Chem 305 Instructor s Edition Partner Section (Circle) M Tu W Th F Date WORKSHOP: Matter and Working with Significant Figures Part 1: Classifying Matter: Circle the appropriate words to make the statements true. 1. A mixture (is/is not) a chemical combining of substances. is not 2. In a compound the (atoms/molecules) are (chemically/physically) combined so atoms chemically that the elements that make up the compound (retain/lose) their identities and lose (do/do not) take on a new set of properties. do 3. The smallest identifiable unit of a compound is a(n) molecule, which is made up of atoms which are chemically bonded. 4. (True or False): A mixture is always made up of a combination of elements. False 5. In a mixture, the substances (lose/retain) their identities. retain 6. In a mixture the substances involved (can/cannot) be separated by a simple physical process. can In a compound the elements involved (can/cannot) be separated by a simple physical process cannot because the elements are (physically combined/chemically bonded). chemically bonded 7. (True or False): An element can be broken down into a simpler substance. False (protons, neutrons & electrons don t have properties of a substance. 8. The smallest identifiable unit of an element is a(n) atom. 9. From the following list of substances, circle the ones that are elements: silver # carbon dioxide wood alcohol chromium# water hydrogen # carbon # nitrogen # oxygen # gold # sugar salt air sulfur # magnesium # nickel # 10. How would you separate sand and water in a mixture? Filter the mixture. Water will flow through the filter but sand will be trapped in the filter. 12. Explain how to separate the sugar and water in a solution of sugar and water. Let the water evaporate. (This can be done faster by heating). The solid sugar will be left behind. 2 1 Adapted from Lalibert, 7/17/08
13. Classify the following as pure substances (pure) or as mixtures (mix): air: mix gasoline: mix orange juice: mix tap water: mix sugar: pure gold: pure mercury: pure oxygen: pure salt water: mix 14. Classify the following as heterogeneous (Het) or as homogeneous (hom): sand & salt mix: het hydrogen: hom iron: hom salt water: hom filtered air: hom iron with rust: het pure water: hom an apple: het nitric acid: hom tossed salad: het granite: het wood: het 15. Classify the following as an element, a compound, a homogeneous mixture, or a heterogeneous mixture: aluminum: element raisin bread: hetero mix carbon dioxide: compound pure water: compound sugar and water: homo mix sodium chloride: compound stomach acid: homo mix mercury: element an orange: hetero mix water & instant coffee: homo mix a pencil: hetero mix carbon particles & sugar: hetero mix hydrogen: element methane: compound gasoline: homo mix neon: element Adapted from Lalibert, 7/17/08 2 2
Part 2: Physical and Chemical Changes to Matter Place a check in the appropriate column: Change Salt dissolves in water. Hydrochloric acid reacts with magnesium to produce hydrogen gas. A piece of copper is cut in half. A sugar cube is ground up. Water is heated and changed to steam. Iron rusts. (reacts with oxygen) Ethyl alcohol evaporates. Ice melts. Milk sours (goes bad). Milk sugar (lactose) turns to acid Sugar dissolves in water. Sodium and potassium react violently with water. An antacid relieves hearburn. Grass grows on a lawn. A tire is inflated with air. Oxygen and hydrogen combine to form water. Water is absorbed by a paper towel. Ethyl alcohol boils at 79 C. Paper burns. Water freezes at 0 C. Fireworks produce colors. Alka-Seltzer gives off carbon dioxide when added to water. Clouds form in the sky. Physical Change Chemical Change 2 3
