I understand that it breaks up into Al3+ and Br-, and Br- is negligible in regards to pH but Al3+ isn't. My question is this - how does Al3+ increase the H30+ concentration? It has no H's to donate!
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Aluminum hydroxide, Al(OH)3 is not soluble in water, because the Al+3 ion has strong covalent bond with the 3 OH-1 ions.
The concentration of OH-1 ions in pure water = 1 * 10^-7 mole/ liter
The concentration of H3O+1 ions in pure water = 1 * 10^-7 mole/liter
When AlBr3 dissolves in water, it produces Al+3 ions and Br-1 ions. The Al+3 ions bond with the OH-1 ions to produce Al(OH)3 molecules. Now the concentration of OH-1 ions is less than 1 * 10^-7 mole/ liter. So the concentration of H3O+1 ions is greater than 1 * 10^-7 mole/ liter.
A solution is acidic if the concentration of H3O+1 ions is greater than 1 * 10^-7 mole/ liter. So, the solution is slightly acidic!
Water can become acidic by adding H3O+1 ions, or by removing OH-1 ions!
The concentration of OH-1 ions in pure water = 1 * 10^-7 mole/ liter
The concentration of H3O+1 ions in pure water = 1 * 10^-7 mole/liter
When AlBr3 dissolves in water, it produces Al+3 ions and Br-1 ions. The Al+3 ions bond with the OH-1 ions to produce Al(OH)3 molecules. Now the concentration of OH-1 ions is less than 1 * 10^-7 mole/ liter. So the concentration of H3O+1 ions is greater than 1 * 10^-7 mole/ liter.
A solution is acidic if the concentration of H3O+1 ions is greater than 1 * 10^-7 mole/ liter. So, the solution is slightly acidic!
Water can become acidic by adding H3O+1 ions, or by removing OH-1 ions!
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Various salts can dissolve in water to make solutions which can be neutral or acidic or basic. It depends upon the ability of the anion or cation to react with water. Hydrolysis is the term used for reacting with water. The cations and anions of strong bases and acids to not hydrolyze.
Therefore, bromide ion, being the anion of the strong acid HBr, won't hydrolyze. But aluminum ion will react with water to make some or all of the following: AlOH^2+, Al(OH)2^+, Al(OH)3, Al(OH)4^-, along with H+. The H+ comes from water.
Al3+ + HOH --> AlOH^2+ + H+
Therefore, bromide ion, being the anion of the strong acid HBr, won't hydrolyze. But aluminum ion will react with water to make some or all of the following: AlOH^2+, Al(OH)2^+, Al(OH)3, Al(OH)4^-, along with H+. The H+ comes from water.
Al3+ + HOH --> AlOH^2+ + H+