M3: Exam
Question 1
pts
Click this link to access the Periodic Table. This may be helpful throughout the exam.
Show the calculation of the molar solubility (mol/L) of Mg(OH)2, Ksp of Mg(OH)2 = 1.8 x 10-11.
Your Answer:
ksp= [Mg+2] [OH−] 2
= (s ) (2s) 2
s 3 = 1.8 x 10 −
s= 3 ( 1.8 x 10 − 11 4 )
s= 1.65 x 10 − 4 mol/L
Mg(OH)2 (s) Mg+2 (aq) + 2 OH-1 (aq)
(s) (s) (2s)
1.8 x 10-11 = [Mg+2] x [OH-1]2
1.8 x 10-11 = [s] x [2s]2
, 1.8 x 10-11 = 4 s3
s = 1.65 x 10-4 mol/L
Format exponents correctly.
Question 2
pts
Click this link to access the Periodic Table. This may be helpful throughout the exam.
Show the calculation of the Ksp of MnS if the solubility of MnS is 0.0001375 g/100 ml.
MW of MnS = 87.01
MnS (s) Mn+2 (aq) + S-2 (aq)
Your Answer:
mol sol MnS= ( 0.0001375 g/100ml) x (1000ml/1L) x (1 mol/87.01 g)
mol sol MnS= 1.375 x 10 − 6 x 1000 x .01149
mol sol= 1.58 x 10 – 5 mol/L
ksp= (1.58 x 10 – 5 ) (1.58 x 10 – 5 )= 2.50 x 10 – 10
molar sol of MnS = (0.0001375 g/100 ml) x (1000 ml / 1 L) x (1 mol / 87.01 g MnS)
molar sol MnS = 1.58 x 10-5 mol / L
This means that as 1.58 x 10-5 mol / L of MnS dissolves, 1.58 x 10-5 mol / L of Mn+2 and 1.58 x
10-5 mol / L of S-2 are formed since one mole of each ion forms from 1 mole of MnS
Ksp = [Mn=2] x [S-2] = (1.58 x 10-5) x (1.58 x 10-5) = 2.50 x 10-10
Question 1
pts
Click this link to access the Periodic Table. This may be helpful throughout the exam.
Show the calculation of the molar solubility (mol/L) of Mg(OH)2, Ksp of Mg(OH)2 = 1.8 x 10-11.
Your Answer:
ksp= [Mg+2] [OH−] 2
= (s ) (2s) 2
s 3 = 1.8 x 10 −
s= 3 ( 1.8 x 10 − 11 4 )
s= 1.65 x 10 − 4 mol/L
Mg(OH)2 (s) Mg+2 (aq) + 2 OH-1 (aq)
(s) (s) (2s)
1.8 x 10-11 = [Mg+2] x [OH-1]2
1.8 x 10-11 = [s] x [2s]2
, 1.8 x 10-11 = 4 s3
s = 1.65 x 10-4 mol/L
Format exponents correctly.
Question 2
pts
Click this link to access the Periodic Table. This may be helpful throughout the exam.
Show the calculation of the Ksp of MnS if the solubility of MnS is 0.0001375 g/100 ml.
MW of MnS = 87.01
MnS (s) Mn+2 (aq) + S-2 (aq)
Your Answer:
mol sol MnS= ( 0.0001375 g/100ml) x (1000ml/1L) x (1 mol/87.01 g)
mol sol MnS= 1.375 x 10 − 6 x 1000 x .01149
mol sol= 1.58 x 10 – 5 mol/L
ksp= (1.58 x 10 – 5 ) (1.58 x 10 – 5 )= 2.50 x 10 – 10
molar sol of MnS = (0.0001375 g/100 ml) x (1000 ml / 1 L) x (1 mol / 87.01 g MnS)
molar sol MnS = 1.58 x 10-5 mol / L
This means that as 1.58 x 10-5 mol / L of MnS dissolves, 1.58 x 10-5 mol / L of Mn+2 and 1.58 x
10-5 mol / L of S-2 are formed since one mole of each ion forms from 1 mole of MnS
Ksp = [Mn=2] x [S-2] = (1.58 x 10-5) x (1.58 x 10-5) = 2.50 x 10-10
