8.3 Identification of ions by chemical and spectroscopic means

• What type of reactions often result in chemical tests for cations?

  Precipitate formation
• Match the anion with the reagent used for its identification:

  Sulfate (SO42-) ↔️ Barium Chloride (BaCl2)

  Halides (Cl-, Br-, I-) ↔️ Silver Nitrate (AgNO3)
• Silver iodide (AgI) is insoluble in ammonia.


  True
• Flame tests are a quantitative method for determining ion concentrations.

  False
• Which cation produces a lilac flame color?

  Potassium (K+)
• The atomizer in AAS converts the sample into a gas phase.
• What reagents are commonly used in chemical tests for cations?

  NaOH and NH3
• The reaction of sulfate ions with barium chloride forms a white precipitate of barium sulfate.
• Match the cation with its flame test color:

  Sodium ↔️ Yellow

  Copper ↔️ Green

  Potassium ↔️ Lilac

  Calcium ↔️ Orange-red
• Match the cation with its flame test color:

  Potassium ↔️ Lilac

  Calcium ↔️ Orange-red

  Copper ↔️ Green
• Atomic Absorption Spectroscopy (AAS) measures the amount of light absorbed by free metal atoms
• Steps in the AAS procedure

  1️⃣ Prepare standard solution

  2️⃣ Atomize standard and sample

  3️⃣ Shine light from HCL

  4️⃣ Measure absorbed light

  5️⃣ Compare absorption to standards
• An excitation source in AES can be a flame, plasma, or electric arc.

  True
• What is the name for the light spectrum emitted by excited atoms in AES?

  Emission spectrum
• Iron(II) (Fe2+) reacts with sodium hydroxide (NaOH) to form a green precipitate.
• Order the silver halide precipitates based on their color from lightest to darkest:

  1️⃣ White (Chloride)

  2️⃣ Cream (Bromide)

  3️⃣ Yellow (Iodide)
• Match the cation with its flame test color:

  Sodium (Na+) ↔️ Yellow

  Potassium (K+) ↔️ Lilac

  Calcium (Ca2+) ↔️ Orange-red

  Copper (Cu2+) ↔️ Green
• What is the purpose of a flame test?

  Identify certain cations
• Flame tests are more quantitative than AAS.

  False
• What is the role of the monochromator in AAS?

  Select target wavelength
• Match the cation with its reaction with NaOH and NH3:

  Fe2+ ↔️ Green precipitate with both NaOH and NH3

  Al3+ ↔️ White precipitate soluble in excess NaOH

  Cu2+ ↔️ Blue precipitate soluble in excess NH3
• Which halide forms a cream-colored precipitate with silver nitrate?

  Bromide
• What is the purpose of flame tests?

  Identify certain cations
• Flame tests are quantitative methods for identifying cations

  False
• A hollow cathode lamp in AAS emits light at a specific wavelength that the target element absorbs.


  True
• What type of light does AAS measure to determine elemental concentration?

  Absorbed light
• What does a monochromator do in AES?

  Separates light wavelengths
• What is Atomic Emission Spectroscopy (AES) used for?

  Elemental composition analysis
• The monochromator in AES separates light into its component wavelengths.

  True
• Steps in using AES

  1️⃣ Introduce the sample into the excitation source

  2️⃣ Pass the emitted light through the monochromator

  3️⃣ Detect the intensity of separated wavelengths

  4️⃣ Compare the spectrum to reference data
• AES is particularly useful for analyzing complex samples
• The mass analyzer in MS separates ions based on their m/z ratios.

  True
• Steps in using MS

  1️⃣ Ionization of neutral molecules

  2️⃣ Separation of ions based on m/z ratios

  3️⃣ Detection of ion abundance

  4️⃣ Interpretation of mass spectrum
• Copper(II) (Cu2+) forms a blue precipitate that is insoluble in excess NaOH but soluble in excess NH3.


  True
• Silver chloride (AgCl) is soluble in dilute ammonia.
• In a flame test, when a compound containing sodium (Na+) is heated, it emits a yellow color.
• The flame test color for sodium (Na+) is yellow
• What does AAS measure to determine elemental concentration?

  Light absorbed by atoms
• AAS can analyze multiple elements simultaneously.

  False
• Which reagent is used to test for sulfates?

  Barium chloride