Laboratory Module

LABORATORY REPORT

EBT 251

ENGINEERING MATERIALS CHEMISTRY

Semester 1 (2012/2013)

School Of Materials Engineering

Universiti Malaysia Perlis

Student’s Name : Ng Hui San 111041127

: Nabilah Binti Othman 111041103

: Muhammad Harith Bin 121041217

Badrul Hisham

Experiment’s Title : CHEMICAL EQUILIBRIUM: LE CHATLIER’S PRINCIPLE

Experiment Date : 6 November 2012

Submission Date : 21 November 2012

Lecturer’s Name : Dr. Norzilah binti Abdul Halif

EXPERIMENT 4

Engineering Materials Chemistry EBT 251

CHEMICAL EQUILIBRIUM : LE CHATLIER’S PRINCIPLE

1.0 OBJECTIVE

To use Le Chatelier's principle for determining changes in equilibrium systems.

2.0 INTRODUCTION

Any system at equilibrium will remain at equilibrium unless the conditions

of the system change. Le Chatelier’s principle states that a system at equilibrium

will react to a stress on the system in such a way so as to reduce the stress which are

concentration, pressure and temperature as well as to stabilize new equilibrium. If a

dynamic equilibrium is disturbed by changing the conditions, the position of

equilibrium moves to oppose the change.

If the forward reaction dominates in order to allow the changes, we say the

system “shifts to the right” or “shifts toward products” in order to restore

equilibrium conditions. The concentration of the products will increase and the

concentration of the reactants will decrease. However, if the reverse reaction

dominates in order to allow the changes, the result will be opposite from the

forward reaction. The changes will not return the system to the original conditions,

but to a new set of conditions that establish equilibrium.

For the general reaction equation,

aA + bB <======> cC + dD

The cequilibrium constant for concentration can be expressed as,

Kc = [C] c [D] d

[A]a [B]b

Where [A], [B] are the reactant concentrations and [C], [D] are the product

concentrations.

2.1 Concentration effect

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Equilibrium of Fe (III)-SCN ion complexes

Fe3+ (aq) + (SCN)-(aq) <======> Fe(SCN)2+ (aq)

(yellow) (dark red)

2.2 Temperature effect

2.2.1 Equilibrium of Co (II) ion complexes

Co(H2O)62+ (aq) + 4 Cl- (aq) <======> CoCl4

2- (aq) + H2O (l)

(red) (blue)

2.2.2 Equilibrium of Cu (II) ion complexes

CuCl42- (aq) + H2O (l) <======> Cu(H2O)6

2+ (aq) + 4Cl- (aq)

(yellow) (blue)

3.0 APPARATUS

Beaker

Thermometer

Water bath

Conical flask

Test tube

Graduated cylinder

Chemicals:

Hydrochloric acid

Kalium thiocyanate solution (KSCN) 0.1 M

Ferum (III) nitrate solution (Fe(NO3)3) 0.1 M

Cobalt (II) chloride solution (CoCl2) 0.2 M

Cuprum (II) chloride solution (CuCl2) 0.2 M

Natrium hydroxide solution (NaOH) 10 %

4.0 PROCEDURE

3


4.1 Concentration effect on Fe (lll)- SCN ion complexes

Figure 1

4.1.1 1 ml Fe(NO3)3 and 1 ml of KSCN solution were mixed up together into

100ml beaker.

4.1.2 The 25 ml distilled water has added into the mixture and the solution was

stirred.

4.1.3 All the 4 test tubes was cleaned and labeled as A1, A2, A3, and A4 as shown in

figure 1.

4.1.4 The solution has divided into all the 4 tubes evenly.

4.1.5 A1 test tube was added by 1 ml an additional of Fe(NO3)3, A2 test tube

was added by KSCN solution by 1 ml and NaOH solution was dropped 8

times into the test tube A3.

4.1.6 All the solution had been stirred gently and the solution was compared the

colour with the solution in test tube A4.

4.2 Temperature effect on Co (ll) and Cu (ll) ion complexes

4


(a) In the ice (b) In the water bath (c) At room temperature

Figure 2

4.2.1 The CoCl2 and the CuCl2 were prepared 5 ml for each in two separate conical

flasks.

4.2.2 The HCl was added into both flasks and was done in fume cupboard.

4.2.3 Both solution were stirred until cobalt solution was turning to purple and

cuprum solution was turned to green.

4.2.4 The 6 clean test tubes were being labeled as B1, B2, B3, and C1, C2, C3.

4.2.5 The cobalt solution was evenly divided into the test tube B1, B2, B3, and

cuprum solution to C1, C2,C3.

