O. (b) Given a molar mass for lactic acid of 90 g/mol, and a molar mass for CH 2

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1 Simplifyin (dividin each value by the lwest), we btain a rati f 1000 : 199 : 1000, r alst exactly 1 : 2 : 1, makin the empirical frmula fr the lactic acid CH 2 O (b) Given a lar mass fr lactic acid f 90 /l, and a lar mass fr CH 2 O (the empirical frmula) f 3003 /l, the lecular frmula must be triple the empirical rati, r C 3 H 6 O 3 Applyin Inquiry Skills 7 (a) Prcedure 1 Use a centiram balance t measure the masses f a penny and f a quarter, t Use a deciram balance t measure the ttal masses f the pennies and f the quarters, t 01 3 Divide the ttal mass f the pennies by the mass f ne penny t calculate the number f pennies 4 Divide the ttal mass f the quarters by the mass f ne quarter t calculate the number f quarters Express the numbers f the tw types f cins as a rati (b) A parallel prcedure a scientist miht use: 1 Use a reference t find the lar masses f each kind f atm in the cmpund, t 001 /l 2 Use a cmbustin analyzer t measure the ttal masses f each kind f atm in the cmpund, t Divide the ttal mass f each type f atm by the lar mass, t calculate the aunt f atms 4 Express the numbers f the different types f atms as a simplest interal rati CHAPTER 4 REVIEW (Pae 199) Understandin Cncepts 1 Every cmpund has a specific prprtin f cnstituent substances This led scientists t the cncept f specific kinds f atms fr each element, and t cmparin their cmbinin masses t btain a relative scale f masses f atms 2 The relative atmic mass wuld be (exactly) 24 u 3 A hydren atm wuld be 18/12 f its current mass, r u, r 12 u 4 Relative atmic masses cannt be assined crrectly unless the cmbinin rati is crrectly knwn; s the crrect lecular frmula is necessary Elements cnsist f atms with identical numbers f prtns and electrns The nuclei f atms f elements, hwever, may vary in numbers f neutrns, which has neliible effect n chemical prperties, but des chane the atm s mass sinificantly Fr nearly every element there are several f these istpes, and the averae mass f atms f such an element is a value that depends n the mass f these istpes and als their prprtin in nature The classic example is chlrine, where ruhly 3/4 f any sample will cnsist f chlrine-3 atms (lar mass 300 /l), and ruhly 1/4 f the sample will be chlrine-37 atms (lar mass 3700 /l) The lar mass f chlrine, then, is the averae lar mass f all the chlrine atms in a sample, which wrks ut t 34 /l 6 Fr silicn, with sinificant aunts f three istpes, and if we assume the lar mass f istpes is the same as the mass number, t tw decimals (which is apprximately valid, althuh the last diit is uncertain ) M = [( ) + ( ) + ( )] /l M = 2811 /l (The actual value is 2809 /l) 7 (a) 12 u exactly (by definitin) (b) 12 exactly (by definitin) (c) Avadr s cnstant is (by definitin) the number f entities in exactly 12 f pure carbn-12 This number is used t define the le, which is the (numerical) aunt f any substance that is this number f entities (atms, ins, lecules, r frmula units) (d) The symbl M represents the quantity, lar mass, in /l units 8 (a) Frmula: CaCO 3(s) M = [(4008) + (1201) + (1600 3)] M = /l Cpyriht 2002 Nelsn Thmsn Learnin Chapter 4 Quantities ihemical Frmulas 10

2 (b) Frmula: N 2 O 4() M = [(1401 2) + (1600 4)] M = 9202 /l (c) Frmula: Na 2 CO 3 10H 2 O (s) M = [(2299 2) + (1201) + (1600 3) + ( )] M = /l Nte: The last slutin abve assumes that students will have merized the lar mass f water an extremely useful quantity t cmmit t mery Fr future study, merizatin f the lar mass f carbn dixide, 4401 /l, will be alst as useful, because it is a prduct in s many reactins 9 (a) m NaCl = 1000 k M NaCl = 844 /l n NaCl = 1000 k 8 44 n NaCl = kl = k f table salt is 171 (b) m CO2 = 1000 k M CO2 = 4401 /l O2 = 1000 k O2 = kl = 2272 l 1000 k f dry ice is 2272 l (c) m H2 O = 1000 k M H2 O = 1802 /l 2 O = 1000 k O = 0049 kl = 49 l 1000 k f water is 49 l 10 (a) 2 = 10 l M O2 = 3200 /l 2 = 10 l l m 2 = l f liquid xyen is 480 (b) = 10 ml M H = 2009 /l m H = 10 ml l m H = 301 m (r 0301 ) 10 ml f liquid mercury is 301 m (c) n Br2 = 10 kl M Br2 = 1980 /l m Br2 = 10 kl l 106 Unit 2 Quantities ihemical Reactins Cpyriht 2002 Nelsn Thmsn Learnin

