WRITING FORMULAS NOTES

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UNIT 7 – CHEMICAL FORMULASWRITING FORMULAS NOTESEXAMPLES:1. carbon tetrachloride2. calcium oxide3. iron (III) bromide4. lead (II) nitrate5. aluminum hydroxide6. ammonium chromateWRITING FORMULAS WORKSHEET1. sodium nitrate2. aluminum sulfide3. iron (III) sulfate4. strontium hydroxide5. copper (I) phosphate6. cesium carbonate7. nickel (II) oxide8. silicon dioxide9. potassium bromide10. zinc chlorate11. barium acetate12. iron (II) phosphide13. magnesium chromate14. calcium nitrideNotes/Worksheets1

UNIT 7 – CHEMICAL FORMULAS15. silver sulfite16. sodium hydrogen carbonate17. copper (II) chloride18. ammonium dichromate19. rubidium bromate20. lead (II) permanganate21. beryllium chlorite22. cadmium iodide23. phosphorus trichloride24. lithium nitrite25. tin (IV) sulfite26. chromium (III) iodate27. manganese (II) perchlorate28. cobalt (II) hypochlorite29. zinc selenide30. magnesium cyanideNAMING COMPOUNDS NOTESEXAMPLES:1. P2O52. MgSO43. CuCl24. (NH4)3PO45. FeCO36. K2ONotes/Worksheets2

UNIT 7 – CHEMICAL FORMULASPOLYATOMIC IONS (LISTED moniumNH4 1hydrogen carbonate(or bicarbonate)HCO3-1perchloratebromateBrO3-1hydrogen eCN-1NAMING COMPOUNDS WORKSHEET1. NaCl2. Ba3(PO4)23. Al(MnO4)34. Ni(ClO)25. CuSO46. ZnCr2O77. MgSe8. LiBrO39. (NH4)3PO410. AgHCO311. Pb(NO3)212. Fe(C2H3O2)313. K2CO314. Co(ClO4)215. Be(NO2)216. Cu2CrO417. SrSO318. Al(OH)319. RbNO220. N2O21. FeBr222. AgClO223. N2O324. CaI225. Cu(ClO3)226. SO2OXIDATION NUMBERS NOTES Any uncombined element (element not in a compound) has an oxidation number of 0.Fluorine always has an oxidation number of -1 in a compound.Oxygen has an oxidation number of -2 in all compounds except when it is part of a binary compound witha halogen.Hydrogen has an oxidation number of 1 except when it is in a binary compound with a metal.The algebraic sum of the oxidation numbers in a compound is zero.The algebraic sum of the oxidation numbers in a polyatomic ion is the charge on the ion.To find the oxidation number of another element in a compound, use this general formula:Notes/Worksheets3

UNIT 7 – CHEMICAL FORMULASΣ (# of each element in cmpd . oxidation # of each element) 0Let x unknown oxidation numberEXAMPLE: Find the oxidation number of carbon (C) in Na2CO3.x carbon’s oxidation numberNa 1O -2(2 . 1) (1 . x) (3 . -2) 0NaCO2 x–6 0 x–4 0 x 4 is carbon’s oxid. # in Na2CO3Find the oxidation number of the underlined element in each compound.1. KMnO42. MnO23. LiNO34. Ca(NO2)25. NaClO6. Ba(ClO4)2OXIDATION NUMBERS 4S:16.Na:Na:17.NH3N:PERCENT COMPOSITION NOTESPERCENT COMPOSITION: the percentage by mass of each element in a compoundFORMULA FOR % COMPOSITION:% composition mass of element in compoundmolar mass of compoundx 100EXAMPLE 1:Find the % composition of copper (I) sulfide, Cu2S. Finding % composition means that you have to find the % of each element in the cmpd.molar mass of Cu2S:% Cu x 100 % S Cu: x S: x MM of Cu2S Notes/Worksheetsx 100 4

