Question

1.)Write the net-ionic equation for the following titration at the equivalence point

Strong acid (HA) and Strong Base (MOH)

Weak acid (HB) and Strong Base (MOH)

Weak base (B) and Strong acid (HA)

1. a) draw the titration curves for each of the following; be sure to show where the equivalence point, and midpoint would occur!

Adding 100 mL of 1.0M NaOH to 50.0 mL of 1.0M HCl

Adding 100 mL of 1.0 M NaOH to 50 mL of 1.0M HCN

c) Adding 100 mL of 0.10 M HCl to 50 mL of 0.10 NH₃:

3.)Write a formula of determining the amount of titration required to reach the equivalence point

Can I titrate a solution of unknown concentration with another solution of unknown concentration and still get a meaningful answer? Explain your answer in a few sentences.

Answer 1

Net-ionic equation for the following titration at the equivalence point..

1. Strong acid (HA) and Strong Base (MOH):

HA + MOH = M⁺A^- + H₂O

2. Weak acid (HB) and Strong Base (MOH):

HB + MOH = M⁺B^- + H₂O

At equivalence point salt will be hydrolysed..

B^- + H₂O = HB + OH^- .... Net reaction at equivalence point.

3. Weak base (B) and Strong acid (HA):

HA + BOH = B⁺A^- + H₂O

B⁺ + H₂O = BOH + H⁺.... Net reaction at equivalence point.

The titration curves:

1. Adding 100 mL of 1.0M NaOH to 50.0 mL of 1.0M HCl.

This is a titration of strong acid with a strong base. Use the relation V₁S₁=V₂S₂ to determine the conc of H+ in the solution and determine pH.

Volume of alkali added                                 pH

0                                                                         0.00

25                                                                       0.48(mid point)

50                                                                       7.00(eqv point)

50.1                                                                   11.00

50.5                                                                   11.70

2. Adding 100 mL of 1.0 M NaOH to 50 mL of 1.0M HCN.

HCN andNaCN will act as buffer upto eqv point. Before eqv point pH can be measured using Henderson equation pH= pK_a + log [salt]/ [acid]. At mid point salt and base concentration will be same, hence pH= pK. At eqv point CN^- will be hydrolysed and pH can be measured using the eqn pH= 0.5[pK_w + pK_a + logC].After eqv point pH can be measured simply by determining conc of OH^- in the solution.

Volume of alkali added                                 pH

0                                                                         0

25                                                                       9.2

50                                                                       11.4

50.5                                                                   11.7

3. Adding 100 mL of 0.10 M HCl to 50 mL of 0.10 NH₃:

Same method as above. The equations will be slightly changed.

pOH = pK_b + log [salt]/[base] upto eqv point

pH= 14 -pOH

At eqvpoint, pH= 0.5[pK_w - pK_b - logC]

Volume of acid added                                   pH

0                                                                         13.3

25                                                                       9.3

50                                                                       5.3

50.1                                                                   4

If the eqv point comes at pH=7, then you can assume that the solutions you are using are strong acid and base. If eqv point comes below 7 you can assume that the acid is strong and the base is weak. If eqv point comes above 7, the base is strong and the acid is weak.