Thin Layer Chromatography (Ch.7)

What is TLC?

A chromatography technique where a mixture is separated based on interactions with a stationary phase (silica/alumina) and a mobile phase (solvent).

What is the purpose of TLC?

To separate compounds, identify substances, check purity, and monitor reaction progress.

What is the mobile phase in TLC?

An organic solvent or mixture of solvents

How does TLC work?

Solvent moves up the plate by capillary action, carrying compounds at different rates depending on polarity and attraction to stationary phase.

Which compounds travel farther: polar or nonpolar (on silica)?

Nonpolar (silica is polar → holds polar compounds more strongly).

Define chromatography.

Separation of mixture components based on differential interactions with mobile and stationary phases.

Define analyte.

The compound being analyzed.

Define adsorbent.

Solid surface that molecules adhere to (e.g., silica gel).

Define elution.

Process where the analyte travels through the stationary phase using the mobile phase.

Name 4 uses of TLC.

Determine number of components in mixture

Identify substances

Check purity

Monitor reaction progress

What type of compounds can TLC analyze?

Very small sample sizes (micrograms) and mixtures.

What are the three main steps in TLC?

1. Choosing solvent (eluent)

2. Spotting the TLC plate

3. Developing the plate

Why must you use a pencil for marking the plate?

Ink dissolves in organic solvents and will distort results.

Why are most organic compounds invisible on the TLC plate?

They are colorless.

Common method for visualizing TLC spots?

UV light (plate contains fluorescent dye).

What is Rf in TLC?

Retention factor =distance traveled by compound/ distance traveled by solvent

What influences the Rf value?

Polarity of analyte

Polarity of mobile phase

Strength of adsorption to stationary phase

What are typical Rf values for:Polar compounds?Nonpolar compounds?

Polar: low Rf (stick to silica)

Nonpolar: high Rf (travel far)