Experimental Data

1)pH

pH of the samples:

2) Alkalinity measurement: SAMPLE #1:

Volume of water sample:_

Titrant:_Titrant concentration:_

mL of titrant

pH

mL of titrant

pH

Volume of titrant to reach pH Volume of titrant to reach pH

SAMPLE #2: Volume of water sample: Titrant:__

Titrant concentration:

mL of titrant

PH

mL of titrant

pH

Volume of titrant to reach pH = 8.3:_

Volume of titrant to reach pH = 4.5:_

SAMPLE #3:

Volume of water sample:_

Titrant:_Titrant concentration:

mL of titrant

pH

mL of titrant

pH

mL of titrant

pH

mL of titrant

pH

Volume of titrant to reach pH= 8.3:_

Volume of titrant to reach pH= 4.5:_

SAMPLE #4:

Volume of water sample:_

Titrant: Titrant concentration:

mL of titrant

pH

mL of titrant

pH

Volume of titrant to reach pH Volume of titrant to reach pH

SAMPLE #5:

Volume of water sample:_

Titrant: _Titrant concentration:_

mL of titrant

pH

mL of titrant

pH

Volume of titrant to reach pH = 8.3:_

Volume of titrant to reach pH = 4.5:_

PART A. Data analysis:

1. From the experimental data obtained with each sample tested, report the alkalinity values and the concentration of each alkalinity species present (as mg/L of CaCO^).

Why is distilled water considered to have no buffering capacity?

To calculate the alkalinity, apply the following formula:

(V acid, mL) (M, acid solution)(100 g/mol CaC03) (1000 mg/g)

Alkalinity, mg/L CaC03 =

Sample

P-Alkalinity as CaC03

M-Alkalinity as CaC03

Total Alkalinity as CaC03

#1

#2

#3

#4

#5

To determine the approximate concentration of hydroxide, carbonate and bicarbonate ions in each sample, one can use the following relationships and assumptions:

Volume of titrant to reach the endpoint

Predominant chemical species

Concentration of the chemical species

vp = o

HCO^

= M alkalinity

VM= 0

OH"

= P alkalinity

II £

cor

= P alkalinity

VP > VM

cor

= (P — M) alkalinity = M alkalinity

Vp < Vm and the pH is between 8.2-9.6

HCO^

= 2P alkalinity = (M — 2P) alkalinity

Vp < VM and pH > 9.6

OH-

= 2(M - P) alkalinity = (2P - M) alkalinity

Note: The P (Phenolphthalein) endpoint = pH 8.3, and the M (methyl orange or bromocresol green) endpoint = pH 4.5.

Note: The P (Phenolphthalein) endpoint = pH 8.3, and the M (methyl orange or bromocresol green) endpoint = pH 4.5.

The dominant species at 4.5 are assumed to be bicarbonate and carbonate, and when OH- ions are present, no bicarbonate ions can be present. It is also assumed that [H+] is not relevant in alkaline pH values, and that one half of the carbonate ions present become neutralized at the 8.3 endpoint. With the above information, determine the speciation of the alkalinity in each sample:

Sample

[H"]

[Off]

[HCO3-]

[C032]

m

#2

#3

#4

#5

2. Observe the differences between the values of these samples and indicate what has influenced the composition of these samples.

Tap water

D.I. water

3. Based on the experimental values of ANC obtained with the different samples, classify these samples according to their sensitivity to acid discharge.

Sample

Sensitivity

Justification

#1

#2

#3

#4

#5

PARTB. BUFFERING CAPACITY

B.l.a EXPERIMENTAL DATA

Volume of water sample:_

Titrant:_Titrant concentration:_

mL of titrant

pH

AVb

ApH

-

-

Volume of water sample:

Titrant:

Titrant concentration:

mL of titrant

pH | AVb

ApH

r

-

Volume of water sample:

Titrant:

Titrant concentration:

mL of titrant

pH

AVb

ApH

-

-

Volume of water sample:_

Titrant: _Titrant concentration:

mL of titrant

pH

AVb

ApH

-

-

B. Lb Determine the buffering capacity of each sample:

For this purpose, you must consider the largest volume of base added in order to raise the pH by one unit. Then, convert this volume into moles of base consumed per initial volume of buffer (considered in liters).

