FACULTY OF APPLIED SCIENCES

(AS1205C)

CHM361

EXPERIMENT 2

Title : Quantitative Analysis of Cations : Ag+, Fe3+, Cu2+ and Ni2+

Name : Dayang Nor Shafiqah Binti Awang Shukeran

Student ID : 2017296442

Laboratory partner :

Name Student ID

1. Amira Nasirah Binti Jemat 2017403616

2. Nur Syasya Farzana Binti Mohd Taib 2017441662

Lecturer’s name : Mdm. Rabuyah Binti Ni

Date of experiment : 3 October 2019

Date of submission : 7 November 2019

TITLE

Quantitative Analysis of Cations : Ag+, Fe3+, Cu2+ and Ni2+

OBJECTIVES

1. To understand the rationale and the procedure behind the separation for various cations.
2. To determine the cation present in the unknown solution using established schemes.

INTRODUCTION

Heating solutions
It is necessary to heat a solution to speed up the reaction. Heat the test tubes in a boiling
water bath. Set up this water bath when beginning work in the lab because it may take time to
heat the water bath to the appropriate temperature.

Stirring solutions
Each time a reagent is added to the test tube, the solutions needs to be stirred. A stirring rod
that is flattened to the bottom can be used as the plunger to effectively mix solutions in a
narrow test tubes.

Separating solids from solutions

Centrifuge the solutions so that the solid settles at the bottom of the test tubes. Let the
centrifuge spin for 30 minutes and the supernatant liquid can be decanted from the
precipitate.

1. Never fill the centrifuge tubes to its maximum capacity. Keep liquids level at least
1cm from the top.
2. Label all centrifuge tubes before inserting to avoid mix-up.
3. Place the test tubes in a symmetrical fashion, the objective being to keep the rotor
balanced and fill all tubes to same height.
4. Follow manufacturer’s directions.
5. If only one test tube needs to be centrifuged, achieve balance by inserting an
additional tube containing the same volume of the liquid.
Washing precipitates
Necessary to wash precipitates to free them from ions that might cause confusion in later
steps. Add 1mL or 2mL of water to the precipitate, stir, centrifuge and discard the wash
water.

Checking the pH
To check the pH of a solution, put a piece of litmus paper or pH paper on a clean glass plate
or watch glass. Dip the stirring rod into the solution in the test tube and touch the stirring rod
the paper.

Safety precautions
Work with care and wear goggles. Wash hands thoroughly with soap and water before leave.
APPARATUS
 Small test tubes
 Test tube rack
 Small test tube stoppers
 Test-tube holders
 Hot plate
 Centrifuge
 250 mL beakers
 Spatula
 Glass rod
 Distilled water
 Dropping pipette
 Litmus paper
 Vial containing unknown solution

CHEMICALS

Unknown Cationic Solutions

1. 0.05 M silver nitrate AgNO3 (aq)
2. 0.05 M copper (II) nitrate Cu(NO3)2 (aq)
3. 0.05 M nicker nitrate Ni(NO3)2 (aq)
4. 0.05 M iron (III) nitrate Fe(NO3)2 (aq)
5. 6 M HCl (aq)
6. 6 M HNO3 (aq)
7. 6 M H2SO4 (aq)
8. 6 M H2SO (aq)
9. 6 M CH3COOH (aq)
10. 6 M NaOH (aq)
11. 0.1 M K4[Fe(CN)6]
12. 0.1 M KSCN
13. Unknown solution
PROCEDURE
Flow chart of cations
Pre-Lab Questions

1. Test for Ag+, Cu2+, Fe3+

Several drops of 6 M HCl are added to a solution that may contain the three ions. A white
precipitate forms.

Ions present : Ag+ Ions absent : None Ions undetermined : Cu2+, Fe3+

2. Test for Cu2+, Ag+, Ni2+

Several drops of 6 M HCl are added to a solution that may contain the three ions. No
precipitate forms. The addition of 6 M NaOH until the solution is basic results in no
formation of precipitate.

Ions present : Ni2+ Ions absent : Ag+, Cu2+ Ions undetermined : None

3. Test for Cu2+, Fe3+, Ni2+

Several drops of 6 M NaOH are added to a clear solution that may contain the three ions
until the solution is basic and a dark precipitate forms. The precipitate totally dissolves in
6 M H2SO4. The addition of 6 M NH 3 to this acidic solution until it basic results in a clear
solution containing a dark precipitate. The resulting dark precipitate completely dissolves
in 6 M H2SO4.

