Elements,Compounds,Mixtures

• What are the three main categories of substances discussed in this chapter?

  Elements, compounds, and mixtures
• Why is air considered a mixture?

  Because it contains elements and compounds
• What is the significance of separating mixtures in forensics?

  It is important for the analysis of substances
• What are the properties of pure substances compared to mixtures?

  • Pure substances have fixed melting and boiling points.
  • Mixtures may melt or boil over a range of temperatures.
• What experimental techniques are used for the separation of mixtures?

  1. Simple distillation
  2. Filtration
  3. Paper chromatography
  4. Fractional distillation
  5. Crystallisation
• What is the definition of an element?

  An element is a substance that cannot be split into anything simpler by chemical means.
• How are elements represented in models or diagrams?

  They are shown as atoms of a single color or size.
• What is the key point about elements and isotopes?

  • Elements consist of atoms with the same atomic number.
  • Most elements are mixtures of isotopes with different mass numbers.
• What does a chromatogram provide information about?

  A chromatogram provides information about the composition of a mixture.
• How can R_f values be used in chromatography?

  R_f values can be calculated to identify the components of a mixture.
• What practical investigation can be conducted using paper chromatography?

  • Investigate inks or food colorings.
• What is the composition of a gold ring made from 18-carat gold?

  It is 75% gold and usually contains copper.
• What is pure water classified as?

  Pure water is a compound.
• Why might diagrams or models not show differences between isotopes?

  Because they usually focus on atoms of a single type.
• What is the atomic number of an element?

  The atomic number is the number of protons in an atom.
• What is the relationship between isotopes and atomic number?

  Isotopes have the same atomic number but different mass numbers.
• How does the presence of isotopes affect the classification of elements?

  It shows that elements can consist of different forms of the same atom.