Acids And Bases

Question 1

According to Arrhenius what is an acid

Answer 1

Substance that dissociates in water to produce H+ ions

Question 2

According to Brønsted-Lowry what is an acid?

Answer 2

A proton donor

Question 3

According to Arrhenius what is a base?

Answer 3

Substance that dissociates in water to produce OH- ions

Question 4

According to Brønsted-Lowry what is a base

Answer 4

a proton acceptor

Question 5

According to Arrhenius what is a strong acid (e.g. HNO3, HCl, H2SO4)

Answer 5

Substance that almost completely dissociates in water to give hydrogen ions

Question 6

According to Brønsted-Lowry what is a strong acid (e.g. HNO3, HCl, H2SO4)

Answer 6

A good proton donor

Question 7

According to Arrhenius what is a weak acid e.g. Ethanoic acid

Answer 7

Substance that only slightly dissociates in water to give hydrogen ions

Question 8

According to Brønsted-Lowry what is a weak acid e.g. Ethanoic acid

Answer 8

A poor proton donor

Question 9

According to Arrhenius what is a strong base

Answer 9

Substance that almost completely dissociates in water to give hydroxide ions

Question 10

According to Brønsted-Lowry what is a strong base

Answer 10

A good proton acceptor

Question 11

According to Arrhenius what is a weak base

Answer 11

Substance that only slightly dissociates in water to give hydroxide ions

Question 12

According to Brønsted-Lowry what is a weak base

Answer 12

A poor proton acceptor

Question 13

What is an alkali

Answer 13

A base that is soluble in water

Question 14

What are the limitations to Arrhenius’s theory of acids and bases (according to his theory)

Answer 14

1. H+ ions do not exist on their own in solution. They form the H3O+ ion
2. Arrhenius’s definitions are restricted to aqueous solutions. Water is not the only solvent: other solvents include liquid ammonia and benzene.

E.g. NH4 + HCl <=> NH4Cl
According to Arrhenius’s definition of acids and based, the above reaction would not be classed as an acid-base reaction because the reaction doesn’t happen in water.

3. NH3 can’t be considered a base- doesn’t dissociate go OH- ions in solution
4. water cannot be considered amphoteric (act as both an acid and base)

Question 15

Compare Arrhenius theory

Answer 15

• theory restricted to aqueous solutions
• Bases produce OH- ions in water
• some items cannot be classified as acids/bases due to strict definition (e.g. NH3 is not considered a base according to Arrhenius’s def)
• does not take hydronium ion formation into account
• does not explain how some substances can act as both an acid and a base in some reactions (amphoteric)

Question 16

Compare Brønsted-Lowry’s theory

Answer 16

• not restricted to aqueous solutions and can involve reactions that occur in the gaseous state
• not all bases produce OH- ions in solutions. NH3 is a base and does not produce OH- ions.
• broader range of acids and bases
• takes hydronium ion formation into account
• explains in terms of proton transfer how some substances can be amphoteric e.g. water and HpO4-2

Question 17

When does an acid become a conjugate base?

Answer 17

When it donates a proton

Question 18

When does a base become a conjugate acid

Answer 18

When it accepts a proton

Question 19

What is a conjugate acid base pair

Answer 19

Any pair consisting of in acid and a base that differ by a proton
An acid becomes it’s conjugate base after it has donated a proton