2. Today’s Lab: Synthesizing Ni(NH3)n
Cl2
• By Dr. Robert D. Craig, Ph.D.

3. Today’s Lab: Synthesizing Ni(NH3)n
Cl2
• Today You will be asked to start with
• NiCl2.6H2O
• And make Ni(NH3)nCl2 and
• Determining the Mass Percent in NH3 in
Ni(NH3)n Cl2 : (backtitration)
The # of moles of NH3 =
mole of HCl - # of mol of NaOH

4. So, we will talk about . . .

5. A great tale

6. That many great TEACHERS have
told me!

7. Synthesizing Ni(NH3)n Cl2
1. Determining the Mass Percent in NH3 in
Ni(NH3)n Cl2
2. Determining the Mass Percent Ni2+ Ion
in Ni(NH3)nCl2 by spectrophotometry
3. Determining the Empircal Formula and
percent Yield fo Ni(NH3)n Cl2

8. How will You find this???
• Mass of NH3 in Ni(NH3)nCl2 =
• ( # of mol NH3) ( 17.03 gram ) =
• (1 mole NH3 )
• 1st titrate with HCl
• 2 nd back titrate with NaOH

9. Mixed indicator????
• Indicator:
• From a pH of 3.8 to 5.4 – BromCresol
Green
• From a pH of 4.2 to 6.2 – Methyl Red
• Must see this at equivalence point
• Orange Yellow  Green Blue

11. Lets begin

12. For Your assistance!!!
And – remember to work in pairs
• I will place the instructions up as a class.
As you reach certain points
• Look at power point for tips- You will need
the addendum as well
• First see figure 1 and figure 2 pg 42
• Prepare a warm bath with a 600 mL
beaker and tap water

13. Make this happen!

14. Adjust a ring stand
• Adjust a ring stand
• Stabilize an Erlenmeyer in the beaker the
Hot plate
• Weight out 4.0 grams (see addendum) of
NiCl2.6H2)
• Record the mass of the solid and paper on
Data sheet 1
• Transfer the solid to a clean 125 mL
Erlenmeyer flask.

15. Then-this happen!

16. What to do??
• Add 10 mL of distilled water to the NiCl2-
6H2O in the flask
• Place the flask in the 60oC water bath and
clamp the flask in position, (see figure 2)

17. • Stir the mixture in the flask with a clean
125 mm glass stirring rod until the
NiCl2.6H2O has dissolved.
• Remove flash-attach into alternate ring
stand
• Allow to cool for 1-2 min.
• Pg 42

18. Look here for help!! And BE
CAREFULL!!
• Slowly with strirring add 25 mL of
concentrated NH3 solution to the NiCl2-
6H2O solution in the flask.
• Cover the top of flask with a wet paper
towel. After adding the concentrated nH3
solution, suspend the flask in the warm-
water bath by clamping it to the ring stand.

19. Lab procedure
• Make sure the water temperature is
between 50 oC and 60oC
• Leave the flask in the bath for 15 min.
During this time periodically stir the
mixture

20. buchner funnel-basic setup ok

21. Alternate setup with trap

22. Coming around – do not attack
me!!

23. the filtering apparatus
• Note: For the filtering apparatus
described below your lab instructor (Rob)
will inform you whether you are to place a
trap between your filter and the water
aspirator and whether you are to place a
Buchner funnel in a rubber Filter Vac, a
bored stopper, or a rubber filtering
adapter.

24. Look Here!!!
• Do not turn off the aspirator before
removing the tubing from the side arm of
the filter flask
• While the above reaction proceeds
• Assemble your filtering apparatus as
shown in figure 3

25. SEE FIGURE 3
• (SEE FIGURE 3) PG 44
• Clamp a 250 mL taped filtering flask to
your other ring stand and place a Buchner
funnel in the flask
• Place a flat circle of filter paper in the
funnel.

26. Can do this….
• Attach a piece of pressure tubing to the
flask
• After isolating the solid disconnect and
Reassemble

27. Be careful
• WARNING
• THE AMMONIA AND THE ETHYL
ALCOHOL ARE EXTREMELY
DANGEROUS-ANY SIGNS OF
DIZZINESS, OR
• HEAT EXHAUSTION-PLEASE LET ME
KNOW
• WHEN THESE CHEMICALS HIT THE
SKIN-WASH IMMEDIATELY

28. The theory needed for exp
• .

29. Why are you doing this???
• Two important tasks many chemist
perform are the synthesis and analysis of
compounds
• Synthesis involves not only preparing the
compoiund , but also maximizing the yield
of pure product. After isoloating the
product, the chemist must analyze it to
ascertain its chemical composition

30. First . . . . .
• Analyzing Ni(NH3)nCL2 Determining th
Mass Percent NH3

31. A complicated titration
• Ammonia is a base. Theoretically, you
could determine th NH3 content of
NI(NH3)nCL2 by titrating a know mass of
the compound with an acid solution of
known concentration, called a
standardized solution.
• However, in this case , the procedure
gives inaccurate results for two (really 3)
reasons.

