Physical Chemistry Answers

Calculate the pH of pure water at 80oC if Kw of water at 800 C is 10-13.

A buffer was prepared by mixing 2.00 mole of liquor ammonia and 2.00 mole of

ammonium chloride to form an aqueous solution with a total volume of 5.00 litres.

To 1000 mL of this solution was added 30.0 mL of 1.00 M HCl. What will be the

change in pH of this solution? [pKb of Ammonium Hydroxide = 4.75]

A solution is 0.0010 M in both Ag+ and Au+. Some solid NaCl is added slowly until

the solid AgCl just begins to precipitate. What is the concentration of Au+ ions at this

point? At what concentration of Cl- ions will Ag+ precipitate as AgCl [Given: Ksp for

AgCl = 1.8 x 10-10 and for AuCl = 2.0 x 10-13]

A swimming pool in a club is maintained sufficiently alkaline so that the

CO2 absorbed from the atmosphere produced in the pool a solution which was 2 x 10-4 M in CO3 2- after about a day of refilling the swimming. If the pool water was originally 4 x 10-3 M in Mg2+, 6 x 10-4 M in Ca2+ and 8 x 10-7 M in Fe2+, then which of the following precipitates should be formed immediately a day after refilling of the swimming pool:

(a) only MgCO3

(b) only CaCO3

(c) only FeCO3

(d) only CaCO3 and FeCO3

(e) MgCO3, CaCO3 and FeCO3

Calculate the percentage change in the number of H+ ions during the titration of an

acid initially at pH = 3, when its pH increases to 5 on addition of a small amount of

alkali during the course of titration.

Derive an expression for Entropy Change accompanying an isothermal reversible

expansion of an ideal gas.

Hydrofluoric acid has a Ka value of 7.2x10−4. What is the pH of a 0.04M solution

of hydrofluoric acid?

A Carnot engine absorbs heat from a source at a higher temperature of 800 Kelvin

and the efficiency of the Carnot engine is 50%.

To what value the higher temperature should be increased for efficiency to increase

to 80%, if the lower temperature is kept constant.

In a Laboratory, you have the following chemicals available:

1.0 M NaOH, 1.00 M HCl, 1.00 M H3PO4, NaH2PO4 (s), Na2HPO4 (s), and Na3PO4 (s).

Describe TWO ways of making 1000 mL of a buffer of pH = 12 (Use only the above

chemicals, plus distilled water.)

[Given: H3PO4 - Ka1 = 6.9 x 10-3; NaH2PO4 - Ka2 = 6.2 x 10-8 ; Na2HPO4 - Ka3 = 4.8 x 10-13]

Describe the effect on the pH that results by adding

a. NaNO2 to HNO2

b. NaNO3 to HNO3