3 m Br2 = 240 k 10 kl f liquid brmine is 240 k 11(a) C2 H 3 O = 042 l 2 N HC2 H 3 O = 042 l l N HC2 H 3 O = l f acetic acid is 2 10 lecules (b) O = l N CO = l ml N CO = l f carbn nxide is lecules (c) m CCl4 M CCl4 r = 100 = 1381 /l Cl4 = Cl4 = 060 l N CCl4 = 060 l l N CCl4 = l N CCl4 = ml N CCl4 = f carbn tetrachlride is lecules (d) m H2 S = 100 = 3408 /l M H2 S r 2 S = S = 293 l N H2 S = 293 l ml N H2 S = l m N H2 S = ml N H2 S = f hydren sulfide is lecules 0 Cpyriht 2002 Nelsn Thmsn Learnin Chapter 4 Quantities ihemical Frmulas 107

4 12 (a) M C14 H 18 N 2 O = [( ) + (101 18) + (1401 2) + (1600 )] /l M C14 H 18 N 2 O = /l The lar mass f Aspartame is /l (b) m C14 H 18 N 2 O = 3 m M C14 H 18 N 2 O = /l 14 H 18 N 2 O = 3 m H 18 N 2 O = 012 ml 3 m f Aspartame is 012 ml (c) 14 H 18 N 2 O = 012 ml = l N C14 H 18 N 2 O = l ml N C14 H 18 N 2 O = N H = N H = m f Aspartame cntains hydren atms 13 (a) Assume ne le f cmpund, fr cnvenience m Na m l l 2299 m NaN3(s) 602 % Na % Na + 336% ` The percentae, by mass, f sdium ins in NaN 3(s) is 336% (b) Assume ne le f cmpund, fr cnvenience m Al m l 2 l 396 m Al2 O (s) % Al % % Al % The percentae, by mass, f aluminum ins in Al 2 O 3(s) is 292% (c) Assume ne le f cmpund, fr cnvenience m N 1401 m l 1 l 1401 m C8 H 11 NO (s) 1401 % N 100% % N 914% The percentae, by mass, f nitren atms i 8 H 11 NO 2(aq) is 914% 14 (a) An empirical frmula ives the simplest interal rati f the cnstituent atms f a cmpund, while a lecular frmula als ives the crrect actual number f atms in ne lecule 108 Unit 2 Quantities ihemical Reactins Cpyriht 2002 Nelsn Thmsn Learnin

5 (b) An empirical frmula is just a prprtin f atms, and cannt ive a crrect number f atms per lecule withut evidence f the mass f the lecule it is like sayin Tm is twice as ld as Harry, when, withut the ae f ne, the ther s ae cannt be determined 1 (a) Assume a sample, fr percentae cnversin cnvenience m C = 49 M C = 1201 /l m H = 1 M H = 101 /l m N = 289 M N = 1401 /l = (by subtractin) = 16 M O = 1600 /l = = 412 l = = 10 l n N = n N = 206 l = = 103 l The le rati, C : H : N : O, is 412 : 10 : 206 : 103 Simplifyin (dividin each value by the lwest), we btain a rati f 400 : 49 : 200 : 100, r alst exactly 4 : : 2 : 1, makin the empirical frmula fr the caffeine C 4 H N 2 O (b) Since the lar mass f the caffeine is 19 /l, abut duble the value f 9711/l that we et fr C 4 H N 2 O, the lecular frmula must be C 8 H 10 N 4 O 2 16 (a) m C = 3161 M C = 1201 /l m H = 0266 M H = 101 /l = 102 M O = 1600 /l = = l = = 0263 l = = 0067 l The le rati, C : H : O, is : 0263 : 0067 Simplifyin (dividin each value by the lwest), we btain a rati f 400 : 400 : 100, makin the empirical frmula fr the ester C 4 H 4 O (b) Since the lar mass f the ester is 136 /l, abut duble the value f 6808 /l that we et fr C 4 H 4 O, the lecular frmula must be C 8 H 8 O 2 17 Assume a sample, fr percentae cnversin cnvenience m C = 632 M C = 1201 /l Cpyriht 2002 Nelsn Thmsn Learnin Chapter 4 Quantities ihemical Frmulas 109

