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MrMuchimi
3 years ago
6

Consider the following weak acids and their Ka values: Acetic Acid Ka = 1.8×10^−5 Phosphoric Acid Ka = 7.5×10^−3 Hypochlorous Ac

id Ka = 3.5×10^−8. What weak acid-conjugate base buffer system from the acids listed is the best choice to prepare the following buffers. Explain your reasoning.
a. pH 2.8
b. pH 4.5
c. pH7.5
Chemistry
1 answer:
vfiekz [6]3 years ago
7 0

Answer:

a. Phosphoric Acid

b. Acetic Acid

c. Hypochlorous Acid

Explanation:

A buffer works when the pH of this one is in pKa ± 1. That means, to find which buffer system works in some pH you need to find pKa:

pKa = -log Ka

<em>pKa Acetic acid:</em>

-log1.8x10⁻⁵ = 4.74

<em>pKa phosphoric acid:</em>

-log7.5x10⁻³ = 2.12

<em>pKa hypochlorous acid:</em>

-log3.5x10⁻⁸ = 7.46

a. For a pH of 2.8 the best choice is phophoric acid because its effective range is: 1.12 - 3.12 and 2.8 is between these values.

b. pH 4.5. Acetic acid. effective between pH's 3.74 - 5.74

c. pH 7.5. Hypochlorous acid that works between 6.46 and 8.46

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For the reaction C2H4(g) + H2O(g) --&gt; CH3CH2OH(g)
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Answer : The value of equilibrium constant for this reaction at 262.0 K is 3.35\times 10^{2}

Explanation :

As we know that,

\Delta G^o=\Delta H^o-T\Delta S^o

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\Delta G^o = standard Gibbs free energy  = ?

\Delta H^o = standard enthalpy = -45.6 kJ = -45600 J

\Delta S^o = standard entropy = -125.7 J/K

T = temperature of reaction = 262.0 K

Now put all the given values in the above formula, we get:

\Delta G^o=(-45600J)-(262.0K\times -125.7J/K)

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The relation between the equilibrium constant and standard Gibbs free energy is:

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where,

\Delta G^o = standard Gibbs free energy  = -12666.6 J

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Now put all the given values in the above formula, we get:

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