two gchem questions

[gooperwooper]

why is van hoff factor of methanol 1? isn't it 2 because methanol loses the H in water? is it just 1 because methanol is such a weak acid?

and does Li3PO4- form a basic solution? I thought it did but got the question wrong.

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[aLemon]

Methanol has a van hoff factor of 1 since it is a non-electrolyte, it doesn't readily dissociate into two or more species. Electrolytes are basically your strong acids, bases and any ionic salt. When you add NaCl to an aqueous solution, NaCl dissociates into 2 ions (Na+ and Cl-)

Technically, methanol has a van hoff factor that is slightly greater than 1 (weak acid dissociation) but for the simplicity of the DAT we round it off.

I'm not sure about lithium phosphate producing a basic solution. Li+ is in group one so its a neutral cation. I would think the phosphate is only slightly basic, its kb value must be considerably small. Consider if the kb of the anion is smaller than the kb of water, it would make little effect on the pH of the solution!

 

[DAT Destroyer]

why is van hoff factor of methanol 1? isn't it 2 because methanol loses the H in water? is it just 1 because methanol is such a weak acid?

and does Li3PO4- form a basic solution? I thought it did but got the question wrong.

Methanol is not very acidic, it has a pKa of approximately 16 in water,,,,,thus gives very few hydronium ions.....Like virtually all organic compounds ( carboxy acids, sugars, alcohols ) i = 1 !!!!! They are essentially all non-electrolytes. Li3P04 will indeed form a basic solution.....it is derived from LiOH, a strong base and a relatively weak acid, H3PO4.

Hope this helps.

Dr. Romano

 

[gooperwooper]

perfect thank you Dr. Romano!

 

[Denevistas]

I am having trouble understanding why the answer here is B....

 

[gooperwooper]

you can see that the oxidation potential of the reaction from h2o to o2 is -1.23 (it's negative because the table shows reduction potentials). so to create a spontaenous reaction that will actually progress you need reduction potentials of the halogens that are greater than 1.23, chlorine and fluorine have potentials greater than 1.23 so they will successfully oxidize h2o to o2 but bromine is only 1.07V which results in a negative E which means the rxn is nonspontaneous and won't proceed.

 

[Denevistas]

I see. So we do not consider the reduction of BrO3- (+1.52) at all?