4.2.6 B1 and C1 test tube soaked in the ice as hown in Figure 2 (a).

4.2.7 B2 and C2 were soaked in hot water approx T~ 66 degree celcius as hown in

Figure 2(b). B3 and C3 test tubes in room temperature as hown in Figure 2(c).

4.2.8 The entire solution colour were compared after 5 minutes soaked.

5.0 RESULTS

5


5.1 Concentration effect on Fe (III)-SCN ion complexes

TEST TUBE A1 A2 A3

Colour Changes

Dark orange

Red (A1)

Dark orange

Dark red (A2)

Dark orange

light red (A3)

Reaction

Direction

The reaction shifts

to right

The reaction shifts

to right

The reaction shifts

to left

Reaction

Equation

Fe3+(aq)+(SCN)-

(aq)

Fe(SCN)2+(aq)

Fe3+(aq)+(SCN)-

(aq)

Fe(SCN)2+(aq)

Fe3+(aq)+(SCN)-

(aq)

Fe(SCN)2+(aq)

Species

Decrease(SCN)-(aq) Fe3+(aq)

Fe3+(aq) Fe(SCN)2+

(aq)

Species

IncreaseFe(SCN)2+(aq) Fe(SCN)2+(aq)

(SCN)-(aq) ,

[Fe(OH)6]3-(aq)

Table 5.1 Result of Concentration effect on Fe (III)-SCN ion complexes

5.2 Temperature effect on Co (II) ion complexes

6


Test tube B1 B2

Colour

Changes

Purple Pink Purple Violet

Reaction

DirectionThe reaction shifts to the left The reaction shifts to the right

Reaction

Equation

Co(H2O)62+ (aq)+ 4Cl– (aq)+ heat

CoCl42– (aq)+ 6H2O(aq)

Co(H2O)62+ (aq)+ 4Cl– (aq)+ heat

CoCl42– (aq)+ 6H2O(aq)

Table 5.2 Temperature Effect on Co (II) ion complexes.

5.3 Temperature effect on Cu (II) ion complexes

Test tube C1 C2

Colour

Changes

Green Light Green Green Dark Green

Reaction

DirectionThe reaction shifts to the left The reaction shifts to the right

Reaction

Equation

CuCl42- (aq)+ 6H2O(l)

Cu(H2O)2+(aq) + 4Cl-

CuCl42- (aq)+ 6H2O(l)

Cu(H2O)2+(aq) + 4Cl-

Table 5.3 Temperature Effect on Cu (II) ion complexes.

6.0 Lab Questions

7


6.1 Explain and show the calculation in solution prepared .

Kalium thiocyanate solution (KSCN) 0.1 M

KSCN= 0.1mol/L

No of moles KSCN: 0.1x (250/1000) =0.025mol

Molecular weight of KSCN = 39+32+ 12+14 = 97

Mass of KSCN = mole x molecular weight

= 0.025 x 97

= 2.425 gram

Ferum (III) nitrate solution (Fe(NO3)3) 0.1 M

(Fe(NO3)3) = 0.1mol/L

No of moles (Fe(NO3)3) : 0.1x(250/1000)=0.025mol

Molecular weight of (Fe(NO3)3) = 55.85+3[14+3(16)]=241.85

Mass of (Fe(NO3)3) = mole x molecular weight

= 0.025x241.85

= 6.05 gram

Cobalt (II) chloride solution (CoCl2) 0.2 M

(CoCl2) = 0.2mol/L

No of moles (CoCl2): 0.2x(250/1000)=0.05mol

Molecular weight of CoCl2 = 58.93+2(35.5)=129.93


= 0.05x129.93

= 6.497gram

Cuprum (II) chloride solution (CuCl2) 0.2 M

(CuCl2) = 0.2mol/L

No of moles (CoCl2): 0.2x(250/1000)=0.05mol

Molecular weight of CuCl = 63.55+2(35.5)=134.55


= 0.05x134.55

= 6.73 gram

Natrium hydroxide solution (NaOH) 10 %

8


10% of NaOH = 10 g / 100 ml of solution

Molarity = moles / litres

moles = mass / molar mass

molar mass NaOH = 23+16+1 = 40.0 g/mol

Moles NaOH = 10g / 40.0 g/mol

= 0.25 moles of NaOH

Mass of NaOH = 0.25 x 40

= 10 gram

6.2 Identify the reactant and the products for each reaction.

Test tube Reactant Product

A1 Fe3+(aq)+(SCN)-(aq) Fe(SCN)2+(aq)



