What is a mesure of the acidity of a compound?

2 Answers
Apr 20, 2017

Answer:

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.

compoundchem.com

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 :)

Apr 20, 2017

Answer:

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.