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Solutions and suspensions


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Solutions & Suspensions

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Solutions and suspensions

  1. 1. Solutions and Suspensions Volume A Chapter 7
  2. 2. Lesson Objectives By the end of the lessons students sbat •distinguish among solute solvent, solution •deduce the nature of solutions and suspensions by simple laboratory tests •state the factors affecting solubility •state the factors affecting rate of dissolving •distinguish between a solution and a suspension
  3. 3. Quick Recap • Matter can be classified as elements, compounds and mixtures. • Element – An element is a substance that cannot be broken down into simpler substances. – Examples: carbon, gold, iron, oxygen
  4. 4. Quick Recap • Compound – A compound is a substance made up of 2 or more elements chemically combined together. – A compound is a substance that can be broken down into simpler substances by chemical methods. – Examples: water, carbon dioxide, ethanol
  5. 5. Quick Recap • Mixture – A mixture is a substance made up of 2 or more elements and/or compounds not chemically combined together. – A mixture is a substance that can be broken down into simpler substances by physical methods – Examples: air, seawater, crude oil, steel
  6. 6. Quick Recap A mixture can further be classified as a solution. or a suspension Matter Pure substances Elements Compounds Mixtures Solutions Suspensions
  7. 7. Solutions • When salt is added into water, salt dissolves in water. – Salt is known as the solute (substance that dissolves in the solvent). – Water is known as the solvent (substance that dissolves the solute). – The final mixture is known as the solution.
  8. 8. Solutions salt (solute) water (solvent) salt-water mixture (solution)
  9. 9. Wake Up Call 1 substance 1 solute or substance solute or solvent? 2 example solvent? a carbon dioxide water aerated drinks b water salt saline solution c alcohol iodine tincture of iodine solution b dishwashing detergent oil washing dishes
  10. 10. Suspensions • When a solid does not dissolve in a liquid, a suspension is formed. • A suspension is a mixture in which insoluble particles are suspended in a liquid or a gas.
  11. 11. Comparing solutions and suspensions 1 2 3 Solutions Homogeneous (Colour, density of the solution is the same.) When left to stand, solute does not separate from solvent. Suspensions Heterogeneous When left to stand, the insoluble particles will sink to the bottom of the container. When filtered, no residue is When filtered, the left on the filter paper. insoluble particles are left as residue on the filter paper
  12. 12. Wake Up Call 2 Mixture Solution or suspension? a. mud b. honey (a mixture of different sugars) c. flour in water d. paint e. some medicines that require shaking before use (e.g. paracetamol mixture) f. perfumes (oils in alcohol)
  13. 13. Solubility • Salt dissolves easily in water. – However there is a limit to how much salt can dissolve in water. – This limit depends on the solubility of the solute. Solubility is the maximum amount of solute that can dissolve in 100 g of solvent at a given temperature.
  14. 14. Factors affecting solubility Factor 1. Nature of solvent 2. Nature of solute 3. Temperature Explanation iodine dissolves better in alcohol than in water. Hence, iodine has higher solubility in alcohol than in water. Different solutes have different solubility in the same solvent. E.g. salt dissolves in water better than baking soda does. More substance can dissolve in the same amount of solvent at a higher temperature. E.g. coffee dissolves
  15. 15. Rate of dissolving Think! •To make a cup of tea, a teabag is placed in a cup of water. Sugar is then added. How can sugar be made to dissolve faster?
  16. 16. Rate of dissolving 1. Use hot water / heat up the tea 2. Stir the tea 3. Use sugar crystals instead of large lumps of sugar. The rate of dissolving is the speed at which the solute dissolves in a fixed amount of water.
  17. 17. Rate of dissolving • What are the factors that affect the how fast a solute dissolves (rate of dissolving)? Factor How rate of dissolving is affected 1 Temperature The higher the temperature, the faster the solute dissolves. (i.e. rate of dissolving increases with higher temperature) 2 Rate of stirring The faster the mixture is stirred, the faster the solute dissolves. 3 Size of particles The smaller the solute particles, the faster the solute dissolves. (E.g. 10 g of powdered sugar dissolves faster than 10 g of rock sugar.)
  18. 18. Particle size • For a cube of dimension 2 cm by 2 cm by 2 cm, its total surface area would be: 2 cm Total surface area = 2 x 2 x 6cm = 24 cm2
  19. 19. Particle size • If the 2 x 2 x 2 cube was cut into 1 x 1 x 1 cubes, cut 1 cm X 8 cubes
  20. 20. Particle size 1 cm X 8 cubes Total surface area = [1 x 1 x 6] x 8 = 48 cm2 What can you conclude from this? •When the particles are smaller, for the same mass of substance, there is higher total surface area coming into contact with the solvent, therefore smaller particles dissolve faster.
  21. 21. Wake Up Call 2 • Vitamin C tablets are very soluble in water.
  22. 22. Wake Up Call 2 • An experiment was conducted to find out how ONE factor affects the rate of dissolving. • Procedure: – Place some distilled water into a beaker. Label the beaker A. – Place some warm distilled water into another beaker. Label the beaker B. – To each beaker, add one Vit C tablet. – Measure & record the time taken for the table to completely dissolve.
  23. 23. Wake Up Call 2 1. What is this experiment investigating? 2. Other than the time taken for the tablet to completely dissolve, state another reading that should be taken. 3. What factors in this experiment should be kept constant? What is the variable factor? 4. State two other factors that affect the rate of dissolving.