chemistry laboratory report

pH of strong acid: Prepared 10mL 0.1M hydride chlorine HCl, 20mL 0.1M sodium hydroxide NaOH and 100ml 0.01M sodium hydroxide NaOH solution in different pipette.. Firstly, took LOmL 0.1M

VIETNAM NATIONAL UNIVERSITY HO CHI MINH CITY INTERNATIONAL

UNIVERSITY

——[L ÌL ÌL ]Ì_ —

CHEMISTRY LABORATORY REPORT

EXPERIMENT 2: pH AND BUFFERS

EXPERIMENT 2: pH AND BUFFERS

Group member:

Seq Full name Student ID % Contribution | Sginature Score

Table of Contents

CHEMISTRY LABORATORY REPORT

I INTRODUCTION:

1 Objective:

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Il METHODS:

pH of deionized water:

pH of salts:

Bw

pH is an indicator that determines the chemical properties of water, which is a measure of the acidity and basicity of water The pH scale is only from 0-14, so the highest pH is 14 Theoretically, the neutral pH of water is 7 When pH > 7, the solution is alkaline (basic) The solution is acidic when the pH is less than 7 Thus, the lower the pH, the stronger the acidity, and the higher the pH, the stronger the basicity The pH scale is a logarithmic function calculated using the formula pH = -log[H+] The experimenter knows whether acids and bases are strong or weak and whether solutions are neutral through different pH values Additionally, this experiment provides additional calculations regarding the pH value and how the buffer controls

pH

1 Objective:

- Know the definition of pH, and how to dilute solutions

- Distinguish strong or weak acids

- Calculated pH of several qualities such as water, acids, salts, and buffers

- Prepare and calculate the buffer solution and check its buffering capacity

2 Techniques:

a) Equipements:

b) Chemicals:

IL METHODS:

1 pH of deionized water:

Prepared deionized water Step 1, poured 50 ml deionized water in beaker Step 2, used the stirring to stir in 20 seconds, recorded pH, and noted the data Step 3, used the stirring to stir in

20 seconds, recorded pH, and noted the data Step 4, used the stirring to stir in 20 seconds, recorded pH, and noted the data Step 5, kept doing until no significant change in pH value

2 pH of strong acid:

Prepared 10mL 0.1M hydride chlorine (HCl), 20mL 0.1M sodium hydroxide (NaOH) and 100ml 0.01M sodium hydroxide (NaOH) solution in different pipette Firstly, took LOmL 0.1M HCl and recorded the pH value Next, added 90mL distilled water into the container including HC]

before, and recorded the pH value Then added LOmL 0.1M NaOH into the container before and recorded the pH value Finally, added more 90mL 0.01M NaOH and recorded the pH value

3 pH of weak acid:

Prepared 3 flasks with 20mL solution A: 0.1M hydroxyacetaldehyde (CH3COOH), solution B:

0.01M CH3COOH, and solution C: 0.001M CH3COOH respectively, then recorded pH value

and calculated Ka Used formulas Mi*Vi=Mf*Vf for diluted and the equilibrium constant Ka =

(TH+]*[A-])/(THA))

4 pH of salts:

Prepared 20m1 0.1M NaCl, 20ml 0.1M CH3COOa, and 20ml1 0.1M NH4C1 for solutions A ,B, and C respectively Solution A: took 20m] 0.1M NaCl by the cylinder and put it into a beaker, recorded the beaker of solution A and noted Solution B: took 20ml 0.1M CH3COOa by the

cylinder and put it into a beaker, recorded the beaker of solution B, and noted Solution C: took 20ml 0.1M NH4C1 by the cylinder and put it into a beaker, recorded the beaker of solution C,

and noted

5 pH of buffers:

Prepared 100 mL each of 0.1 M acetic acid and 0.1 M CH3COONa into separate beakers and

divided into buffer A (LOmL 0.1M CH3COOH and 40 mL 0.1M CH3COONa), B (40 mL 0.1M CH3COOH and 10 mL 0.1M CH3COONa) Spareted buffer A to 2 solutions include 25mL and

did the same with buffer B Added HC] 0.1M and NaOH 0.1M into 4 buffers and record pH until

pH change

Ill PROCEDURE:

1 pH OF DEIONIZED WATER

Observed pH

- Because deionized water interacted with

oxygen while being stirred, the pH of the water

see what happens during this process:

CO? + H20<H2CO3

140

160

- When weak acid HCO appeared, pH decreased

Comments:

There was a significant difference in measurement results between the two groups

This difference arises because of differences in the equipment used to measure the pH value and the technique used in the experiment

Despite the difference in values, the statistics of group 2, as the explanation demonstrates

2 pH OF STRONG ACID

- The values measured

differently from the theory may be because the container still had water after washing and evaporated from the

distilled water

- After diluting with distilled water, [H*] was decreased, so the pH value was increased + The values measured closely

[Add 10 mL of 0.1M

NaOH

| After put 0.1M NaOH, pH

+ Then added 0.01M NaOH,

pH changed sharply to pH base because [H*] was not enough neutralized

Comments:

