Nuggets: Terms and Matter; Sig Figs; Temperature Conversion; Density; SI Units; Unit Conversions; Atomic Theory; Periodic Table

Transcription

1 CHEMISTRY 103 Help Sheet #1 Chapter 1 and Appendi A Do the topics appropriate for your lecture Prepared by Dr. Tony Jacob (Resource page) Nuggets: Terms and Matter; Sig Figs; Temperature Conversion; Density; SI Units; Unit Conversions; Atomic Theory; Periodic Table TERMS Matter: has mass and volume; States of matter: solid, liquid, and gas Classification of Matter Heterogeneous Matter: chemical substance that has an uneven teture visible with the eye or a microscope; many can be separated by physical means (e.g., salt and pepper) Homogeneous Matter: chemical substance with uniform consistency comprised of two or more substances (e.g., sodium chloride dissolved in water) Solutions: Homogeneous miture with varying compositions Substances: containing only one chemical substance (e.g., H 2 O or NaCl) with a constant composition (e.g., H 2 O; other tets may refer to this as a Pure Substance) Compound: a substance with two or more elements bonded together in fied proportions (e.g., CO 2 or NO) Element: a substance that contains a single type of atom and cannot be decomposed into two or more substances; one of about 110 unique substances on the periodic table Atom: the smallest chemical substance that has the properties of that element (e.g., He or Fe) Molecule: smallest discrete substance (e.g., O 2 (g) or CH 4 (g)) that maintains the chemical characteristics of that species Chemical Change or Chemical Reaction: a chemical process often showing starting (reactants) and finished substances (products) being transformed into new substances (e.g., going from C(s) to CO 2 (g)) Chemical Property: how a substance reacts chemically (e.g., C(s) can react with O 2 (g) to form CO 2 (g)) Physical Property: characteristics of chemicals (e.g., solubility, boiling/melting point, density, etc.) Physical Change: a change in the state of matter (e.g., H 2 O(s) to H 2 O(l)) (note: other tets may use slightly different diagrams) Matter Is the matter uniform? No Heterogeneous matter (Fe(s)+NaCl(s)) Yes Homogeneous matter Does it have a variable composition? Yes Solution or Homogeneous Miture (Na 2 S(aq)) No Substance or Pure Substance (SO 2 (g), CaCO 3 (s), Al(s)) Compound (2 or more elements) (SO 2 (g), CaCO 3 (s)) Element (Al(s))

2 SIGNIFICANT FIGURES (Appendi A) Number < 1: digits to the right of decimal are significant (e.g., sig figs); leading zeros are not significant (e.g sig figs); trailing zeros are significant (e.g., sig figs) Number > 1 o with decimal point: all zeros right of the decimal point are significant (e.g., sig figs; sig figs) o without decimal point: trailing zeros are not significant (e.g., sig figs; sig figs) Defined quantity: Infinite sig figs (100cm infinite sig figs) Scientific notation: All numbers of the significand or mantissa are significant (e.g., sig figs; sig figs) Manipulating Sig Figs Multiplication/Division: answer has the same number of sig figs as the smaller number of sig figs; for A B or A B: [e.g., (1.23) ( ) ; with sig figs: because has 2 sig figs which is the smaller number of sig figs for the two values in the equation] Addition/Subtraction: answer has the same number of decimal places as the smaller number of decimal places; for A + B or A B: [e.g., (2.34) + (4.9) 7.24; with sig figs: 7.2 because 4.9 has 1 decimal place that is significant] Addition/Subtraction and Multiplication/Division: Do higher priority first: 1) parentheses; 2) multiplication/division; 3) addition/subtraction; keep etra sig figs but note where last sig fig is; round at end Precision measure of how close several measurements are to one another Accuracy how close a measured value is to the accepted value TEMPERATURE CONVERSIONS K C (or C K ) mass DENSITY volume units: g/ml (liquids), g/cm3 (solids), or g/l (gases) SI UNITS G giga c centi M mega m milli k kilo µ micro n nano p pico l L 3 1Ångstrom 1Å m M larger units k m, l, g pivot line smaller units c all conversions go thru this pivot line m µ n Å p meters

