Question

A range of different compounds is listed below: O2, CO2, HCl, NaCl, CH4, C8H18, CH3CH2OH, (CH3)2CHNH3 +Cl- , CH3(CH2)6OH.

2. Find and compare their molar solubilities (mol/L) in water at ambient conditions. Briefly discuss how solubility is related to molecular structure. Describe possible effects of raising temperature and pressure on solubility of these species.

I only need to know how to calculate their molar solubilities in mol/L. A step by step solution to only one compound is necessary and I can go from there.

Answer 1

Answer:

According to tables, the solubility in water (in g/mL) for each compound at 20 ºC is:

Compound		solubility
O2	gas	0.009 g / L
CO2	gas	1.70 g / L
HCl	gas	710 g / L
NaCl	solid	360 g / L
CH4	gas	0.023 g / L
C8H18	liquid	insoluble
CH3CH2OH	liquid	infinitely soluble
(CH3)2CHNH3+Cl-	solid
CH3(CH2)6OH	liquid	0.54 g / L

With this data and the molecular weight of each compound you can transform solubity in g/ L to molar solubility:

• For oxygen:

Compound	solubility	MW	Molar solubility
O2	0.009 g / L	32 g/mol	2.81x10-4 mol/L
CO2	1.70 g / L	44 g/mol	0.0386 mol/L
HCl	710 g / L	36.5 g/mol	19.45 mol/L
NaCl	360 g / L	58.4 g/mol	6.164​​​​​​​ mol/L
CH4	0.023 g / L	16 g/mol	1.44x10-3​​​​​​​ mol/L
C8H18	insoluble	114 g/mol	insoluble
CH3CH2OH	infinitely soluble	46 g/mol	infinitely soluble
(CH3)2CHNH3+Cl-	soluble	95.5 g/mol	soluble
CH3(CH2)6OH	0.54 g / L	130 g/mol	4.15x10-3​​​​​​​ mol/L

• In general, gas compounds are less soluble in water than liquid compounds with similiar molecular weight.
• For liquids and solids, the solubility in water depends of the structure of the molecule
• Polar compounds (HCl, CH2CH2OH) are more soluble in water than apolar compounds (CH4)
• In organic compounds, long chains of carbons reduce the solubility in water: CH3CH2OH > CH3(CH2)6OH
• Some functional groups, as -OH, increases solubility in water: CH3CH2OH > CH4
• Increasing pressure only affects the solubilty of gas compounds. A higher pressure = higher solubility of gas in water
• Increasing temperature affects the solubilty of all compounds.
  • Gas => higher temperature = lower solubility of gas in water
  • Liquids and solids => higher temperature = higher solubility of gas in water