Will 0.10 M aqueous solutions of the following salts be acidic , basic or neutra

Question

Will 0.10 M aqueous solutions of the following salts be acidic , basic or neutral? (Assume a solution is neutral if its pH is 7.00±0.05). Equilibrium constants may be found in an appendix of textbook.

ammonium formate (NH4CHO2)
sodium acetate (NaC2H3O2)
ammonium acetate (NH4C2H3O2)
ammonium sulfide ((NH4)2S)
sodium dihydrogen citrate (NaH2C6H5O7)

Using tabulated Ka and Kb values, calculate the pH of the following solutions.
Answer to 2 decimal places.

A solution containing 1.9×10-1 M HNO2 and 2.4×10-1 M NaNO2.

700.0 mL of solution containing 7.0 g of HF and 15.0 g of NaF.

A solution made by mixing 110.00 mL of 1.100 M CH3COOH with 35.00 mL of 0.750 M NaOH.

I can get Ka/Kb values if needed from my textbook.

Explanation / Answer

ammonium formate (NH4CHO2)

pKa Formic acid = 3.75

pKb Ammonia = 4.75

Since pKa < pKb, expect a higher hydrolysis of the acid...

Formate will form formic acid, therefore pH will be basic i.e. greater than 7

sodium acetate (NaC2H3O2)

pKa = 4.75

acetate will form acetatic acid, therefore pH will be basic i.e. greater than 7

Ammonium acetate (NH4C2H3O2)

pKa = 4.75

pKb = 4.75

Since both weak acid/base have the same hydrolysis power, expect H+ and OH- in smae quantities

acetatewill form acetic acid, Then NH4+ will form NH3, giving up H3O

Kb = Ka (coincidence) thereofre this will be neutral

the pH will be near 7

ammonium sulfide ((NH4)2S)

Sulfide will form S-ions, therefore HS and H2S

NH4 will free NH3 and H+ ions, expect pH near 7

pKa = 7

pKb = 4.75

pKB < pKa, therefore expect hydrolysis of ammonia, forming an acidic solution

sodium dihydrogen citrate (NaH2C6H5O7)

NaH2C6H5O7 --> Na+ and H2C6H5O7-

H2C6H5O7- May:

H2C6H5O7- + H2O <---> HC6H5O7-2 + H3O+

or

H2C6H5O7- + H2O <---> H3C6H5O7 + OH-

Compare pKa vs. pKb

pKa = 4.74

pKb = (14-4.74) = 9.26

Since pKa < pKb, expect hyrolysis of the acid....

Citric acid will donate 1 H+ proton

citric acid has Ka, therefore will get H+ ions form H2O, to get OH- in solution, expect acidic solution

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