Part 3 Mixed Practice Name INSTRUCTIONS: Write het in the blank if the material is heterogeneous or hom if it is homogeneous. 1. face cream hom 6. dirt het 2. filtered green tea hom 7. sausage pizza het 3. gravel het 8. laundry bleach hom 4. Lucky Charms het 9. store-bought milk hom 5. salt hom 10. gold hom INSTRUCTIONS: Classify each of the following as an element [E], a compound [C], or a mixture [M]. 11. calcium E 16. pancake syrup M 12. nitrous oxide C 17. carbon monoxide C 13. seawater M 18. silver E 14. sugar C 19. ice C 15. a chocolate sundae M 20. a Big Mac M INSTRUCTIONS: Classify each of the following properties of matter as physical [P] or chemical [C]. 21. Color P 26. Reacts violently with chlorine C 22. Density P 27. Good conductor of heat P 23. Burns easily (flammable) C 28. Dissolves readily in water P 24. Not affected by acids C 29. Melts at 145 C P 25. Boils at 450 C P 30. Malleable (bendable) P INSTRUCTIONS: Classify each of the following changes in matter as physical [P] or chemical [C]. 31. Grinding chalk into powder P 36. Burning gasoline C 32. Dissolving salt in water P 37. Hammering gold into foil P 33. Dissolving zinc in acid C 36. Melting ice P 34. Tearing a piece of paper P 39. photosynthesis by plants C 35. Stretching copper into wire P 40. Making hydrogen from water C 2 4
Part 4: Significant Figures, Scientific Notation, & Rounding How can we determine how many significant numbers a measurement has? The following rules apply to determining the number of significant figures in a measured quantity: 1. All NONZERO digits ARE significant: 457 cm (three significant figures) 0.25 g (two significant figures). 2. IMBEDDED ZEROS (between nonzero digits) ARE significant 1005 kg (four significant figures) 1.03 cm (three significant figures). 3. LEADING ZEROS (to the left of the first nonzero digits in a number) ARE NOT significant; they merely indicate the position of the decimal point: 0.02 g (one significant figure) 0.0026 cm (two significant figures). 4. ENDING ZEROS that are to the right of the decimal point ARE significant 0.0200 g (three significant figures) 3.0 cm (two significant figures). 5. ENDING ZEROS that are not to the right of a decimal point MAY BE significant: 130 cm (two or three significant figures) 10,300 g (three, four, or five significant figures). The way to remove this ambiguity is described on the following page. Use of standard exponential notation avoids the potential ambiguity of whether the zeros at the end of a number are significant (rule 5). For example, a mass of 10,300 g can be written in exponential notation showing three, four, or five significant figures: 1.03 x 10 4 g (three significant figures) 1.030 x 10 4 g (four significant figures) 1.0300 x 10 4 g (five significant figures) In these numbers all the zeros to the right of the decimal point are significant (rules 2 and 4). 1. Determine the number of significant figures in each of the following measured values: a) 200,073 6 b) 0.00084 2 c) 5.001 4 d) 0.0620 3 e) 107.010 6 f) 3400 2-4 (ambiguous) g) 3.400 x 10 3 4 h) 3.40 x 10 3 3 2 5
Rounding When we express a value to the correct number of significant figures, this often requires rounding. To round off decimals: Find the place value you want (the "rounding digit") and look at the digit just to the right of it. If that digit is less than 5, do not change the rounding digit but drop all digits to the right of it. If that digit is greater than or equal to five, add one to the rounding digit and drop all digits to the right of it. To round off whole numbers: Find the place value you want (the "rounding digit") and look to the digit just to the right of it. If that digit is less than 5, do not change the "rounding digit" but change all digits to the right of the "rounding digit" to zero. If