Name AP CHEM / / Chapter 1 Chemical Foundations

Transcription

1 Name AP CHEM / / Chapter 1 Chemical Fundatins Metric Cnversins All measurements in chemistry are made using the metric system. In using the metric system yu must be able t cnvert between ne value and anther. YOU MUST MEMORIZE THE FOLLOWING PREFIXES AND FACTORS FOR THE AP EXAM: Example: Cnvert 18.3 x 10-1 kilgrams t centigrams. Step 1. Subtract the pwer f ten value yu are slving fr frm the pwer f ten value yu are given. In this prblem yu are given 18.3 kilgrams and yu are cnverting t centigrams. Kilgrams have a pwer f ten value f 3; centigrams have a pwer f ten value f (-2) = 5 Step 2. Write yur result as the pwer f ten value f yur answer. In this prblem ur answer is 18.3 x 10-1 x Factr Name Prefix Symbl 1 x 10 6 millin mega- M 1 x 10 3 thusand kil- k 1 x 10 2 hundred hect- h 1 x 10 1 ten deca- D 1 x 10 0 base units x 10-1 tenth deci- d 1 x 10-2 hundreth centi- c 1 x 10-3 thusandth milli- m 1 x 10-6 millinth micr- µ 1 x 10-9 billinth nan- n Step 3. Put yur answer in prper scientific ntatin x 10-1 x 10 5 is cnverted t 1.83x10 4. Remember that when multiplying using pwers f ten yu add. Here is a pneumnic: Mach kangars head deadly Burmese drug cartels making millins nervus. Uncertainty in Measurement Depends n the precisin f the measuring device Fr example a measurement f grams is a mre precise measurement than 1.7 grams Reliability in Measurements Accuracy the clseness t the actual scientific value Precisin getting repeated measurements in repeated trials Types f Errrs Randm: errr in measurement has equal prbability f being high r lw Systematic: errrs all ccur in the same directin General Rules fr determining if a Number is Significant 1. All nn-zer numbers are significant. Example: has seven significant figures. 2. Zers appearing between nn-zer figures are significant. Example: has fur significant figures. 12, has eight significant figures. 3. Zers that appear in frnt f nn-zer figures are NOT significant. Example: has fur significant figures has ne significant figure. 4. Zers at the end f a number and t the right f a decimal are significant. Example: has five significant figures has ten significant figures. 5. Zers at the end f a number but t the left f the decimal may r may nt be significant. If such a zer has been measured r is the first estimated figure, it is significant. On the ther hand, if the zer has nt been measured r estimated but is just a placehlder, it is NOT significant. T avid ambiguity, if a number is measured, a decimal will be written at the end indicating that all zers befre it are significant. If n zer is written, yu can assume that the zers n the end are place

2 hlders and shuld nt be cnsidered significant. Example: 2000 cntains ne significant figure cntains fur significant figures 6. Exact numbers are numbers that were nt determined using measuring devices but instead were determined by cunting. Example: There are 26 students in this AP Chemistry class. There are 179 schl days remaining. Srry. Additin r Subtractin using Significant Figures: The answer has the same number f decimal places as the least precise measurement. Example (precise fur places t the right f the decimal) (precise fur places t the right f the decimal) (precise three places t the right f the decimal) runds ff t (answer must be precise three places after the decimal) Multiplicatin r Divisin using Significant Figures: The answer can have n mre significant figures that there are in the measurement with the smallest number f significant figures. Example: (5 ttal significant figures) x (4 ttal significant figures) runds ff t (4 ttal significant figures) HINT: Students ften have difficulty remembering the rules fr using significant figures in calculatins and that makes them very sad putting them in A SAD MODE. A: additin M: multiply S: subtractin O: r A: after D: divide D: decimal E: everything If yu Add r Subtract, lk After the Decimal fr significant figures. If yu Multiply Or Divide lk at Everything fr significant figures. AP trick: The AP exam nly penalizes students wh have tw r mre t many r tw few significant figures in their answers. Fr example, if the crrect answer is 75.8, the AP wuld accept r 76. T make it easy, always use three significant figures in yur final answer. That will help t save yu time and minimize pint deductins. Scientific Ntatin In chemistry, we ften use numbers that are either very large (1 mle = atms) r very small (the mass f an electrn = kg). Writing numbers with s many digits wuld be tedius and difficult. T make writing very large and small numbers easier, scientists use an abbreviatin methd knwn as scientific ntatin. In scientific ntatin the numbers mentined abve wuld be written as x and x As yu can see these numbers are written as pwers f ten. The pwer f ten is used because as yu mve ne place t the right r left f a number yu are changing by a value f ten. (1 x10 10 x x x r ) Cnverting a number t r frm scientific ntatin If yu mve the decimal place t the left, the pwer f 10 value increases. If yu mve the decimal place t the right, the pwer f 10 value decreases. T remember this, think: Left (sunds like lift) smething Up and Right (sunds like write) smething Dwn Example: Let s lk at the first number frm abve: T put this number in scientific ntatin yu wuld mve yur decimal place until there is ne number t the left f the decimal. T d this, we must mve ur decimal 23 places t the left. When yu mve the decimal t the left, the pwer f 10 value increases. It increases frm 0 t 23. Thus, the answer is x Let s lk at the secnd number frm abve:

