International University, Vietnam National University - HCMC GENERAL CHEMISTRY LABORATORY
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REPORT
EXPERIMENT 4: CHEMICAL EQUILIBRIUM
Group: ____3______ Section: ___4______ Date: ___13/11/2014____
Group members: ____Äặng Thá» Lá» Hằng________
____Ngô Hoà ng Huân_______
____Lê ThỠThùy Hương_____
_______________________________
Score:__________
International University, Vietnam National University - HCMC GENERAL CHEMISTRY LABORATORY
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1. ACID/BASE EQUILIBRIA
Equilibrium System: 2CrO42 ï + 2H+(aq) ï« Cr2O72
ï + H2O(l)
Descriptio n of conditions
Predicted outcome
Observation Explanation
Initial solution
The yellow solution
The yellow solution
This is the original color of potassium chromate. The colors come from the negative ions: CrO42-(aq)
+ Conc. HCl
The orange solution
The solution change the color into orange
Hydrochloric acid is a source of H+ ions. The concentration of H+ is increased. So, more H+ react with CrO42- to yielding Cr2O72- and resulting solution is orange. This is the color of Cr2O72-
+ 6 N NaOH
The yellow solution
The color of solution turn back to yellow
Sodium hydroxide (NaOH) removes H+ ions by the equation : H+ + OH- ï H2O. The H+ (aq) concentration can be decreased by adding a solution of NaOH. This lead to the turning some of the Cr2O72- back into the CrO42- , so the orange color turns back to yellow.
Comment: The addition of acid encourages the equilibrium towards the right, producing more orange- coloured Cr2O72- ions. The addition of base or hydroxide ions causes the concentration of hydrogen ions to decrease, and this brings the equilibrium back to the left-hand side, regenerating yellow CrO42- ions. In general, the equilibrium of acid/base is changed the direction when change in the concentration of H+ by adding H+ or remove H+
ï· Initial tube When solid potassium chromate, K2CrO4 is dissolved in water it forms a yellow solution which is color...