Analytical Chemistry: Spectroscopy and Chromatography for A-Level Chemistry (WJEC

What type of laboratory method is used to identify functional groups in organic compounds?

Test-tube reactions

Reagents produce characteristic colour changes, precipitates or gas evolution.

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What reagent is used to test for the presence of a carbon–carbon double bond?

Bromine water

Alkenes rapidly decolourise orange bromine water.

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Fill in the blank:

When an alkene reacts with bromine water, the solution changes from orange to _______.

colourless

The bromine adds across the C=C bond.

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True or False:

Carboxylic acids produce effervescence when reacted with carbonates.

True

CO₂ gas is released during the reaction.

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What gas is produced when a carboxylic acid reacts with sodium carbonate?

Carbon dioxide

The reaction forms CO₂, water and a salt.

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True or False:

Alcohols produce a colour change with acidified potassium dichromate when oxidised.

True

The solution changes from orange to green.

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Fill in the blank:

The reagent commonly used to oxidise alcohols in identification tests is acidified potassium _______.

dichromate

K₂Cr₂O₇ turns from orange to green during oxidation.

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What reagent forms a silver mirror when reacting with aldehydes?

Tollens’ reagent

Aldehydes reduce Ag⁺ ions to metallic silver.

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True or False:

Ketones give a positive result with Tollens’ reagent.

False

Ketones are not readily oxidised under these conditions.

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Fill in the blank:

Fehling’s solution gives a _______ precipitate when reacting with aldehydes.

brick red

Cu²⁺ ions are reduced to Cu₂O.

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What functional group produces carbon dioxide when reacting with sodium carbonate?

Carboxylic acid

The –COOH group reacts with carbonate ions releasing CO₂.

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Why are test-tube reactions useful in organic chemistry analysis?

Functional group identification

Observations help distinguish between different types of organic compounds.

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What analytical technique is used to determine the molecular mass of a compound?

Mass spectrometry

It measures the mass-to-charge ratio of ions produced from molecules.

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What property of ions is measured in a mass spectrometer?

Mass-to-charge ratio

This is often written as m/z.

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Fill in the blank:

In mass spectrometry, the horizontal axis of the spectrum represents _______.

m/z

It shows the mass-to-charge ratio of detected ions.

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True or False:

Mass spectrometry can be used to determine the molecular formula of a compound.

True

Precise molecular mass helps identify the exact combination of atoms.

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What peak in a mass spectrum usually represents the molecular ion?

Molecular ion peak

This corresponds to the mass of the intact molecule.

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True or False:

The molecular ion peak normally has the highest intensity in the spectrum.

False

The base peak has the highest intensity.

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Fill in the blank:

The most intense peak in a mass spectrum is called the _______ peak.

base

It is assigned a relative abundance of 100%.

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What type of masses are used when calculating molecular formula using mass spectrometry data?

Precise atomic masses

These allow accurate determination of molecular composition.

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True or False:

The molecular ion in mass spectrometry is formed by removing an electron from the molecule.

True

This produces a positively charged ion (M⁺).

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Fill in the blank:

The molecular ion formed in mass spectrometry is usually written as _______.

M⁺

It represents the intact molecule with a positive charge.

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Why are precise molecular masses important in determining molecular formulas?

Distinguish formulas

Different formulas can have similar relative molecular masses.

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What information can be determined by combining atomic masses with the molecular ion mass?

Molecular formula

The exact composition of atoms in the molecule can be deduced.

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What **analytical technique** is used to identify **functional groups by measuring absorption of infrared radiation**?

Infrared spectroscopy ## Footnote Different bonds absorb infrared radiation at characteristic frequencies.

What **property of molecular bonds** allows them to absorb **infrared radiation**?

Bond vibrations ## Footnote Bonds stretch and bend when absorbing infrared energy.

# Fill in the blank: In **infrared spectroscopy**, absorption is usually measured using _\_\_\_\_\_\_ numbers.

wavenumbers ## Footnote Wavenumber is measured in cm^-1.

# True or False: Different **chemical bonds** absorb **infrared radiation** at characteristic wavenumbers.

True ## Footnote This enables identification of specific functional groups.

What **region of an infrared spectrum** is unique for each molecule and used for identification?

Fingerprint region ## Footnote This region provides a distinctive pattern for each compound.

# True or False: The **fingerprint region** is identical for most organic compounds.

False ## Footnote It is highly specific and differs between molecules.

# Fill in the blank: **Infrared spectroscopy** helps identify _\_\_\_\_\_\_ groups within organic molecules.

functional ## Footnote Each functional group absorbs IR radiation at characteristic values.

What additional information can **infrared spectra** provide besides identifying functional groups?

Impurities ## Footnote Unexpected peaks may indicate the presence of impurities.

# True or False: **Infrared spectra** can be compared with **reference spectra** to identify unknown substances.

True ## Footnote This comparison process is known as fingerprinting.

# Fill in the blank: **Greenhouse gases** absorb infrared radiation and contribute to _\_\_\_\_\_\_ warming.

global ## Footnote Molecules like CO₂, CH₄ and H₂O trap heat in the atmosphere.