Ions present : Fe3+ Ions absent : Ni2+ Ions undetermined : Cu2+

EXPERIMENTAL PROCEDURE

Note that the following directions are written for a "known" solution that contains all of the
cations. An "unknown" solution will probably not be able to form all of the products
described in this procedure.

1. Separation of the silver from iron, copper and nickel ions.

a) 8 drops of 6 M HCl was added to the solution to be analysed and stirred. A white
precipitate indicated that the Ag+ ion was present.

b) The solution was centrifuged and tested with one drop of 6 M HCl to make sure the
precipitate was completed. 6 M HCl was continued added if more precipitate occurred
until it was completed.

c) Centrifuged, decanted (pour off), and the clear solution has been saved into a second
test tube for procedure 3.

d) The precipitate was washed by adding 1mL distilled water and stirred. The wash water
was centrifuged and discarded. The precipitate was saved for procedure 2.

2. Confirmation of silver.
a) 1mL of 6 M NH 3 was added to the precipitate from 1d, which is AgCl, 1 mL of 6 M
NH3 was added.

b) It was stirred until the precipitate was completely dissolved.

c) 15 drops of 6 M HCl was added to the solution. The solution was then fumed and the
reaction between the strong acid and the base gave off heat whether or not silver was
present. The test tube may get warm.

d) The solution was stirred and tested with pH indicator paper or litmus paper to ensure
the solution was acidic. More HCl was added if it is not acidic. White AgCl precipitate
occurred in the acidic solution confirmed the presence of silver.

e) The silver compound was disposed as directed by the instructor.

3. Separation of iron and copper from nickel.
a) 6 M NaOH was added to the solution saved from procedure 1c with stirring until the
solution was basic and 3 more drops were added.

b) The test tube was stirred and placed in the hot water bath for 3 minutes. The presence
of either copper or iron or both was indicated by the formation of the precipitate.

c) The solution was then centrifuged and the clear solution was separated from the solid.
The clear solution was saved for procedure 6.
d) The precipitate was washed with a mixture of 10 drops of 6 M NaOH and 10 drops of
water.

e) The wash water was centrifuged and discarded and saved for procedure 4.

4. Separation of iron from copper; confirmation of copper.

a) 5 drops of water were added to the precipitate from procedure 3.

b) 6 drops of 6M H2SO4 were added wised until the solution was acidic and tested with
litmus paper and stirred to dissolved the precipitate.

c) 6 M aqueous NH3 was added to the solution until it was basic to litmus and was added
1 mL extra.

d) The supernatant liquid was separated from the precipitate after centrifuged. The
precipitate was kept for procedure 5. The presence of blue Cu(NH3)42+ ion was
confirmed the test for copper.

e) 6 M CH3COOH, acetic acid was added to the solution containing Cu(NH 3)42+ to
confirm the test until the blue colour fades and the solution became acidic. 2 drops of
0.1 M K4[Fe(CN)6] were then added and the presence of a red-brown precipitate of
Cu2[Fe(CN)6] reconfirmed the presence of copper.

f) The copper solution was disposed as directed by instructor.

5. Confirmation of iron.
a) The precipitate of iron hydroxide was washed from the procedure 4d.

b) 6 M H2SO4 was added drop wise until the precipitate dissolved.

c) 5 drops of 0.1 M KSCN were added to the solution. The presence of deep red
[FeSCN]2+ ion confirmed the presence of iron.

d) The iron solution was disposed as directed by the instructor.

6. Steps 1-5 was repeated for the cation unknown sample. The results were recorded for
each step.
RESULTS

Known solution Unknown solution

Step Procedure (be specific)
Results Conclusion Results

Adding HCl to the initial White There is a

No precipitate
1 sample for known and precipitate presence of
formed
unknown solution. formed cation

Confirmation of silver, White

No precipitate
2 adding NH3, then HCl until precipitate Ag+ present
formed
acidic to litmus. formed
Cu2+ : Dark
blue/black
precipitate
formed
Cu2+ and/or
Adding NaOH to the
Fe3+
solutions until the solution is Fe3+ : Lime Dark blue/black
3 present
basic. (Separation of iron precipitate precipitate formed
and copper from nickel) formed
Ni2+ absent
Ni2+ : No
precipitation
occured (-)
Adding H2SO4 drop wise
until the solution is acidic
when tested with litmus Blue
Presence of Blue Cu(NH3)42+
paper, then add NH3 to the Cu(NH3)42+
4 Cu2+ ion solution
solution until basic to litmus, ion solution
confirmed appeared
and then add 1 mL extra to appeared
confirm the presence of
copper.

