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4.11Chemistry 01. Materials And Their Structure

Know that purity is a way to describe how much of a specific… — Cambridge Checkpoint Science 0893 Revision Notes & Topical Questions

5 min read 5 parts Lesson 11 of 11 1 quiz

📚 Cambridge Checkpoint Science 0893 Hub / Topical Revision
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4.11 Purity: how much of a substance is pure — CHECKPOINT - Lower Secondary Science 0893 notes: Know that purity describes how much of a specific substance is present in a sample and calculate percentage purity.Pure substance — contains only one substance.A pure element has atoms…

  • Alloy of gold
  • Impurities in diamond
  • Composition
  • Obtaining salt
  • Importance
  • Single product

Section 1 of 5Meaning of purity

  • Pure substance
    • contains only one substance.
    • A pure element has atoms that are all of one type.
  • Purity
    • a measure of how much of a specific substance there is in a sample.

Section 2 of 5Percentage purity

  • Formula
    • percentage purity = × 100
      • (mass or parts of the pure substance ÷ total mass or parts)
  • Gold
    • carats show the number of parts out of 24 that are gold.
    • 24 carat is pure gold and 18 carat is 18 parts in 24, so it is 75% pure.
  • Silver
    • hallmarks show parts out of 1000.
    • Silver marked 925 contains 925 parts out of 1000, which is 92.5% silver.
    • Silver marked 900 is of lower purity than silver marked 925.

Section 3 of 5Alloys and impurities

  • Alloy of gold
    • a mixture of gold with metals such as copper or silver.
  • Impurities in diamond
    • pure diamond is colourless carbon.
    • A few nitrogen atoms make it yellow.
    • Boron atoms make it blue.
    • Nitrogen, nickel or hydrogen can make it green.

Section 4 of 5Seawater

1Composition3 points
  • 1000 g of seawater contains about 35 g of salts.
  • About 68% of the salts is sodium chloride.
  • The rest is mainly magnesium chloride, sodium sulfate and calcium chloride.
2Obtaining salt2 points
  • evaporating seawater gives sodium chloride that is only about 68% pure.
  • Other salts must be removed to get pure sodium chloride.

Section 5 of 5Pure products from reactions

  • Importance
    • products such as medicines must be free from impurities that might stop them working or harm the patient.
  • Single product
    • in a simple reaction there is only one product, such as magnesium oxide.
  • More than one product
    • products are mixed together and with unused reactants.
    • They must be separated and purified.

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