32. Reasons here
• First, aqueous Ni(NH3)Cl2 solutions slowly
evolve NH3,
• So some NH3 may evaporate before the sample
is completely titrated. Second, the procedure
takes longer than normal because the bonds
between NH3 and Ni2+ ion must be broken
before NH3 can react with the titrant. This bond
breaking is slow and the titration reaction itself is
fast
• So some of the indicator may react with the acid
before all the NH3 is released , causing a
premature end point.

33. What is a backtitration?
• Goto handout – Rob – upload power point
now!!

34. Volitile sample
• To minimize NH3 evoluiton and ensure
complete disruption of all NH3-Ni2-
bonds , you will use an indirection titration
method- a back titration.
• You will add a known volume of standard
hydrochloric acid solution (HCl) that
contains more moles of HCl than ther are
moles of NH3**** in the Ni(NH3)nCl2

35. Not accurate
• The HCl wil react with the Ni(NH3)nCl2
sample as shown in equation 5
• Ni(NH3)nCl2 (aq, bluish purple) + NHCl
(aq)  n NH4+ 9aq) + Ni2=(aq, green)
= (n + 2) Cl- 9aq)

36. See manual
• The excess acid and a favorable
equilibrium constant drive the reaction in
Equation 5 to completion
• Then you will titrate the excess HCl with
standard sodium hydroxide soltution
(NaOH) in a process called back tritration
• The back titration reaction is shown in
Equation 6

37. neutralization
• The back titration reaction is shown in
Equation 6
• HCl(aq) + NaOH(aq)  NaCl(aq) +
H2O (l0

38. Your job
• You wil detect the equivalence point of the
back titration, the point at which the
number of moles of NaOH added is
stoichimetrically equivalent to the number
of mole of HCl present, by observing an
indicator color change.

39. Equivalence point
The point at which the indicator changes
color is the end point Of the titration . In
order to select the proper indicator for a
particular titration, one that will produce an
end point that is close to the equivalence
point, your must consider chemical
behavior of the species present in solution
at the equivalence point.

40. Need better indicator
• In this case , if the titration mixture
contained only products shown in equation
6, The equivalence point would be at pH
7
• Hence, phenolphthalein, which changes
color at pH 8 , would be a satisfoactory
indicator

41. complications
• However, the reaction misture also
conatins ammoniumion (NH4+) which
hydrolyzes as shown in equation 7,
causing the titration mixture to be acidic at
the equivalence point.
• NH4+(aq) + H2O(aq)  NH3l(aq) +
H3O+ (Eq &

42. Mixed indicator
• Therefore , phenolphthalein is not a good
indicator for this titration, Because the
end point would occur after more than an
equivalent amount of NaOH had been
added. Instead, you will use a mixed
indicator solution, composed of
bromocresol green and methyl red.

43. Mixed indicator
• Bromcresol green changes form jelow to
blue over a pH range of 3.8 to 5.4 and
methyl red changes from red to yellow
over a pH range of 4.2 to 6.2

44. Mixed indicator
• The mixed indicator changes from rose to
green at pH 5.1 which is the pH at the
equivalence point of the titration .
• Due to the presence of green Ni2+ ion in
the misture the color change you will see
is orange-yellow to green-blue

45. Final calculation
• From the volume and concentration of
HCL solution added you will calculate the
number of moles of HCl, added using
equation 8

46. In a nutshell
• Record the results of following calculations on Data Sheet 1
• Calculate the mass of NiCl2.6H20 used in the synthesis
• Calculate the mass of synthesized Ni(NH3)nCl2
• Determining the Mass Percent in NH3 in Ni(NH3)n Cl2
• Calculate the mass of Ni(NH3)nCl2 sample titrated
• Calculate the number of moles of HCl added to Ni(NH3)nCl2
solutioin
• Calculate the number of moles of NaOH required for the titration
• Calculate the number of moles of NH3 present in the Ni(NH3)n Cl2
sample
• Calculate the mass percent NH3 in Ni(NH3)n Cl2
• Calculate the mean mass percent NH3 in Ni(NH3)n Cl2