Page 95 - Basic physical chemistry for the atmospheric sciences

Solution chemistry and aqueous equilibria M l

(i) Although the solubility product (K,P) and the molar sol­
ubility of a slightly soluble substance are related , they
are never equal.
(j) How would you induce the precipitation of a soluble
substance from a solution? Give an example.
4. 1 0 . A solution f density . 8 8 g mL - 1 consists of 9 g f toluene
8
o
o
0
.
)
(C7H ) in 452 g of benzene (C6H6 . What is the concentration
8
of toluene in the solution as a mass/total mass percentage, as
a molarity, as a molality, and as a mole fraction?
4. 1 1 . Show that if a solute dissolves in a liquid with an endother­
mic heat of solution, the solubility of the solute in the liquid
will increase with increasing temperature.
4. 1 2. Eighty cubic centimeters of hydrogen sulfide gas (H 2 S),
1
measured at STP, can dissolve in 8 . 3 g of water. What will
be the molal concentration of a saturated solution of
H2S(aq) in water at 8 . 0 atm pressure?
i
4 . 1 3 . A constant humidity can be produced n a small enclosure
by placing in the enclosure an aqueous solution of the ap­
propriate concentration. How much glycerin (C3H903)
would have to be placed in 1 . 00 kg of water to achieve a
water vapor pressure of 2 .0 mm of mercury at 20°C. (Satu­
1
rated vapor pressure of water at 20°C is 1 7 . 5 mm of
.
mercury )
4. 1 4 . What proportions (by volume) of water and ethylene glycol
(C2H 0 2 ) must be mixed to form a solution with a freezing
6
point of - 1 0 °C? (Kr = l 8 6°C molality - I for water; density
.
3
of ethylene glycol is 1 . 1 2 g cm - . )
4. 1 5 . Which of the following compounds are soluble n water (i. e . ,
i
e
have solubilities ;;:::: 0 . 1 M) and which have low solubiliti s :
l
CuCI, Ag , Ba(OHh, KN03, H2S04, Mg(OH)z, and HC ?
I
4. 1 6 . A m monium nitrate (NH4N03) dissolves in water with an
endothermic heat of reaction of 26.4 kJ mol - 1 • How much
ambient heat will be absorbed when 2.0 kg of ammonium
nitrate dissolves in water? (This reaction is utilized in in­
i
stant ice packs for treating injuries. Solid ammonia nitrate s
contained inside a thin-walled plastic bag, which is sealed
inside a thicker bag that also contains some water. The
inner bag can be broken by pressing the outer bag, thereby
allowing the ammonium nitrate to form a solution with the
water which gets quite cold. )