Chemistry_Grade_10-12 (1).pdf

Factors that affect solubility are the quantity of

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Factors that affect solubility are the quantity of solute and solvent , temperature , the intermolecular forces in the solute and solvent and other substances that may be in the solvent. Exercise: Summary Exercise 1. Give one word or term for each of the following descriptions: (a) A type of mixture where the solute has completely dissolved in the solvent. (b) A measure of how much solute is dissolved in a solution. (c) Forces between the molecules in a substance. 2. For each of the following questions, choose the one correct answer from the list provided. A Which one of the following will readily dissolve in water? i. I 2 (s) ii. NaI(s) iii. CCl 4 (l) iv. BaSO 4 (s) (IEB Paper 2, 2005) b In which of the following pairs of substances will the dissolving process happen most readily? Solute Solvent A S 8 H 2 O B KCl CCl 4 C KNO 3 H 2 O D NH 4 Cl CCl 4 (IEB Paper 2, 2004) 3. Which one of the following three substances is the most soluble in pure water at room temperature? Hydrogen sulphide, ammonia and hydrogen fluoride 4. Briefly explain in terms of intermolecular forces why solid iodine does not dis- solve in pure water, yet it dissolves in xylene, an organic liquid at room tem- perature. (IEB Paper 2, 2002) 106
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Chapter 7 Atomic Nuclei - Grade 11 Nuclear physics is the branch of physics which deals with the nucleus of the atom. Within this field, some scientists focus their attention on looking at the particles inside the nucleus and understanding how they interact, while others classify and interpret the properties of nuclei. This detailed knowledge of the nucleus makes it possible for technological advances to be made. In this next chapter, we are going to touch on each of these different areas within the field of nuclear physics. 7.1 Nuclear structure and stability You will remember from an earlier chapter that an atom is made up of different types of particles: protons (positive charge) neutrons (neutral) and electrons (negative charge). The nucleus is the part of the atom that contains the protons and the neutrons, while the electrons are found in energy orbitals around the nucleus. The protons and neutrons together are called nucleons . It is the nucleus that makes up most of an atom’s atomic mass , because an electron has a very small mass when compared with a proton or a neutron. Within the nucleus, there are different forces which act between the particles. The strong nuclear force is the force between two or more nucleons, and this force binds protons and neutrons together inside the nucleus. This force is most powerful when the nucleus is small, and the nucleons are close together. The electromagnetic force causes the repulsion between like-charged (positive) protons. In a way then, these forces are trying to produce opposite effects in the nucleus. The strong nuclear force acts to hold all the protons and neutrons close together, while the electromagnetic force acts to push protons further apart. In atoms where the nuclei are small, the strong nuclear force overpowers the electromagnetic force. However, as the nucleus
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