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Chemistry > 12. Acid Base Equilibrium > Flashcards

12. Acid Base Equilibrium Flashcards

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1
Q

What is a bronsted Lowry acid

A

A proton donor that releases hydrogen ions when they’re mixed with water

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2
Q

What is a bronsted Lowry base

A

A proton acceptor. When in solution they grab hydrogen ions from the water molecules

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3
Q

What is a strong acid

A

An acid that dissociates almost completely in water. - nearly all of the H+ ions will be released

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4
Q

What is a weak acid

A

A weak acid only slightly dissociates in water so small amounts of H+ ions are formed

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5
Q

What is a conjugate pair

A

Species that are linked by the transfer of a proton and are always on opposite sides of the reaction.

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6
Q

What is a conjugate base

A

The species that has lost a proton and the species that has gained the proton is the conjugate acid

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7
Q

What happens when acids and bases react together

A

A salt and water is produced

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8
Q

What does the concentration of H+ ion have to be equal to, to form a neutral solution

A

OH- ions

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9
Q

What is the standard enthalpy change of neutralisation

A

The enthalpy change when solutions of an acid and a base react together under standard conditions to produce 1 mole of water

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10
Q

What is the pH scale

A

A measure of the hydrogen ion concentration

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11
Q

Equation for pH

A

pH = -log [H+]

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12
Q

What can strong acids be called and what does it mean

A

Monoprotic - it means that one mole of acid produces one mole of hydrogen ions as they can only release 1 protons into solution

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13
Q

What is a polyprotic acid

A

An acid that can release more than one proton into solution so one mole of acid released more than one mole of [H+] ions

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14
Q

How to find the pH of weak acids

A

Ka=[H+][A+]/[HA]

Ka=[H+]^2/[HA]

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15
Q

Why can water be an acid and a base

A

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.

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16
Q

Why is the concentration of water considered to be a constant value

A

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

17
Q

Equation for Kw

A

Kw = [H+][OH-]

18
Q

Kw for pure water is….

A

Always the same value at a given temperature.

19
Q

pKw =

A

-log Kw

20
Q

Kw from pKw =

A

10^-pKw

21
Q

How to measure the pH of a solution using a pH meter

A

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

22
Q

What do pH titrations tell you

A

Exactly how much base is needed to neutralise a quantity of acid.

23
Q

How to plot a pH curve

A

Plot the pH of the titrated mixture against the amount of base that has been added.

24
Q

How to choose an indicator for a pH titration

A

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

25
Q

What is a Buffer

A

A solution that has minimal changes in pH when small amounts of acid or bases are added.

26
Q

What is an acidic buffer

A

They have a pH less than 7 and are made up of an equilibrium between a weak acid and its conjugate base.

27
Q

Buffer action on a titration curve

A

When the curve levels off this is due to a buffer solution formed to resist further dramatic change to pH

28
Q

What pH does blood need to be kept at

A

pH 7.4

29
Q

How is the pH of the blood controlled

A

Using carbonic acid-hydrogen carbonate buffer system. Carbonic acid dissociates into H+ ions and HCO3- ions which react with excess H+ ions if the concentrations of these in the blood rises.

If the concentration of H+ ions falls then H2CO3 from the buffer system dissociates and equilibrium shifts so that the original value of H+ ions returns

30
Q

What are levels of H2CO3 controlled by

A

Respiration by breathing out CO2

31
Q

What are the levels of HCO3 controlled by

A

The kidneys with excess being excreted in the urine

32
Q

What is the Henderson-Hasselbalch equation

A

pH = pKa + log ([A-]/[HA])

33
Q

First equivalence point is…

A

When enough base has been added to neutralise the first acidic proton

34
Q

The second equivalence point is…..

A

When enough base has been added to neutralise the second acidic proton in polyprotic acids

Chemistry (14 decks)

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