matter + separation

What does the atomic number of an atom tell you?

number of protons

What does the mass number (top number) tell you about an atom?

number of protons + neutrons

What is meant by an element?

substance only made up of one type of atom

Approx. how many elements are there?

100

What is an isotope?

different forms of same element with same number of protons but different number of neutrons

What is meant by relative atomic mass?

average mass of all isotopes of an element

Formula for relative atomic mass

sum of isotope abundance x isotope mass number / sum of abundances of all isotopes

What meant by a compound? (2)

• substance formed of 2 or more elements in fixed proportions

• held together by chemical bonds

What is meant by a mixture?

group of different elements or compounds that are not chemically bonded together

What is a molecule?

substance that contains 2 or more atoms together held together by chemical bonds

Do compounds have the same properties as the elements they are made from?

No

6 methods through mixtures can be separated

• filtration

• chromotography

• crystallisation

• simple distillation

• fractional distillation

• evaporation

Describe filtration process (4)

• filter paper in funnel and place over beaker

• pour mixture into funnel

• insoluble solids caught by filter paper

• liquid and dissolved substances will pass through (filtrate)

Describe process of crystallisation (5)

• pour solution into evaporation dish

• heat with bunsen burner

• stop heating when crystals form and allow them to cool

• leave it to allow the rest of the water to evaporate or use filtration

• dry the crystals in a warming oven

What is the benefit of using crystallization rather than evaporation?

excess heat in evaporation can cause the crystals to break down via thermal decomposition

What is chromatography used for?

separating components based on their solubility

What is a ‘pure’ substance?

only contains one element or compound

Define ‘solution’

mixture containing solute (solid) dissolved in a solvent (liquid)

Purpose of simple distillation

separate liquid from a mixture when we want to keep the liquid

Describe process of simple distillation (3)

• solution placed into flask and heated until liquid evaporates

• vapour passes into a condenser where it condenses back into liquid

• liquid collected in beaker

Why can you not use simple distillation for mixtures that contain multiple liquids?

if they have similar boiling points they may evaporate at the same time

Describe process of fractional distillation (5)

• solution in flask is gently heated

• liquid with lowest boiling point evaporates and enters fractionating column

• passes into condenser and collected in a beaker

• if another liquid evaporated, the glass rods in the fractionating column would cause the it to condense again

• process repeats

What are is the fractionating column in laboratory fractional distillation filled with + why?

• small glass rods

• provide large sa so gases will condense back into liquid if temp is below their boiling point