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. 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. Thus, calcium will require a confirmatory test, and will form a white precipitate when treated with ammonium oxalate (NH4)2C2O4. When a salt containing Fe3+ is treated with potassium thiocyanate (KSCN) solution, a blood-red colored solution will form. By now you should have determined which cation is present in your Testing for the Anion of the Unknown Salt You should observe only one positive test for the anion in your unknown. 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. 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. Sulfate ions will form a permanent white precipitate when treated with barium chloride (BaCl2(aq)) and nitric acid (HNO3). 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). A positive result would indicate which anion? By now you should have determined what anion is present in your 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. Deliverable A student was given an unknown solid that gave the following test results: A portion of the solution of unknown emitted bubbles of a colorless, odorless gas when hydrochloric acid solution was added. Another portion of the solution gave a blood-red colored solution with potassium thiocyanate solution. a) Which ions are present? Cation ______ Anion ______ b) Name the unknown salt. __________________________ c) Write the correct formula for the salt. _________________ Another student's unknown gave the following test results: a portion of the solution of unknown gave a yellow precipitate with ammonium molybdate reagent. A flame test on some of the solution resulted in a bright yellow flame. a) Which ions are present? Cation ______ Anion ______ b) Name the unknown salt. ___________________________ c) Write the correct formula for the salt._________________
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.
- 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.
Thus, calcium will require a confirmatory test, and will form a white precipitate when treated with ammonium oxalate (NH4)2C2O4.
- When a salt containing Fe3+ is treated with potassium thiocyanate (KSCN) solution, a blood-red colored solution will form.
- By now you should have determined which cation is present in your
- Testing for the Anion of the Unknown Salt
You should observe only one positive test for the anion in your unknown.
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.
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.
Sulfate ions will form a permanent white precipitate when treated with barium chloride (BaCl2(aq)) and nitric acid (HNO3).
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). A positive result would indicate which anion?
- By now you should have determined what anion is present in your
- 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.
Deliverable
A student was given an unknown solid that gave the following test results: A portion of the solution of unknown emitted bubbles of a colorless, odorless gas when hydrochloric acid solution was added. Another portion of the solution gave a blood-red colored solution with potassium thiocyanate solution.
a) Which ions are present? Cation ______ Anion ______
- b) Name the unknown salt. __________________________
- c) Write the correct formula for the salt. _________________
Another student's unknown gave the following test results: a portion of the solution of unknown gave a yellow precipitate with ammonium molybdate reagent. A flame test on some of the solution resulted in a bright yellow flame.
a) Which ions are present? Cation ______ Anion ______
b) Name the unknown salt. ___________________________
c) Write the correct formula for the salt._________________
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