3 DIMENSIONAL ANALYSIS (UNIT CONVERSIONS) Eample 1: m, l, g M k d c cm?m 1 step conversion: directly to pivot line 5cm cm m Which conversion factor is correct? (At first glance they all look ok but 2 are incorrect!) cm cm m m cm The 1st one says: A large number of small ones (cm) 1 large one (m) Correct! Eample 2: M m, l, g k d c m µ n Eample 3: Question: /?mg/ cm The 2nd one says: A fraction of a small one (cm) 1 large one (m) Incorrect! Question: 5cm?nm m cm m nm cm 9 nm cm Answer: multi-step conversion: must go through the pivot line re-write as a "vertical" fraction: / mm mm mm Simplified: The 3rd one says: One small one (cm) A large number of large ones (m) Incorrect! Answer: 2 step conversion: must go through the pivot line nm mm mm mm work on each unit conversion separately-doesn't matter which conversion is done first; we'll work on the bottom conversion first ( ) m 3 and kg g mg Common error: mm mm mm cm mm g g cm mg mg cm mg mg (epanded notation) cm Wrong answer! g m The 4th one says: 1 small one (cm) A fraction of the large one (m) Correct! mg mg common error is to place the power of 3 for the /1000mm conversion inside the parentheses only on the units instead of outside the parentheses which would then raise the numbers to the third power as well Kinetic Molecular Theory: Matter consists of tiny particles in constant motion; Solids: particles packed in a close regular array, vibrate but do not move; is rigid and volume is fied; Liquids: particles are randomly arranged, touch and move past one another; Gases: has no fied shape or volume; fill the container they re in; can be compressed; particles move quite rapidly. Dalton's Atomic Theory: 1. matter is made from atoms which are very tiny 2. atoms of one element have identical chemical properties 3. compounds contain two or more elements in whole number ratios 4. chemical reactions involve shifting atoms around; atoms are not created or destroyed

4 Law of Conservation of Mass: Mass is neither created nor destroyed Law of Constant Composition: atoms are always found in the same proportions by mass for a particular substance (e.g., in zinc sulfide, there is 32.9% by weight sulfur and 67.1% by weight zinc) PERIODIC TABLE: Family or Groups (these often need to be memorized) columns: alkali metals (Group IA), alkaline earth metals (Group IIA), halogens (Group VIIA), noble gases (Group VIIIA); other groups on the Periodic Table: transition metalsactinides; lanthanides Period row; Three types of elements: metals, non-metals, metalloids Diatomic Elements: F 2, Cl 2, Br 2, I 2, N 2, O 2, H 2 (the diatomic elements often need to be memorized) Phases of elements: Liquid elements: Br 2 (l), Hg(l); Gaseous elements: noble gases: He(g), Ne(g), Ar(g), Kr(g), Rn(g); others: F 2 (g), Cl 2 (g), H 2 (g), N 2 (g), O 2 (g); All other elements are solids Biological Building Blocks: H, O, C, N; Biological Major Minerals: Na, K, Mg, Ca, P, S, Cl 1. Classify each of the following as a physical property or a chemical property. a. Density b. Melting temperature c. Substance that decomposes into two elements upon heating d. A substance that does not react with sulfur 2. Classify each of the following as a physical or chemical change. a. Rusting of iron b. Burning gasoline c. Water evaporating from a lake 3. Consider the following separations of materials. State whether a physical process or a chemical reaction is involved in each separation. a. Sodium chloride is obtained from sea water by evaporation of the water. b. Mercury is obtained by heating the substance mercury (II) oide; oygen is also obtained. 4. Do the following unit conversions. a ng is equivalent to mg. b mm is equivalent to pm. c. A density of 50.0 g/ is equivalent to kg/m 3. d. How many feet are there in 2960 cm? (2.54 cm 1.00 inch) e. The speed of light is m/s. What is this speed in mi/hr? (2.54cm 1.00inch; 5280feet 1.00mile) 5. If a runner ran a 50.6 mile race in 8.00 hours and 23.0 minutes, how long would it take them to run a marathon (26.2 miles) in hours and minutes at the same average speed they ran the longer race? 6. The density of homogenized milk is 1.03 g/ml. How much does 237 ml (1.00 cup) weigh in kg? 7. A cube of metal has a side length of 2.0 cm and a mass of 40.0 grams. What is its density in g/? 8. An irregular shaped piece of metal has a density of 3.76g/ and when placed in a graduated cylinder containing water, the water rises from 31.25ml to 32.58ml. What is the mass of the metal in grams? (recall l 3 ) 9. A sample titanium foil is 13.9m 2 and has a mass of 24.0 oz. The density of titanium is g/. Calculate the thickness of titanium foil in cm. (1.00 oz 28.4g) 10. Draw a separate picture to represent each of the following: H 2 O(s), H 2 O(l), and H 2 O(g).

