chemistry lab report on standardization of acid and bases

Purpose: To prepare standardize solution of sodium hydroxide and to determine the

concentration of unknown sulfuric acid solution.

Data and Calculations: This experiment is divided into two parts (Part A and Part B). In the first

part of experiment, the standardize solution of sodium hydroxide is

prepared by titrating it with base Potassium hydrogen phthalate (KHP).

The indicator Phenolphthalein is used to determine that whether titration

is complete or not.

PART A:

Standardization of a Sodium Hydroxide solution

NaOH Sample Code = O

Trial 1

Mass of KHP transferred = 0.42 g

Volume of Distilled water = 25 mL

Volume of NaOH used = 22.50 mL

Molar mass of KHP = 204.22 g/mol

No. of moles of KHP = Mass of KHP used / Molar mass

= 0.42 g / 204.22 g/mol

= 0.0021 moles

Concentration of NaOH = No. of moles / Volume

= [0.0021 mol / {(22.50 + 25) / 1000} L] * 100

= 4.4 M

Trial 2






= 0.4139 g / 204.22 g/mol

= 0.0020267 moles


= [0.0020267 mol / {(22.80 + 25) / 1000} L] * 100

= 4.24 M

Trial 3






= 0.4239 g / 204.22 g/mol

= 0.0020757 moles


= [0.0020757 mol / {(23.10 + 25) / 1000} L] * 100

= 4.32 M

Trial 4






= 0.4311 g / 204.22 g/mol

= 0.0021109 moles


= [0.0021109 mol / {(22.60 + 25) / 1000} L] * 100

= 4.43 M

Table:

Trail 1 Trial 2 Trial 3 Trial 4

Mass weighing bottle + KHP (g)

11.561 11.6217 11.6113 11.6329

Mass empty weighing bottle (g)

11.1461 11.2078 11.1874 11.2018

Mass of KHP transferred (g)

0.4200 0.4139 0.4239 0.4311

Initial volume of burette, Vi

(mL)4.30 6.30 10.1 33.20

Final Volume of burette, Vf

(mL)26.80 29.10 33.20 55.80

Volume of NaOH used (mL)

22.50 22.80 23.10 22.60

Concentration of NaOH (moles/L)

4.4 4.24 4.32 4.43

Average concentration of NaOH = [4.4 M + 4.24 M + 4.32 M + 4.43 M] / 4

= 4.35 M

1. % Difference between Trial 1 and Trail 2 = [4.24 M / 4.4 M] * 100 %

= 96.3 %

Difference = (100 – 96.3) %

= 3.7 %


= 98.1 %

Difference = (100 – 98.1) %

= 1.9 %


= 97.5 %

Difference = (100 – 97.5) %

= 2.5 %

Observations:

KHP is white color crystals and has definite shape.

NaOH is clear and transparent solution with no color.

In the first trial, after adding 90 drops of NaOH solution there was repeatedly appearance

and disappearance of light pink color.

When the whole solution of KHP and water get titrated then, the color of solution

becomes light pink and it stays permanently.

The same color changes happen with the next three trials.

Concentration of NaOH was almost similar for every trials.

PART B:

Concentration of Sulfuric Acid solution

H2SO4 Sample Code = 34

Trial 1:

Volume diluted acid = 25 mL


H2SO4 (aq) + 2NaOH (aq) 2H2O (l) + 2Na2SO4 (aq)

Average concentration of NaOH = 4.35 M

No. of moles of NaOH = (Average concentration of NaOH) * (Volume of NaOH used)

= 4.35 M * (14.39 / 1000) L

= 0.0626 moles

No. of moles of H2SO4 = 0.0626 mol / 2

= 0.0313 moles

Concentration of H2SO4 = No. of moles / (volume of diluted acid / 1000)

= 0.0313 mol / (25 / 1000) L

= 1.2 M

Trial 2:






= 4.35 M * (13.51 / 1000) L

= 0.0588 moles


= 0.0294 moles


= 0.0294 mol / (25 / 1000) L

= 1.2 M

Trial 3:






= 4.35 M * (14.10 / 1000) L

= 0.0613 moles


= 0.0307 moles


= 0.0307 mol / (25 / 1000) L

= 1.2 M

Trial 4:






= 4.35 M * (14.20 / 1000) L

= 0.0618 moles


= 0.0309 moles


= 0.0309 mol / (25 / 1000) L

= 1.2 M

% Difference between Trail 1 and Trail 2 = [1.2 M / 1.2 M] * 100 %

= 100 %

Difference = (100 – 100) %

= 0 %


= 100 %

Difference = (100 – 100) %

= 0 %


= 100 %

Difference = (100 – 100) %

= 0 %


= 100 %

Difference = (100 – 100) %

= 0 %

Table 2:

Trail 1 Trail 2 Trial 3 Trial 4

Volume diluted acid titrated (mL)

25 25 25 25

Initial Volume of burette, Vi (mL)

2.41 17.20 8.50 22.60

Final Volume of burette, Vf

(mL)16.94 30.71 22.60 36.80

Volume NaOH used (mL) 14.39 13.51 14.10 14.20

Concentration Of Sulfuric Acid

1.2 M 1.2 M 1.2 M 1.2 M

Observations:

The H2SO4 is colorless and transparent liquid.

