Investigation 3 October 5, 2015

What is the relationship between atoms, molecules and compounds? What is a chemical formula? Describe two or more important physical properties of matter, solubility and miscibility

Atoms can combine to form very different compounds. Different elements bond with each other to form a variety of molecules and compounds. Oxygen, hydrogen and sulfur combine to form different molecules and compounds. Both O2 and H2 are gases. However, we breathe O2 gas to stay alive, H2 gas is extremely flammable. It is used a fuel for spacecraft. Oxygen and hydrogen atoms combine with each other to form water. Oxygen, hydrogen and sulfur atoms combine to form the sulfuric acid molecule, a very acidic liquid.

A chemical formula tells how many atoms of each element are in a compound molecule (sugar) The model of sucrose on this slide also shows that the individual atoms of C, H and O are bond to each other in a very specific arrangement. This chemical formula tells us which atoms are present in the sucrose molecule (carbon, hydrogen, and oxygen), it also tells us how many atoms of each element are present (12 carbon, 22 hydrogen, and 11 oxygen). The arrangement of atoms in any molecule tells its physical and chemical properties. Physical changes that occur in matter do not involve breaking or rearranging chemical bonds, but chemical changes do. A chemical change results in one or more entirely different molecules than ones that existed prior to the chemical reaction.

The table in this slide lists all of the compounds that you will work with in Investigation 3. The first column gives the common name of the compounds. The second column gives the chemical formula. The third column shows the elements present. The fourth column tells the number of atoms of each element present.

Solubility is the ability of a solute to dissolve in a solvent. The Lab for Investigation 3 will give you repeated practice mixing various solutes with a solvent (water). In general, solutes are solids and solvents are liquids. In this Investigation, we will use the solvent water when studying solubility and then the solvents vinegar, rubbing alcohol and vegetable oil when studying miscibility.

Miscibility is the ability for two liquids to mix with each other. We can mix oil paints together to create new colors because oil paints are miscible with each other. (We would get a very different result if we tried mixing oil paint with a water-based paint like tempera or watercolors). Salad oil and water or vinegar is also a common example of immiscible liquids. ** When two liquids that are not miscible with each other are mixed they often form two layers with the more dense of the two liquids on the bottom (yellow) and the less dense liquid “floating” on top (blue).