Why is solubility of HBr Less Than HCl ?

In summary, the maximum concentration of dissolved HBr (8.9 moles/L) is lower than that of HCl (12 moles/L). However, various sources suggest that HBr should be more soluble at STP in 1 liter of water due to its enthalpy of formation and hydration/dissociation being more negative, lower vapor pressure, higher Ka value, and a more negative free energy. Additionally, the size of the ion may also play a role in the solubility of HBr.
  • #1
morrobay
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The maximum concentration of dissolved HBr , 8.9 moles/L is less than HCl 12 moles/L
The values from table below from various sources suggest that HBr should be more soluble at STP in 1 liter water ?
.........HBr.......HCl
enthalpy of formation....-53kJ.mole >>>>>>>>>>>>>>>-96kJ/mole
enthalpy of hydration/dissociation -64kJ/mole<<<<<<<<<<<<<<<-60kJ/mole
vapor pressure...... 16mmHg<<<<<<<<<<<<<<<<<28mmHg
Ka .........9>>>>>>>>>>>>>>>>>>>>>>7
ΔG=-RTlnKeq(Ka)......<<<<<<<<<<<<<<<<<<<<<<<<
Acid strength........>>>>>>>>>>>>>>>>>>>>>>>>
pH.........-.95>>>>>>>>>>>>>>>>>>>>>-1.08
dissolved mass......712g>>>>>>>>>>>>>>>>>>>>>>432g
 
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  • #2
morrobay said:
The maximum concentration of dissolved HBr , 8.9 moles/L is less than HCl 12 moles/L
The values from table below from various sources suggest that HBr should be more soluble at STP in 1 liter water ?
.........HBr.......HCl
enthalpy of formation....-53kJ.mole >>>>>>>>>>>>>>>-96kJ/mole
enthalpy of hydration/dissociation -64kJ/mole<<<<<<<<<<<<<<<-60kJ/mole
vapor pressure...... 16mmHg<<<<<<<<<<<<<<<<<28mmHg
Ka .........9>>>>>>>>>>>>>>>>>>>>>>7
ΔG=-RTlnKeq(Ka)......<<<<<<<<<<<<<<<<<<<<<<<<
Acid strength........>>>>>>>>>>>>>>>>>>>>>>>>
pH.........-.95>>>>>>>>>>>>>>>>>>>>>-1.08
dissolved mass......712g>>>>>>>>>>>>>>>>>>>>>>432g

Correction : Vapor pressures at above concentrations HCl , 12 m/l = 15 mm Hg
HBr, 8.9 m/l = 4.5 mm Hg.
Dissolved mass is for general information only
Just based on a more negative free energy alone should indicate a higher maximum concentration for HBr
 
  • #3
I have a gut feeling we can't ignore size of the ion - while the molar values are different, there is only so much of a substance that fits given volume.

Or at least that would be the starting point for my analysis. Doesn't have to yield any explanation.
 

1. Why is HBr less soluble than HCl?

The solubility of a compound is influenced by factors such as the strength of the intermolecular forces and the polarity of the molecules. In the case of HBr and HCl, HCl has stronger intermolecular forces due to its smaller size and higher electronegativity, making it more soluble in water compared to HBr.

2. How does temperature affect the solubility of HBr and HCl?

Generally, as the temperature increases, the solubility of most substances also increases. This is because higher temperatures provide more energy for the molecules to overcome intermolecular forces and dissolve in water. However, in the case of HBr and HCl, the difference in solubility becomes less significant at higher temperatures due to the formation of hydrogen bonds between the molecules and water.

3. Why does the solubility of HBr decrease with increasing concentration?

At low concentrations, the solubility of HBr is higher due to the formation of HBr-H2O complexes. However, as the concentration of HBr increases, these complexes become more crowded and less stable, leading to a decrease in solubility.

4. What is the effect of pH on the solubility of HBr and HCl?

The pH of a solution can affect the solubility of acids, including HBr and HCl. In acidic solutions, the solubility of HBr and HCl increases as they dissociate into their respective ions, making them more soluble. However, in basic solutions, the solubility of these acids decreases as they are less likely to dissociate.

5. How does the solubility of HBr and HCl change with pressure?

The solubility of gases in water decreases with increasing pressure. Since HBr and HCl are both gases at room temperature, their solubility decreases with increasing pressure. This means that at higher pressures, more of these gases will remain in their gaseous form rather than dissolving in water, resulting in lower solubility.

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