General chemistry laboratory report

Practice:1/ With calorimeter:Determining heat capacity of calorimeter- Place 50 ml at room temperature to beaker, measure temperature - Place 50 ml at about 60 C to calorimeter, wait for

VIET NAM NATIONAL UNIVERSITY HO CHI MINH CITY

UNIVERSITY OF TECHNOLOGY FACULTY OF CHEMICAL ENGINEERING

-*** -General Chemistry Laboratory

REPORT

Course: CH1004

Group: 10

Group members:

1 Trần Quốc Thái - 2153795

2 Lê Minh Tiến – 2153884

Semester: HK213

Lecturer: Đặng Văn Hân

Unit 2: Heat of reaction

I Introduction

Purpose:

Determine heat reaction, confirm Hess’s law

Hess's law states that the enthalpy or heat change accompanying a chemical process depends only on the initial and final states and is independent of the pathway Principle of calculation: in non – phase change process

(cal/mol)

Calorimeter: well insulated container equipped with stir rod and thermometer

II Practice:

1/ With calorimeter:

Determining heat capacity of calorimeter

- Place 50 ml at room temperature to beaker, measure temperature

- Place 50 ml at about 60 C to calorimeter, wait for the temperature stable, o read temperature Keep thermometer inside the calorimeter

- Using funnel, quickly transfer the water from beaker to calorimeter Cap, wait for the temperature stable, read the temperature

- Determine of the clorimeter from the heat balance equation

In which, m: mass of 50 ml water

c: heat capacity of water (1cal/g.K)

2/ Neutralization reaction between HCl and NaOH

- Prepare burette containing NaOH 1M In preparation step, measure the temperature of NaOH After measurement, rinse the thermometer

- Prepare burette containing HCl 1M and transfer 25 ml HCl 1M to

calorimeter, measure the temperature Keep thermometer inside calorimeter

- From burette containing NaOH 1M, transfer 25 ml to calorimeter Cap and mix the solution, measure the temperature

- Canculate the heat quantity Q và ΔHr

Assume heat capacity of diluted solution is 1cal/g.K Specific weight of salt solution is 1.02 g/ml

3/ Heat of dissolution of anhydrous (copper (II) sulfate)

- Place into calorimeter 50 ml water Measure the temperature t1

- Weight exactly about 4 g anhydrous

- Quickly transfer to the calorimeter, stir to dissolve completely, measure the temperature t2

- Determine the heat Q and ΔH solution Confirm Hess’s law

Heat capacity of CuSO4 varies with temperature (K)

We choose Cp at average temperature

4/ Heat of dissolution of

- Similar to previous section 3, replace by

Note: How to determine the temperature after the reaction

- Measure the temperature before the reaction

- Place reactant into the calorimeter, measure the temperature each 30s

- Draw the graph of temperature versus time

- Determine Δt using graph as the following figure It is the maximum difference temperature

x

3

X

Experimental report of unit 2

Experiments are conducted three times, if the results of two times are similar, the third time is not necessary.

I Experimental results

Experiment 1

Temperature Co First time Second time Third time

t1

-t2

-(ave) = 4.261 cal/K

(Detail calculation of one value of )

Experiment 2

Temperature Co First time Second time Third time

252.653

(Detail calculation of one value of Q and ΔH)

(cal)

(cal/mol)

Experiment 3

Temperature Co First time Second time Third time

(Detail calculation of one value of Q and ΔH)

Experiment 4

Temperature C o First time Second time Third time

(Detail calculation of one value of Q and ΔH)

II Answer the questions

1 ΔH of the reaction HCl + NaOH NaCl + H2O is calculated

based on the molar of HCl or NaOH when 25 ml of HCl 2M

solution react with 25ml of NaOH 1M solution? Explain

Answer:

NaOH completely reacts The reaction is calculated based

on the molar of NaOH

2 If replace HCl 1M by 1M, the result of experiment 2 will

change or not?

