Acids and bases Flashcards
Define a bronstead lowry acid
proton donor
What is a conjugate acid?
The substance formed from the base.
What is the formula for pH
-log[H+]
How do you work out [H+] in a monoprotic strong acid?
Same as the concentration of the acid.
How do you calculate pka?
-logka
How do you calculate ka?
10^-pka
Or [H+]^2 / [HA]
Using their Ka values, how can you tell which weak acid is stronger?
Higher Ka value, stronger weak acid
Lower Ka value, weaker weak acid
How can Le Chateliers Principle predict the change in pH of water?
- Dissociation of water in endothermic.
- Increasing T shifts eq. To the right.
- Higher [H+].
- Lower pH.
How can you improve the accuracy of a titration curve experiment?
- Maintaining constant temperature.
- Calibrating pH meter.
Strong acid - strong base titration curve?
_____)———
Weak acid strong base titration curve
________)———
/
Weak acid - weak base titration curve.
No steep curve vague line increasing.
Using a titration curve, how do you work out the Ka for a weak acid given a weak acid strong base curve?
- Find the volume of the base needed for the equivalence point.
- Halve the volume.
- Find pH at this volume.
- pH here = pka
What is a buffer solution?
One where the pH doesn’t change significantly if small amounts of acid or alkali are added to it.
What is an acidic buffer?
Made from a weak acid and the salt of that weak acid
E.g. Ethanoic acid and sodium ethanoate
What is a basic buffer?
Made from a weak base and salt o that weak base.
E.g. ammonia and ammonium chloride
How do buffer solutions work if small amounts of acid are added?
- Equilibrium shifts to the LHS
- To use up all of the H+ ions added
- As there is a large [ ] of the salt ion in the buffer, the ratio of [HX] / [X-] remains almost constant
- pH remains almost constant
Explain why [H2O] isn’t included in the Kw formula (2m)
- H2O conc is very high compared to [H+] and [OH-]
- H2O conc is effectively constant
Explain why choloroethanoic acid is a stronger acid than ethanoic acid (2m)
- Electronegative Cl withdraws electrons
- Weakens O-H bond as stabilises COO-
When do you observe the buffer region for a weak base and strong acid?
Greater than 7
When do you observe the buffer region for a weak acid and string base?
Below 7
Suggest how a titration curve procedure could be refined to identify a suitable indicator?
- Repeat with each proposed indicator
- Select one that has the most rapid colour change within the steep/vertical region of the graph- pH x-y
