5. Calculate the mass of NH 3 in the Ni(NH 3 )nCl 2 sample.
   ..
   .

mol NH

mol NH

gNH

1 gNH

0 00329 17 04

1 3 0 0561^3

3

3

# =

6. Calculate the mass percent of NH 3 in Ni(NH 3 )nCl 2.

n

%.%

.

.

gNi NH Cl

gNH

100 43 2

0 130

0 0561

32

==^3 #

^h

Mass Percent of Ni2+in Ni(NH 3 )nCl 2

Recap: 50. mL samples of known concentration of [Ni(NH 3 )n]2+were made up by

using NiSO 4 ⋅6 H 2 O. The concentrations were then plotted versus their absorbance.

The unknown solution’s absorbance was then extrapolated from this graph and used

in the calculation for the mass percent of Ni2+.

7. Calculate the number of moles of NiSO 4 ⋅6 H 2 O added to form the standard solution.

.

.

g NiSO H O

g NiSO H O

mol NiSO H O

1

0 3000

262 88

(^61)
6
(^426)
42
: # 42
:
: = 0.0041 mol of NiSO

4 ⋅6 H 2 O

8. Calculate the number of moles of Ni(NH 3 )nCl 2 in the standard solution.
   . mol of NiSO H O
   mol of NiSO H O

mol Ni NH Cl

1

0 001141

1

6 1

6

(^42) n
42
32

:
^h
= 0.001141 mol Ni(NH 3 )nCl 2

9. Calculate the concentration of Ni(NH 3 )nCl 2 in the standard solution.

.

..
mL.

mol Ni NH Cl

L

mL

50 0 M

0 001141

1

1000

n 0 0228

32

# =

^h

10. Calculate the absorbance of the standard (known) and unknown solutions of
    [Ni(NH 3 )n]2+from their measured transmittance.
    absorbance of standard solution = 2.000 – log (32.6) = 0.487
    absorbance of unknown solution of Ni(NH 3 )nCl 2 = 2.000 – log (22.4) = 0.650


11. Calculate the concentration of the unknown solution of Ni(NH 3 )nCl 2 , given that

c

A b

c

ε A

s

s

syn

==syn

where As= absorbance of [Ni(NH 3 )n]2+from standard solution, Asyn= absorbance of

[Ni(NH 3 )n]2+from synthesized Ni(NH 3 )nCl 2 , cs= concentrations of standard solution

and csyn= concentrations of synthesized solution.

..

L..

mol M

1

0 650 0 0228

0 487

##^1 =0 0304

12. Calculate the concentration of the Ni2+(aq)ion in the unknown solution.
    .
    L.

mol Ni NH Cl

mol Ni NH Cl

0 0304 mol Ni M

1

n (^1) 0 0304
n
32
32
2

=

^ +
^
h
h

13. Calculate the mass of Ni2+(aq)ion in 50.0 mL of the unknown solution.
    
    
    • 
      
      
      
      • 
        
      
      
      • 
        

        .. .'
        L

        
        
      
      
      
      
    
    
    
    

mol Ni

mol Ni

gNi mL sol n

mL

0 0304 L

1

58 69

1

50 0

1000

(^21)
2
2
###= 0.0892 g Ni2+
Part III: AP Chemistry Laboratory Experiments