# Help with titration post lab questions and formal lab report.

Data Sheet:Unknown acid 7

(letter or number on the unknown bottle)

Mass of the Unknown acid:

0.2008

Concentration of NaOH(aq):

0.09211

AM

Volume NaOH added

pH

Volume NaOH added

pH

0.00

4.44

4.74

Os

IS. I

8.67.

5.23

8.75

16.5

8.02

2

6.00

17 ă

3.97

2.5

6.90

17.5

9.15

3

6.57

9.24

3.

6.77

18.5

9.59

y

19

9.72

10.12

9,5

5

5.5

6.88

6.99

1.09

7.17

20

10.44

11.22

20.5

21

6

7.27

12.44

6.5

7.37

7

7.US

7.52

8

7.60

8.5

7.66

9

7.72

9.5

7. 81

7.ĹŻb

10.5

3.28

11

1.49

B.

12

8.16

12.5

8.14

8.2.3

13.5

suo

14.5

8.46

Partner’s Names:

Karina G.

4

Titration of a weak Acid: Calculations and Post lab questions

Name:

Denis Osono

Unknown acid

7 (letter or number on unknown bottle)

Mass of Unknown acid: 0.2009

Concentration of NaOH(aq):

0.09211

1. Plot the titration curve as pH vs. mL of NaOH added using a computer graphing

program. Make sure you have chosen the correct X and Y axes. Please include gridlines

and print out a 8 12 x 11 plot. You must attach the graph to the Lab Report.

2. Locate the equivalence point(s) on the titration curve. It is very unlikely that the

equivalence point(s) will be actual data points. You will need to either manually draw a

smooth curve connecting your data points, or select the option in your graphing program

that will draw the best-fit curve for you. Then find the steepest point(s) on the curve.

This is/these are the equivalence point(s). Label the equivalence point(s) on the curve.

(For polyprotic acids, label all the equivaence points.)

3. How many equivalence points does your graph show?

4. Recall that at the first equivalence point, moles of acid = moles of base added.

Volume of NaOH added at the first equivalence point:

Moles of NaOH added at the first equivalence point:

Volume of NaOH added at the Second equivalence point (if your unknown is polyprotic)

5. Use the mass of the acid, the concentration of NaOH and the volume of NaOH added at

the first equivalence point to calculate the molar mass of the acid: (Show your work

clearly and include proper units.)

Calculated Molar mass of the unknown acid=

6. Label the areas of the curve where a buffer is present. Locate the point where pH=

pKa (halfway to the equivalence point.) Label pKa on the graph. If the acid is

polyprotic, label the pKa for each equivalence point on the graph.

un

pKal

graph)

pK a2

(from the

7. Calculate Ka for your unknown acid. f your unknown is polyprotic, calculate Ka at both

the equivalence points. (Show work)

Kal

Ka2 =

8. What is the identity of your unknown? Explain your reasoning behing your choice of

unknown.

9. Calculate the initial concentration of your acid. Recall that the original volume of the

solution was 0.100 L

[Acid]initial

Using your calculated value of Ka and the initial concentration of the acid, calculate the

initial pH of your acid.

Set up the ICE table. You may need to use the quadratic formula.

Initial pH from the titration:

Calculated initial pH:

Was the calculated initial pH higher or lower than initial pH from the curve ? Calculate

the % error

10. Look up the actual literature value of the pKa of your unknown in an appropriate source.

(CRC handbook or the NIST webbook)

Literature value of pKa =

Calculated pKa

(List both pKa’s if your acid is polyprotic)

Source of the data :

Was the actual value higher or lower than the pKa from your graph ? Calculate the %

error.

Initial pH from the titration:

Calculated initial pH:

Was the calculated initial pH higher or lower than initial pH from the curve ? Calculate

the % error

10. Look up the actual literature value of the pKa of your unknown in an appropriate source.

(CRC handbook or the NIST webbook)

Literature value of pKa =

Calculated pKa

(List both pKa’s if your acid is polyprotic)

Source of the data :

Was the actual value higher or lower than the pKa from your graph ? Calculate the %

error.

