Acids and Bases

Question 1

What is a bronstead acid?

Answer 1

A bronstead acid is a molecule that can donate a proton to a base e.g CH₃COO^- + H⁺

Question 2

What is a bronstead base?

Question 3

What is a base?

Answer 3

A molecule that can pick up a proton

Question 4

What is an acid?

Answer 4

Any molecule that contains H joined to a more electronegative atom

Question 5

What is the pH equation?

Answer 5

pH= -log [H₃O⁺]

Question 6

What is the equation for [H₃O⁺]?

Answer 6

[H3O+] = 10^-pH

Question 7

What is the K_a equation?

Answer 7

Ka = [A^-][H₃O⁺] / [HA]

Question 8

What does a high pKa mean?

Answer 8

A high pK_a means that it is a weak acid. A weak acid has a strong conjugate base. A pK_a can go into negative digits.

Question 9

What makes a strong acid?

Answer 9

1. More positive or less negative charge
2. Charge stabilisation by;
   
   • Inductive effects
   • Delocalisation

Question 10

What does the following tell us?

1. pH < pK_a
2. pH = pK_a
3. pH > pK_a

Answer 10

When pH is less than pK_a there is more acid then base with pH equals pK_a they are equal when pH is greater than pK_a there is more conjugate base then acid

Question 11

What is speciation?

Answer 11

Speciation is the amount of each species in solution when they are at different forms. This occurs different pH levels depending on the pK_a of each acid and conjugate base

Question 12

What is interesting about amino acids at pH 7?

Answer 12

The form a zwitterion which is whern the CHOO^- group has lost an H but the NH₃⁺ has an extra charge so the whole molecule has no net charge however both of the side chains are charged

Question 13

What changes on an amino acid between pH 7 and pH 1?

Answer 13

At pH 7 there is a zwitterion where as pH 1 the COO- group has an H = COOH therefore the whole amino acid is +ve charged

Question 14

What changes on an amino acid between pH 7 and pH 12?

Answer 14

At pH 7 a zwitterion forms however at pH 12 the NH3 group has lost an H and is no longer +ve this means that the whole molecule is now has a -ve charge

Question 15

What is one assumption we make when a strong acid reacts with water?

Answer 15

Only the strong acids contributes to the H30+ concentration this is not true when the calculated pH is > 6

Question 16

What is one assumption we make when a strong base reacts with water?

Answer 16

We make the assumption that only strong bases contribute to the OH^- concentration this is not true when the pH < 8.

It is important to remember that pH = 14 - pOH

Question 17

What is an amphoteric species? what is the equation?

Answer 17

An amphoteric species can be both a weak acid and a weak base.

pH =0.5 (pK_a1 = pK_a2)

Question 18

What is a buffer?

Answer 18

The buffer is when a weak acid and its congee get bass exist in water this resists changes to pH when other acids or bases added.

Question 19

What is the difference between a pH buffered solution and an unbuffered solution

Answer 19

A buffered solution will not be affected by dilution however an Unbuffered solution Will be affected by dilution

Question 20

What is important about the Half- equivalence point?

Answer 20

It is where pH = pK_a

Question 21

what is the equivalence point?

Answer 21

Where the reaction is 100% complete and there is only conjugate acid present

Question 22

What are indicators?

Answer 22

Acids and bases