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Chapter 3

Chapter 3. Physical and Chemical Properties Physical and Chemical Changes. Physical Properties. Physical properties can be observed or measured without changing the composition of matter. Physical properties are used to observe and describe matter.

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Chapter 3

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  1. Chapter 3 • Physical and Chemical Properties • Physical and Chemical Changes

  2. Physical Properties • Physical properties can be observed or measured without changing the composition of matter. Physical properties are used to observe and describe matter. • Physical properties include: appearance, texture, color, odor, melting point, boiling point, density, solubility, polarity, and many others. • NOT RELATED TO INTERACTION WITH OTHER MATERIALS

  3. What physical properties can you observe?

  4. Physical Properties of Magnesium • Description: • Grayish-white metal. • Atomic Mass Average: 24.305 amu • Boiling Point: 1363K 1090°C 1994°F • Conductivity • Density: 1.738g/cm3 • Enthalpy of Fusion: 8.95 kJ/mole • Melting Point: 922K 649°C 1200°F • Molar Volume: 13.97 cm3/mole • Physical State (at 20°C & 1atm): Solid • Specific Heat: 1.02J/gK

  5. Chemical Properties • Chemical properties of matter describes its "potential" to undergo some chemical change or reaction by virtue of its composition. •  It is quite difficult to define a chemical property without using the word "change". Eventually you should be able to look at the formula of a compound and state some chemical property. At this time this is very difficult to do and you are not expected to be able to do it.

  6. Chemical Properties • “Reactivity” is really the only chemical property. Anything that describes how a substance reacts is a chemical property. • For example hydrogen has the potential to ignite and explode given the right conditions. This is a chemical property. • Metals in general have they chemical property of reacting with an acid. Zinc reacts with hydrochloric acid to produce hydrogen gas. This is a chemical property.

  7. Chemical Properties • A chemical property of magnesium is that it reacts with carbon dioxide producing an intense light. Magnesium reacting with dry ice.

  8. Physical Changes • A physical change takes place without any changes in composition. The same element or compound is present before and after the change.

  9. Chemical Changes or Reactions • Chemical changes result in one or more substances of entirely different composition from the original substances. The elements and/or compounds at the start of the reaction are rearranged into new compounds or elements. • Magnesium reacts with oxygen from the air producing an extremely bright flame. This is a chemical change since magnesium oxide has completely different properties than magnesium metal or oxygen. • The atoms are rearranged - diatomic oxygen molecules are split apart so that one oxygen atom combines with one magnesium atom.

  10. Physical Change Chemical Change Changes of State are physical changes but can accompany a chemical change Precipitate

  11. Precipitate • A solid insoluble substance that forms when solutions are mixed.

  12. Distillation • Distillation is used to purify a compound by separating it from a non-volatile or less-volatile material. When different compounds in a mixture have different boiling points, they separate into individual components when the mixture is carefully distilled.

  13. Distillation • Distillation is used to purify a compound by separating it from a non-volatile or less-volatile material. When different compounds in a mixture have different boiling points, they separate into individual components when the mixture is carefully distilled. • Distillation is the process of heating a liquid until it boils, capturing and cooling the resultant hot vapors, and collecting the condensed vapors.

  14. Distillation • Distillation is used to purify a compound by separating it from a non-volatile or less-volatile material. When different compounds in a mixture have different boiling points, they separate into individual components when the mixture is carefully distilled. • Distillation is the process of heating a liquid until it boils, capturing and cooling the resultant hot vapors, and collecting the condensed vapors. • Mankind has applied the principles of distillation for thousands of years. Distillation was probably first used by ancient Arab chemists to isolate perfumes evidence of which dates back to 3500 BC.

  15. Distillation • Distillation is used to purify a compound by separating it from a non-volatile or less-volatile material. When different compounds in a mixture have different boiling points, they separate into individual components when the mixture is carefully distilled. • Distillation is the process of heating a liquid until it boils, capturing and cooling the resultant hot vapors, and collecting the condensed vapors. • Mankind has applied the principles of distillation for thousands of years. Distillation was probably first used by ancient Arab chemists to isolate perfumes evidence of which dates back to 3500 BC. • In the modern organic chemistry laboratory, distillation is a powerful tool, both for the identification and the purification of organic compounds.

  16. Fractional Crystallization • Separates different solutes from a solution based on differences in their solubility. • A process by which a chemical compound is separated into components by crystallization. In fractional crystallization the compound is mixed with a solvent, heated, and then gradually cooled so that, as each of its constituent components crystallizes, it can be removed in its pure form from the solution.

  17. What is the solubility of KNO3 at 80ºC?

  18. At what temperature is the solubility of KBr equal to 60g/100g H2O?

  19. Example of Fractional Crystallization • The solubility of compounds changes with temperature, and different compounds will respond differently to a decrease in temp.  For example, if compound A is soluble at 30 to 35ºC, but compound B is insoluble at 30 to 35ºC, and if they are both soluble at 50ºC, then what happens if you lower the temperature of a mixture of the two solutions from 50 to 30ºC?

  20. Example of Fractional Crystallization • The solubility of compounds changes with temperature, and different compounds will respond differently to a decrease in temp.  For example, if compound A is soluble at 30 to 35ºC, but compound B is insoluble at 30 to 35ºC, and if they are both soluble at 50ºC, then what happens if you lower the temperature of a mixture of the two solutions from 50 to 30ºC?Answer: Compound A will still be in solution, but compound B will have precipitated (crystallized).

  21. Homework • Chap 3 Worksheet 3-1

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