chemical equilibrium

Essay by lehang November 2014

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International University, Vietnam National University - HCMC GENERAL CHEMISTRY LABORATORY





Group: ____3______ Section: ___4______ Date: ___13/11/2014____

Group members: ____Đặng Thị Lệ Hằng________

____Ngô Hoàng Huân_______

____Lê Thị Thùy Hương_____



International University, Vietnam National University - HCMC GENERAL CHEMISTRY LABORATORY




Equilibrium System: 2CrO42  + 2H+(aq)  Cr2O72

 + 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-  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+

 Initial tube When solid potassium chromate, K2CrO4 is dissolved in water it forms a yellow solution which is color...