Acids and Bases - Section 19.1 A-level Chemistry CAIE

What is the main difference between a strong acid and a weak acid?

• Strong acids are more concentrated than weak acids.

• Strong acids completely dissociate in water, while weak acids only partially dissociate.

• Strong acids have a higher pH than weak acids.

• Strong acids are more corrosive than weak acids.

Answer explanation

Strong acids, such as HCl and HNO3, completely dissociate in water to produce H+ ions, whereas weak acids, such as CH3COOH and HCN, only partially dissociate.

Which of the following is an example of a strong base?

• NaOH

• NH3

• CH3NH2

• H2O

Answer explanation

NaOH is a strong base because it completely dissociates in water to produce OH- ions.

What is the pH of a neutral solution?

• 0

• 7

• 14

• -1

Answer explanation

A neutral solution has a pH of 7, which is the pH of pure water.

What is the conjugate base of the acid HCN?

• CN-

• H2CN+

• HCN

• H+

Answer explanation

The conjugate base of an acid is the species formed when the acid donates a proton (H+). In this case, HCN donates a proton to form CN-.

Which of the following is an example of a buffer solution?

• A solution of HCl and NaCl

• A solution of CH3COOH and CH3COONa

• A solution of NaOH and HCl

• A solution of H2O and H+

Answer explanation

A buffer solution is a mixture of a weak acid and its conjugate base, which resists changes in pH. In this case, CH3COOH and CH3COONa form a buffer solution.

What is the Ka value of a strong acid?

• 1

• 10

• 100

• undefined

Answer explanation

Strong acids completely dissociate in water, so their Ka values are undefined.

What is the Kb value of a strong base?

• 1

• 10

• 100

• undefined

Answer explanation

Strong bases completely dissociate in water, so their Kb values are undefined.

Which of the following is an example of a Lewis acid?

• H+

• BF3

• NH3

• H2O

Answer explanation

A Lewis acid is a species that accepts a pair of electrons. BF3 is a Lewis acid because it accepts a pair of electrons from a Lewis base.

What is the pH of a solution with a pOH of 4?

• 10

• 6

• 8

• 2

Answer explanation

pH + pOH = 14, so if pOH = 4, then pH = 10.

Which of the following is an example of a salt of a strong acid and a weak base?

• NaCl

• NH4Cl

• CH3COONa

• NaNO3

Answer explanation

H4Cl is a salt of the strong acid HCl and the weak base NH3.