweens
Transmittance vs. Absorbance - ANSWER-100% T = 0 A
50% T = 0.3 A
10% T = 1 A
1% T = 2 A
Absorbance as logarithm
A student records in transmittance (67%) instead of absorbance, can absorbance be
found - ANSWER-Yes, can convert with A = log (1/T)
A = log (1/0.67)
A = 0.187
You were able to see your specimen using the 10x objective, but switching to 100x
you can't find it. You should - ANSWER-Adjust fine focus
Move stage around
Go back to 10x, make sure sample is in centre
100x needs oil
When should the spectrophotometer be re-zeroed - ANSWER-When ever the
controlled variable is changed (water vs ethanol)
Changing the wavelength
Changing the cuvette
Absorption spectrum pattern - ANSWER-Is unique to each compound
• can measure sample at multiple wavelengths to find optimum
The colour of light that is NOT absorbed is - ANSWER-The colour of appears
What wavelength should be used to measure a specific compound in an impure
mixture - ANSWER-A wavelength where only the specific compound is found
