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Questions and Answers
What occurs when an electron becomes excited?
What occurs when an electron becomes excited?
Which metal ion produces a bright yellow color during a flame test?
Which metal ion produces a bright yellow color during a flame test?
What happens when an excited electron returns to its ground state?
What happens when an excited electron returns to its ground state?
Which of the following ions produces a crimson red color when subjected to a flame test?
Which of the following ions produces a crimson red color when subjected to a flame test?
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Why might some metal ions not produce visible flame colors during a flame test?
Why might some metal ions not produce visible flame colors during a flame test?
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What is the term for the conversion where a reagent induces a change resulting in an analytic signal?
What is the term for the conversion where a reagent induces a change resulting in an analytic signal?
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Which of the following ions results in a blood red complex when reacted with KCNS?
Which of the following ions results in a blood red complex when reacted with KCNS?
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In the reaction of NH4Cl with NaOH, what gas is produced upon heating the reaction mixture?
In the reaction of NH4Cl with NaOH, what gas is produced upon heating the reaction mixture?
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What type of precipitate is formed when Pb2+ ions react with 2I– ions?
What type of precipitate is formed when Pb2+ ions react with 2I– ions?
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What is the primary goal of qualitative analysis in analytical chemistry?
What is the primary goal of qualitative analysis in analytical chemistry?
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Which of the following statements about electrolytes is correct?
Which of the following statements about electrolytes is correct?
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Which of the following is a characteristic of an ion exchange reaction that is reversible?
Which of the following is a characteristic of an ion exchange reaction that is reversible?
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When CO32- ions react with H+, what observable effect occurs?
When CO32- ions react with H+, what observable effect occurs?
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Which of the following reactions results in the formation of a white precipitate due to the presence of SO42- ions?
Which of the following reactions results in the formation of a white precipitate due to the presence of SO42- ions?
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What describes a non-electrolyte?
What describes a non-electrolyte?
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What characteristic of analytic reactions relates to the ability to detect minimal test material amounts?
What characteristic of analytic reactions relates to the ability to detect minimal test material amounts?
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In an irreversible ion exchange reaction, which of the following products indicates the formation of a difficultly soluble compound?
In an irreversible ion exchange reaction, which of the following products indicates the formation of a difficultly soluble compound?
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In the provided reactions, which ion forms a white precipitate when interacting with Ba2+?
In the provided reactions, which ion forms a white precipitate when interacting with Ba2+?
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Which reagent is involved when detecting Pb2+ ions with a color change to yellow precipitate?
Which reagent is involved when detecting Pb2+ ions with a color change to yellow precipitate?
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Which equation represents the short ionic equation for the reaction that produces a gas?
Which equation represents the short ionic equation for the reaction that produces a gas?
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What is the observed signal when NH4+ reacts with OH– ions?
What is the observed signal when NH4+ reacts with OH– ions?
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What occurs during the reaction of weak electrolytes?
What occurs during the reaction of weak electrolytes?
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Which of the following molecular equations results in the formation of a complex compound?
Which of the following molecular equations results in the formation of a complex compound?
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What parameter quantifies the sensitivity of an analytic reaction?
What parameter quantifies the sensitivity of an analytic reaction?
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What defines a specific reaction in terms of analytic reactions?
What defines a specific reaction in terms of analytic reactions?
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Which group of cations does not form precipitates with hydrochloric acid?
Which group of cations does not form precipitates with hydrochloric acid?
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Which reagent is NOT typically used for the classification of cations?
Which reagent is NOT typically used for the classification of cations?
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In Group 1 of cations, which of the following ions does NOT belong?
In Group 1 of cations, which of the following ions does NOT belong?
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The classification of cations based on the reaction to hydrochloric acid primarily considers what?
The classification of cations based on the reaction to hydrochloric acid primarily considers what?
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Which group consists of cations whose sulphides are insoluble in ammonium polysulphide?
Which group consists of cations whose sulphides are insoluble in ammonium polysulphide?
