Chemical vs. Physical Change - PowerPoint PPT Presentation

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Chemical vs. Physical Change

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  1. Chemical vs. Physical Change

  2. Physical Change • Any process involving a substance changing from one state of matter to another without altering the chemical composition. • These changes are often considered ‘easy’ to undo. • Ex. Ice melting, water boiling, sugar dissolving. PhysicalChange1_Part1 PhysicalChange1_Part2

  3. Chemical Change A change that occurs when one or more substances are changed into a new substance. These changes cannot be reversed. Some observations that occur during a chemical change are: color, fizzing, precipitate (solids forming), heat change (hot or cold). ChemicalChange1_Part1 ChemicalChange1_Part2

  4. Acids & Bases • Acids are compounds which produce hydrogen ions when combined with water. • Hydrogen ions have an overall positive charge (H+) • Bases are compounds that produce hydroxide ions when combined with water. • Hydroxide ions have an overall negative charge (OH-)

  5. The pH scale • Substances that are acids or bases can be measured on a scale from 0 to 14. • This scale is called the pH scale. • “pH” stands for ‘potential hydrogen’ • Acids have a pH less than 7 • Bases have a pH higher than 7.

  6. Turning Blue/Black • Iodine solution contains iodine, potassium iodide, water, and alcohol. • This is a good indicator for starch molecules. • When combined with starch molecules it will turn blue in color. • This is due to a chemical change between the starch and iodine atoms.

  7. Turning Pink/Orange/Green • This is also a chemical change. • Many fruits or vegetables contain pigments which will change color when added to an acid or base. • These pigments will change color as their molecules change.

  8. Bubbling/Fizzing • Bubbling or fizzing is also a chemical change. • Bubbles are a result of the formation of Carbon Dioxide. • Carbon Dioxide is formed when molecules recombine to form a new substance. Often times carbon dioxide is left over and given off as a gas.

  9. The Crystal Lab • You will be investigating several crystals by examining their physical properties. • You will utilize your results to try to identify an ‘unknown’ crystal.

  10. Crystal - Size • Crystal size is determined by many variables. These can include: • Time of formation • Amount of substance • Rate of evaporation (Typically, the more time, amount of substance, and slower rate….. The larger the crystals will be.)

  11. Crystal - Color • The color of a crystal is determined by the substance and the elements which are found in the substance. • Each crystal of the same substance should have a similar color although variations may exist.

  12. Crystal - Shape • The Shape of a crystal is determined by the atomic structure of the substance in the crystal. • There are some common crystalline structures that are often seen in the natural world. They include….. • Cubic/Hexagonal/Triclinic/Monoclinic/ Orthorhombic/Rhomobohedral/ Tetragonal

  13. Crystal - Luster • Luster describes how light reflects off the surface of a crystal. • Terms to describe luster: • Glossy • Metallic • Dull • Pearly • Silky

  14. Crystal – Light Transmission • Light Transmission is used to describe how light passes through a crystal. • Terms used to describe light transmission include: • Translucent/Transparent/Opaque

  15. Monosodium Glutamate

  16. Salt

  17. Epsom Salt

  18. Lab activity A Sense-ational Activity In the Sense-ational Activity you will be conducting an experiment to test your skills of observation. In the first part of this experiment, you will be observing 5 white powders with each of you senses. In the second part of this experiment, you will be observing how each of these powders reacts (chemically / physically) when mixed with various solutions. Your ability to observe with all of your senses will be tested.

  19. Powder ‘A’ • Powder A was cornstarch. • Corn starch is an agent used as a thickener. • It is composed of longer starch molecules and has a neutral pH.

  20. Powder ‘B’ • Powder B was Baking Soda (sodium bicarbonate) • Baking soda is used to generate bubbles in recipes that contain acidic ingredients. • This is a weak base.

  21. Powder ‘C’ • Powder C was Cream of Tartar • Cream of Tartar is used to prevent sugar from crystallizing during the making of candy. • It is acidic.

  22. Powder ‘D’ • Powder D was powdered sugar. • Powdered sugar is made of smaller sucrose molecules.

  23. Powder ‘E’ • Powder E was baking powder (combination of baking soda and calcium acid phosphate and corn starch) • This will cause bubbles whether or not other ingredients are acidic.