3 T put this number in scientific ntatin we must mve ur decimal 31 places t the right. REMEMBER: Yu must always have ne (and nly ne) digit t the left f the decimal when writing numbers in scientific ntatin. Since we are mving ur decimal t the right, we must decrease ur pwer f 10 value. It decreases frm 0 t 31. Our answer is x Rules fr multiplying & dividing using scientific ntatin: When multiplying tw numbers in scientific ntatin, ADD their pwer f 10 values. Fr example: (3.45 x 10 6 )(4.3 x 10 5 ) = x But, we must als remember t express ur answer in significant figures. Thus, the final answer is 1.5 x When dividing numbers in scientific ntatin, SUBTRACT the denminatr s pwer f 10 value frm the numeratr s pwer f 10 value. Fr example: (2.898 x ) (3.45 x ) = x 10-3 (I had t add the zer at the end t get the three significant figures needed.) I gt 10-3 because = 3. Make sure yur answer is in prper scientific ntatin (ne number t the left f the decimal). In this prblem we have t mve the decimal ne place t the right. When we mve ur decimal t the right, we decrease ur pwer f decreases by 1 t 4. Our final answer is: 8.40 x 10-4 Dimensinal Analysis Used t cnvert a number frm ne system f units t anther. This prcess will help yu when perfrming difficult calculatins later in the year. Yu will find a cmplete listing f English/Metric Equivalents in Appendix Six f yur text bk, page A27 Example: In Octber I will run in a 5 mile race. Calculate hw many kilmeters I will run. Slutin: (Needed Equivalents: 1 mile = 1760 yards, 1 meter = yards) 5 miles x 1760 yards x 1 meter x 1 kilmeter = 8.04 (runded t) 8 kilmeters 1 mile yards 100 meters Example: Cnvert 55.0 miles/hur t meters/secnd Slutin: (Needed Equivalents: 1 mile = 1760 yards, 1 meter = yards, 1 hur = 60.0 minutes, 1 minute = 60.0 secnds) 55.0 miles x 1760 yards x 1 meter x 1 hur x 1 minute = (runded t) 24.6 m/s hur 1 mile yards 60.0 minutes 60.0 secnds General Rules fr Runding Numbers in Chemistry: As a rule, when perfrming a series f calculatins, wait until the very end t rund ff t the prper number f significant figures instead f runding ff each intermediate result. Example: = WRONG: = (runded t 13.3) = (runded t) 15.9 CORRECT: = (runded t) 16.0 Rule 1. If the digit fllwing the last significant figure is less than 5, the last significant figure remains unchanged. The digits after the last significant figure are drpped. Example: Rund t three significant figures. Answer: 23.4 Explanatin: 4 is the last significant figure. The next number is 3. 3 is less than 5. Thus, 4 remains unchanged and 37 is drpped. Rule 2. If the digit fllwing the last significant figure is greater than 5, then 1 is added t the last significant figure. The digits after the last significant figure are drpped. Example: Rund t tw significant figures. Answer: 5.4 Explanatin: 3 is the last significant figure. The next number is 8. 8 is greater than 5. Thus, 1 is added t 3 making it 4. The 83 is drpped.