Which **atmospheric gas** absorbs infrared radiation and contributes significantly to the **greenhouse effect**?

Carbon dioxide ## Footnote Its molecular vibrations absorb infrared radiation.

Why do molecules such as **CO₂**, methane and water vapour contribute to **global warming**?

Infrared absorption ## Footnote They absorb and re-emit infrared radiation, trapping heat in the atmosphere.

What analytical technique provides information about the **positions of ¹H or ¹³C** atoms in a molecule?

Nuclear magnetic resonance (NMR) spectroscopy ## Footnote NMR identifies chemical environments of nuclei in organic compounds.

Why does **¹³C NMR** give simpler spectra than **¹H NMR**?

Fewer signals and no coupling ## Footnote ¹³C atoms are less abundant and coupling with ¹H is often decoupled.

# Fill in the blank: In **NMR spectroscopy**, chemical shifts are recorded on the _\_\_\_\_\_ scale.

δ ## Footnote The δ scale measures resonance relative to TMS in ppm.

# True or False: The chemical shift of a nucleus depends on its **molecular environment**.

True ## Footnote Electron density around the nucleus affects the magnetic shielding.

What does the **integration of ¹H NMR signals** indicate?

Relative number of protons ## Footnote The area under a peak is proportional to the number of equivalent hydrogens.

# True or False: NMR samples are typically dissolved in **deuterated solvents** to avoid interference from ¹H.

True ## Footnote Solvents such as CDCl₃ or CCl₄ are commonly used.

# Fill in the blank: **Tetramethylsilane** (TMS) is used as a standard because it produces a single signal at δ = _\_\_\_\_\_.

0 ## Footnote It is inert, volatile and gives a sharp reference peak.

How can **¹H NMR spectra** be used to **deduce the number of protons** in different environments?

Integration and chemical shift ## Footnote Each unique hydrogen gives a peak; integration shows relative numbers.

# True or False: The **n+1 rule** predicts the number of peaks due to spin–spin splitting in ¹H NMR.

True ## Footnote A proton with n adjacent non-equivalent protons splits into n+1 peaks.

# Fill in the blank: In aliphatic compounds, spin–spin splitting can produce doublets, triplets and _\_\_\_\_\_.

quartets ## Footnote These arise from coupling with neighbouring protons.

Why is TMS suitable as an **NMR standard**?

* Chemically inert and produces a single signal * It is non-toxic * It has a low boiling point (26°C) and so can be easily removed from the sample afterwards ## Footnote Its δ = 0 peak provides a reference point for chemical shifts.

How can ¹H and ¹³C NMR data be used to suggest **molecular structures**?

By comparing chemical shifts and splitting ## Footnote Peaks, integration and multiplicity reveal the types and connectivity of hydrogens and carbons.

When would you use **CCl4 as a solvent**?

When analysing non polar compounds.

When would you use **deuterated solvents** in NMR?

When analysing polar compounds.

What is the purpose of **chromatography** in chemistry?

To **separate and identify components** of a mixture. ## Footnote Different types of chromatography are chosen depending on the sample and stationary/mobile phases.

Name three common types of **chromatography**.

* Thin-layer chromatography * Column chromatography * Gas chromatography ## Footnote TLC uses a plate, CC uses a packed column, GC uses a gas mobile phase with a column.

# Fill in the blank: In TLC, a plate is coated with a _\_\_\_\_\_ and a solvent moves up the plate.

solid ## Footnote The solid acts as the **stationary phase** while the solvent is the **mobile phase**.

# True or False: In **column chromatography**, the solvent moves down the column.

True ## Footnote The stationary phase (solid) is packed in the column and components are separated by interaction with it.

What factor determines the separation of substances in **chromatography**?

Relative solubility and retention ## Footnote Compounds with higher solubility in the **mobile phase** move faster; retention is determined by affinity for the **stationary phase**.

# Fill in the blank: The ratio used to quantify the movement of a spot in TLC is called the _\_\_\_\_\_ value.

Rf ## Footnote Rf = distance travelled by substance / distance travelled by solvent front.

# True or False: **Retention time** in gas chromatography can be compared with standards to identify substances.

True ## Footnote Each compound has a characteristic retention time under specific conditions.

How can **mass spectrometry** be combined with **gas chromatography**?

To analyse separated components. ## Footnote GC separates compounds and MS provides molecular weight and structural information.

# Fill in the blank: In TLC, the Rf value is always between _\_\_\_\_\_ and 1.

0 ## Footnote Rf = 0 if the substance does not move and Rf = 1 if it moves with the solvent front.

What is the **mobile phase** in gas chromatography?

Gas ## Footnote A carrier gas, such as helium or nitrogen, transports components through the column.

# True or False: Rf values and **retention times** are compared with standards to identify unknown substances.

True ## Footnote This allows identification of compounds in mixtures.

What laboratory application uses **TLC** to identify analgesics or metal ions?

Test-tube separation and identification ## Footnote TLC separates components for visualisation and comparison with known standards.

Analytical Chemistry: Spectroscopy and Chromatography Flashcards

Interpret analytical data using IR, NMR, MS, and chromatographic techniques. (62 cards)