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? Cobalt Chloride is used in many weather-forecasting devices. Based on your observations in the laboratory, explain how an alcohol solution of CoCl2 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_0)_6] ^2+(aq,blue)+4Br^-(aq)<-> (aq,green)+6H_2_0(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, blub 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

#Have you played in the lab with dissolving Mg(OH)2? When it dissolves, does it release heat? If that's the case, then the solubility reaction can be though of as an equilibrium:

Mg(OH)2 <--> Mg2+(aq) + 2 OH-(aq) + heat

For any compound that dissolves exothermically, increasing the temperature of the solution (adding heat) will make the compound LESS soluble.

#Create a barometer using the alcohol and use the cobalt sat to color the solution. This color makes it easier to see the solution which would otherwise be clear.

Take a tube sealed at one end. Fill it with your solution. closing the open end invert the tube and place it is a dish of your solution. Uncover the open end. You now have a barometer.

If the level in the tube falls, the atmospheric pressure is lower and this indicates rain.

#a) Adding sodium bromide to the solution would provide more reactant, which the equilibrium system would use to create more product (CuBr42-) thus shifting the reaction to the right and making the solution visibly more green.

b) The fact that the solution turned green after being heated indicated that the reaction is endothermic, as it requires heat in order to carry out the reaction.

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