Sample

Buffering capacity

#1

#2

#3

#4

#5

Which of the measured samples has the highest buffering capacity? At what pH does this solution buffer?_

B.2 Factors that affect the buffering capacity B.2.A

Buffer:_

Volume of sample:_

Titrant:_Titrant concentration:

mL of titrant

PH

AVb

ApH

0

-

mL of titrant

pH

AVb

ApH

Estimate the pH value at which the maximum rate of change of pH per unit of volume (i.e., ApH/A V) occurs:_

Buffer B.2.2

Buffer:_

Volume of sample:_

Titrant:

Titrant concentration:

mL of titrant

pH

AVb

ApH

Estimate the pH value at which the maximum rate of change of pH per unit of volume (i.e ApH/AF) occurs:_

Buffer B.2.3

Volume of sample:_

mL of titrant

pH

AVb

ApH

-

-

Estimate the pH value at which the maximum rate of change of pH per unit of volume (i.e., ApH/AF) occurs:_

Butter B.2.4

Volume of sample: __

Titrant: _ Titrant concentration:_

mL of titrant

pH

AVb

ApH

-

-

Buffer:_

Titrant:_Titrant concentration:_

mL of titrant

pH

AVb

ApH

-

-

B.2.b.l Determine the buffering capacity ofeach sample:

For this purpose, you must consider the largest volume of base added in order to raise the pH by one unit. Then, convert this volume into moles of base consumed per initial volume of buffer (considered in liters).

Buffer

Buffering capacity

B.2.1

B.2.2

B.2.3

B.2.4

B.2.5

Which of the measured samples has the highest buffering capacity? At what pH does this solution buffer?_

B.2.b.2 Determine theoretically the btffering index of each of the buffers mentioned above.

Buffer

Buffering Index

B.2.1

B.2.2

B.2.3

B.2.4

B.2.5

Buffer

Buffering Index

B.2.1

B.2.2

B.2.3

B.2.4

B.2.5

Include the pertinent graphs and calculations.

B.2.b.4 Relate the differences in composition of the different buffers to the corresponding responses: pH, buffering capacity, buffering index. What do you conclude With respect to their differences and responses?

PARTC: CALCULATION, PREPARATION, AND EVALUATION OF A SPECIFIED pH BUFFER SOLUTION

Btiffer assigned to your team:_

Include all the calculations needed to arrive at the composition and volumes used in the preparation of the corresponding buffer:

C. l.a Acid buffering capacity

Buffer:_

mL of titrant

PH

AVb

ApH

Estimate the pH value at which the maximum rate of change of pH per unit of volume (i.e. ApH/AF) occurs:_

C. l.b Base buffering capacity

Buffer:_

Titrant: _Titrant concentration:

mL of titrant

PH

AVac

ApH

C.2.a How does the experimental pH value ofthe buffer SQlution that you prepared compare with the theoretical pH? Is there a deviation greater than 0.5 pH units? Why do you think this is so?

C.2.b Determine experimentally the acid and base buffering capacity of your buffer solution: For this purpose, you must consider the largest volume of base added in order to raise the pH by one unit Then, convert this volume into moles of base consumed per initial volume of buffer (considered in liters).

Buffering capacity

Acid

Base

Include all your calculations.

Considering the other buffers prepared in part B, how does yours compare in buffering capacity? C.2.b.2 Determine theoretically the buffering index of the prepared buffers.

Buffer

Buffering Index

Include all the equations and calculations.

C.2.b.3 Determine experimentally the buffering index of the prepared buffer.

Buffer

Buffering Index

Include all the pertinent graphs and calculations.

Include all the pertinent graphs and calculations.

Was your prediction about the buffering index of your assigned solution correct?

What percentage deviation did it present?_

Suspected reasons:__

0 0

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