B1 Co(H2O)62+ (aq)+ 4Cl- (aq ) CoCl4

2– (aq)+ H2O(l)

B2 Co(H2O)62+ (aq)+ 4Cl- (aq ) CoCl4

2– (aq)+ H2O(l)

C1 CuCl42−(aq) +H2O(l) Cu(H2O)6

2+(aq)+ 4 Cl−(aq)

C2 CuCl42−(aq) +H2O(l) Cu(H2O)6

2+ (aq)+ 4 Cl−(aq)

6.3 Write the equilibrium expression for each reaction.

A1 : Fe3+(aq)+(SCN)-(aq) Fe(SCN)2+(aq) ;



]][[

])([ 2

SCNFe

SCNFeK c

]][[

])([3

2

SCNFe

SCNFeK c

])([

]][[2

3

SCNFe

SCNFeK c

9


B1 : Co(H2O)62+ (aq)+ 4Cl– (aq) CoCl4

2– (aq)+ 6H2O(l)

B2 : Co(H2O)62+ (aq)+ 4Cl– (aq) CoCl4

2– (aq)+ 6H2O(l)

C1 : CuCl42- (aq)+ 6H2O(l) Cu(H2O)2+(aq) + 4Cl-

C1 : CuCl42- (aq)+ 6H2O(l) Cu(H2O)2+(aq) + 4Cl-

6.4 Predict equilibrium direction if HCl is used instead of NaOH in A3 test tube.

Please explain your answer.

If HCl is added into the A3 test tube instead of NaOH , the colour of the solution will

still the same . When HCl is added , it provide H+ ions that will combine with SCN- ions to

form conjugate acid , thiocyanic acid (HSCN) . HSCN have triple bond and not easy to

form . They are still free to form Fe(SCN)2+ions . The direction of equilibrium still the same

.

Fe3+ (aq) + SCN- (aq) ⇌ [FeSCN] 2+ (aq)

][

]][)([24

4262

CoCl

ClOHCoK c

4262

24

]][)([

][

ClOHCo

CoClK c

][

]][)([24

4262

CoCl

ClOHCoK c

4262

24

]][)([

][

ClOHCo

CoClK c

10


7.0 DISCUSSION:

7.1 Effect of Concentration

In this experiment, Le Chatelier’s principle is used to explore the effect of

concentration on equilibrium system. Fe(NO3)3 and KSCN were used where the changes

colour between the reaction indicated the equilibrium system of a solution. When 1ml

yellow colour of Fe(NO3)3 mixed with 1ml colourless KSCN, the dark red Fe(SCN)2+ ion

complexes are formed. After all, the colour was too beneath, therefore, 25ml distilled water

was added into the mixed solution so that the solution was diluted enough to be seen the

colour changes in the system. The solution was then distributed equally in 4 test tubes.

In test tube A1, 1ml Fe(NO3)3 is added. Since Fe3+ is added to system which was

already in equilibrium, this caused too much Fe3+ present in the system. According to Le

Chatelier’s principle, the equilibrium shifted to the right to remove excess Fe3+. The colour

changes in solution will be more darker. The result obtained from the experiment is

consistent with the principle of Le Chatelier’s. In test tube A1, the colour changes turned

from light red to red.

Fe3+ (aq) + SCN-(aq) Fe(SCN)2+(aq)

(yellow) (colourless) (dark red)

In test tube A2, 1ml KSCN was added. When SCN- was added to the system which

was already in equilibrium, this would have been too much SCN- present in the system.

According to Le Chatelier’s principle, the equilibrium shifted to right in order to remove

excess SCN- to maintain the equilibrium of the system. Thus, the colour of solution in A2

changed to be darker. The result obtained from experiment is consistent with the principle

of Le Chatelier’s principle. For test tube A2 the colour changed from light red to dark red

as there was more SCN- .

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In test tube A3, 8 drops of NaOH were added. Even though NaOH was not part of

the equilibrium reaction given, it still affect the system of equilibrium. When NaOH was

added into the solution, Fe3+ in the equilibrium system reacted with OH- ion presented in

NaOH added to form precipitate Fe(OH)3. Fe(OH)3 was insoluble in water. Adding of

NaOH precipitated the Fe3+ as Fe(OH)3 from the equilibrium system. The reaction equation

is as below.

Fe3+(aq) + 3OH-(aq) Fe(OH)3(aq)

(from equilibrium) (from NaOH) (solid precipitate)

Since insoluble Fe(OH)3 was precipitated, amount of Fe3+ in equilibrium system

decreased. With reference to Le Chatelier’s principle, to maintain the equilibrium back, the

equilibrium shifted to left to restore Fe3+ and the colour in test tube changed to be lighter.