6 m H = 26 M H = 101 /l = 316 M O = 1600 /l = = 26 l = = 2 = = 198 l Simplifyin (dividin each value by the lwest), we btain a rati f 266 : 263 : 100, which is nt an interal rati Triplin this rati ives 797 : 789 : 300, r alst exactly 8 : 8 : 3, makin the empirical frmula fr the vanillin C 8 H 8 O 3 18 m Na u u m P 3097 u u 1600 u 4 m Na3 PO 4(aq) 6400 u u % Na % % Na % 3097 % P 100% % P 1889% 6400 % O 100% % O 3904% The percentae cmpsitin f Na 3 PO 4(aq) is 4207% sdium ins, 1889% phsphrus atms, and 3904% xyen atms, by mass 19 m Na u u m As 3097 u u 1600 u u m Na3 AsO 4(aq) u % Na % % Na % 7492 % As 100% % As 3604% 110 Unit 2 Quantities ihemical Reactins Cpyriht 2002 Nelsn Thmsn Learnin

7 6400 % O 100% % O 3079% The percentae cmpsitin f Na 3 AsO 4(aq) is 3318% sdium ins, 3604% arsenic atms, and 3079% xyen atms, by mass Applyin Inquiry Skills 20 (a) Analysis m Zn = ( ) = 0641 M Zn = 638 /l m cmpund = ( ) = 1330 m Cl = ( ) = 0689 M Cl = 34 /l n Zn n Zn l n Cl n Cl l Simplifyin (dividin each value by the lwest), we btain a rati f 100 : 198, r alst exactly 1 : 2, makin the empirical frmula fr the cmpund ZnCl 2 (b) Evaluatin The desin is simple and straihtfrward, and is likely t prvide reliable evidence, frm which the answer can be easily calculated 21 (a) If the mass f the nail is measured befre and after reactin, the mass difference will be cpper, and can be used t determine the number f atms (b) Besides the evidence frm (a), the lar mass f cpper and the value f Avadr s cnstant will be needed (c) If the mass f cpper(ii) sulfate is initially measured, and the reactin is cntinued until all f the cpper(ii) ins react, then masses can be btained t allw the determinatin f percentae by mass f cpper in the cmpund 22 (a) The crucible and lid are preheated t drive ff any cmbustible r vaprizable material, s the mass f the crucible will nt chane later when heated (b) Handlin ht equipment means wearin prper clthin, usin heat-resistant lves r tns, and bein careful nt t set ht materials dwn n unprtected bench tps Subtractin the mass f the element frm the mass f the xide frmed shuld ive the mass f xyen reacted Makin Cnnectins 24 Carbn nxide and carbn dixide are frmed frm the same elements; but ne f these cmpunds is hihly txic t humans, and the ther is nt 2 Mles are used fr medical materials because the reactin quantities are the principal cncern, and reactin equatins are dependent n numerical aunts Fr fds, masses are cmn because that is the easy and cnvenient way t measure hw much fd there is in a packae r cntainer 26 Typical answers miht include (a) Fd testin Water treatment Cement manufacturin Plastics manufacturin Prescriptin lens rindin (b) Natural as treatment labs Water quality test labs Steel cmpsitin analysis Lubricant cntaminatin analysis Air quality test facilities Cpyriht 2002 Nelsn Thmsn Learnin Chapter 4 Quantities ihemical Frmulas 111

8 Explrin 27 Typical infrmatin Salicylate cmpunds were knwn t be painkillers by the th century BC In an attempt t find a relief frm arthritic pain fr his father, Felix Hffmann first synthesized acetylsalicylic acid in 1893 The cmpund was named Aspirin and was bein marketed by the Bayer crpratin in 1897 By 1899 Heinrich Dreser was rutinely usin this dru t treat arthritis GO TO wwwsciencenelsncm, Chemistry 11, Teacher Centre 28 Typical infrmatin The st recent value fr Avadr s cnstant is btained by precise measurin f atmic (inic) sizes in metallic crystals, yieldin a value with 9 sinificant diits entities GO TO wwwsciencenelsncm, Chemistry 11, Teacher Centre 29 Typical infrmatin Cheese has been made fr at least 00 years The prtein casein, in milk, clumps int curds upn the additin f rennin Cttae cheese is sld in this initial stae These curds may be heated, pressed, r strained t reve liquid whey Cheddarin is the prcess f cmpressin curds t reve isture Many cheeses are als ripened by treatment with bacteria and/r ulds, which may be added int the cheese (internal treatment, like Rquefrt) r rubbed n the surface (surface treatment, like Brie r Camembert) The texture and flavur f cheeses depends primarily n their isture cntent and the aents used t ripen them The hles in Swiss cheese are frmed durin ripenin by ases prduced by the bacteria used t create the characteristic flavur GO TO wwwsciencenelsncm, Chemistry 11, Teacher Centre 112 Unit 2 Quantities ihemical Reactins Cpyriht 2002 Nelsn Thmsn Learnin