Dr. Kevin Moore CHM 111

Transcription

1 Dr. Kevin Moore CHM 111

2 the science that deals with the composition and properties of substances and various elementary forms of matter Burdge Study of matter and the changes it undergoes

3 Health and Medicine Chemistry of living systems Pharmaceutical Industry is dominated by chemists Energy and Environment Energy can be obtained from chemical reactions Energy can be stored in chemicals Materials Creation of substances from other substances Food and Agriculture Fertilizers, Pesticides and Herbicides

4 Used to systematically approach scientific problems Define Problem Observe and Experiment Hypothesis Preliminary explanation for a set of observations Law verbal or mathematical statement to which there are no known exceptions Theory explanation of a group of observations and/or laws related to them

5 Real science is a collaborative effort Results are duplicated by others researching in the same field without reproduction of data, fraud can take place Cold Fusion (Stanley Pons) Stem Cell Research (Hwang Woo-suk)

6 Anything which occupies space and has mass Element substance which cannot be separated into a simpler substance chemically Compound substance which is made up of two or more elements in fixed proportions

7 Standard State physical state of an element at 25 C Solids state in which particles are held very tightly primarily vibrational motion only Liquids state in which particles are held tightly, but some motion allowed particles can change their association Gases state in which particles have no restriction on motion Particles do not interact

8 Mixture - combination of substances in which the substances maintain separate identities Heterogeneous Mixture - mixture containing more than one phase Homogeneous Mixture - uniform mixture containing a single phase

9 Chemical Property - Property which involves a change to the chemical makeup of a substance Physical Property - Property which does not change the chemical makeup of a substance

10 Extensive Property property which depends on the amount of matter present Intensive Property property which is independent of the amount of matter present

11 Measurement Quantitative Observation Direct Measurements 20.5 cm piece of wood Unit Accepted standard of measurement Metric System

12 Système International d Unitès Internationally accepted units of measurements Physical Quantity Unit Abbreviation Mass Kilogram kg Length Meter m Time Second s Temperature Kelvin K Amount of Substance Mole mol Electric Current Ampere A Luminous intensity Candela cd

13 Metric System uses a system of Prefixes to adjust from small to large Prefix Symbol Meaning Power of 10 Examples Mega M 1,000, MHz Kilo k 1, kg, km Centi c cm Milli m mg, ml, mm Micro μ μg, μm Nano n nm Pico p pm

14 Convert between Units (g--->kg) Use Dimensional Analysis convert 20. 0gkg 1 kg g g kg Video

15 Let the units determine your steps convert 025. kg mg Current units go on the bottom 025. kg g kg Place conversion factor with the smaller unit 1000 g 025. kg 1000 mg mg 1 kg 1 g

16 Convert 15.5 cm to km centi means 100 kilo means 1000 convert to the base unit

17 Accuracy - Closeness to true or known value Measured by % Error. %Error Actual Measured Actual 100 A student measures the % salt in salt water. Three trials give 3.28 %, 3.64 % and 3.09 %. The salt water is actually 3.48%. What is the % Error? % Error % Error 40. %

18 Precision - Closeness between data points Reproducibility Accuracy is important, but precision is our focus Are the data points reproducible? Video Precise: g, g, g Not Precise: g, g, g

19 Every Device is calibrated TD or TC TD - To Deliver (Buret, Pipette, etc) TC - To Contain (Graduated Cylinder, Beaker) Uncertainty is known in calibration Listed as an amount (±0.001 g, ±0.01 ml) Listed as a percentage (±5%, ±0.1%) Data has no meaning beyond its uncertainty

20 Precision is determined by calculating the average deviation of a series of measurements. Deviation Measurement Average Measurement # of deviations is identical to # of experimental data points (# of trials) Salt Problem (Accuracy slide) Average 334. Deviations #: # 2: #: Avg Dev:

21 Mass - amount of matter contained in an object Gram - metric unit of measurement Kilogram is the SI standard Length Meter - metric unit of measurement Volume - amount of space an object occupies Derived Unit (unit created from other units) m 3 is the SI standard (1000 Liters)

22 Last Digit is estimated Marks on beaker are at 25 ml Error is 5% (1.25 ml) Ability to estimate is normally: 0.1 of smallest division (2.5 ml) 0.2 if you are less confident Read the beaker 285 ml? EVERY MEASUREMENT HAS UNCERTAINTY Video

23 Reflect the precision (not accuracy) of the measurement The last digit is affected by the precision of the instrument being used to perform the measurement 252 g and 254 g are both within the precision of the device 252 g and 239 g are probably not within the precision of the device

24 Precision: Reproducibility of a data point Significant Figures represent all parts of the data that are known to be within the precision of the instrument Significant Figures come from real life measurements they have a limit!

25 All non-zero digits are significant 252 g ---> 3 significant figures All zeros between non-zero digits are significant 2006 g ---> 4 significant figures Trailing zeros are not significant unless a decimal point is present 200 g ---> 1 significant figure g ---> 4 significant figures Leading zeros are not significant mg ---> 3 significant figures Video

26 ml 5 significant figures cm 4 significant figures L 2 significant figures 240 mg 2 significant figures 770. ml 3 significant figures

27 Addition/Subtraction Position of the uncertainty is the key No significant figures can exist beyond any position of uncertainty Round up or down based on values after last sig fig g g g Video round up g g g no rounding g 18. g

28 Multiplication/Division Calculate based on the fewest # of significant figures Round up or down based on values after last sig fig sig figs sig figs no rounding sig figs sig figs sig figs roundi up sig figs Multiplication/Division requires a knowledge of the number of significant figures

29 Exact Conversions - statements in which the equivalence is by definition (prefixes) No effect on significant figures 1000 g = 1 kg 1 cc (cm 3 ) = 1 ml 1 cm = 10 mm Measured Statements - statements in which the equivalence is measured Significant Figures are important J = Calorie

30 Method of representing very large or very small number The value of the data is the mantissa Only one (1) non-zero digit to the left of the decimal The magnitude of the data is the exponent Use the EE or Exp key on your calculator

31 Addition/Subtraction Power of exponent must be the same 4 2 convert exp Correct sig figs Multiplication/Division Multiply mantissa and add exponent Divide mantissa and subtract exponent Sci Notation Correct sig figs

32 Derived Unit: ratio of mass to Volume Amount of matter contained in a certain volume Often refer relative to water (Specific Gravity) C ~ 1.00 g/ml D m V

33 A metal sample has a mass of 8.99g and volume of ml. Is it Gold (D Au =19.31 g/ml)? D m V D D Au Pb 899. g ml The density of NaCl is 2.16 g/ml. Calculate the volume of a sample having a mass of 485 g of NaCl. g ml g ml g ml V m D 485 g 216. g ml ml 225 ml

34 Using difference in volume to determine the volume of an irregular solid This is typically done in water, but any solvent will work Must not dissolve in solvent Must not react with solvent An initial amount of water is put in and measured. Solid is added and also measured. The difference is the volume of the solid. Video

35 Measure of the content of heat of a substance Thermometer - device used to measure Temperature C - Common unit of measurement Kelvin - SI unit of Temperature Based on Absolute Zero - Temp at which molecular motion ceases No heat content Scale is identical to Celcius

36

37 C = 0 K What is the Kelvin Temperature of 22 C? 22 C K What is the Celcius Temperature of 325 K? 325K C

38 Scientific Method Precision and Measuring Instruments Significant Figures Units of Measurements and Prefixes Dimensional Analysis Density and Temperature