YEAR 9 – Topic 2 – Elements, Mixtures and Compounds Flashcards
How do you determine whether a substance is pure using boiling or melting points?
A pure substance has a fixed melting and boiling point.
How do you determine whether a substance is a mixture with melting or boiling points?
A mixture may melt or boil over a range of temperatures.
What is simple distillation?
Simple distillation is a method of separating a solvent from a solution. Eg water from a salt water solution. It works because the solvent may have a lower boiling point than the solute.
What is fractional distillation?
Fractional distillation is the method of separating a liquid from a mixture of two or more liquids. It works because different liquids have different boiling points.
What is crystallisation?
The process to obtain crystals from a saturated solution.
How can chromatography be used to separate a mixture?
It can separate mixtures of substances into their components.
How does a chromatogram provide information about the composition of a mixture?
Chromatography separates out a mixture of soluble solids. You can tell what a substance is made up of. You can then compare it to other substances and see whether they have a similar composition.
What is the RF value?
Rf= Retention Factor
RF= distance travelled by component/distance travelled by solvent
IT IS ALWAYS SMALLER THAN 1!!!
How do you calculate the RF value?
Rf value = distance travelled by component/ distance travelled by solvent
How does the RF value help you determine the components of a mixture?
Certain components of a mixture in a certain solvent will travel a certain distance. The Rf value shows this.
What is a molecule?
2 or more atoms chemically bonded together.
What is an element?
A substance that only contains one type of atom.
What is a compound?
A substance made up of 2 or more different elements chemically bonded together.
What is a mixture?
2 or more substances together which are not chemically bonded.
What is a pure substance?
May be an element or a compound. Contains only 1 substance and one type of particle.
How do you know if you calculated the Rf value wrong?
The Rf value should be below 1, if it isn’t then it is wrong and try again.
What mixture is separated in decanting?
A mixture of immiscible liquids and insoluble solids from liquids. Eg. Oil and water.
What mixture is separated in filtration?
Insoluble solids and liquids. Eg. Sand and water.
What mixture is separated in evaporation?
Solute from a solvent. Eg. Salt from a salt solution.
What mixture is separated in distillation?
Solvent from a solution. Eg. Alcohol from a sugar solution. Or water from a salt solution.
What mixture is separated in fractional distillation?
A mixture of miscible liquids. Eg petrol and diesel from crude oil.
What mixture is separated in a separating funnel?
Mixture of immiscible liquids. Eg. Oil and water.
What mixture is separated in chromatography?
Mixture of soluble solids. Eg. Mixture of food dye.
What does immiscible mean?
Two or more substances that do NOT mix up.
What does miscible mean?
Two or more substances that DO mix up.
What is the solvent?
It is a liquid that dissolves a solute to form a solution.
What is a solute?
A solute is the substance that dissolved into the solvent to form a solution.
Why can samples have a different Rf value in different solvents (chromatography)?
Because substances have different levels of solubility in different solvents. The more soluble a sample is in a solvent, the higher up the chromatography it will get.
What NOT to do in chromatography?
- draw the baseline in pen because it will dissolve and run up the paper ruining your results
- make the solvent over the baseline because it will wash off the solutes and the will dissolve into the solvent.
