Buffer and Salt Hydrolysis Lab Report PDF

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Buffer and Salt Hydrolysis Ja’Moni Sanders November 10, 2021 Professor Yawovi

Abstract: For this lab, tests will be conducted on the hydrolysis of salts while in a buffer solution. The Hydrolysis of salts occurs when a chemical is broken down because it is mixed with water. The results of these salts are cations and anions. When the anions of weak acids react with a solution, like water, the concentration of OH- ions increase and the pH increases to more than 7. On the flip side, cations react the complete opposite when reacted with water. H+ ions increase, and the pH level is lowered to below 7. Cations are the products of strong bases but do not hydrolyze or affect the pH level. When salts are formed from strong acids or bases, neither cations or anions will hydrolyze thus the pH will remain the same (pH 7). When the salt of a weak acid or base is formed, the only part that hydrolyze is the ion, resulting in an increase of OH concentration and increasing the pH to above 7. Similarly, when the salt of a weak acid or base is created, cations and anions hydrolyze. Overall pH is found by determining the extent for each ion that undergoes hydrolysis. A buffer solution, that is used as a pH buffer, is made of an aqueous solution with a weak acid and its conjugate base. In general, the pH does not change very much when a small or large amount of strong acid or base is added. This is its intended purpose to stop large changes in the pH. The buffer allows the pH to remain constant while in a large amount of chemicals Procedure: Part I ● ● ● ● ● ● ● ● ● ● ● ● Part II ● ● ● ● ● ● ● ●

Obtain a pH meter and calibrate if necessary Collect a 400-mL beaker and fill with distilled to 200 mL Collect a hot plate and set the water on the plate to boil Boil the 200 mL of distilled water for about 5 minutes Allow the water to cool to room temperature While you are waiting for the water to boil and cool, obtain the about 25 mL of distilled water in a 50-mL beaker Measure and record the pH of the boiled and unboiled water Using large test tubes, obtain enough of each of the six salt solutions provided to cover the probe tip of your pH meter Measure and record the pH of each solution. Be sure to rinse the probe with boiled distilled water and pat dry between each solution Weigh about 3.5 g of NaOAc ∙ 3H2O to the nearest 0.001 g, record the mass in your lab notebook Add the NaOAc ∙ 3H2O to a 150-mL beaker Measure exactly 8.8 mL of 3.0 M HOAc in a 10-mL graduated cylinder and add it to the beaker containing NaOAc ∙ 3H2O Measure exactly 55.6 mL of distilled in a distilled 100-mL graduated cylinder and add it to the solution of HOAc (acetic acid) and NaOAc ∙ 3H2O (sodium acetate)

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Stir until all of the sodium acetate is dissolved. This is a buffer solution Measure and record the pH of the buffer solution Split the buffer solution into four parts of 16.1 mL each into four small beakers. Label the beakers 1-4 Pipet 1.0 mL of 3.0 M NaOH into the beaker 1 buffer solution. Mix, then measure and record the ph. Repeat the addition recording the new pH after each addition until the pH has changed by 1 pH unit. Rinse the pH probe. Pipet 1.0 mL of 3.0 M NaOH into the beaker 2 buffer solution. Mix, then measure and record the ph. Repeat the addition recording the new pH after each addition until the pH has changed by 1 pH unit. Rinse the pH probe and put up the PH meter. Measure and add 16.1 mL of boiled water into beakers 3 and 4. Mix thoroughly Pipet 1.0 mL of 3.0 M HCl into one of the beakers containing the diluted buffer. Mix, then measure and record the pH. Repeat the addition recording the new pH after each addition until the pH had changed by 1 pH unit. Rinse the pH probe. Pipet 1.0 mL of 3.0 M NaOH into one of the beakers containing the diluted buffer. Mix, then measure and record the pH. Repeat the addition recording the new pH after each addition until the pH had changed by 1 pH unit. Rinse the pH probe and put up the pH meter.

Data Solution

Ion Hydrolyzed

Spectator Ion(s)

0.1 NaCl

Na+ ,Cl

0.1 M NaC2H3O2

C2H3O2 -

Na+

0.1 M Na2CO3

CO3 2-

Na+

0.1 M NH4Cl

NH4 +

Cl

0.1 M KAI(SO4)2

Al+3

K + ,SO4 2-

0.1 M ZnCl2

Zn+2

Cl

Solution

H3O

NaOAc pH=8.0 10-8.0= 1.0 ∙ 10-8 M

OH

Kb

pOH=14-8=6 10-6.0= 1.0 ∙ 10-6M

Kw/Ka of HOAC 1.0 ∙ 10-14/1.0 ∙ 10-5= 5.6 ∙

10-10 NaCl pH=7.7

10-7.7= 2.0 ∙ 10-8-M

pOH=14-7.7=6 .3 10-6.3= 5.01 ∙ 10-7

Kw/Ka NaCl 1.0 ∙ 10-14

KAI(SO4) ∙ 11 H2O pH=2.9

10-2.9= 1.26 ∙ 10-3-M

pOH=14-2.9=1 1.1 10-11= 7.94 ∙ 10-12

Kw/Ka Al(OH)3 1.0 ∙ 10-14

ZnCl2 pH=6.2

10-6.2= 6.31 ∙ 10-7-M

pOH=14-6.2=7 .8 10-7.8= 1.58*10-8

Kw/Ka Zn(OH)2 1.0 ∙ 10-1

NH4Cl pH=7.1

10-7.1= 7.94 ∙ 10-8-M

pOH=14-7.1=6 .9 10-6.9=1.26 ∙ 10-7

Kw/Ka HCO3 1.0 ∙ 10-14

Na2CO3 pH=10.6

10-10.6= 2.51 ∙ pOH=14-10.6= 10-11- M 3.4 10-3.4=3.98 ∙ 10-4

Kw/Ka HCO3 1.0 ∙ 10

Conclusion: In this lab we calculated the determination of the Ka and Kb of each of the salts by testing a series of weak acids and bases. Then we used their salts in the pH meter and created a buffer solution. This buffer solution stabilized a neutral pH for each of the salt solutions. We calculated the Ka and Kb values within the equation Ka (Kb) = Kw (Kw). The Ka values were given by calculating the acid dissociation constants. Kb for each reaction is Kb =Kw/Ka. There are a couple potential errors that could have occurred in the experiment. Our pH values were not on accurate and therefore could have led to a negative impact on our data....