12. Acid Base Equilibrium Flashcards
(34 cards)
What is a bronsted Lowry acid
A proton donor that releases hydrogen ions when they’re mixed with water
What is a bronsted Lowry base
A proton acceptor. When in solution they grab hydrogen ions from the water molecules
What is a strong acid
An acid that dissociates almost completely in water. - nearly all of the H+ ions will be released
What is a weak acid
A weak acid only slightly dissociates in water so small amounts of H+ ions are formed
What is a conjugate pair
Species that are linked by the transfer of a proton and are always on opposite sides of the reaction.
What is a conjugate base
The species that has lost a proton and the species that has gained the proton is the conjugate acid
What happens when acids and bases react together
A salt and water is produced
What does the concentration of H+ ion have to be equal to, to form a neutral solution
OH- ions
What is the standard enthalpy change of neutralisation
The enthalpy change when solutions of an acid and a base react together under standard conditions to produce 1 mole of water
What is the pH scale
A measure of the hydrogen ion concentration
Equation for pH
pH = -log [H+]
What can strong acids be called and what does it mean
Monoprotic - it means that one mole of acid produces one mole of hydrogen ions as they can only release 1 protons into solution
What is a polyprotic acid
An acid that can release more than one proton into solution so one mole of acid released more than one mole of [H+] ions
How to find the pH of weak acids
Ka=[H+][A+]/[HA]
Ka=[H+]^2/[HA]
Why can water be an acid and a base
It can act as an acid by donating a proton but can also act as a base by accepting a proton. This means that hydroxonium and hydroxide ions are present in water at the same time, therefore water is in equilibrium.
Why is the concentration of water considered to be a constant value
This is due to water only dissociating a small amount and the amount of water compared to the amount of H+ and OH- meaning its concentration is deemed constant
Equation for Kw
Kw = [H+][OH-]
Kw for pure water is….
Always the same value at a given temperature.
pKw =
-log Kw
Kw from pKw =
10^-pKw
How to measure the pH of a solution using a pH meter
Make sure the pH meter is correctly calibrated by placing into deionised water and setting the reading to 7. Doing the same for solutions pH 4 and pH 10. Make sure to rinse with deionised water between readings.
Place the probe in the solution and leave to settle before recording a result.
Ensure you rinse the probe with deionised water between each measurement
What do pH titrations tell you
Exactly how much base is needed to neutralise a quantity of acid.
How to plot a pH curve
Plot the pH of the titrated mixture against the amount of base that has been added.
How to choose an indicator for a pH titration
Choosing the correct indicator is important as some indicators only work in between a certain pH range.
Methyl orange red 3.1 ——-4.4 yellow
Phenolphthalein colourless 8.3 ——-10 pink
