The ethylammonium ion, CH3CH2NH3+, has a pKa of 10.81. It reacts with water to form ethylamine, CH3CH2NH2 and H3O+.
Which of the following statements is true at pH 7?
A.) ethylamine predominates
B.) ethylammonium ion predominates
C.) the pH is higher than pKa of the ethylammonium ion
D.) the concentration of ethylamine equals that of ethylammonium ion
To determine which statement is true at pH 7, we need to compare the pH to the pKa value of the ethylammonium ion.
The pKa value represents the acidity of a substance. If the pH is higher than the pKa, it means the solution is more basic (alkaline) and vice versa.
pH 7 is considered neutral, so we need to compare it to the pKa value of 10.81.
Since pH 7 is lower than the pKa value of 10.81, we can conclude that the ethylammonium ion will predominately be in its protonated form (CH3CH2NH3+) rather than being deprotonated to form ethylamine (CH3CH2NH2).
Therefore, the correct answer is B.) ethylammonium ion predominates.
To determine which statement is true at pH 7, we need to compare the pH with the pKa of ethylammonium ion, which is 10.81.
pH is a measure of the concentration of H3O+ ions in a solution. A pH of 7 means that the concentration of H3O+ ions is equal to 10^(-7) M.
pKa represents the acidity of a compound. A pKa of 10.81 indicates that ethylammonium ion is a weak acid and tends to lose a proton to form ethylamine. When the pH is higher than pKa, it means that the concentration of H3O+ ions is lower than the concentration of the conjugate acid, ethylammonium ion.
Now let's analyze the statements:
A.) ethylamine predominates
This statement suggests that ethylamine is the major species formed. Since the pKa of ethylammonium ion is higher than the pH of 7, ethylammonium ion tends to lose a proton and form ethylamine. Therefore, statement A is correct.
B.) ethylammonium ion predominates
Given that the pKa of ethylammonium ion is higher than the pH of 7, ethylammonium ion tends to lose a proton and form ethylamine. Therefore, statement B is incorrect.
C.) the pH is higher than pKa of the ethylammonium ion
This statement is correct. The pH of 7 is lower than the pKa of the ethylammonium ion, which is 10.81.
D.) the concentration of ethylamine equals that of ethylammonium ion
Since the ethylammonium ion tends to lose a proton and form ethylamine, the concentration of ethylamine would be higher than that of the ethylammonium ion. Therefore, statement D is incorrect.
In conclusion, at pH 7, statement A is true: ethylamine predominates.