Experience teaches us that most solids are more soluble in warm water than in co

Question

Experience teaches us that most solids are more soluble in warm water than in cold water. Does the solubility of Mg(OH)_2 fit this pattern? Briefly explain. Cobalt chloride is used in many weather-forecasting devices. Based on your observations in the laboratory, explain how an alcohol solution of CoCl_2 could be used to predict rain. A student is studying the equilibrium described by the net ionic equation shown in Equation 18. [Cu(H_2 O)_6]^2+ (aq, blue) + 4 Br^- (aq) CuBr_4^2- (aq, green) + 6 H_2 O(l) The student adds sodium bromide solution (NaBr) to a sample of the blue equilibrium mixture in order to increase the Br^- ion concentration. Predict what the student will observe, and explain your prediction. The student draws some of the blue solution into the bulb of a Beral pipet. The pipet is placed, bulb down, in a hot-water bath. After a short time, the solution changes from blue to green. Is the forward reaction in Equation 18 endothermic or exothermic? Briefly explain

Explanation / Answer

1. Solubility increases with temperature. Mg(OH)2 also shows the same pattern and its solubility is seen to increase at higher temperature as compared to low temperature.

2. CoCl2 in presence of water or moisture would show the following equilibrium reaction,

CoCl2(blue) + 6H2O <==> CoCl2.6H2O(pink)

Anhydrous CoCl2 under non-rain condition is blue. When it is about to rain the atmosphere gets saturated with water. The water present in atmosphere thus reacts with CoCl2 to form hydrated CoCl2 which is pink in color. Thus by looking at the color of CoCl2 one may predict If it is about to rain or not.

3. For the reaction of,

[Co(H2O)6]^2+ + 4Br- <==> [CoBr4]^2- + 6H2O

1. According to LeChatellier's principle any change at equilibrium in a reaction will make the reaction go in a direction so as to compensate the change occured and reestablish the equilibrium.

When NaBr is added, we have excess Br- which forces the reaction towards product side, that is right handside and we get more of CoBr4^2- formed.

2. When heated the blue solution turned green. So the forward reaction here is endothermic in nature.

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