acids and bases

• What do acid-base equilibria involve?


  The transfer of protons between substances
• How are substances classified as acids or bases?


  Based on their interaction with protons
• What is a Brønsted-Lowry acid?


  A proton donor
• Give an example of a Brønsted-Lowry acid.


  Ammonium ions (NH$_4^+$)
• What is a Brønsted-Lowry base?


  A proton acceptor
• Give an example of a Brønsted-Lowry base.


  Hydroxide ions (OH$^-$)
• What does acid strength refer to?


  It does not refer to the concentration of a solution
• How is a strong acid defined?


  An acid that completely dissociates to ions when in solution with pH 3-5
• What is the pH range of a strong acid?


  pH 3-5
• How is a weak acid defined?


  An acid that only slightly dissociates when in solution with pH 0-1
• What is the pH range of a weak acid?


  pH 0-1
• What are the pH ranges for strong and weak bases?


  Strong bases have pH 12-14 and weak bases have pH 9-11
• What does pH measure?


  Acidity and alkalinity
• What type of scale is pH?


  A logarithmic scale from 0 to 14
• What does a pH of 0 indicate?


  An acidic solution with a high concentration of H$^+$ ions
• What does a pH of 14 indicate?


  A basic solution with a low concentration of H$^+$ ions
• How can the concentration of H$^+$ ions be determined?


  Using the pH value
• What is the equilibrium constant for the dissociation of water?


  K$_w$ = 1 x 10$^{-14}$ at 25°C
• How does temperature affect the value of K$_w$?


  The value changes as temperature changes
• What type of reaction is the forward reaction in the equilibrium of water?

  Endothermic
• What happens to the acidity of water as temperature increases?


  Water becomes more acidic as temperature increases
• What is the equilibrium dissociation constant for weak acids and bases?


  K$_a$ for weak acids and K$_b$ for weak bases
• How can pKa be found?


  Using the relationship with K$_a$
• How can the pH of weak acids and bases be determined?


  Using the relationships of K$_a$, pKa, and [H$^+$]
• What are the methods to find pH depending on the reaction and relative concentrations?


  • HA in excess: Use [HA] and [A$^−$] along with K$_a$ to find [H$^+$], then pH.
  • A$^−$ in excess: Use K$_w$ to find [H$^+$], then pH.
  • HA = A$^−$: pKa is equal to pH, therefore find pKa.
• What does a pH titration curve show?


  How pH of a solution changes during an acid-base reaction
• What is the neutralisation point in a titration curve?


  A large vertical section through the neutralisation or equivalence point
• How is a titration curve investigated?


  By slowly adding alkali to an acid and measuring the pH
• What is the effect of smaller added volumes in a titration?


  The more accurate the curve produced
• What is the neutralisation point for a strong acid-strong base reaction?


  Occurs around pH 7
• What is the neutralisation point for a strong acid-weak base reaction?


  Less than pH 7 (more acidic)
• What is the neutralisation point for a weak acid-strong base reaction?


  Greater than pH 7 (more basic)
• What is the neutralisation point for a weak acid-weak base reaction?


  Normally pH 7 but hard to determine
• Why are specific indicators used in titrations?


  They indicate a pH change within a certain range
• What are the two most common indicators used at A-Level?

  Methyl orange and phenolphthalein
• What color does methyl orange turn at the neutralisation point?


  Turns yellow from orange
• What color does phenolphthalein turn at the neutralisation point?


  Turns colorless from pink
• What is a buffer solution defined as?


  A solution that resists changes in pH when small volumes of acid or base are added
• What do acidic buffer solutions contain?


  A weak acid and the salt of that weak acid
• What do basic buffer solutions contain?


  A weak base and the salt of that weak base