The NaOH solution is colorless, odorless and transparent liquid.

While doing the first trail, there were continuous appearance and disappearance of light

pink color.

After adding 10 mL of NaOH solution the pink color starts appearing.

At certain volume the light pink color appeared, indicating that titration is done.

The indictor phenolphthalein has no color and there was no specific odor of reagent.

Discussion: Average concentration of NaOH solution was 4.35 M. There are many sources of

error in this experiment as we got some percentage differences in the two different

trials. For the Trial 1 and Trial 2, the percentage difference is 3.7 % which is

significant difference to be noted. This percentage difference could occur due to

many reasons such as not measuring the KHP properly as we got 0.42 g for first trial

and 0.4139 g for second trial of KHP for performing titration but it is more than

required value as per literature value is concerned (0.40 g). The almost same

percentage difference occurs for next two trials (1.9 % and 2.5 %). The KHP is

always 99.9 % pure, so the titration should give perfect results (Lab Manual). The

other possible errors was due to the disturbance on the shelf by other students where

analytical balance is placed in balance room, as it cause variability in the values in

weight of KHP. In Part B of experiment, the average concentration of sulfuric was

found to be 1.2 M and there was 100 % titration of both reagent (NaOH and H2SO4).

This 100 % results comes due to significant figures, if significant figures would not

be concerned then there would be error of 1.0 % to 2.0 % in every two trials. There

was identical difference of volume of NaOH used to titrate the acid for each trial due

to some possible errors. The possible errors in this Part of experiment were same as

for Part A, as the process is followed in the same way.

The most significant error could occur by not shaking the flask properly while adding

sodium hydroxide solution and not recognizing the pink color on the instant it appears

and adding the NaOH solution vigorously into the sulfuric acid.

Questions:

The 10 mL volumetric pipette is rinse 2 or 5 times to make sure there is no bubble inside

because air bubble can cause error in the measurement of concentration because the

actual volume of unknown will be less.

The accuracy and precision for both sets of experiment was almost same as there were

percentage difference of concentrations lies only in 2 % to 4 %. The endpoints of titration

for each set of trails in both cases (Part A and Part B) were almost same but there is little

difference in volume of NaOH used which cause errors in accuracy and precision of

experiment.

Using the analytical balance is really careful job as it is most accurate weighing machine

with accuracy of 0.0004 g (Lab Manual) and we need to be précised using the balance but

some few disturbance can cause big error such as disturbance other students on the shelf

it is placed on and not reading the balance properly and taking measurements fastly.

Using Volumetric glassware is other method to be more accurate in experiment but there

are some possible random error while reading the values such as not reading the lower

meniscus of liquid cause error and not removing the air bubble from the burette and using

the beaker in place graduated cylinder in case of volume as graduated cylinder is more

accurate as compared to beaker (0.02 g) (Lab Manual).

Sources of Experimental Error include:

The Analytical balance could give wrong reading because of the disturbance due to other

students on the shelf it is placed on. Also, taking the reading rapidly and not considering

the reading when balance display gets steady.

The possible error can occur using wrong glassware like using beaker instead of

graduated cylinder.

The error could occur while taking reading through graduated cylinder and not

considering the lower meniscus of liquid.

The air bubble in burette can cause error in the true value of NaOH used.

Few drops of liquid remain in burette and volumetric pipette which causes the error.

Not shaking the flask properly while adding the NaOH solution.

Adding the NaOH solution vigorously into the flask.

Not recognizing the pink color instantly as it appears.

Adding the more drops of indicator as needed (2 or 3 drops).

The biggest error occur due to leaking of NaOH solution form burette, we lost 4 drops

during every one trial and it cause the significant error in reading the volume of NaOH

used.

There is water left after washing the glass wares which can cause the error.

This lab could be improved by improving the method of drying the graduated cylinder and

beaker before filling it with the NaOH solution. The glassware could be dried by small amount

of acetone. Any acetone could be removed by evaporation. Finally, the experimenter should

remove the clinging droplets to the neck of burette and volumetric pipette by using Kim Wipe.

Conclusion: After careful consideration of all the results and all the possible concentration, it is

concluded that the average concentration of NaOH (sample code O) was 4.35 M and

average concentration of H2SO4 (sample code 34) was 1.2 M.

References:

Lab manual:

Koczanski, Krystyna; Xidos, James D. CHEM 1300 Laboratory Manual; UMSU Copy

Centre: Winnipeg, MB, Canada, 2013, pp 16.

Book with authors:

Olmested, John III; Williams, Gerg; Burk, Robert C. Chemsitry, Ist Canadian ed.; John

Wiley and Sons Ltd: Mississauga, Canada, 2010, pp 399 – 406.

CHEM 1300Experiment 4

Standardization of Acids and Bases Using Titrations

Date of experiment: 10/25/2013

Date of submission:10/29/2013

Room no.:240

Rotation: 1

Friday morning

Locker number: 111

Name: Karanvir singh Sidhu

Student number: SIDKD1303

chemistry lab report on standardization of acid and bases

Technology