Acids and bases Flashcards
Acid + Metal –>
Salt + Hydrogen
Acid + Metal Oxide –>
Salt + Water
Acid + Metal Hydroxide
Salt + Water
Acid + Metal carbonate
Salt + CO2 + H2O
Define an acid
Proton donor
Define a base
proton acceptor
What does amphoteric mean?
Water can act as either an acid or a base
How to calculate pH
-log[H+]
How to calculate [H+] using pH
10^-pH
Key points for the pH scale
The smaller the pH, the greater the concentration of H+ ions. A differnce of 1 on the scale means a differnce in x10 of [H+]
Define a strong acid
Fully dissociates
What does Ka stand for
equilibrium constant in terms of acid dissoiation
Ka equation
products over reactants
What is the differnce between monoprotic, diprotic and triprotic
Te amount of [H+] ions it contains
x1
x2
x3
Define a weak acid
Only partially dissociates
Ka for weak acid
[H+][A-]/[HA]
What type of acid is a craboxyllic acid
weak
H+ using Ka
(square root)Ka[HA]
pKa equation
-log[KA]
Ka using pKa
10^-pKa
Kw expression
[H+][OH-]
H+ using Kw
Square root of Kw
PH changes with temperature
At temp higher than 298K, equilibrium shifts to the right in the endothermic direction to oppose change. [H+] increases. However does not mean it goes more acidic as [H+]=[OH]-
Calculating pH
State why calibrating a pH meter just before it is used improves the accuracy of the pH measurement
After storage, it will not provide the right reading
describe how you would obtain the pH curve for the titration
measure pH of acid, add alkali, stir, measure pH after each addition- repeat until in excess
suggest why the conc of NaOH in a solution slowly decreased when left open in air
Reacts with Co2 in the air
Explain why the temp rise is less
same amount of Q distributed over a larger volume
pH of magnesium hydroxide compared to calcium
lower- Mg is less soluble
Draw the displayed formula of H2SO4
explain why H2O is not shown in the Kw expression
[H2O] is constant
suggest why the pH probe is washed with distilled water between each measurement
to reduce contamination
explain why the volume of NaOH added between each pH is smaller as the end point is approached
to avoid missing endpoint
suggest a suitable piece of apparatus that could be used to measure out the sodium hydroxide solution, explain why this apparatus is more suitable than a pipette
burette- can deliver variable volumes
why would the end point of the graph is difficult to judge accurately
the change in pH is gradual, would change colour over a range of volumes
a practical procedure to obtain data that a graph could be plotted from
place in a fixed volume of alkali in a flask or beaker. add acid in small portions from burette, stir and use pH meter to record pH after each decision
suggest how the practical procedure could be refined
repeat with indicator- select the indicator that changes colour rapidly from pH 7 to 4
