aqeous chemistry

• HCl


  strong acid
• HBr


  Strong acid
• HNO3


  Strong Acid
• H2SO4


  Strong Acid
• KOH


  Strong Base
• NaOH


  Strong Base
• NH3


  Weak base
• CH3NH2


  Weak Base
• CH3COO-


  Weak base
• HF


  Weak Acid
• CH3COOH


  Weak acid
• NH4+ 


  Weak Acid
• justifying ranking of species of a weak acid

  • WA partially dissociates, and so the equilibrium lies to the LHS/favours the reactants; therefore WA is present in the greatest amounts.
  • H3O+ and CONJBAS are produced in equal amounts, but there is a small contribution to H3O+ from water therefore H3O+ > CONJBASBecause there is a relatively high [H3O+], the [OH–] is very low in order to maintain Kw
• electrical conductivity

  SA and SB and ALL salts are all GOOD conductors as their ionisa�on / dissocia�on is complete. WA and WB are POOR conductors as their reac�on with H2O is incomplete and so [ions] is low.
• pKa relationship of strength of acid

  For a weak acid, lower Ka / higher pKa means a weaker acid. So if there are two weak acids of the same concentration, the one with lower Ka / higher pKa will have the higher pH as it will be less dissociated. so [H3O+] will be less, hence pH will be higher
• buffers

  solutions that resist change in pH when small amounts of acid and base are added. Contain a weak acid and its conjugate base e.g. CH3COOH & CH3COO- OR a weak base and its conjugate acid e.g. CH3NH2 and CH3NH3+.

  • Buffer range is pK ±1 pH unit. Outsid
• Effect on solubility of complex ion

  Formation of complex ion favours forward reaction of eqm. to REPLACE used up Ag+, making less solid, hence solubility increases.
• Effect of reaction of basic anion (OH- or CO32-) with added acid

  The CO32- ion reacts with added acid. Removal of CO32- favours

  the forward Reaction of basic anion (OH- or CO32-) with added acid. 3 2+ 32- 32- 3+ 2 2

  forward reaction of equilibrium to REPLACE used up CO32-making less solid, hence solubility increases
• when is equivalence point reached

  The equivalence point is reached when the moles of acid and base are equal.
• Titration At EP calculation for WA SB

  • all the weak acid has been converted to its conjugate base so do a WB calculation to find pH
• What is included and not included in Ks expression?

  The solid itself is not included but the ions are.
• What's a saturated solution?

  a solution that contains the maximum amount of dissolved ions
• How to find solubility of an AB type salt?

  Use Ks=s^2
• How to find solubility of an A2B type salt?

  Use Ks = 4s^3
• What is the common ion effect? Explain using principles of Ks and Equilibrium.


  Adding (common ion) increases the concentration of (common ion), and decreases concentration of (other ion on RHS) in order to maintain the same value of Ks as it is a constant. Equilibrium will act to minimize the disturbance of increased concentration and oppose this change, so the position of equilibrium will shift to the left hand side to decrease the concentration of (common ion). This also decreases the concentration of (OTHER ION ON RHS). This means that solid becomes less soluble. The common ion causes Ks to be initially exceeded, causing precipitation until the new concentrations satisfy the value of Ks again.
• How to predict precipitation?

  If Qs is less than Ks then no precipitate.

  - the Queen is sad when less than King, she will be sad and soft.

  
  

  If Qs is greater than Ks, precipitate forms

  - the queen is strong and greater than king. she is solid and powerful

  
  

  If Qs = Ks,

  they are both equal and there is no precipitate
• How to calculate Qs?


  Exact same calculation as for Ks
• What is the effect of pH (H3O+) on solubility?


  If sparingly soluble compound contains an ion that reacts with acids and pH is reduced below 7, the compound becomes more soluble as the the H3O+ ions will react with the (basic ions ex; F-, CH3XOO-, CO32-, OH-) to produce water. As per equilibrium principles, as products are removed from the equilibrium, the position of equilibrium will move to the right, thus decreasing the amount of reactants in the system.

  
  

  HOWEVER, if there is no ion in the compound that can react with H3O+, then there will be no impact on the solubility of the compound of acidic conditions.
• What is the effect of pH (OH-) on solubility?


  Basic conditions increase solubility of sparingly soluble ionic compounds IF the metal cation is able to form complex ions with the complex ion.

  
  

  The solubility of (Compound) is greatly increased in a solution of ____ as (basic anion) are removed from the equilibrium when they form the complex ion ; (identify). The position of equilibrium will shift to the right to replace the 'lost' silver ions, thereby reducing the amount of (compound)
• How to find the pH of a strong acid?


  -log[H3O+]

  For strong acids, their concentration = [H3O+]
• Write an answer for the relative species produced when a weak acid dissociates.


  HA is a weak acid, it only partially dissociates, therefore the equilibrium lies to the left of the equation. As a result, HA is the species highest in concentration as very few molecules dissociate. For each HA molecule that dissociates, equal amounts of A- and H3O+ formed by the dissociation of water. This will mean that the concentration of H3O+ ions will be slightly higher than the H- (due to the presence of H3O+ ions already present due to the dissociation of water). As [H3O+] is greater than 10^-7, [OH-] must be less than 10^-7 to maintain Kw=10^-14.
• What are the key things I want you to remember?

  1. For Qs calculations, if one of the ions is coming from an A2B/AB2 salt, multiply dilution factor by 2 :)

  2. when using n=cV, remember that V is in Litres
• When does water go into the actual equation?


  For strong acids, weak acids, weak bases. BUT NOT FOR STRONG BASES OR SALTS because they are just breaking apart (ex; NaOH -> Na+ + OH-)
• What is a buffer solution?


  A solution made up of a mixture of a weak acid/base (IDENTIFY) and its conjugate base/acid (IDENTIFY) that undergoes minimal change in pH when small amounts of base or acid are added.

  
  

  When an acid is added, it will react with basic (__) ions so there is almost no change in [H3O+] present in the solution. WRITE EQUATION

  
  

  When a base is added, it will react with acidic (__) ion so there is almost no change in [OH-] present in the solution. WRITE EQUATION

  
  

  The equations above show that the ratio of acid/base:conjugate changes slightly but will not significantly affect the pH. Make a statement about effectiveness of buffer.
• Discuss the different effectivenesses of a buffer solution under different conditions


  1. Weak A/B and its conjugate are in equal concentrations - Buffer solution will be equally effective at resisting a change against added acid or base. SO pH = pKa

  
  

  2. pH is greater than pKa which means solution is likely more basic, and thus buffer will be more effective against addition of excess acid.

  
  

  3. pH is less than pKa which means means there is more acid than conjugate base, and the solution is more effective against added base.
• How to convert gL-1 to molL-1


  Divide by molar mass
• State the relationships between Ka, acids and conjugates.

  Smaller the Ka, the weaker the acid. The weaker an acid, the stronger its conjugate base. Alternatively, the stronger an acid, the weaker its conjugate base.
• Conditions for electrical conductivity

  To conduct a current, a substance requires mobile charged particles which can carry electrical charge.
• tell me the important stuff about titrations

  1. For a strong acid strong base titration which produces neutral salt, pH at equivalence point will be 7.
• Indicators


  A substance which changes color according to the pH. Most are weak acids. The acid is one color and its conjugate base is another color. Its working range is pKa +- 1 pH unit. The indicator will be successful when it is in the vertical region of the titration curve