The concentration of H*: [H*]=[HC1]=0.1M

The concentration of H* after added distilled water: [H*]=

— pH= -log[H*] = -log[0.01] =2

The concentration of H* and OH after added 0.1M NaOH: [NaOH ]=[HC1]=0.1M in 110mL

— The solution was neutral => pH = 7

The concentration of OH- in the final: [OH™] = 0.01+0.09 0.2 =4.5*103

— pH = 14 - pOH = 14 — log[OH"] = 14 — 2.35 = 11.65

After OH” reacted with H”, the solution was only OH and the solution became alkaline

3 pH OF WEAK ACID

Measured pH

Group 2 | Group 1

+ The chemical properties of weak

0.1M acetic acid 2.83 3.17 2.19x10°

acid were dissociates in solution,

So it had a low concentration of

+ The concentration of solution decreased that the H* dissociated was reduced

+ pH was related to the

equilibrium constant Ka If pH was higher, the Ka would be lower

+ The values were different from each group because of impurities

In container and the volume used

Comments:

The formula of the equilibrium constant Ka: Ka = TH

Acetic acid (CH3COOH) had [H*]=[A]

—3.0832

K, of 0.01M CH:COOH = °°—”ˆ= 6.9210",

—4.0332

K; o[0.001M CH:COOH = CC “= 871*109,

4 pH OF SALT

Predicted pH| Measured pH

0.1M NaCl 7 575 5.29 Because NaC] is a salt formed by the

a neural salt Therefore, the pH value

is predicted to be 7.0

Because CH3COONa is a _ salt

0.1IM NH4Cl

4.71

formed by ion Na+, a strongly basic ion, and CH3sCOO- is a weakly acidic ion, CH3;3COONa is a basic salt

Therefore, the pH value is predicted

to be greater than 7.0

Because NHC] is a salt formed by ion NH4+ which is a weak base ion and Cl- is a strongly acidic ion, NH4&Cl is an acidic salt Therefore, the

pH value is predicted to be smaller

Comments:

The pH of salts is determined by the compound of that substance; if the compound is

a strong nonmetal such as Na and a weak acid component such as CH3COO-, the pH is

greater than 7, and if the compound is a weak acid component such as CH3COO-, the pH is

less than 7, and if two components are strong acid/base, the solution becomes neutral

5 The pH of BUFFERS:

Buffers | Volume (mL)

0.1M

CH:COOH

Volume (mL) 0.1M

CH:COONa

[Acid]

2s

Commenfs:

The pH was approximate

Data calculation:

Determining the concentration of [Acid], [Base], and the values of pH:

For the Solution A:

[Acid] = [CHzCOOH] = (10mL) (0.1M) / (10mL + 40ml) = 0.02M

[Base] = [CHzCOONa] = (40mL) (0.1M) /(10mL + 40mL) = 0.08M

pH of Buffer A:

The concentration of H”: [H']:

Ka = [CH:COO'] [H”] / [CH:COOH]

(The equilibrium constant of CH:COOH is Ka = 1.8 x 10°.)

1.8 x 105 = (0.08M +X) X/ (0.02 - X) Approximation: the acid is weak, so assuming x << 0,1

=> 18x 10° = (0.08M) X / (0.02M) X=4.5 x 10° (M)

So, pH = -log [H*] = -log[X]

pH = 5.34

For Solution B, apply the same measure as Buffer A

Solution A and B were in turn divided equally into 4 separate beakers, marked as Al and A2, B1

and B2

Part I: Addition of 10 drops of 0.1M HCl

10 drops of 0.1M NaOH were added, and the pH was measured After that, NaOH was added

drop by drop, enough to change the pH by one unit from the sta

by one (pH -1)

CH3COO,, which was combined with the

Bl 4.80 3.98 222(drops) additional H* in HCl, thus the pH of the

buffer was not significantly reduced when

10 drops of HC] were added

Comments:

When HCI was added into buffers :

CH:COOH HCl

= CH3COO"

As more HC] was added, the values of pH decreased

Part II: Addition of 10 drops of 0.1M NaOH

10 drops of 0.1M NaOH were added, and the pH was measured After that, NaOH was added

drop by drop, enough to change the pH by one unit from the sta

CH3COOH, which was reacted with the

the pH of the buffer from dropping much when 10 drops of NaOH were added

Comments:

CH3COONa > CH3COO" + Na

Since more OH- is present, the pH value decreases when basic NaOH is introduced to the buffer Discussion:

The highest pH was Buffer A because it contained more CHsCOONa, and the lowest pH was Buffer B because contained more CH3COOH H* rose when the acid HCl was added to the buffer, and the pH values declined When NaOH was added, however, the concentration of H+ reduced, causing the pH to rise

IV CONCLUSION:

The pH of a solution is a measure of the concentration of charged H20 ions in that solution Buffers have the property of maintaining the pH value by resisting large changes in pH when H or OH is added Through this experiment, the experimenter learns how to measure pH levels and how to calculate these values