1/25/2018 12:00 AM60/100 Gradebook PrintCalculatar Periodic Table Question 4 of

Question

1/25/2018 12:00 AM60/100 Gradebook PrintCalculatar Periodic Table Question 4 of 5 General Chemistry 4th Edition University Science Books presented by Sapling Leaming A mineral sample is analyzed for its cobalt and calcium content. A sample is dissolved, and then the cobalt and calcium are precipitated as Co(OH)2(s) and Ca(OH)2(s). At what pH can Co(OH)2(s) be separated from Ca(OH)2(s) at 25 °C? Assume that an effective separation requires a maximum concentration of the less soluble hydroxide of 1x 10-6 M KspCo (OH),] = 5.9 × 10-15 Number K,[Ca(oH)-5.0x 10 What is the concentration of the more soluble hydroxide at this pH? Number Previous Give Up & View Solution e Check Answer Next Exit Hint

Explanation / Answer

Maximum concentration of less soluble hydroxide = 1.0 x 10^-6 M

[Co(OH)2] = [Co+2] = 1.0 x 10^-6 M

Ksp of Co(OH)2 = 5.9 x 10^-15

Ksp = [Co+2][OH-]^2

5.9 x 10^-15 = 1.0 x 10^-6 x [OH-]^2

[OH-] = 7.68 x 10^-5 M

pOH = -log [OH-] = -log (7.68 x 10^-5)

pOH = 4.12

pH = 9.88

At pH = 9.88 , concentration of Ca(OH)2

Ca+2 = 5.0 x 10^-6 / (7.68 x 10^-5)^2

[Ca+2] = 843.3 M

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