Titration of a weak Acid: Calculations and Post lab questions

Name:

Denis Osono

Unknown acid

7 (letter or number on unknown bottle)

Mass of Unknown acid: 0.2009

Concentration of NaOH(aq):

0.09211

1. Plot the titration curve as pH vs. mL of NaOH added using a computer graphing

program. Make sure you have chosen the correct X and Y axes. Please include gridlines

and print out a 8 12 x 11 plot. You must attach the graph to the Lab Report.

2. Locate the equivalence point(s) on the titration curve. It is very unlikely that the

equivalence point(s) will be actual data points. You will need to either manually draw a

smooth curve connecting your data points, or select the option in your graphing program

that will draw the best-fit curve for you. Then find the steepest point(s) on the curve.

This is/these are the equivalence point(s). Label the equivalence point(s) on the curve.

(For polyprotic acids, label all the equivaence points.)

3. How many equivalence points does your graph show?

4. Recall that at the first equivalence point, moles of acid = moles of base added.

Volume of NaOH added at the first equivalence point:

Moles of NaOH added at the first equivalence point:

Volume of NaOH added at the Second equivalence point (if your unknown is polyprotic)

5. Use the mass of the acid, the concentration of NaOH and the volume of NaOH added at

the first equivalence point to calculate the molar mass of the acid: (Show your work

clearly and include proper units.)

Calculated Molar mass of the unknown acid=

6. Label the areas of the curve where a buffer is present. Locate the point where pH=

pKa (halfway to the equivalence point.) Label pKa on the graph. If the acid is

polyprotic, label the pKa for each equivalence point on the graph.

un

pKal

graph)

pK a2

(from the

7. Calculate Ka for your unknown acid. f your unknown is polyprotic, calculate Ka at both

the equivalence points. (Show work)

Kal

Ka2 =

8. What is the identity of your unknown? Explain your reasoning behing your choice of

unknown.

9. Calculate the initial concentration of your acid. Recall that the original volume of the

solution was 0.100 L

[Acid]initial

Using your calculated value of Ka and the initial concentration of the acid, calculate the

initial pH of your acid.

Set up the ICE table. You may need to use the quadratic formula.

Initial pH from the titration:

Calculated initial pH:

Was the calculated initial pH higher or lower than initial pH from the curve ? Calculate

the % error

10. Look up the actual literature value of the pKa of your unknown in an appropriate source.

(CRC handbook or the NIST webbook)

Literature value of pKa =

Calculated pKa

(List both pKa’s if your acid is polyprotic)

Source of the data :

Was the actual value higher or lower than the pKa from your graph ? Calculate the %

error.

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C

8. DISCUSSION – This is an important section of your report and is generally written in third person,

passive tense. This should take the form of an analysis of your results and must include the following:

(i)- Summarize briefly what was done in the lab. Form a hypothesis. State whether or not the results from

the lab procedure fully support your hypothesis, do not support the hypothesis, or support the hypothesis

but with certain exceptions. Identify specific data from your lab that led you to either support or reject

your hypothesis (do not repeat calculations). If the results relate to a table, graph, or other figure, make

specific reference to it.

(ii)- Compare your results to reference values when possible. Calculate percent error or standard

deviations and discuss their significance.

(iii)- Give the possible sources of error (any mistakes you might have made or any precautions you took

while conducting the experiment) that could have affected the data. Think of as many as you can.

(iv)- All pertinent chemical reaction equations and formulas used in the experiment must be stated in this

section.

(V)- Conclusion: Conclude your experiment by answering (the question addressed in the problem

statement/purpose of the experiment.

(vi)- Relate the lab to the real life (applications for this lab).

(vii)- Answer the questions if asked.

You must submit, at a minimum, your discussion to Safe Assign on CANVAS. I will instruct you

on the procedure to submit these.

9. PARTNER’S NAME (if any) – Print the names of those who worked with you on the experiment

10. SIGNATURE – You should sign your report after the completion of each experiment. Your signature

is an affirmation that the work you are submitting is your own.

Completed report (sections I-III) along with Formal Report Evaluation rubric is due at the

beginning of your next lab class.

LABORATORY REPORTS GRADING

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