buffers
what are buffers made of?
a weak conjugate acid/base pair
if Qsp<Ksp, what saturation is it?
unsaturated
what is the equivalence point?
when mols of the acid = mols of the base
what type of titration forms a neutral (pH≈7) equivalence point?
strong acid-strong base titration
what two pieces of info do you need to determine a solution’s saturation and if it forms a precipitate or not?
Qsp vs Ksp
what do buffers do?
resist changes in pH when small amount of strong acids/bases are added
which levels of saturation do NOT form a precipitate?
unsaturated and saturated
what is the end point?
the point at which an indicator changes colour
will the equivalence point of a weak acid-strong base titration be acidic, basic, or neutral?
basic, pH≈9
you add a strong acid to a buffer and discover the pH does not drastically change. why? (think about what is reacting)
because the conjugate base in the buffer neutralizes the added H⁺
what 2 things make a buffer effective?
high [conc]’s and relatively equal [conc]’s of the acid + base components
what happens to saturation and Qsp when a precipitate does form?
it is supersaturated and Qsp>Ksp
when choosing an indicator, what do you want its pKin to be as close as possible to?
the pH at the equivalence point in order to minimize titration error
on what type of titration graphs does a buffer region occur?
on weak acid-strong base/weak base-strong acid titration graphs because buffers are formed from a weak conjugate A/B pair
AgCl is slightly soluble. what will happen if you add NaCl to its solution?
solubility will decrease due to common ion effect
what happens to pH when the concentrations of the acid and base are equal?
pH = pKa
how does adding a common ion affect solubility?
it decreases the solubility because it shifts the equilibrium to the left, reducing the amount of compound that can dissolve
if bromothymol blue changes from yellow to blue over pH 6.0–7.6, what color will the solution be at pH 5.5?
yellow because the pH is below the indicator’s color-change range
what do the two shapes of lines on a titration graph represent?
curvy line=buffer, straight line=strong A/B
a solution is made with 0.5 M acetic acid and 0.5 M sodium acetate. if the pH is 4.1, what is the pKa?
what is the effective range for a buffering system?
1 pH unit on either side of pKa (pH= pKa +/- 1)
if a compound contains a basic ion, how will the addition of a strong acid affect its solubility?
adding a strong acid will increase the solubility because it will react with the base to neutralize it, shifting equilibrium to dissolve more compound
true or false: the colour change of an indicator always occurs at pH=7.
false, indicators change colour over a specific pH range depending on their pKin value
which indicator would be best for titrating a strong acid with a strong base: phenolphthalein (pKin≈9.4) or methyl orange (pKin≈3.7)?
phenolphthalein, because a strong acid and strong base titration forms an equivalence point with a pH≈7 (neutral) and phenolphthalein has a pKin closer to 7
a strong acid is added to a solution of CaCO₃. what happens to solubility and why?
solubility increases because H⁺ reacts with CO₃²⁻ ion, removing it and shifting equilibrium forward