In this experiment you will analyze a solution that may contain some of the foll

Question

In this experiment you will analyze a solution that may contain some of the following anions and cations: so,-, Cl, and NO,. K', NH,, Pb, Fe", Cr, Ca", Ni, and Zn Pre-Lab Assignment 1. If you determine that Ca is present in your unknown, which anion(s) could not be present? 2. If your unknown is colorless, what can you deduce about Ni", C, and Fe" 3. If SO,- is present in your unknown solution, which cation(s) will not be present? 4is present in youru If your unknown gives a violet flame, what would you predict?

Explanation / Answer

1) None of the above, beacuse there CaNO3, CaSO4 and CaCl2 are all soluble in water.

2) We can say that is not probable that this compounds are present in the sample because there compounds almost everytime form color solutions.

4) You have in your sample K+

Questions:

1)

Kb= [NH4+][OH-]/[NH3]

1,8*10-5= X2/ 0,25

X= (1,8*10-5* 0,25)1/2= 2,1*10-3

pOH= -log[OH-] = -log(2,1*10-3)= 2,67

14= pH+pOH

pH= 14-pOH= 11,33

3) a) The first on precipitate is the Zn because is the one that has the lower value of Kps that has to be reach to start been precipitate.

Kps: Ni+2 1*10-7 , Ca+2 2,3*10-9, Zn 1,4*10-9

b) Kps= [Zn+2][C2O4-2]

[C2O4-2]= Kps/ [Zn+2]= 1,4*10-9/0,030= 4,7*10-8

c) Beacuse Ni and Zn form hydrate salts that won´t precipitate as easily as the CaC2O4.

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