Qualitative analysis of ions lab report. Need answers to 2a, 2b, and 2c. Table 2
ID: 941841 • Letter: Q
Question
Qualitative analysis of ions lab report.
Need answers to 2a, 2b, and 2c. Table 21.1 is included for question 2c. Thanks.
In case the photos are not clear:
2a) Suppose a mixture contains only Al3+ and Mg2+. How would you seperate these cations?
2b) Suppose a mixture contains only Al3+ and Ba2+. An unbuffered solution of NH3 will allow these cations to be separated. Why?
2c) Suppose a mixture contained only Mg2+ and Ba2+. What would happen upon the addition of 1 M NaOH? 1 M K2CrO4? 1 M K2C2O4? Use table 21.1.
In
a. Suppose a mixture contained only Al and Mg". How would you separate these cations?Explanation / Answer
a) NaOH solution when added to Mg2+ and Al3+ mixture, Al(OH)3 and Mg(OH)2 are formed
As ksp of Al(OH)3 <<<ksp of Mg(OH)2,
So Al3+ is least soluble in the aqueous solution ,hence precipitates out ,while Mg(OH)2 will remain in the solution.
Al(OH)3Al3+ +3OH-……………………(1)
Mg(OH)2Mg2+ +2OH-
Ksp of Al(OH)3=[Al3+][OH-]^3
Ksp of Mg(OH)2=[Mg2+][OH}^2
Common ion OH- concentration increases due to dissociation of Mg(OH)2,and as the result the equilibrium of reaction (1) is shifted towards reactant side,and Al(OH)3 gets thrown out from the solution.
b)Aqueous NH3 or NH4OH, when reacts with Ba2+ and Al3+ gives Al(OH)3 and Ba(OH)2.
NH4OH +Ba2+ Ba(OH)2+NH4+
NH4OH +Al3+ Al(OH)3+NH4+
As Ba(OH)2 completely dissociates in aqueous solution so is soluble ,while Al(OH)3 has low ksp so is less soluble, hence precipitates out.
c) As Ba(OH)2 completely dissociates in aqueous solution so is soluble ,while Mg(OH)2 has low ksp so is less soluble, hence precipitates out.
As MgCrO4 completely dissociates in aqueous solution so is soluble ,while BaCrO4 has low ksp so is less soluble, hence precipitates out.
Ksp MgC2O4 >>>ksp BaC2O4 so , MgC2O4 is more soluble and hence remains in solution (due to common ion effect as explained in part a) while BaC2O4 get precipitated,