0.2 Tg physical science - chapter contexts  (Page 5/10)

$O_2(g)\to O_2(\mathrm{aq})$

Step by step guidance is given to understand precipitation reactions and to apply the knowledge when testing for the anions: chloride, bromide, iodide, sulphate and carbonate.

Acid-base and redox reactions also take place in aqueous solutions. When acids and bases react, water and a salt are formed. An example of this type of reaction is:

NaOH (aq) + HCl (aq) →NaCl (aq) + H2O (l)

Redox reactions involve the exchange of electrons. One ion loses electrons and becomes more positive, while the other ion gains electrons and becomes more negative. These reactions will be covered in more detail in Grade 11.

Quantitative aspects of chemical change

As introduction to this topic, educators need to spend time on explanations, so that learners can acknowledge the very small size of atoms, molecules and ions. In the reaction between iron and sulphur, every iron (Fe) atom reacts with a single sulphur (S) atom to form one molecule of iron sulphide (FeS). But how will we know how many atoms of iron are in a small given sample of iron, and how much sulphur is needed to use up the iron? Is there a way to know what mass of iron sulphide will be produced? Concepts to be developed to answer these questions are: relative atomic mass, the mole, molar mass, Avogadro’s constant and composition of substances. Learners need to understand and manipulate the equation below to calculate the number of moles, mass or molar mass of a substance.

$n=\frac{m}{M}$

When learners engage in the suggested group work: “Understanding moles, molecules and Avogadro's number” and the multiple exercises set on moles and empirical formulae and molar concentration of liquids, they will be able to do basic stoichiometric calculations to determine the theoretical yield of a product in a chemical reaction, when you start with a known mass of reactant.

Physics overview

Vectors

Physics describes the world around us. In mechanics we study the motion of objects and the related concepts of force and energy. It takes two qualities: size and direction, to describe force and motion. A vector is such a quantity that has both magnitude and direction. Vectors are not Physics but vectors form a very important part of the mathematical description of Physics. In this section, learners will develop the understanding of the concepts of vectors. They need to master the use of vectors to enable them to describe physical phenomena (events).

The text will direct learners to:

• know and explain with examples the differences between vectors and scalars;
• define vectors in words, with equations, mathematical and graphical representations;
• express direction using different methods as: relative directions (right, left, up, down), compass directions (North, South, East, West) and bearing (in the direction 030);
• draw vectors;
• explore the properties of vectors like equal vectors and negative vectors;
• add, subtract and multiply with vectors;
• define the resultant vector in words, graphically and by calculation; and
• apply their understanding by doing the exercises.