Answer:

Does not change because HCl and are both strong acids,

completely dissociate and this is a neutralization reaction

5

3 Calculate base on Hess’s law Compare to experimental

result Considering 6 reasons that might cause the error

- Heat loss due to the calorimeter

- Thermometer

- Volumetric glassware

- Balance

- Copper (II) sulfate absorbs water

- Assume specific heat of copper (II) sulfate is 1 cal/mol.K

In your opinion, which one is the most significant? Explain? Is

there any other reason?

Answer:

-According to Hess’ law:

-In practice:

The difference is too big

-In my opinion, the heat loss due to the calorimeter is the most

important, due to the incorrect operation, which quickly leads to

heat loss to the outside

- Anhydrous copper sulfate is hygroscopic, taking and weighing

is not fast and careful, it is easy to make absorb moisture

quickly, affecting the thermal effect of

Unit 4: Reaction rate

I Introduction

1 Law of mass action

In which: k – rate constant, constant at defined temperature

n – reaction order with respect to A, m – reaction order

with respect to B

m+n – overall order of the reaction

For simple reaction: exponent equals to stoichiometric

coefficient

For complicated reaction: the exponent are generally not relate

to stoichiometric

coefficient It can be non-integer or negative

2 Initial rate method:

Keep constant ΔC (same turbidity, color, …), keep initial

concentration of all reagents constant except one Vary

concentration of one reactant, we can determine the order with

respect to the varied concentration species

Method 1: obtained from the double initial concentration

expression

Calculate m and get the average

Method 2: using linear regression

Linear regression to obtain m

II Practice:

1 Determining reaction order with respect to

Prepare three test tubes containing and three conical flask

containing and as the following table

V(ml) 0.4M

Erlenmeyer flask

Use graduated pipette to for measuring acid solution

7

Experimental report of unit 4

I Experimental results

1 Reaction order with respect to

Time(

From of experiment 1 and 2, determine (sample calculation)

Reaction order with respect to

2 Reaction order with respect to

Time(

From of experiment 1 and 2, determine (sample calculation)

Reaction order with respect to

II Answer the questions:

1 In the experiment above, what is the effect of the

concentrations of and on the reaction rate? Rewrite the

reaction rate expression Determine the order of the reaction

Answer:

The concentration of Na2S2O3 is proportional to the reaction

rate, the concentration of H2SO4 has almost no effect on the

reaction rate

- Rate expression: V = k

- Degree of reaction: 1.0745 + 0.1305 = 1.205

2 Mechanism of the reaction can be written as

Base on the experimental results, may we conclude that the

reaction (1) or (2) is the rate-determining step, which is the

slowest step of the reaction? Recall that in the experiments, the

amount of the acid is always used in excess

Answer:

- (1) is an ion exchange reaction, so the reaction rate is very

fast

- (2) is a self-oxidation reaction, so the reaction rate is very slow

Reaction (2) is the rate-determining reaction

3 Base on the principle of experimental method, the reaction

rate is considered as instantaneous rate or average rate

Answer:

Velocity is determined by ΔC/Δt because ΔC~0 (the change in

concentration of sulfur is negligible over the time period Δt ) so

the velocity in the above experiments is considered as

instantaneous velocity

4 Reverse the order of adding and , does the reaction order

change? Explain?

Answer:

Changing the order for and , the order of the reaction does not

change At a given temperature the order of reaction depends

only on the nature of the system (concentration, temperature,

surface area, pressure) and not on the order of reactants

9

Uni 8: Volumetric analysis

Introduction

Volumetric analysis is the method to quantitative determination of species

X based on measurement of the volume Volumetric analysis is often referred to

as titration, a technique in which typically the exact volume of unknown concentration of component X (measured by pipette and placed into conical flask) is reacted with the standard solution The standard solution which the concentration is accurately known is usually added gradually to the flask from a burette

The standard solution is called the titrant; the solution being analyzed is called the analyte

Delivery of the titrant until the process is judged to be complete is called a titration

The reaction C+X A+B is called titration reaction

The principle of calculation: law of equivalent proportion

The point at which complete chemical reaction takes place and equivalent quantity of

reagent is used is called equivalence point:

