Temperature Dependence of Ka for a Weak Monoprotic Acid Temperature Dependence o

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Temperature Dependence of Ka for a Weak Monoprotic Acid

Temperature Dependence of Ka for a Weak Monoprotic Acid Experiment 8 - Temperature Dependence of Ka for a Weak Monocratic Acid 1. What is a buffer? 2. What is a buffer made up of? 3. Give two (2) examples of buffer solutions. 4. Define Le Chatelier?s principle 5. Explain how temperature affects a system in equilibrium. & The pKa acetic add at room temperature is 4.75. What is the pH of a solution of acetic add at half the equivalence point? 7. Estimate the pH of a solution of a weak add being titrated with a strong base at the equivalent point. 8. Estimate the pH of a solution of a weak base being titrated with a strong . the equivalent point. 9. Calculate the grams of sodium NaClCH2COO needed to prepare 25mL of a 0.198M NaClCH2COO solution.

Explanation / Answer

1) A solution which resists any change of pH when a small amount of a strong acid or a strong base is added to it, is called a buffer solution or simply as a buffer.

2) Buffer solutions usually consist of a mixture of a weak acid and its salt with a strong base (or)

that of a weak base and its salt with a strong acid

3) e.g.acidic buffer CH3COOH and CH3COONa,

   e.g basic buffer NH4OH and NH4Cl. .

4) Le chatelier's principle: When a system at equilibrium is subjected to change in concentration, temperature, volume, or pressure, then the system readjusts itself to (partially) counteract the effect of the applied change and a new equilibrium is established.

5) if the forward reaction exothermic , backward will be endothermic vice versa.

     Incresing   temperature always favours the endo thermicreaction and decresing temperature always favours exothermic reaction

6)   At equalant point pH=pKa   =4.75

7) ex: (CH3COOH + NaOH) At the equivalence point the pH is greater then 7 because all of the acid (HA) has been converted to its conjugate base (A-) by the addition of NaOH and now the equilibrium moves backwards towards HA and produces hydroxide, that is: A?+H2O?AH+OH?

8)   (HCl + NH4OH)At the equivalence point the pH is less then 7 because all of the base (BOH) has been converted to its conjugate acid (B+) by the addition of HCl and now the equilibrium moves backwards towards BOH and produces hydroxide, that is: B++H2O?BOH + H+

9)

Molarity = (w/Mw) x1000/v

0.198= (w/116.5) x1000/25     (molar mass = 116.5)

weight= 0.57gm

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