(b) elements, compounds and mixtures

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Chemistry

IGCSE Chemistry

Edexcel

Principles of Chemistry

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12 Terms

1
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element (1.8)

an element is a pure substance that cannot be broken down into any other substances

2
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compound (1.8)

a compound is a pure substance that is made from more than one element. these elements are very hard to separate since they are chemically bonded together e.g. H2O or CO2

3
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mixture (1.8)

a mixture is when two or more elements or compounds are present without being chemically bonded together.

4
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melting point (1.9)

a melting point is the temperature at which a substance goes from a solid to a liquid. pure substances have fixed melting points, but mixtures can melt over a range of temperatures

5
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boiling point (1.9)

a boiling point is the temperature at which a substance goes from a liquid to a gas. pure substances have fixed boiling points, but mixtures can boil over a range of temperatures

6
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simple distillation (1.10)

  • the dissolved solute has a higher boiling point than the solvent

  • the solution is heated and the solvent evaporates

  • the solvent moves away and it cools and condenses

  • the remaining solution becomes more concentrated as there is less solvent

<ul><li><p>the dissolved solute has a higher boiling point than the solvent</p></li><li><p>the solution is heated and the solvent evaporates</p></li><li><p>the solvent moves away and it cools and condenses</p></li><li><p>the remaining solution becomes more concentrated as there is less solvent</p></li></ul><p></p>
7
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fractional distillation (1.10)

  • used to separate liquids from a mixture

    • e.g. crude oil

  • each liquid has a different boiling point

  • vapours rise and the column gets cooler at the top

  • liquids are led away / collected on trays

  • lower boiling point is at the top and vice versa

<ul><li><p>used to separate liquids from a mixture</p><ul><li><p>e.g. crude oil</p></li></ul></li><li><p>each liquid has a different boiling point</p></li><li><p>vapours rise and the column gets cooler at the top</p></li><li><p>liquids are led away / collected on trays</p></li><li><p>lower boiling point is at the top and vice versa</p></li></ul><p></p>
8
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filtration (1.10)

used to separate insoluble solids from liquids

<p>used to separate insoluble solids from liquids</p>
9
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crystallisation (1.10)

produces solid crystals from a solution

<p>produces solid crystals from a solution</p>
10
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paper chromatography (1.10 / 1.11)

paper chromatography is used to separate mixtures of soluble substances. these are often coloured substances such as food colourings, inks, dyes or plant pigments.

<p><span>paper chromatography is used to separate mixtures of soluble substances. these are often coloured substances such as food colourings, inks, dyes or plant pigments.</span></p>
11
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Rf value (1.12)

distance travelled by component / distance travelled by solvent

e.g. pigment moved by 3.4cm and solvent moved by 4.8 cm → Rf value = 3.4/4.8 = 0.71

12
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investigate paper chromatography using inks / food colourings (1.13)

here, the brown ink is made of a mixture of the red, blue and yellow inks.

<p>here, the brown ink is made of a mixture of the red, blue and yellow inks.</p>