Chemistry Lab Report Sample

November 09, 2011
Experiment #
Le Chatelier’s Principle

Purpose: The purpose of the laboratory work is to enhance the knowledge in chemical equilibrium and ways to affect that equilibrium.

STEP SUBSTANCE REAGENT RESULT INFERENCE
1 C1)5 drops of 2M MgCl2/HIn 5 drops of 1.0 M NaOH Solution turns pink The equilibrium is shifted to the right hand side
2 C2)5 drops of 2M MgCl2/HIn 5 drops of 1.0 M NaOH Solution turns pink The equilibrium is shifted to the right hand side
3 C3)10 drops of 2M MgCl2/HIn 5 drops of 1.0 M NaOH Solution turns white The equilibrium is shifted to the left hand side
4 C4)10 drops of 2M MgCl2/HIn 5 drops of 1.0 M NaOH Solution turns white The equilibrium is shifted to the left hand side
5 5 drops of 2 M MgCl2/HIn + 5 drops 1.0 M NaOH 1 drop of 6.0 M HCl Pink colour disappears All OHbounds with H+ from HCl
6 5 drops of 2 M MgCl2/HIn + 5 drops 1.0 M NaOH + 1 drop of 6.0 M HCl Excess of 6.0 M HCl Appearance  of a white precipitate Excess of HCl shifts the equilibrium to the right hand side
7 5 drops of 2M MgCl2/HIn + 5 drops of 1.0 M NaOH 1 drop of 0.15 M  Na2EDTA Solution starts to turn pink Na2EDTA forms a complex with Mg2+ what will reduce its concentration in the solution shifting the equilibrium to the right
8 5 drops of 2M MgCl2/HIn + 5 drops of 1.0 M NaOH+ 1 drop of 0.15 M  Na2EDTA Excess of 0.15 M  Na2EDTA Solution turns pink Addition of Na2EDTA shifts the equilibrium to the right by binding Mg2+. This will lead to building up of OHthus basicity will increase.
9 5 drops of 2M MgCl2/HIn + 5 drops of 1.0 M NaOH Hot water Solution turns white The equilibrium is shifted to the formation of Mg(OH)2 (s)
10 5 drops of 2M MgCl2/HIn + 5 drops of 1.0 M NaOH Cold water Solution turns pink The equilibrium is shifted to the formation of Mg2+ (aq) + OH(aq)
11 5 drops of 2M MgCl2/HIn + 5 drops of 1.0 M NaOH from hot bath Cold water Solution turns from white to pink Equilibrium shifts to the right
12 5 drops of 2M MgCl2/HIn + 5 drops of 1.0 M NaOH from white bath Hot water Solution turns from pink to white Equilibrium shifts to the left

Questions:

Reaction observed: Mg(OH)2 (s) → Mg2+ (aq) + 2OH (aq)

                                    White                        Pink

A)Equilibrium for the reaction Mg(OH)2 (s) → Mg2+ (aq) + 2OH (aq) will shift to the right if HCl is added. This will happen because HCl will react with OH removing it from the solution. Appeared white colour proves this to be true. All Mg(OH)2 will initially react with HCl to form MgCl2. The additional excess of Cl will shift the equilibrium of the reaction to the left:

MgCl2→Mg2+ + 2Cl(White colour is MgCl2 solid)

B)The same as in the previous case, the equilibrium for the reaction Mg(OH)2 (s) → Mg2+ (aq) + 2OH (aq) will shift to the right if Na2EDTA is added. Na2EDTA bind Mg2+ by forming a stable complex with this cation. Building up of OHwill increase the basicity.

C)The reaction is exothermic (Deduced from steps 8 and 9). According to Le Chatelier’s Principle increase in temperature will make the endothermic reaction more favourable and vice versa. If the hot bath turns the solution white then endothermic reaction is the one that leads to the formation of Mg(OH)2. Consequently, dissociation of Mg(OH)2 is exothermic.

Mg(OH)2 (s) → Mg2+ (aq) + 2OH (aq) + Energy;    ΔH<0

STEP SUBSTANCE REAGENT RESULT INFERENCE
1 A1)5 drops of 0.1 M NaHSO4 Thymol blue (indicator) pink solution is produced pH is approx. 2
2 A2) 5 drops of 0.1 M NaHSO4
3 A3) 5 drops of 0.1 M NaHSO4
4 A4) 10 drops of 0.1 M NaHSO4
5 A5) 10 drops of 0.1 M NaHSO4
6 A1)5 drops of 0.1 M NaHSO4 + Thymol blue 1 drop of 1 M Na2SO4 yellow colour started to appear

(No yellow colour in A2)

The equilibrium shifts to the left hand side
7 A1)5 drops of 0.1 M NaHSO4 + Thymol blue + 1 drop of 1 M  Na2SO4 1 M Na2SO4 Appearance of intense yellow colour Significant shift of equilibrium  to the left hand side/pH is above 2.8
8 A3)5 drops of 0.1 M NaHSO4 + Thymol blue 3 crystals of NaHSO4 pink colour became more intense then it was for A2 The equilibrium shifts to the right hand side
9 A3)5 drops of 0.1 M NaHSO4 + thymol blue + 3 crystals of NaHSO4 Solid NaHSO4 Appearance of intense red colour Significant shift of equilibrium  to the right hand side/pH is below 1.2
10 A4) 10 drops of 0.1 M NaHSO4 Hot water (900C) Red changes to intense yellow/orange The equilibrium is shifted to the left hand side
11 A5) 10 drops of 0.1 M NaHSO4 Cold water (100C) Appearance of intense pink colour The equilibrium is shifted to the right hand site
12 A4) 10 drops of 0.1 M NaHSO4 from hot bath Cold water (100C) Yellow/orange solution turns pink The equilibrium shifts from left to right
13 A5) 10 drops of 0.1 M NaHSO4 from cold bath Hot water (900C) Pink solution turns intense yellow/orange The equilibrium shifts from right to left

Questions:

Reaction observed: HSO4 (aq) + H2O (l) → H3O+(aq)+SO42-

Yellow                             Pink

A)When Na2SO4 is added the equilibrium shifts to the left hand side. Increase in the concentration of SO42- will push the equilibrium to the left, the solution turns less acidic because the concentration of H3O+ (aq) decreases. This decrease is observed by the indicator turning yellow.

B)When NaHSO4 is added the equilibrium shifts to the right hand side. Increase in the concentration of HSO4will push the equilibrium to the right, the solution turns more acidic as the concentration of H3O+ (aq) builds up. This can be observed by appearance of the red intense colour. Of the indicator.

C)According to Le Chatelier’s Principle increase in temperature will make the endothermic reaction more favourable and vice versa. Hot water shift the equilibrium to the right hand side what is observed by the appearance of the red colour, therefore, the reaction is endothermic.

HSO4 (aq) + H2O (l) → H3O+(aq)+SO42- – Energy;  ΔH>0

Works cited:

Christian, Gary. Analytical chemistry. Washington: John Wiley & Sons, 2004. Print

get best college help