The Physical Properties and Physical Changes of Substances

Ch 11 THE PHYSICAL PROPERTIES AND PHYSICAL CHANGES OF SUBSTANCES Name: Key 1. A beaker of water contains some water that is at 87°C. Describe the temperature of the water: a) in a "qualitative" way - hot b) in a "quantitative" way - 87°C 2. Say whether the following statements describe physical properties or chemical properties. a) C₃H₈ burns in O₂ - chemical b) glass is brittle - physical c) gold does not rust - chemical d) NaCl dissolves in water - physical 3. Fill in the blank. Spelling counts. a) diffusion is the intermingling of fluids as a result of molecular motion.   b) viscosity is the resistance of a fluid to flow. c) malleability is the ability to be rolled or hammered into thin sheets. 4. Give a scientific explanation of each of the following terms: a) substance   - matter with a unique set of properties b) boiling point - temp. at which the vapour pressure of a liquid equals the air pressure. c) chemical property - the ability of a substance to undergo chemical reaction 5. If the boiling point of acetone is 56°C, should the gaseous form of acetone be called a "gas" or a "vapour"? Explain your reasoning. The B.P. of acetone is above room temperature so in gas form it is a "vapour". 6. When some water at room temperature is placed in a bell jar and the air is removed with a vacuum pump, it's pressure starts to boil. Explain why this happens. * When air and its pressure on the water is removed, water is able to boil at a much lower temperature. * The temperature needed to boil is actually a measure of the energy required to allow water molecules to jump into the air. If the pressure exerted by the air's mass is removed, then the energy required by the water to jump into the air will dramatically decrease. As such, it can now jump into the air at a much lower energy amount (temperature). 7. Acetone has   a pressure of 31 kPa at room temperature. Butanol has a vapour pressure of 0.9 kPa at the same temperature. Which of these liquids has the lower boiling point? * Acetone 8. Complete a chart to show how chemists classify matter. Spelling counts. Matter / \ Homogeneous Heterogeneous / \ / \ Pure Substance Mechanical Mixture Suspension / \ Element Compound 9. According to the information given, classify the following materials as completely as possible. Note: You will be using the classifications from the chart completed for question 8. a) a clear yellow liquid has an increasing boiling point. - Solution b) a white liquid slowly clears at the top.   - Suspension c) a pale blue solid has white crystals and blue crystals. - Mechanical Mixture d) a clear blue liquid leaves a blue residue after evaporation. - Solution e) the boiling point of this clear liquid rises slowly until all of the liquid has evaporated. - Solution f) a green solid when heated to 311°C turns black and gives off a colourless gas. - Compound g) a colourless liquid boils at a steady 62°C. - Pure Substance h) a reddish solid melts at 1085°C and boils at 2563°C. Neither additional heat nor electricity will create new substances from it. - Element 10. Name one separation method (from our list of 8 methods) that could be used to easily separate the following mixtures. Spelling counts. a) a solution of methanol in water:   **Distillation** b) sawdust particles floating around in water: **Filtration (gravity)** c) a mixture of I₂ (soluble in CCl₄) and NaCl (soluble in H₂O): **Solvent Extraction** d) brass pellets mixed with glass pellets: **Hand Separation or Gravity** 11. Explain how recrystallization is able to purify many solid substances. You may include a diagram but you must also explain in writing. 1. Pour mixture into an Erlenmeyer flask. 2. Find a solvent in the "big chem book" that will dissolve both parts of   the mixture (usually water). 3. Add 10% by weight of the solvent to the mixture and heat until mixture is fully dissolved. 4. Remove flask from heat and let cool. 5. Product should recrystallize out of solution first (most cases). 6. Pour off water/impurity solution. 7. Recrystallize   again until desired level of purity has been attained. 12. Sketch and label the apparatus that you would use in a science lab to do a distillation.   [Image of a distillation apparatus] 13. a) What is the name for the separation technique wherein a mixture of food colourings can be separated using a strip of filter paper and some water?   Chromatography b) Explain, by describing what is happening with the particles, how this technique is able to cause the separation to occur. Separation is caused by a tug-of-war between the solvent (water) and the paper. The chemical dye is pulled into the solvent as it is dissolved, and then carried up the paper by the attractive forces between the solvent (water) and the chemical dye. Over time the dye will be pulled out of the solvent (water) by the attractive force from the paper. It is the difference in affinities   between the solvent (water) and the paper that allows the chemical dye to travel varying amounts for different chemicals.