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Problem(Set(01(–(Introduction! Chem!105!

1. Define chemistry in 1 sentence. Chemistry is the study of matter – its composition, structure, properties, and the changes it undergoes along with the energy involved in those changes. 2. For each picture, state the class of matter (whether each substance is a pure element, a compound, or a mixture), and explain your reasoning.

a.

b.

c.

Compound 2 types of atoms (colors) combined in 1 molecule

Element 1 type of atom (color)

Mixture 2 elements (1 red, 1 blue) are mixed together

3. For each of the following, state the class of matter. If it is a mixture, state which are homogeneous mixtures and which are heterogeneous mixtures, and explain how you know. a. salt water mixture, homogenous because the concentration of salt is the same throughout b. purified sugar compound c. high pulp orange juice mixture, heterogeneous; concentration of pulp is not the same at the top and bottom of the container d. apple juice mixture, usually homogenous; concentration of components is the same at the top and bottom of the container e. diamond element f. gravel mixture, heterogeneous; different kinds rocks are distinctly visible g. compressed air in a scuba tank mixture, homogenous; concentration is same throughout h. solid butter mixture, homogenous; concentration of components is the same throughout i. baking soda (NaHCO3) compound j. copper plumbing pipes element 4. For each picture, describe the state of matter (solid, liquid, gas) and state your reasoning in 1 sentence.!

a. b. c. a. Liquid: Particles are close together but are free to tumble over one another. b. Gas: Particles are far apart, independent of each other, move freely. c. Solid: Each particle is held in place in a rigid, three-dimensional array.

5. Describe the following changes (are they physical changes or a chemical changes?). Also describe the physical state of each substance.

a.

b. a. Chemical change – a mixture of 2 elements (probably gases or liquids) undergoes a chemical reaction to form a single solid compound (solid because the molecules form an ordered array) b. Physical change- a mixture of 2 elements (probably gases or liquids) is cooled to a temperature at which one of them condenses into either a liquid or solid (liquid more likely because the molecules are close together but not in a completely ordered array)

6. Which of the following processes are physical changes and which are chemical changes? Describe how you know. a. Fish in the fridge smelling more ‘fishy’ with time Chemical Bacteria are decomposing the fish – breaking down the compounds into something else b. Muffins baking in your oven Chemical Baking soda, eggs, & other ingredients are reacting to form a new substance c. Salt crystals forming on a hot day by the Great Salt Lake Physical Before the change you have NaCl in water, after the change you have NaCl out of water; no change in chemical identity d. A spot on your car where the paint was scratched starting to look brown/red Chemical Rust is forming – a metal oxide (Fe2O3) is forming where before there was only metal e. Soda going ‘flat’ as dissolved CO2 comes out of solution Physical Before the change you have CO2 in water, after the change you have CO2 out of water; no change in chemical identity f. Soldering a pipe in your house Physical Solder is melted and then solidifies to join the pipes together. In physical changes, the identity of the elements or compounds involved does not change. In a chemical change, different elements or compounds are formed. 7. Indicate whether each of the following are physical or chemical properties of sodium (Na), and explain your reasoning. a. Its density is greater than that of kerosene, but less than that of water. Physical b. It has a lower melting point than most metals. Physical c. It is a good conductor of heat and electricity. Physical d. It is soft and can be easily cut with a knife. Physical e. Freshly cut sodium rapidly tarnishes when exposed to air. Chemical f. Sodium reacts with water, releasing hydrogen gas (H2) and heat. Chemical Physical properties can be observed or measured without changing the identity of the substance. Chemical properties describe how a substance reacts during chemical changes, in which the identity of the substance changes....