# Microscale Techniques sample essay

1. NaOH is a very corrosive chemical and contact with it can cause burns to body tissue and possible eye damage. Can irriate the lungs and can cause permanent lung damage. also contact with water can generate enought heat to ignite combustibles.

2. In your own words, briefly explain the terms below. Copied answers will receive zero points. a. equilibrium state
When a chemical reaction is equal. when the products and reactients are at equal rates b. the effect of formation of a complex a complex is a term used to describe a substance compused of two other substances.When pushing two substances together they can form a complex which is usually weaker than a regular chemical bond

3. A student is studying the equilibrium represented by the equation 2CrO42-(aq, yellow) + 2H3O+(aq) ← Cr2O72-(aq, orange) + 3H2O(l) →
The mixture obtained by the student is yellow.
a. Describe the color change the student should observe after adding concentrated hydrochloric acid to the equilibrium mixture.
A) Adding acid causes the mixture to become more orange. As H3O+ ion concentration increases, the system converts some of the H3O+ ion to water and dichromate ions. The additional dichromate ion causes the mixture to appear more orange than before.

b. Describe the color change the student should observe after adding solid sodium chromate to the equilibrium mixture.
(HINT: when sodium chromate is dissolved in water, it dissociates into ions.) D) Adding solid sodium chromate causes the mixture to become more orange. As it dissolves, the chromate ion increases and CrO4 -2 ion is converted to dichromate ions. The dichromate ion concentration increases, so the mixture appears more orange.

c. Describe the color change the student should observe after adding excess sodium hydroxide to the equilibrium mixture in (b).
Briefly explain your answer in terms of Le Châtelier’s principle, similar to the answers that were provided earlier in this problem.
No change the solution will remain yellow. In Le Châtelier’s principle it talks about how when stress is put on a reaction the reaction shift to relieve the stress. So when we add more of a reaction or product the reaction will shift to use it up, and shift away from added species. d. Write a net ionic equation to support your answer in (c). 1 H3O + (aq) + 1 OH – (aq) → 2 H2O (l)

4. a. Predict the direction in which the equilibrium should shift when you add sodium sulfate solution to the mixture in well A1. Explain why.

B) The equilibrium will shift to the left. The system wants to lower the concentration of the sulfate ion, which can be done consuming some of the added sulfate ion and thus shifting the equilibrium to the reactant side. b. Predict the direction in which the equilibrium should shift when you add solid sodium hydrogen sulfate solution to the mixture in well A3. Explain why.

C) The equilibrium will shift to the right. The system wants to lower the concentration of the hydrogen sulfate ion, which can be done by consuming some of the added hydrogen sulfate ion and shifting the equilibrium to the product side.

c. Predict the direction in which the equilibrium should shift when you add concentrated hydrochloric acid to the mixture in well C1. Explain why.
A) The equilibrium will shift to the right. The added acid reacts with hydroxide ions to form water, thus reducing the hydroxide ion concentration. The system responds by converting solid magnesium hydroxide to aqueous magnesium hydroxide.

d. Predict the direction in which the equilibrium should shift when you add Na4EDTA solution to the mixture in well C2.
to the right
Explain why.
EDTA purpuse to bind metal cations. So by adding this we reduce the concentration of Mg+2 ions, but we are also adding more OH- ions, and that means that the concentration of OH- ions is decreasing.

e. Predict the direction in which the equilibrium should shift when your TA adds water to the hexaaquacobalt(II) ion mixture. Explain why.
D) The equilibrium should shift to the right. The system lowers the concentration of the water by consuming some of the added water to form the hexahydrate complex, thus shifting the equilibrium to the product side.

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