UNIT 7 – CHEMICAL FORMULASEXAMPLE 2:Find the percent of oxygen in calcium phosphate, Ca 3(PO4)2.molar mass of Ca3(PO4)2:% O x 100 Ca: x P: x O: x MM of Ca3(PO4)2 PERCENT COMPOSITION WORKSHEETDetermine the percent composition of each of the following compounds.1. KMnO4K Mn O 2. HClH 3. Mg(NO3)2Mg Cl N O 4. (NH4)3PO4N H P 5. Al2(SO4)3Al S O O Solve the following problems.6. How many grams of oxygen can be produced from the decomposition of 75.0 g of KClO3?7. How much iron can be recovered from 25.0 g of Fe2O3?8. How much silver can be recovered from 125 g of Ag2S?EMPIRICAL FORMULAS NOTES opposite of percent composition use % to find formula for compoundEMPIRICAL FORMULA: simplest formula; subscript numbers are reduced to lowest termsMOLECULAR FORMULA: subscripts are multiples of empirical formula subscriptsMOLECULAR FORMULAEMPIRICAL ---------------TO SOLVE EMPIRICAL FORMULA PROBLEMS:A sample of a compound is found to contain 36.0 % calcium and 64.0 % chlorine. Calculate the empiricalformula.Step 1: Rewrite % as grams.36.0 g Ca64.0 g ClStep 2: Find moles of each element.Ca: 36.0 g Ca 1 mole Ca 0.898 moles Ca 40.1 g CaCl: 64.0 g Cl 1 mole Cl 1.80 moles Cl 35.5 g ClStep 3: Find mole ratio. (Divide by smallest number of moles.)Notes/Worksheets5

UNIT 7 – CHEMICAL FORMULASCa: 0.898 moles 1Cl: 1.80 moles 20.8980.898* These whole numbers are subscripts in formula.*Step 4: Write the formula.Ca1Cl2 CaCl2Example 2: A sample of a compound contains 66.0 % calcium and 34.0 % phosphorus. What is the empiricalformula?Ca: 66.0 g Ca 1 mole Ca 1.65 moles CaP: 34.0 g P 1 mole P 1.10 moles P 40.1 g Ca 31.0 g PCa: 1.65 1.5P: 1.10 11.101.10Q: So, what happens now? I can't write Ca1.5P1. And 1.5 is not close enough to round to 2.A: The easiest way to get 1.5 to a whole # is to multiply by 2. Remember to multiply both #'s by 2 to get youranswer.Ca: 1.5 x 2 3P: 1 x 2 2So, formula is Ca3P2PRACTICE - A compound contains 43.4 % sodium, 11.3 % carbon, and 45.3 % oxygen. What is the empiricalformula for this compound?EMPIRICAL FORMULAS WORKSHEETFind the empirical formula for each of the following substances. The percent composition is given.1. 88.8 % copper & 11.2 % oxygen2. 10.04 % carbon, 0.84 % hydrogen, & 89.12 % chlorine3. 42.50 % chromium & 57.50 % chlorine4. 38.67 % potassium, 13.85 % nitrogen, & 47.48 % oxygenPart 2 – Determine the empirical formula of the following compounds using the given data.5. Find the empirical formula for sodium sulfite. Sodium sulfite contains 36.5 % sodium, 25.4 % sulfur, and38.1 % oxygen.6. What is the empirical formula for a compound which contains 53.73 % iron and 46.27 % sulfur?7. What is the empirical formula of a compound if the percentage composition is: aluminum 15.77 %,sulfur 28.11 %, and oxygen 56.12 %?8. If 8.87 grams of phosphorus react with 11.43 grams of oxygen, what is the empirical formula of thecompound formed?9. Phosgene, a poisonous gas used during World War I, contains 12.1 % C, 16.2 % O, and 71.7% Cl. What isthe empirical formula for phosgene?Notes/Worksheets6

UNIT 7 – CHEMICAL FORMULASMOLECULAR FORMULAS NOTESTo find the molecular formula, one more piece of information must be given - the molar mass (also calledmolecular mass or formula mass).EX. 1- An organic compound is found to contain 92.25% carbon and 7.75% hydrogen. If the molecular mass is78, what is the molecular formula?STEP 1: Find the empirical formula.C: 92.25 g C 1 mole C 7.69 moles C 12 g C7.69 moles C 17.697.75 moles H 17.69H:So.7.75 g H 1 mole H 7.75 moles H 1gHempirical formula is CH.STEP 2: Find molar mass of the empirical formula.C: 1 x 12.0 12.0H: 1 x 1.0 1.0 MM 13.0STEP 3: Find "multiple" number.MM of molecular formula multiple #MM of empirical formula78 613STEP 4: Write molecular formula.Multiply "multiple" # by all subscripts in the empirical formula.So.molecular formula is C6H6.PRACTICE - An oxide of nitrogen contains 30.4 % nitrogen and 69.6 % oxygen. If the molar mass of thiscompound is 92 g/mole, what is the molecular formula?MOLECULAR FORMULAS WORKSHEET1. A compound is found to be 40.0 % carbon, 6.7 % hydrogen, and 53.5 % oxygen. Its molecular mass is 60.grams per mole. What is its molecular formula?2. A compound is 64.9 % carbon, 13.5 % hydrogen, and 21.6 % oxygen. Its molecular mass is 74 grams permole. What is its molecular formula?3. A compound is 54.5 % carbon, 9.1 % hydrogen, and 36.4 % oxygen. Its molecular mass is 88 grams permole. What is its molecular formula?4. If the molecular mass of an oxide of nitrogen is 108. What is the molecular formula of a compound thatcontains 4.02 grams of nitrogen and 11.48 grams of oxygen?5. There are two different oxides of phosphorus. Both oxides can exist in different forms depending on thetemperature and pressure. Calculate the empirical and molecular formulas from the following data:(A) P: 56.4 %, O: 43.7 %, molecular mass 220(B) P: 43.6 %, O: 56.4 %, molecular mass 2846. Nicotine is a compound that contains 74.0 % carbon, 8.7 % hydrogen, and 17.3 % nitrogen. If the molecularmass is 162, what is the molecular formula?Notes/Worksheets7

