Question 1: A beaker with 1.00 times 102 mL of an acetic acid buffer with a pH o

Question

Question 1:

A beaker with 1.00 times 102 mL of an acetic acid buffer with a pH of 5.000 is sitting on a bench top. The total molarity of acid and conjugate base in this buffer is 0.100 M. A student adds 5.40mL of a 0.440 MHCl solution to the beaker. How much will the pH change? The pKa of acetic acid is 4.760. The beaker will be filled to the 1.00 L mark with the solution. Set the pH to 5.05 by entering the value in the text box provided above the pH scale in the panel called "pH." Once you adjust the pH, note the corresponding OH- ion concentration in M as given in the graph on the right side of the simulation. Make sure to click the option "Concentration (mol/L)" under the "Water components" panel. Click on the Logarithmic scale below the graph. Find the pOH of the solution.

Explanation / Answer

1)let the molarity of the acid be x

so molarity of the base=0.1-x

so,

pH=pKa+log(salt/acid)

or 5=4.74 +log((0.1-x)/x)

or x=0.035 M

so [acid]=0.035 M

[base]=0.1-0.035

=0.065 M

now new pH=4.74+log((100*0.065+5.4*0.44)/(100*0.035-5.4*0.44))

=5.64

so pH change=5.64-5

=0.64

2)pH=5.05

so pOH=14-pH

=14-5.05

=8.95

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