Viva Questions with Answers on an Effect of Change of Concentration on Chemical Equilibrium

During a reversible chemical process, chemical equilibrium is the state in which there is no net change in the number of reactants or products. When a chemical reaction is reversible, the products react with the original reactants as soon as they are created. When the product concentration rises, less product is produced, and the reactant concentration rises as the product concentration falls, shifting the chemical equilibrium in favour of the reactant. A bottle of effervescent refreshing drink is one example of chemical equilibrium. Carbon dioxide has been dissolved in the liquid within the container. There is also carbon dioxide gas in the area between the liquid and the lid.

Table of Content

• Aim

• Apparatus Required

• Theory

• Procedure

• Observation

• Result

• Precautions

• Lab Manual Questions

• Viva Questions

• Practical Based Questions

Aim

To study the change in equilibrium by varying the concentration of [Co(H2O)6]2+ and Cl- ions in their reaction.

Materials Required

• Test tube

• Test tube stand

• Glass rod

• Beakers

• Conical flask

• Burettes

• Conc. HCl

• Cobalt chloride

• Acetone

Theory

• According to Le Chatelier's principle, if a dynamic equilibrium is upset by changing the conditions, the equilibrium position will move to compensate for the change and restore the equilibrium.

• The displacement reaction between [Co(H2O)6]2+ and Cl- take place as follows:

[Co(H2O)6]2++4Cl-→[CoCl4]2- + 6H2O

• The equilibrium constant for the above reaction can be written as:

\[K = \dfrac{\left [ CoCl_4 \right ]^{2-}}{\left [ Co\left ( H_2O \right )^{2+} \right ]\left [ C^{-} \right ]^4}\]

• Now, if at equilibrium, the concentration of either the  [Co(H2O)6]2+  ion or the  Cl- ions are raised, this would result in a rise in the concentration of the [CoCl4]2-ion and retain the value of K as constant. To put it another way, we can argue that when equilibrium shifts forward, the colour will alter to reflect this.

Procedure

1. Dissolve 60 ml of acetone in a 100 ml conical flask to make a blue solution, and add 0.6000 g of CoCl2.

2. Mark five identical test tubes with the letters A, B, C, D and E. 

3. 3.0 mL of cobalt chloride solution should be added to each from “A” to “E” accordingly, as test tubes.

4. Add 1.0 mL now 0.8 mL, 0.6 mL, 0.4 mL and 0.2 mL, respectively, of acetone in these syringes.

5. Add 0.2, 0.4, 0.6 and 0.8 ml of test tubes B, C, D and E, respectively, with water, so that combined, there is 4.0 mL of solution in each test tube.

6. As the amount of water is increased, observe how the mixture gradually turns from blue to pink.

7. Add 5 mL of distilled water to the previously made 10 mL cobalt chloride solution in acetone. You'll get a pink-coloured solution.

8. 1.5 mL of the pink solution from above should be divided among the five test tubes marked 1, 2, 3, 4 and 5. 

9. To make the total amount of solution in the test tubes 4 mL, add 3.0 mL, 3.5 mL, 4.0 mL, 4.5 mL and 5 mL of water to the test tubes labelled from 1 to 5 and 1mL, 1.5 mL, 2 mL, 2.5 mL and 3 mL of concentrated HCl to the test tubes 1 to 5.

10. Take note of how the pink solution gradually turns bright blue as the hydrochloric acid concentration rises.

Five identical test tubes with the letters A, B, C, D and E

Observation

The Shift in Equilibrium - Addition of Water 

The Shift in Equilibrium - Addition of Cl- Ion

Result

In the equilibrium reaction between  [Co(H2O)6]2+ and  Cl-, the equilibrium will shift to the left side (backwards) by increasing the concentration of water (product). And equilibrium will shift to the right side (forward) by increasing the concentration of Cl- ions (reactant).

Precautions

• Take note of the colour shift under diffused sunlight to accurately assess the solution's colour change.

• Use identical-sized boiling tubes.

• Pour distilled water into the test tube.

• For aeration or solution addition, use a graduated pipette or burette.

Lab Manual Questions

1. What is the purpose of using a glass rod to transfer solutions?

Ans: To avoid spills, solutions are poured using glass rods. To prevent the solution from spilling past the lip of a beaker and into the collecting vessel, a glass rod is pushed up against the beaker's pouring edge.

2. Why does acetone keep close after usage?

Ans: Acetone and alcohol are inflammable, do not let the bottles open when not in use. Keep the bottles away from flames.

3. Why were identical-diameter test tubes used in this experiment?

Ans: To measure the introduced solutions precisely to conduct comparison research.