Adding H2SO4 drop wise Deep red

Deep red
until the precipitate dissolve, [FeSCN]2+ ion Presence of
5 [FeSCN]2+ ion
then add KSCN solution to solution Fe3+ confirmed
solution appeared
confirm the presence of iron. appeared

Analysis :
So, since unknown cation solution and Cu 2+ have the most similiar characteristics, it is said
that unknown solution have the presence of Cu2+ ion.
QUESTIONS

1. Write the balanced net ionic equations for all the observations in the analysis of the
known cationic solution. Indicate the colour of the ions and the precipitate underneath the
chemical species.

Step Cation Colour Balanced chemical equation

2 Ag+ White AgNO3 + HCl → AgCl + HNO3

3 Fe3+ Lime yellow Fe(NO3)3 + 3NaOH → Fe(OH)3 + 3NaNO3

3 Cu2+ Blue Cu(NO3)2 + 2NaOH → Cu(OH)2 + 2NaNO3

Cu(NO3)2 + H2SO4 → CuSO4 + 2 HNO3
4 Cu2+ Blue
CuSO4 + 4 NH3 → [Cu(NH3)4]SO4
6Fe(NO3)2 + 9H2SO4 → 3Fe2(SO4)3 + 10HNO3 + 2NO +
5 Fe3+ Deep red 4H2O
Fe2(SO4)3 + 2KSCN → 2[FeSCN]2+ + K2SO4 + 3SO42-

2. What is the precipitating reagent for silver (Ag+)? Would a solution of NaCl work as
well? Why or why not?

The precipitate reagent for the silver (Ag+) is HCl. This is beacuse the Cl has the same (-)
charge in both of HCl and NaCl solutions. This is why it would work so well for NaCl.
The equation for the reaction is Ag+ + HCl- → AgCl, while the equation for the reaction
with NaCl is Ag+ + NaCl- → AgCl. This shows that both solutions would work just as
well.
DISCUSSION

In this experiment, the cations in samples were determined by using analysis technique.
There are two types of samples which are known and unknown sample. In the known
solution, we can conclude that the mixture of solution contain cation Ag +, Fe3+, Cu2+ and Ni2+.
This is because of when added the HCl solution to the initial sample, white precipitate of
AgCl is formed which indicate that there is cation Ag + present. Then, slight excess of HCl
was added to ensure the complete precipitation. Transition elements are usually highly in
coloured. A colorless solution solution should happen if these ions are absent. To know that
all the transition metal cations are present, a colored solution will produce.

Many reagents are used in qualitative analysis but only a few are involved in nearly
every group procedure. The four commonly used reagents are HCl, HNO 3, NaOH and NH3.
Ag+ is located in group 1. Another two are Pb 2+ and Hg2+ and cations produce insoluble
chlorides so they can be precipitated with dilute HCl, while all other cations remain in
solution. In group II, Cu2+ is here and cations produce very insoluble sulphides so they can be
precipitated by low amounts of sulphide ions. This can be achieved by adding an acidic
solution. Fe3+ and Ni2+ are in group III and cations produce slightly soluble sulphides so they
can be precipitated by relatively high amounts of sulphide ion. This can be achieved by
adding a basic solution of NaOH. Nickel (II) hydroxide does not dissolve in excess NaOH.

The unknown solution showed most of the similarities with Cu 2+. So, since unknown
cation solution and Cu2+ have the most similiar characteristics, it is said that unknown
solution have the presence of Cu2+ ion.

Qualitative analysis involves forming and decomposing complex ions. Qualitative

tests are very sensitive, allowing to detect a very small amount present in sample. Due to
sensitivity, cleaning utensils and accurate observations are essential to results. Many basic
principles are applied to determine the impurities or cations.
CONCLUSION

In a conclusion, the purpose of this lab is to identify the cations present in an unknown
solution. Qualitative analysis was used to identify the substances present in the unknown
solution. Qualitative analysis is used by reacting the unknown solution with a number of
different reagents. Based on the results from the lab, the cations found in the unknown
solution is said to have the presence of Cu2+ ions.

REFERENCES

Bartleby Research. (2019). Essay about Qualitative Analysis. Retrieved October 26, 2019
from https://www.bartleby.com/essay/Qualitative-Analysis-F3FEX43VC.

CHM361 notes.

Michelle, E. (2011). QUALITATIVE ANALYSIS OF CATIONS. Retrieved October 26,

2019 from http://ellinamichelle.blogspot.com/2011/06/qualitative-analysis-of-cations.html.