Purity And Separating Mixture Flashcards
What is relative atomic mass? What is relative formula mass? What is empirical formula?
Relative atomic mass is the mean mass of an atom of an element compared to a 1/12 of the carbon 12 atom.
Relative formula mass is the mean mass of a unit of substance compared to a 1/12 of the carbon 12 atoms.
Empirical formula is the simplest who number ratio of the atoms of each element in a compound.
What are the differences between pure and impure substances? How are mixtures useful?
Pure substances consist of one element or compound but Impure substances have multiple.
Pure substances have sharp melting points whilst Impure substances melt over a range.
Mixtures consist of different substances that improve on the element. Alloys are stronger than pure metals.
What happens when a substance dissolves?
A solution forms when a solute dissolves into a solvent. When a solute dissolves, particles separate and become mixed with the solvent. Soluble substances dissolve insoluble substances do not.
How does filtration work? How does crystallisation work?
Filtration separates an insoluble solid from a liquid. The filter paper has tiny holes which allows the filtrate through and the residue is left on top.
Crystallisation separates a solvent and solute. The solution is heated till it becomes saturated. Crystals start forming so you let the solution cool as the solute’s solubility decreases. Filter out crystals.
How does simple distillation work?
Simple distillation separates solvent from solution. The solvent must have a much lower boiling point that the solute. When the solution is heated the solvent boils and escapes in gas state where it is condensed in the condenser and collected.
How does chromatography work?
Paper Chromatography has the stationary phase as absorbent paper and mobile phase as the carrier solvent. The ink being measured dissolves into the solvent and is carried. A chromatogram is produced dependant on the solubility with streaks on the paper that can be identified by comparing it to a similar chromatogram. It separates coloured soluble substances
What is Thin Layer Chromatography? What is Gas Chromatography?
TLC is like paper chromatography but the stationary phase is silica/alumina powder over a glass plate. In gas chromatography, stationary phase is silica/alumina particles packed metal column and the mobile phase is unreactive carrier gas. The chromatogram produced is a graph of the gases as peaks plotted against travel time which is affected by how the gases bond to the stationary phase.
How do you calculate the R value of a chromatogram?
R= Substance Distance///Solvent Distance
RECAP: Which is the best separation method?
Insoluble in Liquid /// Filtration
Solvent of Lower Boiling Point from Solute /// Crystallisation, Simple Distillation
Separate Mixture of Liquids /// Fractional Distillation
Mixture of Solutes /// Chromatography
How does fractional distillation work?
Used to separate two or more substances with different boiling points from a liquid mixture. All gases travel upwards that are boiled. As there is a temperature gradient, it gets colder as it gets further up the fractionating column. Most gases condense as they reach their boiling point but a singular gas would reach the top and condense through the condenser to be separated off.