The equivalence point can only be estimated by observing a physical change such as color change, turbidity The point in titration when this physical change occurs is called end point

Indicators are usually added to the analyte to give a signal of the end point

A titration curve is a plot typically showing the changes of logarithm of the concentration of the titrated solution versus the volume of the added standard solution (titrant)

The inflection point, the steepest part of the titration curve, is the equivalence point

Instant change in curve when a small amount of titrant is added is called titration jump

The requirement for the indicator is the end point within the titration jump The shape of titration curve depends on the concentration, equilibrium constant of titration reaction

Note that the equivalence point will have the pH corresponding to the pH

of the salt solution In case the salt forms when neutralize the strong acid by strong basic (for example HCl and NaOH), the pH at the equivalence point is 7, while neutralize the strong acid by the weak base or weak acid by a strong base, the pH at the equivalence point will differ from 7 The following table shows the transition range of some common indicators

Indicator Color

acid form pH range oftransition basic form

II Practice

1/ Constructing the titration curve

Construct the titration curve of the titration of a strong acid by a strong base

0 2 4 6 8 9 9.2 9.4 9.6 9.8 10 11 12 13

pH 0.96 1.14 1.33 1.59 1.98 2.38 2.56 2.73 3.36 7.26 10.56 11.70 11.97 12.01

Based on the titration curve, determine the pH jump, equivalence point and appropriate indicator

2/ Experiment 2

Rinse burette by NaOH 0.1N, and then pour NaOH to the burette Adjust the liquid level to zero

Use pipette to measure 10 ml HCl solution which the concentration is unknown and transfer to Erlenmeyer flask 150 ml Add 10 ml distilled water and two drops

of phenolphthalein

Open the stopcock to drop slowly NaOH solution to Erlenmeyer flask Swirl the flask while dropping Until the solution in the flask changes to faith-pink, close the stopcock Read the consumed volume of NaOH

Repeat the experiment one more time

3/ Experiment 3

Do similar to experiment 2, but replace the phenolphthalein indicator by methyl orange The color of the solution changes from red to orange

4/ Experiment 4

Do similar to experiment 2, but replace the HCl solution by acid acetic solution Repeat two times, first time using phenolphthalein, the later using methyl orange

11

Experimental report of unit 8

I Experimental results

1 Titration curve of HCl by NaOH

Determine:

The pH jump: from pH 3,36 to pH 10.56

pH at equivalence point: 7.26

Approriate indicator: phenolphthalein

2 Experiment 2: Titration of HCl by Phenolphthalein

Volume (ml)

NaOH 0.1N

= 0.091 N

3 Experiment 3: Titration of HCl by Methyl orange

Volume (ml)

NaOH 0.1N

4 Experiment 4a: Titration of by Phenolphthalein

Volume (ml)

5 Experiment 4b: Titration of by Methyl orange

NaOH 0.1N 1.0 0.90 0.85

II Answer the questions

1 When changing the concentration of HCl or NaOH, does the titration curve change? Explain

Answer:

When changing the concentration of HCl and NaOH, the titration curve does not change because the HCl titration method with NaOH is determined based on the equation:

HCl + NaOH NaCl +

=

- With and does not change, so when increases or decreases, also increases or decreases From this we deduce, whether expanding or contracting, the titration curve remains the same

- Similarly for the case of changing NaOH concentration.

2 The determination of the concentration of HCl in experiment 2 and 3, which one is more precise

Answer:

Determination of HCl acid concentration in experiment 2 gives more accurate results Because phenolphthalein helps us to identify colors more accurately, more clearly, because the color change from colorless to pale pink is more noticeable from red to orange

3 From the result of experiment 4, for the determining concentration of acid acetic solution, which indicator is more precise?

Answer:

Phenol phthalein is more accurate than methyl orange because acetic acid is a weak acid so the titration point is greater than 7 so using phenol phtalein is more accurate than methyl orange (the 3.0 – 4.4 hop is too far)

4 In volumetric titration, if NaOH and HCl are interchanged, does the result change? Explain?

Answer:

No change as this is an equilibrium reaction

13