Question

1. A buffer is composed of .4 mole H2PO4- and 0.4mol HPO4^2- diluted with water to a volume of 1.0L. The ph of the buffer is 7.210. How many miles of HCL must be added to decrease the ph to 6.210?

2. What mass of sodium hydroxide must be added to 80 mL of 0.462 M acetic acid in order to create a buffer with ph of 4.91? Ka for acetic acid is 1.8x10^-5

3. A 25 ml sample of 0.10 M sodium benzoate is titrated with 0.10 M HCL. What is the ph after the addition of 32ml of HCL? Kb of C6H5CO2 is 1.6x10^-10

4. According to the bronsted Lowry definition, An acid

A is a strong electrolyte

B increases H30+ concentrations in an aqueous solution

C is a proton except her

D increases the pH of a solution

E Is a proton donor

Answer 1

Q1. A buffer is composed of .4 mole H2PO4- and 0.4mol HPO4^2- diluted with water to a volume of 1.0L. The ph of the buffer is 7.210. How many miles of HCL must be added to decrease the ph to 6.210?

Apply buffer equation

pH= pKa + log(conjugate/acid)

6.21 = 7.21 + log(ratio)

ratio = 10^(6.21-7.21) = 0.1

conjugate = 0.1 acid

intially we had 0.4 mol of each

so, after adding x mol of acid:

conjugate = 0.4 - x

acid = 0.4 + x

and we know

conjugate = 0.1 acid

so

0.4 - x= 0.1( 0.4 + x)

0.4-x = 0.04 + 0.1x

-1.1x = -0.36

x = 0.32727

so, we need to add 0.32727 mol of HCl

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