4 Rule 3. If the digit fllwing the last significant figure is 5, then 1 is added t the last significant figure if the last significant figure is dd. If the last significant figure is even, it remains unchanged and the digits after the last significant figure are drpped. Example 1: Rund 3.35 t tw significant figures. Answer: 3.4 Explanatin: 3 is the last significant figure. The next number is 5. 3 is an dd number. Odd numbers rund up when the fllwing number is a 5. Example 2: Rund 7.25 t tw significant figures. Answer: 7.2 Explanatin: 2 is the last significant figure. The next number is 5. 2 is an even number. Even numbers remain unchanged when they are fllwed by a five. The 5 is drpped. Rule 4: When runding numbers it is f abslute imprtance t maintain the magnitude f a number. This is dne by adding zers t the end f a number. Example: Rund t tw significant figures. Answer: Explanatin: Zers have t be added t maintain the magnitude f the number. If yu rund the number t 87 yu will have the crrect number f significant figures but it will nt be f the same magnitude. Yur runded number shuld always be apprximately the same as the riginal number. Temperature Cnversin: F: Fahrenheit C: Celsius r Centigrade K: Kelvin (named fr Lrd Kelvin, a.k.a. William Thmsn (SEE PICTURE ) F = (1.8 x C) C = ( F 32.0) 1.8 K = C C = K Lk at the prblem and decide which f the 4 frmulas abve will wrk best. Pick the frmula that has unit fr which yu are ging t slve fr n the left. 2. Plug the given value int the frmula and slve fr the missing value. Example: Cnvert 29.0 C t Fahrenheit. F = (1.8 x C) F = (1.8 x 29.0) F = (52.2) F = 84.2 AP in Density Density (d) is the rati f the mass (m) f a substance t the vlume (v) ccupied by the substance. Pure water is used as the standard in measuring density. The density f pure water is 1.0 g/ml. If a substance has a density less than water, it will flat; if a substance has a density greater than water, it will sink. Mass is expressed in grams (g). Vlume is expressed in either milliliters (ml) r cubic centimeters (cc r cm 3 ). Thus, density can be expressed as g/ml r g/cm 3. T slve a density prblem: 1. List yur variables; d, m & v. 2. Recrd the given values frm the prblem fr each variable. 3. Write yur frmula. T make it easier t crss multiply, write yur frmula as: 4. Fill in yur given data. Call the missing value x. 5. Crss multiply and slve fr the missing variable. 6. Write yur answer in significant figures and use scientific ntatin.

5 7. Write the prper unit after the number. Example: A piece f wd has a vlume f 3350 cm 3. If the density f the wd is g/ml, what is its mass? Steps 1 & 2 Step 3 Step 4 Step 5 Steps 6 & 7 d = g/ml = X. v = 3350 cm X = x 10 3 grams m = x Percent Errr The accuracy f yur measurements can be checked by calculating the percent errr. In a percent errr calculatin yu will cmpare yur experimental value t the accepted scientific value (referred t as the theretical value). Since yu are taking the abslute value f the subtractin, yur percent errr will always be a psitive number. Rund all percent errr calculatins t the tenths place. theretical yield - experimental yield %Errr = x 100 theretical yield Classificatin f Matter Chemistry The study f matter Matter anything that has mass and takes up space Matter exists in states Slid rigid, fixed shape and vlume Liquid definite vlume, takes the shape f the cntainer Gas n fixed vlume r shape, very cmpressible Mst matter exists as mixtures Example: wd, wine Hmgeneus mixtures Visibly indistinguishable parts Called slutins Example: air, brass, salt water Hetergeneus mixtures Visibly distinguishable parts Example: sand in water, il & water Can be separated int pure substances thrugh physical changes Physical changes d nt change the chemical cmpsitin f the matter Ways t separate mixtures Distillatin separatin by biling pint Filtratin separatin methd used with a slid & liquid mixture where a barrier blcks slid particles frm passing thrugh Chrmatgraphy a series f methds that emply a system with tw phases(states f matter) Mbile phase (liquid r gas) Statinary phase (slid) Types f Chrmatgraphy Paper Chrmatgraphy Gas Chrmatgraphy Pure substances Matter made up f nly ne type f element r cmpund Cmpund substance with cnstant cmpsitin that can be brken dwn int elements by chemical means Elements a substance that cannt be decmpsed int simpler substances by chemical r physical means Atms the mst basic unit f matter Prtn psitively charged particle Neutrn neutral particle

6 Electrn negatively charged particle