4. What alters equilibrium when HCl is added?

Ans: When HCl is added,  chloride ion concentration increases dramatically, upsetting the equilibrium.

Viva Questions

1. Define the law of mass action.

Ans: The law of mass action also says that at a condition of chemical equilibrium, the ratio of reactant concentration to product concentration is constant.

2. Define reversible chemical reactions.

Ans: The simultaneous transformation of reactants into products and products back into reactants is known as a reversible reaction.

3. What is meant by the dynamic nature of equilibrium?

Ans: When a system is in a state of dynamic equilibrium, the reversible reaction that is occurring in it no longer changes the ratio of reactants to products, but there is still the movement of substances between the reactants and products.

4. Define the law of chemical equilibrium.

Ans: The product of the molar concentration of the products divided by the product of the molar concentrations of the reactants, each concentration increased to the power corresponding to its coefficients, is constant at a given temperature for a reversible reaction in equilibrium. The name of this constant is the equilibrium constant.

5. What happens at the increasing temperature of an equilibrium system?

Ans: The equilibrium constant's value falls as the temperature rises. A rise in temperature increases the value of the equilibrium constant when the forward reaction is endothermic. As the temperature fluctuates, so does the equilibrium position.

6. What is meant by chemical equilibrium?

Ans: Chemical equilibrium occurs in a chemical reaction when the rate of the forward reaction equals the rate of the backward reaction.

7. What does K indicate in an equilibrium reaction?

Ans: The value of K represents the products-to-reactants ratio at equilibrium.

8. What is KC in an equilibrium reaction?

Ans:  KC stands for Equilibrium constant measured in moles per litre.

9. What is the colour of  [Co(H2O)6]2+ ions?

Ans: Pink

10. What is the colour of  [CoCl4]2- ion?

Ans: Blue

Practical Based Questions

1. If the concentration of any one of the reactants in a reversible chemical process doubles while it is in equilibrium, the equilibrium constant will ____.

1. Be doubled

2. Become one-fourth

3. Be halved

4. Remain the same

Ans: If the concentration of any one of the reactants in a reversible chemical process doubles while it is in equilibrium, the equilibrium constant will remain the same.

2. The rate of forwarding to the reverse reaction if a system is in equilibrium is?

1. Less

2. High

3. Equal

4. None

Ans:  If a system is at equilibrium, the rate of forward-to-reverse reaction is equal.

3. What happens if an equilibrium is added while maintaining the same volume of an inert gas?

1. Less product will form

2. More products will form

3. More reactants will form

4. Equilibrium will remain unchanged

Ans:  If equilibrium is added while maintaining the same volume of inert gas, equilibrium will remain unchanged.

4. What happens to equilibrium on doubling P and V at constant T?

1. Become double

2. Remain constant

3. Become one-fourth

4. None

Ans: The equilibrium remains constant.

5. What happens if the temperature of the chemical equilibrium reaction mixture is increased?

1. Equilibrium remains constant

2. Equilibrium shifts towards an exothermic direction

3. Equilibrium shifts towards an endothermic direction

4. None of the three options

Ans:  The equilibrium shifts towards the endothermic direction if the temperature rises.

6. What is the role of distilled water in laboratories?

1. Indicator

2. Solvent 

3. Universal solvent

4. None 

Ans: Distilled water is used as a universal solvent.

7. Choose the correct statement about chemical equilibrium.

1. It is not affected by pressure

2. It is affected by the catalyst

3. It is affected by P, T and V

4. None of these

Ans: The chemical equilibrium is affected by pressure, volume, and temperature.

8. The colour of  [Co(H2O)6]2+ ion is _____.

1. Blue

2. Black

3. Pink

4. Yellow

Ans: The colour of  [Co(H2O)6]2+ ion is Pink.

9. Select the wrong statement.

1. The colour of  [CoCl4]2- ion is black.

2. P, V and T affect the chemical equilibrium.

3. Equilibrium can shift on change in concentration.

4. None of these

Ans: The colour of  [CoCl4]2- ion is blue.

10.  Which of the following statements is true?

1. The chemical equilibrium is affected by the catalyst.

2. The chemical equilibrium is not affected by the catalyst.

3. A catalyst does not speed up the reaction.

4. None of these

Ans: The chemical equilibrium is not affected by the catalyst.

Conclusion

From the above experiment, we can conclude that a change in the concentration of substances can alter the equilibrium. Here, the increase in the concentration of water shifts the equilibrium to the left and increases in the concentration of chloride ions shift the equilibrium to the right. And this shift is due to Le Chatelier's principle, if a dynamic equilibrium is upset by changing the conditions, the equilibrium position will move to compensate for the change and restore the equilibrium.