Chapter 16

Question 1

5*the common-ion effect

Answer 1

• in any ionic equilibrium, a reaction that produces an ion is suppressed when more of that ion is added to the system
  
  • a shift in the position of an equilibrium
    
    • results in the initial concentrations of the conjugate acid-base pair changing very little before equilibrium is achieved
    • therefore, we can use initial concs to calculate pHs (Henderson-Hasselbach)

Question 2

5*Henderson-Hasselbach equation

Answer 2

• an equation used to calculate the pH of a solution in which the concentrations of acid and conjugate base are known
  
  • when concentrations of acid and base are equal, you get log(1) which is 0 so pH=pKa
  • if [base]>[acid], log term is pos and pH>pKa

Question 3

5*pH buffer

Answer 3

• a solution that resists changes in pH when acids or bases are added to it
  
  • typically a solution of a weak acid and its conjugate base
    
    • common-ion effects plays a key role in controlling the pH of these solns that have relatively high concs of both weak acid and conjugate base
• maintains pH b/c the weak acid of the buffer gives it the ability to neutralize additions of basic substances while the conjugate base allows it to neutralize additions of acids
  
  • common buffers: H2CO3/HCO3-,NH3/NH4+, phosphoric acid/phosphates
• buffer should have a pKa within one pH unit of the target pH

Question 4

5*buffer capacity

Answer 4

• the quantity of acid or base that a pH buffer can neutralize while keeping its pH within a desired range
  
  • the greater the concentration of the conjugate pair components, the greater the buffer capacity
• OR the ability of the buffer to withstand additions of acid or base without a significant change in pH

Question 5

5*pH indicator

Answer 5

• a water-soluble weak organic acid that changes color as it ionizes(aka as pH changes)
• also detect large changes in pH that occur at the equivalence points in acid base titrations

Question 6

5*Acid-base titration steps

Answer 6

1. Assemble a titration apparatus
2. Accurately transfer a known volume of sample to the beaker
3. Either add a few drops of an indicator solution to the sample or insert the probe of a pH meter
4. Fill the buret with a solution(the titrant) of known concentration of a substance that reacts with a solute(the analyte) in the sample
5. Slowly add titrant to the sample, and monitor the change in pH. When the volume of titrant needed to completely consume the analyte has been added, the equivalence point has been reached, as indicated by either a change in indicator color or a large change in pH. This volme of titrant is a measure of the concentration of analyte in the sample.

Question 7

Lewis base

Answer 7

• a substance that donates a lone pair of electrons in a chemical reaction

Question 8

Lewis acid

Answer 8

• a substance that accepts a lone pair of electrons in a chemical reaction

Question 9

Coordinate bond

Answer 9

• a covalent bond formed when one anion or molecule donates a pair of electrons to another ion or molecule

Question 10

complex ion

Answer 10

• an ionic species consisting of a metal ion bonded to one or more Lewis bases

Question 11

ligand

Answer 11

• a Lewis base bonded to the central metal ion of a complex ion

Question 12

formation constant(Kf)

Answer 12

• an equilibrium constant describing the formation of a metal complex from a free metal ion and its ligands

Question 13

solubility-product constant(aka solubility product, Ksp)

Answer 13

• an equilibrium constant that describes the formation of a saturated solution of a slightly soluble salt
  
  • allow us to calculate concentrations of compounds in aqueous solutions
  • allows us to predict whether a particular concentration of an ionic compound is possible or whether a precipitate will form when the solns of two salts are mixed
  • Q(rxn quotient/ion product)
    
    • when Q>Ksp, rectants are favored
    • Q

Question 14

solubility

Answer 14

• Solubility: how much solute dissolves
• varies depending on temperature, pH, and presence of other ions
• solubility: g solute/100 mL of soln
• molar solubility: moles solute/L of soln

Question 15

precipitation

Answer 15

solid comes out of solution