acids and bases

• What do acid-base equilibria involve?

  The transfer of protons between substances
• How can substances be 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 not 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 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 \times 10^{-14}$ at 25°C
• What happens to K$_w$ as temperature changes?


  The value of K$_w$ 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 do weak acids and bases do in solution?

  They only slightly dissociate to form an equilibrium mixture
• What is the equilibrium dissociation constant for weak acids?

  K$_a$

  
• How can the pH of weak acids and bases be determined?

  Using the relationships of K$_a$, pKa, and [H$^+$]

  
• What method is used when HA is in excess?

  Use [HA] and [A$^-$] along with K$_a$ to find [H$^+$], then pH
• What method is used when A$^-$ is in excess?


  Use K$_w$ to find [H$^+$], then pH
• What happens when 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 can only indicate a pH change within a certain range

  
• What are the two most common indicators used at A-Level?

  Methyl orange and phenolphthalein

  
• What is the color change of methyl orange in acids?

  Orange in acids and turns yellow at the neutralisation point

  
• What is the color change of phenolphthalein in alkalis?

  Pink in alkalis and turns colorless at the neutralisation point
• Why is it important to select the correct indicator in a titration?

  To ensure accurate detection of the pH change