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LeChatelier's principle in equilibria

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Observations:
1 1mL Ba(NO3)2 + 0.5mL K2CrO4 + drops HCl? + drops NaOH? "Ba(NO3)2=clear and colourless
Ba(NO3)2 + K2CrO4= yellow turbid solution (precipitate)
HCl= clear yellow solution (precipitate dissolved)
NaOH= yellowish turbid solution (precipitate returns by neutralizing acid) "
2 1mL Ba(NO3)2 + 0.5mL K2Cr2O7 + 10 drops HCl "Ba(NO3)2=clear and colourless
Ba(NO3)2 + K2Cr2O7= orange-yellow slightly cloudy solution (cloudy d/t reaction with distilled water))
HCl= clear yellowish solution (no precipitate) "
3 1mL Ba(NO3)2 + 5 drops HCl + 5 drops K2CrO4 "Ba(NO3)2=clear and colourless
Ba(NO3)2 + HCl= clear and colourless (acidified Barium Nitrate)
+K2CrO4= yellow clear solution (No precipitate d/t rapid conversion to dichromate) "
4 1mL Ba(NO3)2 + 5 drops CH3CO2H + 5 drops K2CrO4 "Ba(NO3)2=clear and colourless
Ba(NO3)2 + CH3CO2H (acetic acid)= clear and colourless
+K2CrO4= yellow cloudy solution (precipitate formed b/c acetic acid is a weak acid) "

1) Explain what happened in each test regarding Le Chateliers principle

2) When few drops if sodium fluoride solution are added to a solution containing iron (III) ions a colourless solution is obtained. However, when a few drops if sodium chloride are added to a solution
Fe³⁺(aq) + 6F‾ (aq) ⇋ FeF₆³‾(aq)
(pale yellow) (colourless)
containing iron (III) ions a pale yellow solution is obtained, with the yellow colour deepening as more sodium chloride is added.
Fe³⁺(aq) + 4Cl‾ (aq) ⇋ FeCl₄‾(aq)
(pale yellow) (Intense yellow)
Predict what will occur, if a solution of sodium fluoride is added to the solution prepared from the iron (III) and sodium chloride solutions. Justify your prediction in terms of Le Chatelier's principle.

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Ba 2+ + 2 NO3- + CrO42- + 2K+ ----> BaCrO4 + K+ + NO3-
colorless yellowish yellow ppt

Adding HCl is like adding H+ ions. The CrO42- ion will react with H+ to form the dichromate ion Cr2O72-. This amounts to a lower concentration of CrO42-, a reactant. In order to counter this stress on the equilibrium, the reaction will form more reactant which can happen if solid BaCrO4 dissolves.
Adding NaOH is like adding OH- ions. The added OH- will react with H+. This means that H+ added in the previous step will ...

Solution Summary

Some examples of LeChatelier's principle are explained using barium and iron salts equilibria.

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Equilibrium Constants and LeChatelier's Principle

1. For a certain chemical reaction, H= -156 kJ. Assuming the reaction is at equilibrium, classify each of the following actions by whether it causes a leftward shift, a rightward shift, or no shift in the direction of the net reaction.
a. a decrease in temperature R L no shift
b. an increase in temperature R L no shift

2. The K of the reaction:
NO2(g) + NO3(g) N2O5(g)
is K = 2.1 * 10-20. What can be said about this reaction?
a. at equilibrium the concentration of products and reactants is about the same
b. at equilibrium the concentration of products is much greater than the concentration of reactants
c. at equilibrium the concentration of reactants is much greater than that of the products
d. there are no reactants left over once the reaction reaches equilibrium

3. For the reaction HCONH2(g)NH3(g) +CO(g); K = 4.84 at 400K What can be said about this reaction at this temperature?
a. The equilibrium lies far to the right (Guessed this and was wrong)
b. The reactions will proceed very slowly
c. the reaction contains significant amounts of products and reactants at equilibrium
d. the equilibrium is far to the left

4. The industrial production of lime (CaO) from calcium carbonate is accomplished via the following reaction: CaCO3(s) CaO(s) + CO2(g)
Given the following data:
Temperature (K) K
298 1.93*10-23
1200 1.01
What can be said about this reaction?
1. lower temperatures result in more lime formation
2. the reaction makes more lime at higher temperature
3. the reaction goes to completion at 1200 K
4. the equilibrium lies far to the right at room temperature

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