Acids & Bases

• What are the traits of an acid?

  Donate hydrogen ions (H+). As such they are called proton donors.
• What is a monoprotic acid?


  Donates one proton per molecule when they dissociate.
• What is a polyprotic acid?


  Donates more than one proton per molecule when they dissociate.
• How to measure a strong acid or base?


  How much it ionises (separates into ions) in a solution. Strong acid fully ionise and a weak acid will partially. Strong bases completely ionise and a weak one will partially.
• What is an electrolyte?


  A substance that conducts electricity when molten or in aqueous solution.
• Water is a weak electrolyte.
• In water a small fraction of H2O molecules react to form H3O+ and OH- ions. This is known as self-ionisation of water. It is an equilibrium constant.
• What kind of reaction is the self ionisation of water?


  An endothermic.
• How does temperature affect self ionisation of water?


  This will favour the products as such Kw will change with temp. (increasing)
• What is the pH scale?


  Is logarithmic. A change in pH by one unit represents a 10-fold change in hydrogen ion conc.
• What is the Bronstead-Lowry Model?


  An equation will show the transfer of ions between the conjugate acid-base pairs. Conjugate acid is when a base accepts protons. Conjugate base is when an acid donates its protons.
• What is the amphiprotic species?


  Are molecules that can either donate or accept a proton. They either act as an acid or base.
• What is a buffer solution?

  A solution that resists change in pH when a small amount of acid or base is added, it contains a weak acid or its conjugate base or a weak base or its conjugate acid.
• Example of buffer solution is human blood with a pH of 7.35-7.45. When this drops it is acidosis, when this rises it is alkalosis. The body maintains a safe pH through a buffer system that consists of weak acid and its conjugate base (Carbonic acid). This or a base, depending on the pH is added into the blood to react. These reactions control the blood pH by eliminating excess H+ or OH- ions.
• Describe how Le Chatelier's principle affects buffer solutions.

  It can be used to predict the response of a buffer solution to the addition of acids or bases.
• General Equation for acid (HA) dissociation.

  HA + H2O = H3O+ + A-
• If Ka > 1 strong acid

  If Ka < 1 weak acid
• General equation for base (B) dissociation:

  B + H2O = BH+ + OH-
• If Kb > 1 strong base

  If Kb < 1 weak base
• What is the relationship between Ka + Kb?

  For an acid and its conjugate base;

  Kw = Ka x Kb
• Kw = 1 x 10^-14
• pKa = -log Ka
• pKb= -log Kb
• Strong acids and bases have low pKa and pKb respectively.
• How to calculate dissociation constants?

  The pH is known and the conc. of the acid or base is known.
• How to calculate the pH with Ka and Kb?

  If Ka/Kb is known and the initial conc. of the weak acid or weak base is known. To do this assume the equilibrium conc. of the weak acid/base is equal to the initial conc. of the weak acid/base, because little ionisation occurs.
• What is a pH indicator?

  Typically a weak acid or base.
• What is titration?

  A precise, analytical method for determining the conc. of an unknown solution by using a solution of a known conc. called a standard solution.
• What is the equivalence point?

  The point where the acid and base have reacted in exact stoichiometric amounts.
• What is the end point?

  The point where the indicator used in the titration changes colour for an indicator to be useful in an acid-base titration, it must change colour close to the equivalence point.
• What is a primary standard?

  A chemical of very high purity. It is weighed and then dissolved in a solvent using a volumetric flask, to create a standard solution which is a solution with a highly accurate conc.
• What is a buffer region?

  The section of a titration curve that is relatively flat because adding more acid or base does not drastically affect the pH.
• What is the half-equivalence point?

  A point in a titration curve where the conc. of the titre is equal tohalf of the original conc. of the unknown.
• At half equivalence point, pH = pKa.