5 11. How many sig figs are in the following numbers/calculations? a b c. 120,000,000 d. 10 e f I. Write the chemical symbols for the elements: a. potassium b. cobalt c. manganese d. iron e. phosphorous II. Write the chemical names for the following symbols: a. Cr b. Ca c. Kr d. S e. Si f. V g. Mn h. Na (Each instructor will clarify how many element names and symbols students are required to memorize.) 13. The following data was obtained when the volume of a solution of sodium chloride was measured: ml ml ml ml Average ml The actual volume of the solution was ml. The above data can best be described as: a. Accurate and precise b. Accurate and imprecise c. Inaccurate but precise d. Inaccurate and imprecise e. The terms accurate and precise do not apply in the above situation. (For more practice, see Practice Sheet #1.103 ( elemental names and symbols); see Practice Sheet #2.103 (SI unit calculations.)) ANSWERS 1. a. physical property b. physical property c. chemical property d. chemical property 2. a. chemical change b. chemical change c. physical change 3. a. physical process b. chemical reaction 4. a mg {50.0ng (/ ng) (1000mg/) mg} b pm {1.75mm (/1000mm) ( pm/) pm} c kg/m 3 {50.0g/ (/1000g) (100cm/) kg/m 3 } d ft {2960cm (1.00in/2.54cm) (1ft/12in) 97.11ft; note that 1ft 12in is a defined quantity} e mi/hr { m/s (60s/in) (60min/1hr) (100cm/) (1.00in/2.54cm) (1.000ft/12.00in) (1.00mi/5280ft) mi/hr; note that 60s in, 60min 1 hr, and the SI conversions are defined quantities} hours and 20.5 minutes {8.00hr (60min/1hr) 480min + 23min 503min; (503min/50.6mi) (26.2mi) min; min (1hr/60min) hr; hr (60min/1hr) 20.45min; 4.00hr and 20.5min} kg {D m/v; m D(V) (1.03g/ml)(237ml) (/1000g) } g/ {D m/v; V 2.0cm) ; D 40.0g/[(8.0cm)] 5.00g/ } g {D m/v; m D(V) (3.76g/ ) ( 3 /l) (32.58ml 31.25ml) (3.76)(1.33) 5.00} cm {D mass/vol; D mass/(length width depth); rearrange equation: depth mass/(length width D); depth mass/(area D) where area length width; convert units: 24.0oz (28.4g/1.00oz) 681.6g; 13.9m 2 (100cm/) 2 139,000cm 2 ; depth 681.6g/(139,000cm g/ ) cm} water 10. solid liquid gas 11. a. 5 b. 2 c. 2 d. 1 e. 6 f I. a. K b. Co c. Mn d. Fe e. P II. a. chromium b. calcium c. krypton d. sulfur e. silicon f. vanadium g. manganese h. sodium 13. c