that digit is greater than or equal to 5, add one to the rounding digit and change all digits to the right of the rounding digit to zero. NOTE: It may be necessary to use scientific notation to correctly 2. Round the value 673.1482 to: 5 sig figs 673.15 3 sig figs 673 2 sig figs 6.7 x 10 2 1 sig fig 7 x 10 2 3. Round the value 50.0696 to: 4 sig figs 50.07 3 sig figs 50.1 2 sig figs 5.0 x 10 1 1 sig fig 5 x 10 1 4. Round the value 273.84 to: 4 sig figs 273.8 3 sig figs 274 2 sig figs 2.7 x 10 2 1 sig fig 3 x 10 2 5. Round the value 48372000 to: 4 sig figs 4.837 x 10 7 3 sig figs 4.84 x 10 7 2 sig figs 4.8 x 10 7 1 sig fig 5 x 10 7 2 6
Scientific Notation Name In scientific notation, all numbers are represented by number with one non-zero digit to the left of the decimal place multiplied by ten raised to the appropriate power. Small number (less than 1) will have negative exponents of 10. Large numbers (greater than 1) will have positive exponents of 10. WORKING WITH SIGNIFICANT FIGURES Addition and Subtraction When adding or subtracting, the number of digits to the right of the decimal point in the answer equals the measurement which has the least number of digits to the right of the decimal point. EAMPLE: adding: 26.46 this has the least digits to the right of the decimal point (2) + 4.123 30.583 rounds off to* 30.58 2 digits to the right of the decimal point EAMPLE: subtracting: 26.46-4.123 22.337 rounds off to 22.34 Perform the following additions or subtractions. Report your results to the proper number of significant figures. a) 28 + 16 + 227 271 (calc & corr) b) 2.222 + 2.22 + 2.2 6.642 (calc) 6.4 (corr) c) 81.42-18.4 63.02 (calc) 63.0 (corr) d) 4732.3 + 55 + 0.54 4787.84 (calc) 4788 (corr) e) 999.0 + 1.7 43.7 957 (calc) 957.0 (corr) f) 564,321 264,321 300,000 (ambiguous) 3.00000x10 5 or 300,000. g) 0.04216 0.0004134 0.0417466 (calc) 0.04175 or 4.175x10-2 (corr) 2 7
Multiplication and Division In multiplying or dividing, the number of significant figures in the answer (regardless of the position of the decimal point) equals that of the quantity which has the smaller number of significant figures. EAMPLE: multiplying: 2.61 x 1.2 this has the smaller number of significant figures (2) 3.132 rounds off to 3.1 has 2 significant figures EAMPLE: dividing: 2.61 / 1.2 2.175 rounds off to 2.2 5. Carry out the following multiplications, expressing your answer to the correct number of significant figures. a) 27.88 x 0.00695 0.193766 (calc) 0.194 (corr) OR 1.94x10-1 b) 3.10 x 5428 16826.8 (calc) 1.68 x 10 4 (corr) NOT 16800 c) 3.00 x 0.4000 1.2 (calc) 1.20 (corr) d) 0.693 x 7.3x10 2 505.89 (calc) 5.1x10 2 (corr) NOT 510 e) 8.6x10-4 x 1.9x10 2 0.1634 (calc) 0.16 (corr) OR 1.6x10-1 (corr) f) 4317 0.88 4905.7 4.9 x 10 3 g) (2.7x10 8 )(0.00149) 2.682 x 10 6 2.7 x 10 6 (0.1500) h) (8.4)(0.03) 147 0.001714 0.002 OR 2 x 10-3 i) (0.1070)(328) (0.01244) 2821.2 2.82 x 10 3 j) 4 (57332)(3.5x10 ) 12 (185)(2x10 ) 5.423 x 10-6 5 x 10-6 2 8
Mixed Practice 1) (1.3 + 9.7)(22) (11.0)(22) 242 2.4 x 10 2 2) (183 x 0.017) + 850. 3.111 + 850. 853.11 853 OR 8.53 x 10 2 3) (12.7 8.3) (18.5 2.2) 4.4 16.3 0.26994 0.27 OR 2.7 x 10-1 4) (3. x 2.2) + (4 x 85) 6.6 + 340 346.6 3 x 10 2 5) ( 0.127 0.038) 0.0445 0.089 0.0445 2.0 don t forget the trailing zero! 6) 3.24x10 5 (187 27) 5 3.24x10 1.514 x 10-7 1.51 x 10-7 214 (438 825) 7) 6 1.234x10 1263 1.0235008 x 10 9 1.024 x 10 9 1.234x10 6 8 4.02x10 8) 385 5 1.4x10 2871.4 + 385 3256.4 3.3 x 10 3 8 4.02x10 9) 385 3 1.4x10 2.87142854x10 11 + 385 2.87143239x10 11 2.9 x 10 11 ( 14.8 12.5) 10) 12.5 2.3 12.5 0.184 0.18 OR 1.8 x 10-1 4 (0.01020)(4.3x10 ) 11) (16 12) 438.6 4 109.65 1 x 10 2 ( 83.4 27.4) 12) 0.0432 56.0 0.0432 1296.3 1.30 x 10 3 don t forget the trailing zero! 2 9