Solution pH [H + ] (M) [OH ? ] (M) Volume for pH = 7 (L) Classification (Acid/Ba

Question

Solution

pH

[H+]

(M)

[OH?]

(M)

Volume for pH = 7 (L)

Classification (Acid/Base/Neutral)

.10M HCl

1.75

1.78*10^-2

6.19*10^-13

5.62*10^-6

Acid

Coke

2.53

2.95*10^-3

3.63*10^-12

3.39*10^-5

Acid

Vinegar

3.05

8.91*10^-4

1.23^10^-11

1.12*10^-4

Acid

Acetic Acid

3.20

6.31*10^-4

1.1*10^-6

1.0*10^-1

Acid

Apple Juice

4.01

9.77*10^-5

1.13*10^-10

1.02*10^-3

Acid

Ammonium Chloride

6.10

7.94*10^-7

1.38^10^-8

1.26*10^-1

Neutral

Sodium Acetate

7.56

2.75*10^-8

3.99*10^-7

3.63

Neutral

Sodium Chloride

7.75

1.78*10^-8

6.19*10^-7

1.62*10^-1

Neutral

Baking Soda

8.00

1.00*10^-8

1.1*10^-6

1.00*10^-1

Neutral

.10M NaOH

12.27

5.37*10^-13

2.05*10^-2

4.88*10^-6

Base

Bleach

12.70

2.00*10^-13

5.51*10^-2

1.81*10^-6

Base

Part II. Reaction of HCl and NaOH

a) Create a well-formatted table below that summarizes your pH measurements for the separate HCl and NaOH solutions and the pH after mixing. Include the [H+] for each set of pH measurements.

b) Write an equation for the neutralization reaction that occurred between HCl and NaOH. Why does this reaction explain the change in the pH? If we were to mix exactly the same number of moles of HCl and NaOH, what would the pH be and why?

Sodium acetate can be prepared by adding sodium hydroxide to acetic acid.

c) Write a reaction for the neutralization of acetic acid and sodium hydroxide.

d) Reacting equal moles of acetic acid and sodium hydroxide results in a basic pH, which is not the case for reacting equal moles of HCl and NaOH. Use your data from this lab to explain why a reaction between equal moles of acid and base does not always produce a pH = 7 solution.

Solution

pH

[H+]

(M)

[OH?]

(M)

Volume for pH = 7 (L)

Classification (Acid/Base/Neutral)

.10M HCl

1.75

1.78*10^-2

6.19*10^-13

5.62*10^-6

Acid

Coke

2.53

2.95*10^-3

3.63*10^-12

3.39*10^-5

Acid

Vinegar

3.05

8.91*10^-4

1.23^10^-11

1.12*10^-4

Acid

Acetic Acid

3.20

6.31*10^-4

1.1*10^-6

1.0*10^-1

Acid

Apple Juice

4.01

9.77*10^-5

1.13*10^-10

1.02*10^-3

Acid

Ammonium Chloride

6.10

7.94*10^-7

1.38^10^-8

1.26*10^-1

Neutral

Sodium Acetate

7.56

2.75*10^-8

3.99*10^-7

3.63

Neutral

Sodium Chloride

7.75

1.78*10^-8

6.19*10^-7

1.62*10^-1

Neutral

Baking Soda

8.00

1.00*10^-8

1.1*10^-6

1.00*10^-1

Neutral

.10M NaOH

12.27

5.37*10^-13

2.05*10^-2

4.88*10^-6

Base

Bleach

12.70

2.00*10^-13

5.51*10^-2

1.81*10^-6

Base

Explanation / Answer

b) The neutralization reaction between HCl and NaOH is given as

HCl (aq) + NaOH (aq) ---------> NaCl (aq) + H2O (l)

HCl is strongly acidic (low pH) while NaOH is strongly basic (high pH). When the two species are mixed, the pH drops to an intermediate value. Infact, the products of the reaction, NaCl and H2O are both neutral and have a pH of 7.00 (middle pH of the pH scale which ranges from 1-14). Therefore, when equal moles of HCl and NaOH are mixed, HCl and NaOH are completely neutralized and the products are neutral, giving a pH of 7.00.

c) The neutralization of acetic acid (HC2H3O2) by NaOH is given as

HC2H3O2 (aq) + NaOH (aq) ---------> NaC2H3O2 (aq) + H2O (l)

d) The products of the above reaction are H2O (neutral) and sodium acetate (NaC2H3O2) which is a salt of sodium (Na+) and acetate (C2H3O2-) ions. C2H3O2- is the conjugate base of the weak acid HC2H3O2 and is itself a weak base. Since, the product of the neutralization reaction between acetic acid and NaOH is basic, hence, the pH at the end point of the neutralization is basic.

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