Chemistry Ch 13 & 14 - Analysis Methods Flashcards
Chromatography:
What does term ‘adsorption’ mean in chromatography?
The term ‘adsorption’ describes the adhesion of molecules or substances to the surface of a solid or liquid. This is why the stationary phase «1 chromatography is either a solid or a liquid. The mobile phase is in either a liquid or a gas state.
What is thin-layer chromatography (TLC)?
Thin-layer chromatography (TLC) is similar to paper chromatography. In TLC, a thin layer of a fine powder, such as alumina (aluminium oxide), is spread on a glass or plastic plate, which acts as the stationary phase.
What is the ‘solvent front’?
‘Solvent front’ is the term used to describe the movement of the solvent during chromatography. It is visible as the wet moving edge of the solvent as it travels along the stabonary phase.
What is required to use R₁ values?
For the R₁ value of a component to be comparable to a set of standard R₁ values, they must be determined under identical conditions.
What are the advantage of Paper Chromatography?
4 points
Paper Chromatography
- Is cheap
- Requires little preparation
- is more efficient for polar and water-soluble compounds
- Is easy to handle and store
What are the advantage of Thin-Layer Chromatography?
4 points
- Detects smaller amounts
- Achieves better separation of less polar compounds
- Can use corrosive materials
- Has a wide range ot stationary phases
What is HPLC
High-performance liquid chromatography (HPLC) is sometimes also referred to as high- pressure liquid chromatography.
What is the advantage of HPLC?
HPLC provides qualitative and quantitative analysis of components in a mixture.
The size of the peaks is due to the amount of light absorbed by each component, and this can be used to calculate the relative amount of each component within the mixture.
In HPLC what is the mobile phase?
In HPLC, the mobile phase is a liquid under pressure.
In HPLC what is the stationanary phase?
In the most common form of HPLC, called reversed-phase HPLC. the stationary phase is silica. The silica used has been moditied to make it non-polar by attaching long hydrocarbon chains to its surface.
Alumina (Al₂O₃) is also used.
In HPLC, what is measured?
In HPLC. retention time is used to identify components in a mixture.
In HPLC, how can concentrations be determined.
The concentration of an individual component in a mixture can be determined by comparing its peak area on a chromatogram with the peak areas of samples with known concentrations of the same chemical.
What is ‘anhydrous’?
The term ‘anhydrous’ indicates there is no water present in the compound. To produce anhydrous sodium carbonate, a sample of sodium carbonate is heated to above 100°C to ensure all of the water is removed. The sodium carbonate is then quickly placed in a desiccator to prevent it absorbing any water from the atmosphere.
What are stock solutions?
Stock solutions are large volumes of common chemicals such as those used in volumetric analysis.
What is a standard solution?
A solution of accurately known concentration is referred to as a standard solution.
How can standard solutions be prepared?
Standard solutions can be prepared from primary standards or by titrating an existing solution with another standard solution to determine its concentration.
What is a titration?
In a titration, a measured volume of a standard solution is reacted with a measured volume of the solution whose concentration is to be determined.
What is the equivalence point in a titration?
The equivalence point of a reaction occurs when the reactants have been mixed in the mole ratio shown by the reaction equation.
What is the end point in a titration?
The end point is the point during the titration when the indicator changes colour.
How should indicators for a titration be chosen?
Indicators for a titration should be selected so that the end point occurs when the equivalence point has been reached.
What are concordant titres?
Concordant titres vary within narrowly specified limits. Three concordant titres are usually obtained during a titration.
How are conical and volumetric flasks rinsed before a titration?
When rinsing glassware before a titration, it is important to ensure that conical and volumetric flasks are rinsed with deionised water
Rinsing with acidic or basic solutions will introduce unmeasured amounts of acids or bases into the flask that can react and affect the results.
How are burette and pipettes rinsed before a titration?
When rinsing glassware before a titration, it is important to ensure that the burette and pipette are rinsed with the acid or base to be transferred by them.
Rinsing with water will dilute the acid or base solution.
