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4  Water

(27th May - 12th August 2009)



Image taken on August 25, 1992 by NOAA GOES-7 weather satellite of the Americas and Hurricane Andrew as it makes landfall on the Louisiana coast.   http://grin.hq.nasa.gov/IMAGES/SMALL/GPN-2000-001444.jpg




CONTEXT

The first astronauts who viewed the Earth from space commented on the beauty of our water-rich blue planet.  Earth’s position in the solar system enables its retention of water in solid, liquid and gaseous forms on and around its surface.  The particular properties of the water molecule assisted the evolution of life and continue to support life processes by maintaining a narrow temperature range on the Earth’s surface.

The concepts of bonding and intermolecular forces are used to increase understanding of the special nature of the water molecule.  The chemistry of solutions is examined in greater detail.

This module increases students’ understanding of the nature and practice of chemistry and the implications of chemistry for society and the environment.



TARGETED OUTCOMES

The targeted outcomes for this unit are: 

(Prescribed Focus Areas)

P5  A student describes the scientific principles employed in particular areas of research in chemistry

(Domain:  Skills)

P11  A student identifies and implements improvements to investigation plans;

P13  A student identifies appropriate terminology and reporting styles to communicate information and understanding

P14  A student draws valid conclusions from gathered information and data




CONTENT

NOTE   This is only that part of the syllabus that specifies outcomes - there is much more to the syllabus.  This content statement is provided to you as a guide to what you should study in preparation for examinations.  It has been copied from the official document, but the numbering  system is my own.

The dot points in regular typeface are prefixed by “Students learn to -” and those in italics are prefixed by “Students -”.



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

1.1 Define the terms solute, solvent and solution;

1.2 Identify the importance of water as a solvent;

1.3 Compare the state, percentage and distribution of water in the biosphere, lithosphere, hydrosphere and atmosphere;

1.4 Perform an investigation involving calculations of the density of water as a liquid and a solid using - density = mass/volume;

1.5 Analyse information by using models to account for the differing densities of ice and liquid water;

1.6 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 a liquid and solid;

   - a natural resource for humans and other organisms;

1.7 Plan and perform an investigation to identify and describe the effect of antifreeze or salt on the boiling point of water;

Notes on 4.14.1.html


2.  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;

2.3 Describe hydrogen bonding;

2.4 Identify water as a polar molecule;

2.5 Process information from secondary sources to graph and compare the boiling and melting points of water with other similar sized molecules;

2.6 Identify data and process information from secondary sources to model the structure of the water molecule and effects of forces between water molecules

2.7 Describe the attractive forces between polar molecules as dipole-dipole forces;

2.8 Explain the following properties of water in terms of its intermolecular forces :

   - surface tension;

   - viscosity;

   - melting and boiling points;

2.9 Choose equipment and perform first-hand investigations to demonstrate the following properties of water:

   - surface tension;

  1. -viscosity.

Notes on 4.24.2.html



3. Water is an important solvent

3.1 Explain changes, if any, to particles and account for those changes when the following types of chemicals interact with water:

   - a soluble ionic compound such as sodium chloride;

   - a soluble molecular compound such as sucrose;

   - a soluble or partially soluble molecular element or compound such as iodine, oxygen or hydrogen chloride;

   - a covalent network structure substance such as silicon dioxide;

   - a substance with large molecules, such as cellulose or polyethylene

3.2 Analyse the relationship between the solubility of substances in water and the polar nature of the water molecule;

3.3 Perform a first-hand investigation to test the solubilities in water of  a range of substances that include ionic, soluble molecular, insoluble molecular, covalent networks and large molecules;

3.4 Process information from secondary sources to visualise the dissolution in water of various types of substances and solve problems by using models to show the changes that occur in particle arrangement as dissolution occurs.

Notes on 4.34.3.html



4. The concentration of salts in water will vary according to their solubility, and precipitation can occur when the ions of an insoluble  salt  are in solution together

4.1 Identify some combinations of solutions which will produce precipitates, using solubility data;

4.2 Construct ionic equations to represent the dissolution and precipitation of ionic compounds in water

4.3 Describe a model that traces the movement of ions when solution and precipitation occur;

4.4 Identify the dynamic nature of ion movement in a saturated dissolution;

4.5 Present information in balanced chemical equations and identify the appropriate phase descriptors (s), (l), (g) and (aq) for all chemical species;

4.6 Perform a first-hand investigation, using micro-techniques, to compare the solubility of appropriate

salts in solution through precipitation reactions;

4.7 Describe the molarity of a solution as the number of moles of solute per litre of solution using c = n/V;

4.8 Carry out simple calculations to describe the concentration of given solutions, given masses of solute

and volumes of solution;

4.9 Explain why different measurements of concentration are important;

4.10 Perform a first-hand investigation to make solutions to specified volume-to-volume and mass-to-

volume specifications and dilute them to specified concentrations (cV = constant)

4.11 Calculate mass and concentration relationships in precipitation reactions as they occur.

Notes on 4.44.4.html



5. Water has a higher heat capacity than many other liquids

5.1 Explain what is meant by the specific heat capacity of a substance;

5.2 Compare the specific heat capacity of water with a range of other solvents;

5.3 Explain and use the equation ΔH = -mCΔT;

5.4 Explain how water's ability to absorb heat is used to measure energy changes in chemical reactions;

5.5 Choose resources and perform a first-hand investigation to measure the change in temperature

when substances dissolve in water and calculate the molar heat of solution;

5.6 Describe dissolutions which release heat as exothermic and give examples;

5.7 Describe dissolutions which absorb heat as endothermic and give examples;

5.8 Process and present information from secondary sources to assess the limitations of calorimetry

experiments and design modifications to equipment used;

5.9 Explain why water's ability to absorb heat is important to aquatic organisms and to life on Earth

generally;

5.10 Explain what is meant by thermal pollution and discuss the implications for life if a body of water is

affected by thermal pollution.

Notes on 4.54.5.html



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