Chapter 10: Flashcards
(41 cards)
Henderson-hassle back equation:
pH = pKa + log (A/HA)
A = concentration of conjugate base
HA = concentration of weak acid.
The pKa of a weak acid in solution is 5.4. If the ratio of weak acid to conjugate base is 10:1, what is the pH in solution?
pH = 5.4 + log(10/1) = 4.4
If a solution has a pH of 4.2, and a 8 parts weak acid to 2 parts conjugate base, what is the pKa of the solution?
pH = Pka + log(A/HA)
4.2 - log(2/8) = pKa = 4.8
A measure of the acidity of a molecule, and its tendency to lose a H+ ions:
pKa
What is the Kw of water under standard conditions? What does this value represent?
10^-14
The product of OH- and H+ produced from the autoionization of water
Which of these two values is larger:
a. 10^-17
b. 9^-15
9^-15
A titration of a strong acid and a strong base will have an equivalence point of:
a. Less than 7
b. Equal to 7
c. More than 7
Equal to 7
A titration of a strong acid and a weak base will have an equivalence point of:
a. less than 7.
b. Equal to 7.
c. More than 7.
Less than 7.
A titration of a weak acid and a strong base will have an equivalence point of:
a. Less than 7.
b. Equal to 7.
c. More than 7.
More than 7.
List the common strong acids - indicate if each one is organic or inorganic:
- HCL - Hydrochloric acid - inorganic.
- HBr - Hydrobromic acid - inorganic.
- HI - Hydroiodic acid - inorganic.
- HNO3 - Nitric acid - Inorganic.
- HClO4 - Perchloric acid - inorganic.
- H2SO4 - Sulfuric acid - inorganic.
List the common weak acids - indicate if each one is organic or inorganic:
- HF - Hydrofluoric acid - inorganic
- CH3COOH - Acetic acid - Organic
- HCOOH - Formic acid - organic.
- C6H5COOH - Benzoic acid - organic.
- C2H2O4 - Oxalic acid - organic.
- HNO2 - Nitrous acid - inorganic.
- H2SO3 - Sulfurous acid - Inorganic.
- H3PO4 - phosphoric acid - inorganic.
List the common strong bases - indicate if each one is organic or inorganic:
- KOH - Potassium hydroxide - Inorganic.
- NaOH - Sodium hydroxide - Inorganic.
- Ba(OH)2 - Barium hydroxide - inorganic.
- CsOH - Caesium hydroxide - inorganic.
- Sr(OH)2 - Strontium hydroxide - inorganic.
- Ca(OH)2 - Calcium hydroxide - inorganic.
- LiOH - Lithium hydroxide - inorganic.
- RbOH - Rubidium hydroxide - inorganic.
List the common weak bases - indicate if each one is organic or inorganic:
- NH3 - Ammonia - Inorganic.
- Al(OH)3 - Aluminium hydroxide - inorganic.
- Pb(OH)2 - Lead hydroxide - inorganic.
- Fe(OH)3 - Ferric acid - inorganic.
- Cu(OH)2 - Copper hydroxide - inorganic.
- Zn(OH)2 - Zinc hydroxide - inorganic.
- N(CH3)3 - Trimethylamine - Organic.
- CH3NH2 - Methylamine - Organic
- Urea - Organic.
What is a buffer, and how do we make them?
A buffer is made by mixing a weak acid and its conjugate base and a cation (salt), or a weak base and its conjugate acid and an anion (salt). These are used to resist changes in pH. When the concentration of acid to base is equal, the buffer is equal to the pKa of the acid.
Considering that the pKa of H2CO3 is 6.35, and the pKa of HCO3- is 10.33. In order to create a buffer with a pH of 8.9, we must:
a. Use equal concentrations of H2CO3 to NaHCO3.
b. Use higher concentration of NaHCO3 to H2CO3.
c. Use a higher concentration of H2CO3 to NaHCO3.
d. Concentration of an acid or base will not change the pH of a buffer.
b - Use a higher concentration of NaHCO3 to H2CO3
When the concentration of base (NaHCO3) is equal to concentration of acid (H2CO3), the pH will be equal to the acids pKa (6.35). In order to raise the pH of the buffer, we must have a higher concentration of base to acid.
You are attempting to denature a cell-surface receptor protein in your laboratory, in order to understand the mechanism by which it selects for its specific fatty acid substrate. This protein is known to unfold in strongly acidic environments. The laboratory has 3 available acids: Acid A (pKa = 7.4), Acid B (pKa = 3.4), and Acid C (pKa = 2.2). Which acid will you use?
- Acid A.
- Acid B.
- Acid C.
- All of these acids will be equally effective at denaturing the protein.
- Acid C - This is because acid strength is inversely proportional to pKa, so the lower pKa - the stronger the acid will be. Since this protein unfolds in highly acidic environments, we should select the strongest acid.
Which of the following acids will produce the strongest conjugate base, following an acid-base reaction?
a. Formic acid (pKa = 3.75)
b. Hydrofluoric acid (pKa = 3.17).
c. Fluoroantimonic acid (pKa = -31).
d. Water (pKa = 14)
d - Water will produce the strongest conjugate base. This is because pKa and acid strength are inversely related, so a high pKa (14) would create a weak acid. All weak acids will have a strong conjugate base.
All weak acids have a:
Strong conjugate base.
All strong bases have a:
Weak conjugate acid.
All weak bases have a:
Strong conjugate acid.
All strong acids have a:
Weak conjugate base.
A company that produces hair straightening products is seeking a weaker acid to use to disrupt the keratin proteins in the hair. The last chemical they tried to use way too acidic and caused severe damage to the hair, as they used acid A with a Ka = 5.6*10^-6. Which of the following acids should they try next?
a. Acid B - (Ka = 4.3 10^-3)
b Acid C (Ka = 3.110^-3)
c. Acid D (Ka = 6.6*10^-6).
d. Acid E (Ka = 10.4 *10^-8)
d - Acid E with a Ka of 10.4*10^-8
Because Ka is directly proportional to acid strength, to find the weaker acid, it must have a smaller Ka than Acid A. Acid E is the only acid with a Ka number smaller than that of Acid A.
Ka is ___________ proportional to acid strength, while pKa is ______________ proportional.
Ka is directly proportional to acid strength, while pKa is inversely proportional.
Which equation relates pH and hydronium (H3O+) ion concentration?
pH = -log(H3O+)
