8.2 The Chemical Earth
1. The living and non-living components of the Earth contain mixtures
Construct word and balanced formulae equations of chemical reactions as they are encountered.
Acid + Base Salt + Water
Acid + Metal Hydrogen + Salt
Acid + Carbonates Salt + Water + Carbon dioxide
Identify the difference between elements, compounds and mixtures in terms of particle theory.
The Particle Theory: states that all matter consists of particles which are constantly moving
Element: a pure substance made up of one type of atom. It cannot be decomposed into simple substances.
Compound: pure substances made up of two or more elements. It can be decomposed into simpler substances.
Mixtures: substances made of parts in which the parts keep their own properties. They are either made of compounds mixed together, element mixed together or both. They do not have a definite composition.
Homogenous: Uniform composition throughout e.g. salt water, petrol
Heterogeneous: non-uniform composition throughout e.g. granite, sand
Identify that the biosphere, lithosphere, hydrosphere and atmosphere contain examples of mixtures of elements and compounds.
Biosphere: consists of living things which are made up of cells. Cells contain large amounts of water, thus, oxygen and hydrogen are abundant, and contain complex carbon compounds such as proteins and fats.
Lithosphere: consists of numerous minerals that are combined in different proportions to form sedimentary, igneous and metamorphic rocks.
Hydrosphere: water is the most abundant compound; therefore, oxygen and hydrogen are the most abundant
Atmosphere: nitrogen and oxygen are the major gases, however, other gases include argon, carbon dioxide, neon, helium and methane.
Describe situations in which gravimetric analysis supplies useful data for chemists and other scientists.
Gravimetrical analysis: used to find out the chemical composition of a substance.
Uses:
- Active ingredients in products
- Drugs and food
- Percentage compositions in compounds
- Mining company: to know the composition of an ore sample to see if it is financially viable, to see whether the soil is appropriate for agriculture or to determine the percentage of particular pollutants in water.
- Health authority: to know the composition of air near an industrial area to see if the air is polluted
- Pharmacies: use the process in mixing various chemicals to manufacture the drugs
2. Although most elements are found in combinations on Earth, some elements are found uncombined.
Explain the relationship between the reactivity of an element and the likelihood of its existing as an uncombined element.
If an element is less reactive, it is more likely to be in an uncombined state like gold, silver, and platinum. However, an element which is more reactive is always found in a combined state like potassium and sodium.
Classify elements as metals, non-metals and semi-metals according to their physical properties.
Metals
Semi-metals
Non-metals
Lustrous
High electrical conductivity
Malleable and ductile
Generally high boiling point
High thermal conductivity
Low sheen
Low electrical conductivity
High thermal conductivity
Moderate malleability and ductility
Very high boiling point
Dull
Poor electrical conductivity
Low thermal conductivity
Brittle
Low boiling point
3. Elements in Earth materials are present mostly as compounds because of interactions at the atomic level.
Ions are formed when atoms gain or lose electrons. Cations are positive ions and anions are negative ions.
Ionic compounds are formed when cations and anions combine in fixed ratios. The attraction between oppositely charged ions is called an ionic bond.
Molecular substances form when non-metal atoms bond to other non-metal atoms by sharing electron pairs in a covalent bond.
4. Energy is required to extract elements from their naturally occurring sources.
Summarise the differences between the boiling and
