Acids and Bases Flashcards
What is a Bronsted and Lowry acid?
A proton (hydrogen ion) donor
How many ionization equilibrium constants/dissociation constant (Ka) would diprotic acids (eg. H2SO4) have?
Two
There would be a Ka value for each of its two ionizable protons
What are common strong bases and weak bases? (not list, just characteristics)
Strong bases include any hydroxide of the group 1A metals.
The most common weak bases are ammonia and any organic amine.
How is the strength of an acid or base determined?
The strength of an acid or base is related to the extent that the dissociation proceeds to the right, or to the magnitude of Ka or Kb; the larger the dissociation constant, the stronger the acid or the base.
How are amino acids examples of conjugate acid-base pairs?
What is an amino acid in blood plasma called (due to its charges..)?
Amino acid bear at least 2 ionizable weak acid groups (a carboxyl and an amino), which act as conjugate bases of corresponding acids. The carboxyl group is thousands of times more acidic than the amino group, thus, in blood plasma, the predominant forms are the carboxylate anions (R-COO-) and the protonated amino group (-NH3+). This form is called a zwitterion.
What is a salt?
An ionic compound in which the anion is not OH- or O2-, and the cation is not H+
Typically, an acid plus a base produces a salt and a neutral compound
What is a buffer?
A buffer is defined as a solution that resists change in pH when a small amount of an acid or base is added or when a solution is diluted. A buffer solution consists of a mixture or a weak acid and its salt, or a weak base and its salt.
Which two characteristics of a buffer determine its buffering capacity?
- The concentration of HA and A-
- Ratio of HA to A- (highest capacity around 1:1)
What is the purpose of titrations?
To determine the concentration of a given sample of acid or base (the analyte) is reacted with an equivalent amount of strong base or acid of known concentration (the titrant)
what is the end point of a titration? How is this usually detected/measured?
When a stoichiometric amount of titrant has been added (equivalent to the stoichiometric amount of analyte)
Usually detected with an indicator dye where pKa is close to the equivalence point, but measured directly by taking pH readings along different points of the titration.
What is the formula for the titration curve?
pH=f(V)
basically pH vs. volume (mL)
How is the equivalence point different between strong/weak acids/bases?
In the case of strong acid-strong base titration, the equivalence point corresponds to a neutral pH (because the salt formed does not react with water). If more titrant is added, the pH increases and corresponds to the pH of a solution of gradually increasing concentration of the titrant base.
In a titration, what is the midpoint?
Weak acid - strong base
- When pH equals pKa
Weak base - strong acid
- pH is equal to 14 - pKb
In both, the midpoint is when the concentration of the weak acid/weak base is equal to the concentration of their conjugate base/acid
Describe a redox titration with KMnO4
KMnO4 salt solutions are colourful since they contain purple MnO4- ion. But the reduced form (Mn++) is colourless.
KMnO4 is added to a reaction mixture with a reducing agent (such as iron), this is done until there is no more reducing agent in the mixture (at which point the solution will again become colourful!).
Thus, if the amount of reducing agent was unknown, it can be calculated using stoichiometry guided by the amount of potassium permanganate used in the reaction.
An aqueous solution of a salt made by mixing which of the following acids and bases displays the lowest pH? Why?
- Strong acid, weak base
- Strong acid, strong base
- Weak acid, weak base
- Weak acid, strong base
Strong acid, weak base
You must think of the salt that is made, and if it will hydrolyze to increase/decrease the concentration of hydrogen ions in solution. For example, a strong acid (HCl) and weak base (NH3Cl) will make the salt NH4Cl and water. NH4+ reacts with water to form NH3 and H3O.
A strong acid and strong base will create a compound such as NaCl (eg. from NaOH and HCl), in this case, neither ion reacts with water (pH = 7).
A weak acid and a weak base will create a compound where both hydrolyzed ions react with water to produce H+ and OH-, which react and tend to cancel each other out, giving a pH near 7.
