Chapter 16: Problem 27
Approximately 0.14 g nickel(II) hydroxide, Ni(OH) \(_{2}(s),\) dissolves per liter of water at \(20^{\circ} \mathrm{C}\) . Calculate \(K_{\text { sp }}\) for \(\mathrm{Ni}(\mathrm{OH})_{2}(s)\) at this temperature.
Short Answer
Expert verified
The solubility product constant, \(K_{sp}\), for Ni(OH)鈧(s) at 20掳C is approximately \(4.37 * 10^{-8}\).
Step by step solution
01
Write the balanced chemical equation for the dissolution of Ni(OH)鈧(s) in water
The balanced chemical equation for the dissolution of nickel(II) hydroxide in water is:
Ni(OH)鈧(s) 鈬 Ni虏鈦(aq) + 2OH鈦(aq)
02
Write the equilibrium expression for this reaction
The equilibrium expression, Ksp, for the dissolution of Ni(OH)鈧(s) in water is given by:
Ksp = [Ni虏鈦篯 * [OH鈦籡虏
where [Ni虏鈦篯 and [OH鈦籡 represent the equilibrium concentrations of the Ni虏鈦 and OH鈦 ions, respectively.
03
Calculate molar solubility, s, of Ni(OH)鈧 in water
We are given that approximately 0.14 g of Ni(OH)鈧 dissolves per liter of water at 20掳C. To convert this mass to moles, we need the molar mass of Ni(OH)鈧:
Molar mass of Ni(OH)鈧 = 58.69 g/mol (Ni) + 2 * (15.999 g/mol + 1.0079 g/mol) = 92.708 g/mol for Ni(OH)鈧
Now, we can find the molar solubility, s:
s = (0.14 g Ni(OH)鈧) / (92.708 g/mol Ni(OH)鈧) = 1.51 * 10鈦宦 mol/L
04
Determine the equilibrium concentrations of Ni虏鈦 and OH鈦 ions in the saturated solution
From the balanced chemical equation, we can see that for every mole of Ni(OH)鈧 that dissolves, one mole of Ni虏鈦 and two moles of OH鈦 ions are produced. Thus, we can use the molar solubility, s, to determine the equilibrium concentrations of Ni虏鈦 and OH鈦 ions in the saturated solution:
[Ni虏鈦篯 = 1.51 * 10鈦宦 mol/L
[OH鈦籡 = 2 * 1.51 * 10鈦宦 mol/L = 3.02 * 10鈦宦 mol/L
05
Calculate Ksp for Ni(OH)鈧(s)
Finally, we can use the equilibrium concentrations of Ni虏鈦 and OH鈦 ions in the saturated solution to calculate Ksp for Ni(OH)鈧(s):
Ksp = [Ni虏鈦篯 * [OH鈦籡虏
Ksp = (1.51 * 10鈦宦)(3.02 * 10鈦宦)虏
Ksp = 4.37 * 10鈦烩伕
So, the solubility product constant, Ksp, for Ni(OH)鈧(s) at 20掳C is approximately 4.37 * 10鈦烩伕.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Dissolution
Dissolution is the process where a solid substance dissolves in a solvent, forming a solution. For nickel(II) hydroxide, Ni(OH)鈧, this involves mixing with water. The solid compound splits into ions. In the classroom or lab, you'd often see it written as:
- Ni(OH)鈧(s) 鈬 Ni虏鈦(aq) + 2OH鈦(aq)
Chemical Equilibrium
In dissolution, chemical equilibrium occurs when the rate of the solid dissolving equals the rate of ions recombining into the solid. At this point, the concentrations of ions in solution remain constant. The equilibrium is depicted by consistent forward and reverse reactions, represented by the double arrow (鈬) in chemical equations.
- This means the dissolution of Ni(OH)鈧 into Ni虏鈦 and OH鈦 ions and their precipitation back to solid form occur at the same rate.
Molar Solubility
Molar solubility represents the number of moles of a substance that can dissolve per liter of solution at a specific temperature. For Ni(OH)鈧, it's calculated from the mass that dissolves in water. Knowing that 0.14 g dissolves in a liter, you'd convert this mass to moles using its molar mass.
- Molar solubility of Ni(OH)鈧: 1.51 x 10鈦宦 mol/L
Equilibrium Concentrations
Equilibrium concentrations indicate the concentrations of ions in a saturated solution at equilibrium. To find them, you relate molar solubility to ion production.
- From Ni(OH)鈧: [Ni虏鈦篯 equals the molar solubility, which is 1.51 x 10鈦宦 mol/L.
- Since each mole of Ni(OH)鈧 produces two moles of OH鈦, [OH鈦籡 is 2 * 1.51 x 10鈦宦 mol/L = 3.02 x 10鈦宦 mol/L.