Core 1- Acids and bases

Question 1

Give a definition and example of arrhenius acid and arrhenius base

Answer 1

Arrhenius acid- ionises in water to give H⁺ and anions

HCl⇒ H⁺+Cl^-

Arrhenius base- ionises in water to give OH^- and cations.

NaOH⇒ Na⁺ + OH^-

Question 2

Give a definition of Bronsted Lowry acid and base and give example of each.

Answer 2

Bronsted Lowry acid- proton donor

CH3COOH + NaOH ⇒ Na⁺CH3COO^- + H2O

Bronsted Lowry base- proton acceptor

NH3 + H2O ⇔ NH4⁺ + OH^-

Question 3

What is lewis acid and lewis base. Give an example of each.

Answer 3

Lewis acid is electron pair acceptor

BF3 + NH3 ⇒ BF3<——NH3

Tranisition metal is also lewis acid

Lewis base is an electron pair donor.

BF3 + NH3 ⇒ BF3<——NH3

ligands in transition metal complex

Question 4

What happens during a neutralization reaction?

Answer 4

Proton is transferred from acid to a base to produce water and give a salt. This reaction is exothermic

Question 5

Which species contribute to acidity?

Answer 5

Hydroxonium ion (H3O⁺)

H+ doesn’t exist on its own and it solvates.

Question 6

What is conjugate acid?

Answer 6

Conjugate acid is base plus a proton

Question 7

What is conjugate base?

Answer 7

Acid minus proton.

Question 8

What is acid ( or base) strength?

Answer 8

It is tendency of an acid to give a proton (or accept a proton). It is governed by equilibria reactions.

Question 9

What is strong acid?

Answer 9

Acid which fully dissociates in a solvent.

Question 10

What is weak acid?

Answer 10

Acid that partially ionizes in a solution.

Question 11

What is Ka and its units?

Answer 11

Ka= ( [H3O⁺][A^-] )/[HA]

moldm^-3

Question 12

What is pKa? Why is it used over Ka?

Answer 12

pKa=-log(Ka)

This is used because Ka values are often very low or very big.

Question 13

Describe solvent levelling.

Answer 13

Solvent levelling is the idea that we can’t discriminate between the strongest acids or bases if sufficiently basic or acidic solvent is used.

Much weaker base or acid would be used to find discriminate between them. Solvent determines acidity of our acid.

Question 14

What is pH? What happens to pH when H+ increases?

Answer 14

pH= -log[H+]

When H+ increases, pH becomes lower. When H+ decreases, pH becomes higher.

Question 15

What is pOH? What happens when we increase OH concentration?

Answer 15

pOH= -log[OH]

As we increase concentration of OH-, pOH decreases and when we decrease concentration of OH-, pOH increases.

Question 16

What is Kw?

Answer 16

Kw=[OH^-][H3O⁺]

1 x 10^-14 mol^2dm^-6

Question 17

Give two relationships:

• between pOH, pH and pKw
• between pKa, pKb, pKw

Answer 17

pOH + pH= pKw

pOH + pH= 14 at 298K

pKa + pKb= pKw

pKa + pKb=14 at 298K

Question 18

What is a buffer solution?

Answer 18

Buffer solution is the solution that resists small changes in pH when small amount of acid or base is added.

Question 19

How is base solution prepared?

Answer 19

Base solution is prepared from a weak base and its conjugate acid (salt) or weak acid and its conjugate base (salt).

Question 20

Will weak acid reacting with strong base require the same amount to neutralise it as strong acid reacting with same strong base?

Answer 20

Yes, because they react in 1:1 ratio.

Question 21

What is Henderson Hasselbalch equation?

Answer 21

Question 22

What is equivalence point?

Answer 22

Equivalence point is the point at which equal amount of acids and bases are added so that they are both neutralised.

Question 23

What is an end point?

Answer 23

End point is the point at which the indicator changes colour. It should be the same as our equivalence point ideally.

Question 24

What is pH indicator? What is it used to monitor and how is it chosen?

Answer 24

pH indicator is a weak acid or a weak base wihch has differently coloured neutral and ionic forms. As pH changes by 1 unit, it goes through complete colour change.

It is used to check when titration is complete to find accurate concentration of our unknown solution. It is chosen so that the pKa=pH at equivalence point.

Question 25

What is mono, di, tri protic acid?

Answer 25

monoprotic acid has one H+ to donate

diprotic acid has 2 H+’s to donate

triprotic acid has 3 H+’s to donate

Question 26

As we start to remove more H+ from an acid, pKa becomes

Answer 26

HIGHER

Question 27

What is speciation curve?

Answer 27

Speciation curve shows us how does the concentration of different ions vary at different pH. Before next deprotonation starts, first acid needs to fully deprotonate.

Question 28

What is the property of amino acids?

Answer 28

Amino acids are amphoteric (amino group and carboxylic group).

Depending on pH, overall charge on an amino acid will change.

Question 29

What is zwitterion and isoelectronic point?

Answer 29

Zwitterion is the amino acids that has equal number of negative and positive charges. It has zero charge overall.

Isoelectronic point is the pH at which we have zwitterion.