The result obtained in experiment is consistent with the principle. The colour in test tube

A3 changed from light red to yellow and precipitate was formed.

7.2 Effect of Temperature

Two experiments were carried out to determine the relationship between

temperature and equilibrium system , which is at water bath and also soak in ice . The

experiments were carried out to study the temperature effect on Co(II) and Cu(II)ion

complex . The CoCl2.6H2O or [Co(H2O)6]Cl2 is a deep purple coloured solid. It forms a

purple coloured solution when is dissolved in water. The colour of [Co(H2O)6]2+ ion is

pink. In equilibrium , the solution has small amount of [CoCl4]2- (blue colour) . The

combination of these two colours produce the final colour of solution which is in purple

colour .

Co(H2O)62+ (aq) + 4Cl- (aq) CoCl4

2- (aq) + 6H2O (l)

(pink) (blue)

12


Firstly , hydrochloric acid (HCl) was added into CoCl2 , the purple coloured

solution appeared . The solution then was evenly distributed to 3 test tubes B1,B2,B3 .

Solution B3 left in room temperature as control variable . Initially both Co(H20)62+ ions

(pink colour) and CoCl42- ions (blue colour) were present , therefore the solution is in

purple colour . The reaction above is an endothermic reaction .

According to Le Chatelier’s principle , when the solution is heated ,

temperature of the system increases , the equilibrium shift to the right to remove excess

heat , forming more CoCl42-ions (blue colour) . The purple colour of solution turned to

darker colour . But if cooling , the equilibrium system shifted to left to replenish the heat .

The Co(H20)62+ ions increases (pink colour) , therefore the solution turned to lighter colour .

The test tube B1 was put in the ice , the solution change from purple to pink colour . The

test tube B2 was put in water bath of 660C , the solution turn from purple to violet colour .

For the second experiment , CuCl2 was used to replace CoCl2 . The colour of

CuCl42- ions are yellow . In equilibrium , the solution contains small amount of Cu(H20)6

2+

ions (blue colour) .

CuCl42- (aq) + H2O(l) Cu(H2O)6

2+(aq) + 4Cl-(aq)

(yellow) (blue)

After adding HCl, the solution was distributed equally into test tube labeled C1,

C2 and C3. Solution in test tube C3 was left in room temperature as a control variable. At

room temperature, both the yellow CuCl42- and blue Cu(H2O)6

2+ ions were present in

significant amounts, giving green color to the solution . The reaction is an endothermic

reaction.

According to Le Chatelier’s principle , heating the solution shifts the

equilibrium to the right in order to remove excess heat, forming more blue Cu(H2O)62+.

Since more Cu(H2O)62+ ions presented, when it mixed with CuCl4

2- ions, the green color of

solution turned to lighter color. But if cooling the equilibrium system shifted to left in order

13


to replenish the heat. More yellow CuCl42- ions appeared. Therefore, the green solution

turned to lighter colour . In test tube C1 where the solution was cooling, the green color

changed to light green color. , in test tube C2 where the solution was heating, the green

color of solution turned to light green color.

A few precautions were taken in the experiment . Before taking acidic HCl

solution , must wear gloves , mask and lab coat . If the acidic solution contact with skin ,

must wash it off quickly with water . The solution after the experiment must be gathered

and neutralized using proper method before throw it. The figure below shows the colour

changes between in test tubes B and in test tubes C.

8.0 CONCLUSION:

The objective is achieved where Le Chatelier's principle is used in this experiment

to determine the changes in equilibrium systems. From the experiment, we found the factor

that affect the equilibrium system which are concentration and temperature. Other than that,

the equilibrium system is also affected by other factors such as pressure and volume.

The Le Chatelier's Principle explained the chemistry phenomenon behind the color

changes taking place in the experiment. It states that if a system is subjected to a stress, the

system will react to remove the stress. To remove the stress, the reactions will either shifted

to the right and formed more products, decreasing the reactants or shifted to the left and

form more reactants, decreasing the products. Le Chatelier's Principle was then predicted

which side the reaction would be shifted.

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7.0 References

http://www.chemguide.co.uk/physical/equilibria/lechatelier.html

http://www.nlu.edu/chemistry/courses/manuals/chem1010/experiment_06.pdf

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http://www.nlu.edu/chemistry/courses/manuals/chem1010/experiment_06.pdf

http://www.chemguide.co.uk/physical/equilibria/lechatelier.html

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