Question

1. what chemical reaction is responsible for the endpoint observed when the NH3/NH4Cl buffer solution is titrated with HCl? Write a balanced ionic equation for the reaction.

2. Compare the rate at which pH changes when HCl is added to the buffer solution to the rate of change when no buffer or base is present (distilled water).

3. What effect does dilution of the buffer have on the initial pH, On the pH at the endpoint? On the volume of HCl required to reach the endpoint?

4.If excess ca(NO3)2 were present. what effect would it have on the solubility of Ca(OH)2 ?

5. If HCl(aq) were added to the NiCO3, precipitate, rather than NH3(aq), what effect would it have on the solubility? Write a balanced ionic equation for the reaction of HCl(aq) with NiCO3(S).

Answer 1

1) The reaction that occurs is:

NH3 + H + + Cl- = NH4Cl

2) The buffer system creates a balance between the amount of acid and conjugate base, which decreases the rate of change of pH if HCl is added, compared to a solution that does not form a buffer.

3) The dilution of the buffer affects the amount of moles of the components of the buffer per solution volume.

The initial pH is not affected. The volume of HCl required to break the buffer is less than when the buffer is concentrated.

4) The solubility of Ca (OH) 2 would decrease, since there is a common Ca + 2 ion effect.

5) The reaction that occurs is:

2 HCl + NiCO3 = NiCl2 + CO2 + H2O

Ionic:

2 H + + 2 Cl- + Ni + 2 + CO3-2 = Ni + 2 Cl2- + CO2 + H2O

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