To determine the factors that affect the solubility of materials *

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1 OpenStax-CNX module: m To determine the factors that affect the solubility of materials * Siyavula Uploaders This work is produced by OpenStax-CNX and licensed under the Creative Commons Attribution License NATURAL SCIENCES 2 Form, reaction and alteration of materials 3 4 EDUCATOR SECTION 5 Memorandum 1. In which glass is the sugar dissolved quickest? In the glass with warm water. 2. Explain why this happens. The solubility of a substance is aected by the temperature. Assignment 13: (Groupwork) 1. How many teaspoons of sugar could you dissolve into the glass of water? The amount depends on the individual experiment. Discus in your group what you could do to dissolve more sugar into the water. The water (solution) can be heated. The sugar crystals (dissolved substance) and be made ner. * Version 1.1: Mar 13, :04 am

2 OpenStax-CNX module: m Assignment 14: Observation: The water has evaporated and small crystals have been formed: copper sulphate crystals. Under the microscope the crystals appear as small blocks or cubes. Conclusion: When a solution is left to stand the opposite of dissolving occurs. The dissolved substance crystallises into a solid in the form of crystals. Assignment 15: 1. Is the amount and type of solvent the same in all three cases? Yes Which substance was dissolved the least after the rst teaspoon? Corn meal Is corn meal insoluble? Yes 4. Which substance dissolved best? Salt Conclusion: Not all substances are equally soluble. Assignment 16: 1. What do you see? Oil does not dissolve. You continue to see drops of oil on the water 2. Where is the oil? While you are stirring it seems that the oil is mixed with the water, but the moment that you stop stirring the oil oats to the surface of the water. 3. Can oil dissolve in water? No 4. What is the reason for the answer above? Particles of oil are strongly attracted to each other. Water particles cannot move in between the oil particles, so oil is not soluble in water. Assignment 17: 1. What happens? The naphthalene akes do not dissolve in water but do dissolve in mentholated spirits. 2. Can you explain why this happens? Naphthalene akes are not soluble in water. 3. Complete. Naphthalene is easily dissolved in mentholated spirits but is not soluble in water

3 OpenStax-CNX module: m LEANER SECTION 7 Content 7.1 ACTIVITY: To determine the factors that aect the solubility of materials [LO 1.1, LO 1.2, LO 1.3] The solubility of a material is determined by: temperature; type of material; and type of solvent. ASSIGNMENT 12 To determine how temperature aects solubility. Requirements: Sugar A glass of cold water A glass of warm water A teaspoon Put one teaspoonful of sugar into the glass of cold water and another into the glass of warm water. Do not stir the water. Observe what happens. 1. In which glass is the sugar dissolved the quickest? 2. Explain why this happens. REMEMBER THE FOLLOWING IN CONNECTION WITH SOLUBILITY Sugar is SOLUBLE in water. The sugar is the DISSOLVED substance. The water is the SOLVENT. The sugar water is the SOLUTION. HEAT increases the process of solution. A saturated solution: Water can only take a certain amount of a dissolved substance like sugar. When the water can not take more of the substance, we say that it is a saturated solution. This is what a saturated solution looks like:

4 OpenStax-CNX module: m Figure 1 (Compare the sketch above to the previous sketch and ensure that you understand the dierence.) ASSIGNMENT 13 (GROUP WORK) To prepare a saturated solution. Requirements: Glass of tap water White sugar A teaspoon Fill the glass half full with tap water. Stir a teaspoonful of sugar into the water until it dissolves. Stir another teaspoonful of sugar into the water. Continue to add sugar to the water, until you observe that the sugar will no longer dissolve. 1. How many teaspoons of sugar dissolved in the water? 2. How are you able to dissolve more sugar in the water? Discuss this in your group. ASSIGNMENT 14 To investigate the formation of crystals.

5 OpenStax-CNX module: m Make a saturated solution of copper sulphate and water. Place a small amount of the solution in a saucer and allow it to stand for a day. Write your observations and conclusions. You may use a microscope. Observation: Conclusion: ASSIGNMENT 15 To determine how the type of substance aects solubility. Requirements: Three clean glasses Salt Maize meal Sulphur Three teaspoons Tap water Place exactly the same amount of water in each glass. Add one teaspoonful of salt to the rst glass and stir carefully. Count how many teaspoons of salt can be added before the solution is saturated. Repeat the experiment using maize meal and sulphur instead of salt. 1. Is the amount of soluble matter the same in each case? 2. Which substance dissolved the least after the rst teaspoonful? 3. Is maize meal soluble? 4. Which substance was most soluble? Conclusion: Not all substances are equally soluble. Solubility depends on the type of substance. ASSIGNMENT 16 Another experiment to show that not all substances are soluble. Requirements: A glass of tap water Cooking oil A teaspoon

6 OpenStax-CNX module: m Half ll the glass with water. Pour a small amount of oil onto the water. Stir the oil and water for a few minutes. 1. What do you see? 2. Where is the oil? 3. Can oil be dissolved in water? 4. What is the reason for your answer above? LIKE WATER OFF A DUCK'S BACK We say this about people who are not overcome by their problems. Water just rolls o a duck's back. The duck doesn't get wet at all. Ducks' feathers are oily. Water and oil cannot mix, that is why the water runs o the duck's back. Most aquatic birds have oily feathers. Penguins and other sea birds become very heavy when they are covered with oil. This happens when the sea is polluted with oil. The birds will eventually drown. To save them, the oil must be washed o their feathers with detergent. When they have been washed they cannot be put straight back into the sea because they will be soaked and will get very cold. The birds have to be looked after for two to three weeks until their feathers have regained the special coating of oil. ASSIGNMENT 17 To determine how a solvent aects solubility. Requirements: Water Methylated spirits Two glass asks Naphthalene akes (or crushed mothballs) Place a small amount of water in one ask and a small amount of spirits in the other. Add a teaspoon of naphthalene akes to each ask and stir. 1. What happens? 2. Can you explain why this has happened? 3. Complete: Naphthalene dissolves easily in but does not

7 OpenStax-CNX module: m dissolve in. REMEMBER: In all the experiments, except the last one, we have used only WATER as the solvent. There are many other solvents that can be used, like spirits, paran etc Assessment Learning Outcome 1:Learners respond condently to their desire to learn about natural phenomena; they investigate relationships and solve problems within the context of science, technology and the environment. Assessment Standard 1.1:We know this when the learnerplans investigations: helps to clarify focus questions for investigation and describes the kind of information which would be needed to answer the question; Assessment Standard 1.2:We know this when the learnerconducts investigations and collects data: conducts simple tests or surveys and records observations or responses; Assessment Standard 1.3:We know this when the learnerevaluates data and communicates ndings: relates observations and responses to the focus question.