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Questions and Answers
What is the main purpose of a reagent in qualitative analysis?
What is the main purpose of a reagent in qualitative analysis?
- To react selectively with one of the ions to produce a change (correct)
- To represent a chemical reaction as a net ionic equation
- To remove the carbonate and phosphate ions from the solution
- To identify the unknown substance
What is the difference between a positive test and a negative test?
What is the difference between a positive test and a negative test?
- A positive test is used to identify the type of ion, while a negative test is used to determine its concentration
- A positive test is used to remove impurities, while a negative test is used to add impurities
- A positive test indicates the presence of an ion, while a negative test indicates its absence (correct)
- A positive test is used to test for anions, while a negative test is used to test for cations
What is the purpose of acidifying the solution in the anion tests?
What is the purpose of acidifying the solution in the anion tests?
- To increase the concentration of the anions
- To produce a gas
- To remove the carbonate and phosphate ions that may affect the observation of other ions (correct)
- To change the color of the solution
What is the result of the chloride ion test?
What is the result of the chloride ion test?
How many anion tests are performed in the experiment?
How many anion tests are performed in the experiment?
What is the term for the change that occurs when a chemical reaction takes place?
What is the term for the change that occurs when a chemical reaction takes place?
What is the result of the reaction between AgNO3 and NaCl?
What is the result of the reaction between AgNO3 and NaCl?
What is the purpose of adding 6M HCl to the solution in the sulfate ion test?
What is the purpose of adding 6M HCl to the solution in the sulfate ion test?
Which reagent is used to test for the presence of nitrate ions?
Which reagent is used to test for the presence of nitrate ions?
What is the observation when carbonate ions are present in the solution?
What is the observation when carbonate ions are present in the solution?
What is the purpose of heating the solution in the phosphate ion test?
What is the purpose of heating the solution in the phosphate ion test?
What is the formula of the compound formed when BaCl2 reacts with Na2SO4?
What is the formula of the compound formed when BaCl2 reacts with Na2SO4?
Flashcards
Reagent's Purpose
Reagent's Purpose
React selectively with one of the ions to produce a detectable change.
Positive vs. Negative Test
Positive vs. Negative Test
Positive: Ion is present. Negative: Ion is absent.
Why Acidify Anion Tests?
Why Acidify Anion Tests?
To remove carbonate and phosphate ions that may interfere with observing other ions.
Chloride Ion Test Result
Chloride Ion Test Result
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Characteristic Change
Characteristic Change
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AgNO3 and NaCl Reaction
AgNO3 and NaCl Reaction
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Purpose of 6M HCl in Sulfate Test
Purpose of 6M HCl in Sulfate Test
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Reagent for Nitrate Ions
Reagent for Nitrate Ions
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Observation with Carbonate Ions
Observation with Carbonate Ions
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Purpose of Heating in Phosphate Test
Purpose of Heating in Phosphate Test
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Formula of the Compound
Formula of the Compound
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Study Notes
Objectives
- Learn to identify anions from their typical chemical reactions
- Learn to represent a chemical reaction as a net ionic equation
Changes in Chemical Reactions
- Formation or disappearance of:
- Colour
- Solid (precipitate)
- Gas
- Light
- Heat
- Change in instrument readings
Qualitative Analysis
- Reagent: a chemical substance that reacts selectively with one ion in the unknown to produce a change
- Two types of tests:
- Positive test: substance (anion or cation) is present in the unknown
- Negative test: substance (anion or cation) is absent or present in low concentration
Anion Tests
- Five anion tests:
- Chloride ion test (Cl-)
- Sulfate ion test (SO42-)
- Nitrate ion test (NO3-)
- Carbonate ion test (CO32-)
- Phosphate ion test (PO43-)
Anion Tests Reactions
- Chloride ion test: AgNO3 + NaCl → AgCl (white ppt) + NaNO3 (acidified with 6M HNO3)
- Sulfate ion test: BaCl2 + Na2SO4 → BaSO4 (white ppt) + 2NaCl (acidified with 6M HCl)
- Nitrate ion test: 8FeSO4 + 2NaNO3 + 4H2SO4 → [FeNO]SO4 (brown ring) + 3Fe2(SO4)3 + Na2SO4 + 4H2O (acidified with 6M H2SO4)
- Carbonate ion test: Na2CO3 + 2HCl → 2NaCl + H2O + CO2 (gas) (using 6M HCl)
- Phosphate ion test: Na3PO4 + 12(NH4)2MoO4 + 24HNO3 → (NH4)3[PO4(MoO3)12] (yellow ppt) + 3NaNO3 + 21NH4NO3 + 12H2O (heated using water bath)
Net Ionic Equation
- Chloride ion test: Ag+ + Cl- → AgCl (ppt)
- Formula: Molecular equation → Total ionic equation → Net ionic equation
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