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Among the following cations, which does react with hydrogen sulphide in dilute mineral acid medium?
Among the following cations, which does react with hydrogen sulphide in dilute mineral acid medium?
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The group that includes cations like calcium (II) and barium (II) is classified as which group?
The group that includes cations like calcium (II) and barium (II) is classified as which group?
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What characteristic is unique to Group 2/b cations compared to Group 2/a?
What characteristic is unique to Group 2/b cations compared to Group 2/a?
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Which cation is part of Group 5 and does not react with the reagents of the previous groups?
Which cation is part of Group 5 and does not react with the reagents of the previous groups?
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Anions of which group form precipitates with silver ions in dilute nitric acid medium?
Anions of which group form precipitates with silver ions in dilute nitric acid medium?
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Which cation forms precipitates with ammonium sulphide in a neutral medium?
Which cation forms precipitates with ammonium sulphide in a neutral medium?
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Which of the following anions is part of Group 2, which does not react with hydrochloric acid?
Which of the following anions is part of Group 2, which does not react with hydrochloric acid?
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Which ion is characteristic of Group 1 anions that results in visible change upon reaction with dilute hydrochloric acid?
Which ion is characteristic of Group 1 anions that results in visible change upon reaction with dilute hydrochloric acid?
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What determines the selectivity of reagents in group reactions?
What determines the selectivity of reagents in group reactions?
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Which anion does not belong to any of the previous anion groups and is identified as a common anion?
Which anion does not belong to any of the previous anion groups and is identified as a common anion?
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What do the cations in Group 3 have in common regarding their reactions with dilute hydrochloric acid?
What do the cations in Group 3 have in common regarding their reactions with dilute hydrochloric acid?
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Which pair of anions are characteristic of Group 4, which do not react with previous reagents?
Which pair of anions are characteristic of Group 4, which do not react with previous reagents?
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Which cation is classified as an iron-based cation that may form precipitates in neutral or ammoniacal medium?
Which cation is classified as an iron-based cation that may form precipitates in neutral or ammoniacal medium?
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Study Notes
Qualitative Analysis
- Qualitative analysis aims to identify the materials present in a sample. This involves determining the chemical identity of species in the sample.
Electrolytes and Non-electrolytes
- Electrolytes conduct electricity in solution due to the presence of ions.
- Examples of electrolytes include acids, bases, and soluble ionic compounds.
- Non-electrolytes do not conduct electricity because they do not dissociate into ions in solution.
- Examples of non-electrolytes include molecular compounds and insoluble ionic compounds.
Reactions in Electrolyte Solutions
- Reactions in electrolyte solutions occur between ions.
- These reactions can be reversible or irreversible.
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Reversible ion exchange reactions occur when easily soluble compounds are formed, like:
- KCl + NaBr ↔ KBr + NaCl
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Irreversible ion exchange reactions occur when:
- Difficultly soluble compounds are formed: AgNO3 + NaCI → AgCI↓ + NaNO3
- Gases are formed: Na2S + 2HCI → 2 NaCI + H2S↑
- Weak electrolytes (acids, bases, water) are formed: HCI + NaOH → NaCI + H2O
- Complex compounds are formed: Fe(CN)2 + 4 KCN → K4[Fe(CN)6]
Analytic Reactions
- Analytic reactions are irreversible ion exchange reactions in electrolyte solutions.
- These reactions produce a visible external effect (analytic signal) that indicates the presence of a specific ion in the solution.
- Analytic signals can be observed as precipitate formation, dissolution, color changes, or gas production.
Pb2+ Ion Analytic Reactions
-
Reaction 1: Pb(NO3)2 + 2HCl → PbCl2↓ + 2HNO3
- Produces a white precipitate of PbCl2.
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Reaction 2: Pb(NO3)2 + 2KI → PbI2↓ + 2KNO3
- Produces a yellow precipitate of PbI2.
Fe3+ Ion Analytic Reaction
- FeCl3 + 6KCNS → K3[Fe(CNS)6] + 3KCl
- Produces a blood-red complex ion, [Fe(CNS)6]3-.
