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BCCB2000 - Practical Exam Latest Update
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BCCB2000 - Practical ExamLatest Update
Water's ImportanceAnswer As most of the chemical reactions that occur in organisms
occur in water.
As many organic chemicals and ions in biochemistry dissolve in water.
As it is what makes molecules mobile and allows for interactions between them.
In transporting nutrients, metabolites, ions, drugs and waste products in vivo. • As it
dissociates to form acidic and basic ions.
Water's DissociationAnswer H2O + H2O ⇋ H3O+ + OH- simplified to H2O ⇋ H+ + OH-
Proton of HAnswer H+
Hydronium IonAnswer H3O+
Hydroxide IonAnswer OH-
What does adding/detaching a H+ change?Answer Can change a molecule's
physical/chemical properties.
H+ EffectsAnswer Has effects on:
The chemical reactions that occur inside and outside of cells.
The physicochemical properties of many small and large molecules.
The structure, function and stability of macromolecules such as proteins.
Biochemical laboratory techniques. • Growth and viability of all cells.
How do we control the effects of H+?Answer We can control these effects by using
buffers.
Buffers interact with H+ to maintain constant pH.
pH (potential of hydrogen)Answer H + concentration defines the pH of a solution.
H + concentration is written as mol/L (M).
pH equationAnswer pH<7 = acidic, pH>7 = basic.
A water-based solution that is neutral (pH = 7) will have 1 x 10-7 M of H+ and 1 x 10-7 M
of OH- , that is there will be 1 x 10-14 M ions in solution.
,H + concentration can be calculated if OH- concentration is known and vice versa.
Acids, basesAnswer Molecules that donate H+ (dissociate) are acids, molecules that
accept H+ (associate) are bases (BrønsteadLowry).
Equilibrium of Acids and basesAnswer HA + H2O ↔ HB + H3O +
(CH3COOH + H2O ↔ CH3COO- + H3O + )
Acid DissociationAnswer [A- ] and [H+ ] = products and [HA] = reactants
What does a small and a large Ka mean?Answer A large Ka = more products, small Ka =
more reactants.
Base DissociationAnswer [B+] and [OH- ] = products and [BOH] = reactants
pKa and it's relation with KaAnswer Ka is usually a small number so instead we work
with pKa (pKa = -logKa).
What does a small and a large pKa mean?Answer This means that a large pKa = more
reactants (weak acid), small pKa = more products (strong acid).
Buffering Region of BuffersAnswer pKa +/- 1
Horizontal region represents buffering range for this system.
Henderson-Hasselbalch EquationAnswer Change in pKa, [acid] or [base] can change
pH. A change in pH can change the ratio of [acid] and [base].
pH and charges of amino acidsAnswer At low pH all amino acids have a net positive
charge. At high pH, all amino acids have a net negative charge
Using Henderson-Hasselbalch Equation for amino acidsAnswer You calculate the
a-amino group and the a-carboxyl group to find the predominant groups and determine
if deprotonated (basic) or protonated (acidic), or even a zwitterion.
Isoelectric Point (pl)Answer pI is the point at which a molecule has no charge, that is, it
is in it's zwitterion form.
Isoelectric Point (pl) FormulaAnswer
Equivalence PointAnswer The point at which all of a titratable side chain has been
converted from its basic form to acidic form (or vice versa depending on the
experiment). Usually indicated by a sharp drop in pH.
Equivalence Point of a-amino groupAnswer First equivalence point will be the point at
which all of the NH2 has been converted to NH3 +
Equivalence Point of a-carboxyl groupAnswer Second equivalence point will be the
point at which all of the COO- has been converted to COOH.
, Significant figures RulesAnswer 1. Rules for identifying the significant figures in a
measurement.
2. Rules for removing non-significant figures in a number (rounding).
3. Rules for determining significant figures in a mathematical operation (such as add,
multiply, divide and subtract) or a series of calculations.
4. Rules for reporting measures of error.
Rule 1 - Identifying significant figuresAnswer The digit that is furthest to the left in a
number is the 'most' significant, digit to the right is the 'least' significant
Non-zero digits are always significant. (1-9)
Zeros at the beginning of a number are not significant.
Zeros between non-zero digits are always significant
Zeros at the end of a number are considered significant unless stated otherwise.
Rule 2 - Removing significant figures (rounding)Answer If the first digit to be removed is
less than 5, then remove that number and all numbers to its right.
e.g., 5.4342 (3 sf) becomes 5.43, where 4 and 2 have been removed, according to rule 1.
If the first digit to be removed is 5 or greater, then remove that number and all numbers
to its right. Increase the number to the left of the first digit to be removed, by 1.
e.g., 5.4362 (3 sf) becomes 5.44, where 6 and 2 have been removed and the number to
the left of the first digit to be removed has been increased by 1, according to rule 2
Rule 3 - Significant figures in calculationsAnswer Carry as many digits as possible
through a calculation. Round answer at the end with the correct number of significant
figures.
Answer should have the same number of decimal places as the number, in the
calculation, with the least number of decimal places (dp)." - unless the number of
significant figures for an answer is specified
Rule 4 - Measures of errorAnswer Measures of uncertainty like tolerance, standard
deviation and absolute error should only ever be reported to 1 significant figure.
Concentration FormulaAnswer n = cv
where n = moles, c = molar concentration (M), v = volume (L)
Mole Formula (Mass)Answer n = m/Mwt
where n = moles, m = mass (g), Mwt = molecular weight (g/mol)
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