Acid-Base Reactions

An ionic compound that does not have H⁺ as the cation or OH^- as the anion

• Metals: H₂(g) and a salt
• Bases: H₂O(l) and a salt
• CO₃^2-(carbonate) or HCO₃-(bicarbonate) ions: CO₂(g), H₂O(l), and a salt

The metal ion (potassium, sodium, calcium, magnesium, aluminum, zinc, iron, tin) replaces the hydrogen in the acid

In a neutralization reaction an acid reacts with a base to produce water and a salt.

The acid reacts with the carbonate or bicarbonate to produce carbonic acid (H₂CO₃) which breaks down rapidly to CO₂ and H₂O

• Example carbonate: CaCO₃(s)
• Example bicarbonate: NaHCO₃(s)

• Step 1: the products are water and a salt
• Step 2: balance the OH- and H+
• Step 3: verify the amounts of reactants and products are equal for the salt

The addition of a base to an acid sample to determine the concentration of the acid

Phenolphtalein is added to identify when the moles of base equal the moles of acid (it turns pink when the solution is neutralized)

The molarity of the acid is calculated using the neutralization equation for the reaction

A buffer is a solution that has a combination of a weak acid and its conjugate base in sufficient concentration so as to counter the pH change of any small addition of acid or base.

Note: when an acid or base is added to water the pH changes drastically

In a buffer, an acid reacts with any OH- added and a base reacts with any H30+ added.  However, that acid and base must not neutralize each other.  Therefore a combination of an acid-base conjugate pair is used in buffers.  Buffers may also contain a salt of a weak acid/base which contains its conjugate base/acid.

No.

In most cases, the buffer solution is inherent in the liquid in question. For example, wine is a buffered solution. It has many components contained in the aqueous/alcohol matrix. But it includes weak organic acids and their conjugate bases, so it is a buffer solution. 

The same is true of most of our bodily fluids. They are buffered because they contain a weal acid and its conjugate base, designed to maintain a pH range that is appropriate for that function. For a TA titration, no additional buffer is used. The 5 mL wine sample is added to the flask and then diluted with distilled water.

You can buy a buffer solution. (This is the case with pH 4 or pH 7 pH meter standardizing solutions.)

There are some analyses that do require the addition of a buffer to maintain the pH in the desired range. An example would be the enzymatic analysis of malate where a buffer is added to insure that the enzyme can function.

Equal concentrations of a weak acid and a salt of its conjugate base.  For example, in a buffer with acetic acid and sodium acetate, the salt produces acetate ions and sodium ions.

Small additions of an acid (H3O+) or base (OH-) are neutralized by the salt and the weak acid respectively.

• Added acid reacts with the salt (shift to reactants):
• HC₂H₃O₂(aq) + H₂O(l) → C₂H₃O₂^-(aq) + H₃O⁺(aq)

• Added base neutralized by weak acid (shift to products):
• HC₂H₃O₂(aq) + OH-(aq) → C₂H₃O₂^-(aq) + H₂O(l)
• Note:  adding a large amount of acid or base may exceed the buffering capacity of the system

Step 1: [H₃O+] = K_a × [weak acid] ÷ [conjugate base]

Step 2: pH = -log₁₀([H₃O⁺])

True:  it depends on the K_a of the weak acid

For example, buffers can be prepared from these acid-base pairs:

• H₂PO₄-/HPO₄^2-
• HPO₄^2-/PO₄^3-
• HCO₃^-/CO₃^2-
• NH₄⁺/NH₃

Alter the ratios of the weak acid and its conjugate base

Buffers in blood plasma:

Arterial blood plasma has a normal pH of 7.35-7.45.  If the pH falls below 6.8 or raises above 8.0, cells cannot function properly and death may result.  Some of the CO₂ produced by cellular metabolism dissolves in blood plasma, forming carbonic acid (H₂CO₃). some of which dissociates to give bicarbonate and H₃O+.  Kidneys supply more bicarbonate, setting up the buffer system in blood plama.

• Acidosis:  higher CO₂ level leads to lower blood pH
• Alkalosis: lower CO₂ level leads to higher blood pH

True