UNIT 7 – CHEMICAL FORMULASHYDRATES NOTESHydrates are compounds with a certain number of water molecules attached to them. Their formulas look thesame except that there is a “. # H2O” after it.Example: MgSO4 . 7 H2OWhen determining the empirical formula for a hydrate, generally you will be determining the number in front ofthe H2O in the formula. In order to determine this number, you will need to find the “mole ratio” between themoles of the compound and moles of water.EXAMPLE:A hydrated sample of sodium carbonate (Na2CO3 . # H2O) has a mass of 29.00 grams. The sample is thenheated and all water is removed. The anhydrous salt that remains has a mass of 10.75 grams. What is theempirical formula for the hydrated sodium carbonate?STEP 1: Find moles of sodium carbonate.10.75 g Na2CO3 1 mole Na2CO3 0.1014 moles Na2CO3 106 g Na2CO3Na: 2 x 23.0 46.0C: 1 x 12.0 12.0O: 3 x 16.0 48.0 106STEP 2: Find moles of water.First, find grams of water hydrated sample 29.00 gramsanhydrous sample 10.75 gramsmass of water 18.25 grams18.25 g H2O 1 mole H2O 1.014 moles H2O 18 g H2OSTEP 4: Find mole ratio of water to sodium carbonate.1.014 moles 10So empirical formula for this hydrate is Na2CO3 . 10 H2O0.1014 molesCOMPOSITION OF HYDRATES WORKSHEET1. A 2.5 gram sample of a hydrate of Ca(NO3)2 was heated, and only 1.7 grams of the anhydrous salt remained.What percentage of water was in the hydrate?2. Strontium hydroxide is isolated as a hydrate, which means that a certain number of water molecules areincluded in the solid. When 6.85 grams of the hydrate are dried in an oven, 3.13 grams of anhydrous Sr(OH)2are formed. What is the empirical formula for this hydrate?3. A 5.0 gram sample of Cu(NO3) 2 . n H2O is heated, and 3.9 gram sample of the anhydrous salt remains. Whatis the value of n?*4. A hydrated sodium salt containing 39.7 % water is analyzed as follows: Na 16.9 %, C 17.7 %, H 6.67 %,and O 58.8 %. What is the empirical formula of this salt?Notes/Worksheets8

UNIT 7 – CHEMICAL FORMULASANSWERS TO SELECT WORKSHEETS:PERCENT COMPOSITION WORKSHEET1. K 24.7%Mn 34.7%2. H 2.74%Cl 97.3%3. Mg 16.4%N 18.9%O 64.7%4. N 28.2%H 8.05%P 20.8%5. Al 15.8%S 28.1%O 56.1%6. 29.4 g7. 17.5 g8. 109 gEMPIRICAL FORMULAS WORKSHEET1. Cu2O2. CHCl33. CrCl27. Al2S3O128. P2O5O 40.5%O 43.0%4. KNO35. Na2SO36. Fe2S34. N2O56. C5H7N5. (A) Emp P2O3, Mol P4O69. COCl2MOLECULAR FORMULAS WORKSHEET1. C2H4O22. C4H10O3. C4H8O25. (B) Emp P2O5, Mol P4O10COMPOSITION OF HYDRATES WORKSHEET1. 32%2. Sr(OH)2 . 8 H2ONotes/Worksheets3. n 3*4. NaC2H3O2 . 3 H2O9

PERCENT COMPOSITION NOTES PERCENT COMPOSITION: the percentage by mass of each element in a compound FORMULA FOR % COMPOSITION: % composition mass of element in compound x 100 molar mass of compound EXAMPLE 1: Find the % composition of copper (I) sulfide, Cu 2 S. Finding % composition means that you have to find the % of each element

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