Important to know . . . What is science? What is Chemistry? Mixtures vs. Substances

Chemistry is the study of matter and that changes that it undergoes. Science is an investigative approach to figuring out how the world works.

What do these have in common? DNA Penicillin HIV/AIDS Pateurization Insulin

Techniques to separate mixtures? (Physical means) Sorting Filtering Distilling Heating Cooling Dissolving

Physical Properties These are the conditions of a substance that can be observed/determined without changing the composition of the substance. Examples of physical properties would be the boiling point, hardness, color, appearance, solubility, odor, density, elasticity, and melting point of a substance.

Chemical Properties These are properties that a substances has due to its internal composition. Chemical properties can only be seen when substances undergo chemical changes - like burning. Evidence of a chemical change could be the formation of a NEW gas (bubbles), a NEW solid, or a NEW liquid. Energy given off (exothermic reaction) and energy taken in to the system (endothermic).

Physical and Chemical changes

Your teacher adds some salt (NaCl, sodium chloride) to a beaker of water and the salt disappears. A. This is an example of a chemical change because a substance disappears. B. This is an example of a physical change because it shows solubility of sodium chloride. C. This is both a physical and chemical change. D. Not enough information

The correct answer is B. By dissolving a substance in water you demonstrate its solubility. Solubility is a physical characteristic. By dissolving the salt in water you have just put it into solution = NaCl(aq)

What if we now heat the salt solution: we see it boil and steam is given off. A. This is an example of a chemical change because a gas is given off. B. This is an example of a physical change because it shows the boiling point of NaCl(aq). C. This is both a physical and chemical change. D. Not enough information

The correct answer is B. Steam is water vapor. This is a phase change for water. It goes from a liquid to a gas (called water vapor or steam). There is no change to the chemical composition of the water molecules. They are still H2O. There is also no change to the table salt. It is still NaCl.

If we burn a piece of magnesium (Mg) ribbon over a bunsen burner and it glows a bright white color before turning into a white powder this is an example of a: A. A chemical change B. A physical change C. Neither a chemical or physical change D. Not enough information

The correct answer is A. When energy is given off in the form of light a chemical change has occurred. Really: 2Mg + O2 2MgO

If you drop a piece of magnesium ribbon (Mg) into hydrochloric acid HCl; you see bubbles and the container becomes hot. The Mg also seems to disappear. This is an example of a: A. A chemical change B. A physical change C. Both a chemical and physical change D. Not enough information

The correct answer is A. The Mg combines with the Cl forming MgCl and H2 gas is given off. This is an exothermic reaction because heat or energy is given off.

If you put a drop of phenolphthalein (a clear liquid) in some sodium hydroxide (a clear liquid) the liquid turns a magenta color. This indicates: A. A chemical change B. A physical change C. Neither a chemical and physical change D. Not enough information

The correct answer is B or C. Phenolphthalein is an indicator. It is also a strong laxative (used in Ex-lax). It indicates if something is basic (or alkaline). It turns magenta or pink in a base and remains colorless in an acid or a neutral solution. Nothing happens to the acid or the base.

What happens if we mix a solution of potassium iodide (KI(aq)) and lead nitrate (Pb(NO3)2(aq))?

You see a yellow substance that was not present before You see a yellow substance that was not present before. If you look closely it appears to be powdery. What do you think this is?