acids ad bases

Question 1

how can an aqueous solution of an acid have hydroxide ions?

Answer 1

the water dissociates

H2O⇌ H+ + OH-

Question 2

explain why a buffer has formed when XS (aq) ethanoic acids reacts with solid calcium carbonate.

Answer 2

the solution contains both CH3COO- and CH3COOH in excess.

Question 3

In biochemistry, buffer solutions based on methanoic acid can be used in the analysis of urine
samples.
(i) Explain what is meant by the term buffer solution.
Describe how a buffer solution based on methanoic acid can act as a buffer.
In your answer you should explain how the equilibrium system allows the buffer solution
to control the pH.

Answer 3

1) a buffer solution is one that resists changes in pH on addition of small amounts of acid or base. (1)
HCOOH ⇌ H+ + HCOO– (1)
when alkali added H+ reacts with the OH to form water however he decrease in H+ means that eq position shifts RIGHT to increase H+ conc
OH + h+ —> H2O
when acids added, HCOO- reacts with the acid(H+) and equilibrium position will shift left.
H+ + HCOO- –> HCOOH

Question 4

The student adds 50.0 cm3 of 0.250 mol dm–3 butanoic acid to 50.0 cm3 of 0.0500 mol dm–3
sodium hydroxide. A buffer solution forms.
(i) Explain why a buffer solution forms.

Answer 4

• because some butaoic acid is n excess

and the sodium salt forms , CH3(CH2)2COO–