NH4+ Ion Analytic Reaction
- NH4CI + NaOH → NH4OH↑ + NaCI
- When heated, the reaction mixture releases ammonia gas with a characteristic odor.
CO32- Ion Analytic Reactions
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Reaction 1: K2CO3 + BaCl2 → BaCO3 + 2KCI
- Produces a white precipitate of BaCO3.
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Reaction 2: K2CO3 + 2HCl → H2CO3 + 2KCI
- Produces carbon dioxide gas (bubbles) when H2CO3 decomposes.
SO42- Ion Analytic Reaction
- Na2SO4 + BaCl2 → BaSO4 + 2NaCI
- Produces a white precipitate of BaSO4.
Characteristics of Analytic Reactions
- Sensitivity: refers to the ability to detect minimal amounts of the substance being tested. Sensitivity is expressed in terms of the minimal amount of substance, concentration, or limit of dilution.
- Specificity: refers to the ability of a reaction to be specific to one ion or molecule, not interfered with by other ions in the solution.
- Selectivity: refers to reactions specific to groups of ions having similar properties.
- Group Reactions: reactions involving reagents that precipitate ions belonging to specific groups, called group reagents.
Classification of Cations
- Cations are classified into five analytical groups based on their reactions with group reagents: hydrochloric acid, hydrogen sulfide, ammonium sulfide, and ammonium carbonate.
- The classification is based on the solubility of their chlorides, sulfides, and carbonates.
- Group 1: Pb2+, Hg22+, Ag+ (form precipitates with dilute hydrochloric acid)
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Group 2:
- 2/a: Hg2+, Cu2+, Bi3+, Cd2+ (form precipitates with hydrogen sulfide in dilute mineral acid)
- 2/b: Sn2+, Sn4+, As3+, As5+, Sb3+, Sb5+ (form precipitates with hydrogen sulfide in dilute mineral acid, but soluble in ammonium polysulphide)
- Group 3: Fe2+, Fe3+, Co2+, Ni2+, Mn2+, Cr3+, Al3+, Zn2+ (form precipitates with ammonium sulfide in neutral or ammoniacal medium)
- Group 4: Ca2+, Sr2+, Ba2+ (form precipitates with ammonium carbonate in the presence of ammonium chloride)
- Group 5: Mg2+, Li+, Na+, K+, NH4+ (do not react with reagents from previous groups).
Classification of Anions
- Anions are classified into four groups based on their reactions with hydrochloric acid and the solubility of their barium and silver salts.
- Group 1: CO32-, SiO32-, S2-, SO32-, S2O32- (react with dilute hydrochloric acid and/or form precipitates)
- Group 2: SO42-, PO43-, Fˉ, BO33- (do not react with hydrochloric acid, but form precipitates with barium ions in neutral medium)
- Group 3: Clˉ, Bˉ, Iˉ, SCNˉ (do not react with hydrochloric acid or barium ions, but form precipitates with silver ions in dilute nitric acid medium)
- Group 4: NO2‾, NO3‾, ClO3‾ (do not react with reagents from previous groups).
Flame Test
- A flame test is a quick method for qualitative detection of some ions by observing the color of the flame when the compound is heated.
- This technique is based on the excitation of electrons in the metal ions. As the excited electrons return to their ground state, they emit energy in the form of visible light.
- Common ions that produce characteristic flame colors include:
- Sodium: bright yellow
- Potassium: pale violet
- Calcium: brick red (orange-red)
- Strontium: crimson (medium)
- Barium: light green
- Lead: pale bluish
- Copper: green or blue
- Not all metal ions produce visible flame colors.
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Description
This quiz focuses on qualitative analysis, electrolytes, and reactions in electrolyte solutions. It covers the identification of materials in samples, the distinction between electrolytes and non-electrolytes, and the types of reactions that occur in solutions. Test your knowledge about these fundamental concepts in chemistry!
