Physical & Chemical Changes

1. Physical & Chemical Changes

2. Physical Changes • Properties displayed that do not change the identity of the substance • Appearance, color, smell, physical state, melting point, boiling point, density, solubility (solids), miscibility (liquids) • Do not cause a change in chemical composition • Do change the appearance • Melting Ice (Solidliquid) • Dissolving salt in water

3. Chemical Changes When two or more substances are chemically transformed into a new set of substances with a different chemical composition Evidence of a Chemical Change • A color change • A solid product (precipitate) is formed when two solutions are mixed • A gas is formed when two solutions are mixed • Energy such as heat, light or electricity is produced • The system doesn’t return to how it started when the system is restored to its original conditions

4. Today Part A: Demonstrations Part B: Boiling Point Determination • Identifying a substance using its known physical properties • Identify a liquid based on its boiling point Part C: Chemical and Physical Properties • Identify a white powder from its physical and chemical properties and comparing it to known substances

5. B: Boiling Point Determination Instructions • Assemble apparatus shown • ¾ fill 250 ml beaker with tap water • Turn on hotplate • Add boiling chip in test tube and 3 mL methanol • Cap test tube with split stopper insert thermometer so its tip is 2 cm above the methanol • When water is boiling turn off the hotplate • Lower clamp with test tube until methanol just below surface of water • When methanol boils and is steadily dripping off tip of thermometer record T • Repeat for a mystery liquid • Identify your liquid based on the BP Vapor methanol Vapor Boiling chip water

6. Part C: Physical and Chemical Changesadding heat Add a pea-size amount of sugar into a dry test tube Using a test-tube holder, gently heat the solid by passing the test tube through the flame several times, until a change is seen Allow the test tube to cool to room temperature Record your observations on the data sheet, on page 27 and determine whether the change is chemical or physical Add a pea-size amount of salicylic acid into another dry test tube and repeat steps 1-4 sugar Salicylic acid

7. Part C: Physical and Chemical Changessolubility • Label 5 test tubes and add the following according to the figure on the right • To #1 stopper and shake the test tube record your observations (soluble or insoluble?) • To #2 do the same #1 • To #3 stopper the test tube and shake, do the liquids stay mixed (miscible) or do they separate (immiscible)? • To #4 do the same as #3 • To #5 do the same as #1 • To #5 then add 10 drops of 6M ammonium hydroxide, does the reagent make the benzoic acid soluble? • Add 30 drops of 6M hydrochloric acid to #5, soluble or insoluble? • Dispose of contents in disposal bottle at the back of the lab 3 1 2 4 5 Pea size amount of sugar and 2 mL of water Pea size amount of sugar and 2 mL of acetone 2 mL Olive Oil & 2 mL of DI water 2 mL Olive Oil & 2 mL of acetone Pea size amount of benzoic acid & 2 mL of DI water

8. Part C: Physical and Chemical Changesmixing chemicals • Label 4 test tubes and add the following according to the figure on the right • To #1 and #2 slowly add 2 mL of vinegar • Record your observations on the data sheet from page 28, is there evidence of chemical change? • Add 2 mL of copper (II) chloride to #3 and #4 • Record your observations on the data sheet from page 28, is there evidence of chemical change? • Dispose of contents in disposal bottle at the back of the lab 3 1 2 4 2 mL of sodium bicarbonate 2 mL of sodium sulfate 2 mL sodium hydroxide 2 mL sodium sulfate