Sample Question Answers - Unit 1 Upon successful completion of this unit, the students should be able to: 1.1 Distinguish among observations, laws, theories, and hypotheses in the scientific approach to knowledge. 1. a. Law b. Theory 2. d 3 No. A law is based upon observations of which there are no known exceptions. It is not possible to actually observe evolution. 1.2 State and apply rules for taking measurements and significant figures. 1. 20.15 2. 64 3. 4.5900 x 106 4. X 0.088070 X 5. 4.477 x 105 6. a. 1481 b. 13.8 7. a. 3.43 b. 1.73 8. 14.7 1.3 Identify the common SI units for mass (kg), length (m), and time (s) and know the meaning of the following metric prefixes (i.e. memorize and be able to apply): giga, mega, kilo, deci, centi, milli, micro, nano, pico. Students should also memorize and be able to apply 1 cm 3 = 1 ml. See sample questions under objective 1.4. 1.4 Perform conversions among different units using dimensional analysis (note: students should be able to apply English to metric and English to English conversion factors, but they do not need to memorize them). 1.? ng = 12.0 x 10-7 mg x -3 10 g mg x 10 ng -9 g = 1.20 ng
1.5 Interconvert temperatures among Celsius, Fahrenheit and Kelvin scales. 1. d 128 K < 273 K and since 273 K = 0 o C, the answer must be a negative value. 2. 1) -268.9 + 40 = -228.9 2) -228.9 (9/5) = -412.02 3) -412.02 40 = -452.0 o F 3. o F to o C: 1) 150 + 40 = 190 2) 190 (5/9) = 105.56 3) 105.56 40 = 65 o C o C to K: K = o C + 273 65 + 273 = 338 K 4. K to o C: K = o C + 273 158 273 = -115 o C o C to o F: 1) -115 + 40 = -75 2) -75 (9/5) = -135 3) -135 40 = -175 o F
1.7 Differentiate between pure substances and mixtures, and correctly use specific terms such as elements, compounds, homogeneous, heterogeneous, states (phases), and solutions. 1. A mixture in which the components are not uniformly distributed. 2. a. element b. heterogeneous mixture 3. a. mixture b. compound (that is assuming it is pure salt, generally table salt has a few additives such as iodide and therefore would be a mixture) c. element d. mixture (brass is an alloy composed of copper and zinc) 4. Only air is a mixture 5. A must be a compound because it decomposes to form other substances. C must be a compound because it has the same properties of what is produced when carbon reacts with oxygen (if carbon, an element, reacts with oxygen, an element, and those are the only two reactants, the product must be a compound composed of the two). It is unclear whether B is an element or compound. 6. 7. Compound 8. a. heterogeneous mixture b. homogeneous mixture 9. Salt water and air are the mixtures
1.8 Differentiate between chemical and physical properties and changes. 1. Physical 2. a. physical b. chemical c. physical d. chemical 3. A physical property is a property that can be measured or observed without the substance undergoing any chemical reaction (that is, there is no change in composition). An example would be that the melting point of ice is 0 o C. When the water is frozen as ice it is H 2 O and when it melts it is still H 2 O. A chemical property is one that can only be measured or observed when a substance undergoes a chemical reaction (that is, there is a change in composition). An example of a chemical property would be that methane (CH 4 ) can burn to produce carbon dioxide (CO 2 ) and water. 4. A chemical change is one that involves a change in composition and a physical change involves no change in composition. Iron rusting would be an example of a chemical change. Iron (Fe) reacts with oxygen and water and is converted to a form of iron oxide (Fe 2 O 3 ). Grinding rock salt into a powder would be an example of a physical change. 5. Chemical changes are rusting iron only. 1.9 Describe how distillation, filtration, and chromatography can be used to physically separate substances. 1. All three of the techniques described are used for physically separating two or more substances but the mechanism of separation is different. Distillation takes advantage of the fact that different substances have different boiling points. If a mixture of two liquids is heated for example, the one with the lower boiling point will boil first. The vapor can be captured and then condensed before the other liquid begins to boil. Filtration, on the other hand is used to separate a solid from a liquid. The mixture is poured onto some filter paper and only the liquid is able to seep through. Chromatography takes advantage of the fact that different substances have different affinities for various substances. Chromatography in general has a stationary phase (a solid) and a mobile phase (a liquid or gas). If a component of a mixture has a high affinity for the stationary phase it will move slowly through the system and eventually be separated from the other component which might have a high affinity for the mobile phase and move more quickly. 2. One way to separate the three would be to first add the mixture to water and stir. The sugar would be the only one to dissolve. The mixture of sand, candle wax, and sugar water could then be poured through onto filter paper. The sugar water would pass through the filter paper but the sand and candle wax would not. The sugar can than be isolated from the water by boiling off the water. The sand and candle wax can be separated from each other by heating the mixture. Only the candle wax will melt. The melted candle wax can then be carefully decanted off the sand (decant means to pour off of).