Water Chemistry: Prelim Notes

Topics: Water, Oxygen, Solubility Pages: 10 (2467 words) Published: October 15, 2013
8.4 Water

Water is distributed on Earth as a solid, liquid and gas

1.1 Define the terms solute, solvent and solution
Solute: The substance that is dissolved
Solvent: The substance that dissolves the solute
Solution: A mixture of a solute dissolved in a solvent in which particles are evenly distributed as single particles. A solution where the solvent is water is called aqueous solution

1.2 Identify the importance of water as a solvent
The importance of water as a solvent
Allows biological processes to occur in aqueous solutions
“Like dissolves like”
Water is polar, dissolves in ionic compounds, polar molecules (unless too large) and very small non-polar molecules Serves as a transport system for nutrients and waste products in living things (blood, lymph systems)  gas exchange of O2 and CO2 Dissolves oxygen and carbon dioxide  important for aquatic animals and all plants; also modifies the greenhouse effect Used as a base in cleaning products, paints, etc.

1.3 Compare the state, percentage and distribution of water in the biosphere, lithosphere, hydrosphere and atmosphere Atmosphere: Water makes up between 1% and 5% of the air and is present as water vapour Lithosphere: Water makes up 10% of solid earth

Hydrosphere: Nearly all water, ocean contains 3% dissolve salt

1.4 Outline the significance of the different states of water on Earth in terms of water as: A constituent of cells and its role as both a solvent and a raw material in metabolism; A habitat in which temperature extremes are less than nearby terrestrial habitats; An agent of weathering of rocks both as liquid and solid; A natural resource for humans and other organisms

Water in its different states play a vital role in cells that makes up the fundamental processes for an organism to live Raw materials for chemical reactions that constitute life
Solvents in which life processes occur
Transport mediums to carry nutrients to cells and remove waste products

Water is known as a good thermal regulator which helps a diverse range of living organisms. The main reason is because of its high heat capacity - it is capable of absorbing great amounts of heat with minimal fluctuation in temperature.

Water also has a big impact on weathering that subsequently helps maintain the composition of water across the different spheres of the earth Water cycle that creates rain, hail and snowfall
Eroding, carving out valleys and wearing down mountains

It is essential to have different states of water in human life as a natural resource For drinking, cooking and washing
For recreation such as swimming and skiing
For transport including ships
For generating hydro-electricity
In industry as a reactant, solvent and cleaning agent

1.5 Perform an investigation involving calculations of the density of water as a liquid and a solid using: density= mass/ volume Density =
Units are or
Water molecules join to form ice, a hydrogen atom from one molecule forms a hydrogen bond

The wide distribution and importance of water on Earth is a consequence of its molecular structure and hydrogen bonding

2.1 Construct Lewis electron dot structures of water, ammonia and hydrogen sulfide to identify the distribution of electrons 2.2 Compare the molecular structure of water, ammonia and hydrogen sulfide, the differences in their molecular shapes and in their melting and boiling points

Compound
Lewis Electron Dot Diagram
Molecular Structure
Water

In water molecule there are two unbounded pairs occupying 3 of the points of the tetrahedron Water molecule is bent because oxygen has stronger electro-negativity High melting point (0°C) and boiling point (100°C)

Structure is bent
Ammonia

Polar moleculre made of three hydrogen atoms covently bonded to nitrogen Contains hydrogen bonding
High melting point (-83°C) and boiling point
(-62°C)
Structure is a pyramidal shape

Hydrogen Sulfide

Dipole-dipole forces
Melting point...
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