C2.1: Purity And Separating Mixtures Flashcards
What is relative atomic mass?
Relative atomic mass tells us how heavy an atom is compared to 1/12th of a carbon-12 atom.
What does a chemical formula show you?
How many of each element there are in a unit of a substance
What is relative atomic number?
How many protons there are in an element
What is the empirical formula?
The simplest whole-number ratio of the atoms of each element in a compound
What is a pure substance?
A substance that consists of one element or compound. It is often difficult to get pure substances.
What is an impure substance?
A substance that consists of more than one element
How can we identify if a subtance is pure or impure?
Pure substances have a sharp melting point
Impure substances melt over a range of temperatures
What is an example of a mixture?
An alloy which is a mixture of a metal with one or more other elements
What is a melting point?
The temperatute at which a substance changes from the solid state to a liquid state
What is filtration?
Separates an insoluble substance in the solid state from substances in the liquid state
How do you determine the melting point?
By heating a substance:
Measure the temperature at which it melts
When does a solution form?
When one substance dissolves in another
What is a solute?
The substance that dissolves
What is a solvent?
The substance the solute dissolves in
What happens when something dissolves?
The solutes particles separate and become completely mixed with the particles of the solvent
What does the term soluble mean?
When a substance can dissolve in a particular solvent
What does the term insoluble mean?
When a substance cannot dissolve
How does filtration work?
Separates an insoluble substance in the solid state from substances in the liquid state
What is actually used in filtration to filter the solid from the liquid?
Filter paper
What is crystallisation?
Used to produce solid crystals from a solution. When the solution is warmed, some of the solvent evaporates leaving crystals behind.
What happens when you conduct crystallisation at too strong temperatures?
You will get a powder instead of crystals
What is simple distillation?
Separates a solvent from a solution. It relies on the solvent having a lower boiling point than the solute
What apparatus is required in simple distillation?
Bunsen burner
Round-bottom flask
Thermometer
Condenser
Test tube
What is fractional distillation?
A type of distillation that separates two or more substances from a mixture in the liquid state. Both liquids must have a different boiling point and a special equipment called a fraction unit column.
What is chromatography?
A process by which it can separate complex mixtures into their component parts
What are the 2 different chemical phases in chromatography?
1) stationary phase - does not move
2) mobile phase - does move
What is the stationary phase in paper chromatography?
The absorbent paper
What is the mobile phase in paper chromatography?
The solvent in the liquid state - such as the water
What is the stationary phase in thin-layer chromatography?
A thin layer of either:
- alumina powder
- silica
Spread over a plate of glass or plastic
What is the mobile phase in thin-layer chromatography?
Solvent in the liquid state
Briefly explain the process of paper chromatography
Used to separate mixtures of dyes or inks.
A drop of the mixture is placed on filter paper.
The paper is dipped in a solvent, which moves up the paper.
Different substances travel at different speeds, separating into distinct spots.
What is the baseline in chromatography?
the starting point from which the movement of these components is measured
What is the solvent front in chromatography?
The point that the solvent has reached as it moves up the paper
Briefly explain the process of filtration
Separates an insoluble solid from a liquid.
A mixture is poured through filter paper in a funnel.
The solid stays on the paper (residue), while the liquid (filtrate) passes through.
Briefly explain the process of distillation
Separates a liquid from a solution based on boiling points.
The solution is heated until the liquid evaporates.
The vapor is cooled in a condenser, turning it back into a liquid.
The pure liquid is collected, leaving impurities behind.
Briefly explain the process of Thin Layer Chromatography
Similar to paper chromatography but uses a thin layer of silica gel or alumina on a glass or plastic plate.
The sample is spotted onto the plate, which is placed in a solvent.
Different substances travel at different speeds, separating for identification.
Briefly explain the process of fractional distillation
Separates two or more liquids with different boiling points.
The mixture is heated, and the liquid with the lowest boiling point evaporates first.
A fractionating column improves separation by allowing repeated condensation and evaporation.
The vapors are cooled, condensed, and collected separately.
How do you calculate the Rf value?
Distance travelled by the substance / distance travelled by the solvent
What is the stationary phase in gas chromatography?
The stationary phase is silica or alumina powder packed into a metal column
What is the mobile phase in gas chromatography?
The mobile phase is an unreactive gas (like nitrogen) which doesn’t react with solvent
Briefly describe the process of gas chromatography
It helps separate and identify different gases or liquids that evaporate easily.
The sample is turned into a gas and pushed through a long tube by a gas like helium.
Inside the tube, different substances move at different speeds, so they separate.
A detector at the end records when each substance comes out.
The results show as peaks on a graph, helping scientists figure out what’s in the sample.
Used for drug tests, crime investigations, and checking food or air quality.
Advantages of thin layer chromatography
Quicker
More sensitive so smaller sample can be used
Larger range of stationary phases and solvents to choose from
What is filtration used to separate?
An insoluble solid from a liquid
What is crystallisation used to separate?
A soluble solid from a solution
What is simple distillation used to separate?
A solvent from a solution
What is fractional distillation used to separate?
One or more liquids from a mixture of liquids
What is chromatography used to separate?
Coloured soluble substances
