Question

What is a mesure of the acidity of a compound?

Answer 1

pH. It measures the concentration of hydrogen ions in a solution.

Explanation:

pH is a measure of the hydrogen ion concentration in a solution.

The higher the concentration, the more acidic the solution.

You can calculate pH by using the formula: `"pH" = -"log"[H^+]`
=> Where `"log"` is the logarthmic sequence for exponents (you don't need to worry about this if you didn't learn this in math - just use it correctly in this equation).
=> Where `H^+` is the concentration of hydrogen ions in the solution, in `"mol"/L`.

Hope this helps :)

Answer 2

Why, the `pH` of its aqueous solution......

Explanation:

When we assess the acidity of a compound we interrogate the completion of the following equilibrium.........

`HX + H_2O rightleftharpoons H_3O^+ + X^-`

As with any equilibrium, we can write the `K_a`:

`K_a=([H_3O^+][X^-])/([HX])`

This is an equation, that we can treat as we would any other equation.......We can take `log_10` of both sides to give.......

`log_10K_a=log_10[H_3O^+]+log_10{[[X^-]]/[[HX]]}`

On rearrangement..............

`-log_10[H_3O^+]=-log_10K_a+log_10{[[X^-]]/[[HX]]}`

But by definition, `pH=-log_10[H_3O^+]` AND

`pK_a=-log_10K_a`

And so, finally...............

`pH=pK_a + log_10{[[X^-]]/[[HX]]}`

So given the `pK_a` of an acid, and a measurement of `pH`, the concentration of the weak acid, and its conjugate base, may be accessed. The final equation is a form of the `"buffer equation"` that you will use extensively.