Self-Check Answers

 

Contact your teacher if your answers vary significantly from the answers provided here.

 

SC 3.

Test the following assumption:

This value is greater than 1000, so the approximation is valid. As a result, the change in the concentration of hydrosulfuric acid due to its ionization is very small, and the equilibrium concentration of hydrosulfuric acid is assumed to be 0.125 mol/L.

 

Let x = [H3O+(aq)]. Therefore,

 

         x = [HS–(aq)]

 

 

 

SC 4.

 

Practice 5.

1. 
   
   
2. 
   

   Amount Concentration	[C2H5COOH(aq)] (mol/L)	[C2H5COO–(aq)]  (mol/L)	[H3O+(aq)] (mol/L)
   Initial	0.100	0	0
   Change	–1.16 × 10–3	+1.16 × 10–3	+1.16 × 10–3
   Equilibrium	0.099	1.16 × 10–3	1.16 × 10–3

   
   
   

   
   

3. As with all equilibrium constants, the value is only constant at the temperature at which the data were collected.

Practice 6.

1. 
   
   
   
2. 
   

Amount Concentration	[C2H5OCOOH(aq)] (mol/L)	[C2H5OCOO–(aq)]  (mol/L)	[H3O+(aq)] (mol/L)
Initial	0.10	0	0
Change	–3.7 × 10–3	+3.7 × 10–3	+3.7 × 10–3
Equilibrium	0.10	3.7 × 10–3	3.7 × 10–3

 

3. The addition of the hydroxyl group increases the Ka by a factor of 10. Therefore 2–hydroxypropanoic acid ionizes ten times more than propanoic acid.