ANALYSIS FOR IONS Name __________________________ Section _________ Date _______________ Determination of Cation and Anion of Unknown Salt Although you are most familiar with table salt, which is the salt used in cooking and seasoning of foods, the family of "salts" has many members. Most are found in nature, such as the chlorides of sodium, potassium and calcium, but all can be formed in the laboratory as a product of a neutralization reaction, that is a reaction between an acid and a base in water. The formation of table salt, NaCl, results by reacting hydrochloric acid and sodium hydroxide as represented by the following equation:HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) Your unknown salt contains only one cation. It may be any one of the following four:Na+, K+, Ca2+ or Fe3+ Your unknown salt contains only one anion. It may be any one of the following four:CO32-, Cl-, SO42- or PO43-Thus, there are many possible combinations, and you must determine which salt is the unknown given to you. 1. Testing for the Cation of the Unknown Salt You should observe only one positive test for the cation in your unknown. a) In a flame tests for Na+, K+, Ca2+, the color of the flame is bright yellow, violet, or orange-red, respectively. However, the orange-red flame for calcium may not be very prominent. b) Thus, calcium will require a confirmatory test, and will form a white precipitate when treated with ammonium oxalate (NH4)2C2O4.c) When a salt containing Fe3+ is treated with potassium thiocyanate (KSCN) solution, a blood-red colored solution will form. d) By now you should have determined which cation is present in your unknown. 2. Testing for the Anion of the Unknown Salt You should observe only one positive test for the anion in your unknown. a) Any salt containing CO32- ions will react promptly with an acid (e.g., HCl(aq)) to form carbon dioxide gas, which will foam and bubble up in the test tube.b) If the unknown solution immediately forms a white precipitate when mixed with silver nitrate (AgNO3), and if the precipitate is permanent (that is, it cannot be dissolved in nitric acid), then it proves that chloride ion (Cl-) is present. c) Sulfate ions will form a permanent white precipitate when treated with barium chloride (BaCl2(aq)) and nitric acid (HNO3). d) The proof that PO43- ions are present is the formation of a bright yellow precipitate when a phosphate salt is treated with ammonium molybdate, ((NH4)2MoO4) and nitric acid (HNO3). precipitate. A positive result would indicate which anion?e) By now you should have determined what anion is present in your unknown. 3. Conclusion The report form contains observations that were made by one of your classmates. Based on these observations, fill in the blanks to indicate if the ions are present or absent. From the overall set of observations decide which of the salts is your unknown by giving its cation and anion, formula, and name at the end of the report sheet. 4. Deliverable Complete the report by answering the questions on page 5. Submit pages 3,4, and 5 to your instructor on the due date. PART A: CATION TESTS OPERATION OBSERVATION CONCLUSION Section 1: Flame test for Na+, K+ and Ca2+ ions NaCl Bright yellow KCl Lavender CaCl2 Not very evident Flame test for unknown Bright yellow Section 2: Test for Ca2+ ions (NH4)2C2O4 with NaCl Clear solution (NH4)2C2O4 with KCl Clear solution (NH4)2C2O4 with CaCl2 White precipitate (NH4)2C2O4 with FeCl3 Clear solution (NH4)2C2O4 with unknown Clear solution Section 2: Test for Fe3+ ions KSCN with NaCl Clear solution KSCN with KCl Clear solution KSCN with CaCl2 Clear solution KSCN with FeCl3 Blood red precipitate KSCN with unknown Clear solution The unknown cation is ___________________
ANALYSIS FOR IONS
Name __________________________ Section _________ Date _______________
Determination of Cation and Anion of Unknown Salt
Although you are most familiar with table salt, which is the salt used in cooking and seasoning of foods, the family of "salts" has many members. Most are found in nature, such as the chlorides of sodium, potassium and calcium, but all can be formed in the laboratory as a product of a neutralization reaction, that is a reaction between an acid and a base in water. The formation of table salt, NaCl, results by reacting hydrochloric acid and sodium hydroxide as represented by the following equation:
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
Your unknown salt contains only one cation. It may be any one of the following four:
Na+, K+, Ca2+ or Fe3+
Your unknown salt contains only one anion. It may be any one of the following four:
CO32-, Cl-, SO42- or PO43-
Thus, there are many possible combinations, and you must determine which salt is the unknown given to you.
1. Testing for the Cation of the Unknown Salt
You should observe only one positive test for the cation in your unknown.
a) In a flame tests for Na+, K+, Ca2+, the color of the flame is bright yellow, violet, or orange-red, respectively. However, the orange-red flame for calcium may not be very prominent.
b) Thus, calcium will require a confirmatory test, and will form a white precipitate when treated with ammonium oxalate (NH4)2C2O4.
c) When a salt containing Fe3+ is treated with potassium thiocyanate (KSCN) solution, a blood-red colored solution will form.
d) By now you should have determined which cation is present in your unknown.
2. Testing for the Anion of the Unknown Salt
You should observe only one positive test for the anion in your unknown.
a) Any salt containing CO32- ions will react promptly with an acid (e.g., HCl(aq)) to form carbon dioxide gas, which will foam and bubble up in the test tube.
b) If the unknown solution immediately forms a white precipitate when mixed with silver nitrate (AgNO3), and if the precipitate is permanent (that is, it cannot be dissolved in nitric acid), then it proves that chloride ion (Cl-) is present.
c) Sulfate ions will form a permanent white precipitate when treated with barium chloride (BaCl2(aq)) and nitric acid (HNO3).
d) The proof that PO43- ions are present is the formation of a bright yellow precipitate when a phosphate salt is treated with ammonium molybdate, ((NH4)2MoO4) and nitric acid (HNO3). precipitate. A positive result would indicate which anion?
e) By now you should have determined what anion is present in your unknown.
3. Conclusion
The report form contains observations that were made by one of your classmates. Based on these observations, fill in the blanks to indicate if the ions are present or absent. From the overall set of observations decide which of the salts is your unknown by giving its cation and anion, formula, and name at the end of the report sheet.
4. Deliverable
Complete the report by answering the questions on page 5. Submit pages 3,4, and 5 to your instructor on the due date.
PART A: CATION TESTS
|
OPERATION |
OBSERVATION |
CONCLUSION |
||||
|
Section 1: Flame test for Na+, K+ and Ca2+ ions |
|
|
||||
|
NaCl |
Bright yellow |
|
||||
|
KCl |
Lavender |
|
||||
|
CaCl2 |
Not very evident |
|
||||
|
Flame test for unknown |
Bright yellow |
|
||||
|
|
|
|
||||
|
Section 2: Test for Ca2+ ions |
|
|
||||
|
(NH4)2C2O4 with NaCl |
Clear solution |
|
||||
|
(NH4)2C2O4 with KCl |
Clear solution |
|
||||
|
(NH4)2C2O4 with CaCl2 |
White precipitate |
|
||||
|
(NH4)2C2O4 with FeCl3 |
Clear solution |
|
||||
|
(NH4)2C2O4 with unknown |
Clear solution |
|
||||
|
|
|
|
||||
|
Section 2: Test for Fe3+ ions |
|
|
||||
|
KSCN with NaCl |
Clear solution |
|
||||
|
KSCN with KCl |
Clear solution |
|
||||
|
KSCN with CaCl2 |
Clear solution |
|
||||
|
KSCN with FeCl3 |
Blood red precipitate |
|
||||
|
KSCN with unknown |
Clear solution |
|
||||
The unknown cation is ___________________
Trending now
This is a popular solution!
Step by step
Solved in 2 steps
