Chem RG Chapter Packet 7 Mole & Chemical Composition. Assign Section # Name Ch 07 Test Review (turn in separately for graded points

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1 Name Period. Chem RG Chapter Packet 7 Mole & Chemical Composition Assign Section # Name Assignment Sheet printed 2. Notes Notes Notes Chapter 7 WS # Chapter 7 WS # Chapter 7 WS #3 Ch 07 Test Review (turn in separately for graded points (Total Points = 7 x 10 = 70) Notes: 1. Your lab report is turned in by itself and receives a separate grade. 2. Your test reviews are graded separately. 3. Website: EVIDENCE (after you take notes.) You should have at least 4 types of evidence for each set of notes. 1. Number new concepts 1,2,3 /A,B,C 2. Delete/Cross out unimportant information Unimportant 3. Circle vocab/key terms Key Terms 4. Identify points of confusion? 5. Underline/Highlight main Ideas Main Ideas 7. Fill in gaps of information. Reword or paraphrase. ^ 6. Identify information to be used on a test, essay 8. Create visuals/symbols of important information * Visuals/symbols

2 Chapter 7 The Mole and Chemical Composition Avogadro s Number & Molar Conversions Identify the mole as the unit to count atoms, ions or molecules. Use Avogadro s number to convert between moles and atoms, ions or molecules. Solve conversions between mass, moles and particles using Avogadro s number and molar mass. Can measure matter 3 ways :, or, or We measure mass in, volume in, pieces in Avogadro s number (N A ) - 1 mol = items What about compounds? In 1 mole of H 2 O molecules there are moles of H atoms and mole of O atoms Mass of one mole of CH 4? 1 mole of C = g; 4 moles of H x 1.01 g = 4.04g 1 mole CH 4 = = g = mass A mole of anything has particles Molar Conversions Remember gmma (gramma) grams moles molec/atoms g mol molec or atoms going to goes on top going from goes on bottom Always show the units Data x bar = bar Data x = Bar = Bar Key AN atoms/molec/ions 1 moles PT_ g

3 Learning Check Show your work here: Number of atoms in mole of Al 2Number of moles of S in 1.8 x S atoms How many molecules are in 2.50 moles of C 12 H 22 O 11? How many molecules of CO 2 are the in 4.56 moles of CO 2? Ans x molecules CO 2 How many atoms of carbon are there in 1.23 moles of C 6 H 12 O 6? Ans x atoms How many moles are 7.78 x formula units of MgCl 2? Ans moles magnesium chloride Example - mass & particles (Show your work below) How many atoms of lithium in 1.00 g of Li? We can t get directly from grams to atoms. This is a problem. Convert g to mol then mol to atoms. Ans x atoms of lithium How many atoms of magnesium in g of Mg? Ans x atoms of Mg How much would 3.45 x atoms of U mass? Ans g of Uranium

4 7.2 Relative Atomic Mass & Chemical Formulas Use the periodic table or isotope data to find the average atomic mass Infer information about a compound from its chemical formula. Determine the molar mass of a compound from its formula. Atomic Mass Average atomic mass - weighted average of the atomic masses of the isotopes of the element. Average = % as decimal x mass + % as decimal x mass + % as decimal x mass + Example of an Average Atomic Mass Cl-35 is about 75.5 % and Cl-37 about 24.5% of natural chlorine. 35 x 75.5 = Weighted average = = x 24.5 = Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of amu & the rest has a mass of amu... Ans. & steps ( ) + ( ) = amu Atomic Mass - You try it show your work below Magnesium has 3 isotopes. 80% magnesium-24, 10% magnesium-25, & the rest is magnesium-26. What s average atomic mass. Answer = 24.3

5 Holt 7.3 Formulas & % Composition a. Determine empirical formula from % composition. b. Determine molecular formula from empirical formula and formula mass. c. Calculate % composition from a molecular formula. Percentage Composition Percentage by of each element in a compound % Composition Example Calculate the percent composition of a compound of 29.0 g of Ag and 4.30 g of S... What s the total mass? = g So, the % of Ag is (29.0 g Ag/33.30 g total)(100%) = 87.1% Ag. What is the % of S? 12.9% (must add up to 100%). Getting % Composition from the formula If we know the formula, then we assume we have 1 mole. From that we can then figure out the pieces and the whole as follows... Calculate the percent composition of C 2 H 4? Assume one mole. # moles of carbon in that one mole? How many grams of carbon is that? How many moles of hydrogen? How many grams of hydrogen is that? What is total grams of C 2 H 4? What is % comp. of carbon? Of hydrogen? Empirical Formula Smallest whole number ratio of atoms in a compound The molecular formula is the ratio of elements in a compound. CH 2 is an formula C 2 H 4 is a formula C 3 H 6 is a formula H 2 O is. Calculating Empirical Just find the lowest whole number ratio. C 6 H 12 O 6 is? CH 3 N is? Empirical Formula 1. Find mass (or %) of each element. 2. Find moles of each element. 3. Divide moles by the smallest # to find subscripts. 4. When necessary, multiply subscripts by 2, 3, or 4 to get whole # s.

6 Find the empirical formula for a sample of 25.9% N and 74.1% O. Show your work below Calculating Empirical It is not just the ratio of atoms, it is also the ratio of of atoms. In 1 of CO 2 there is 1 of carbon and moles of oxygen. In one of CO 2 there is 1 atom of C and 2 atoms of O. Calculating Empirical We can get the ratio from the percent composition. 1st, assume you have g. 2nd,the percentages become grams. 3rd, turn grams to moles (spider or bar = bar ). 4th, find lowest whole number ratio by dividing each subscript by the smallest. 5th, clear fractions by multiplying with the correct factor. Short cut way A compound is % P and % O. What is the empirical formula? P (43.64 g/30.97 g/mol) O (56.36g/16.00 g/mol) P 1.41 O 3.52 P 1.41/1.41 O 3.52/1.41 P 1 O 2.50 Multiply by 2 to clear the fraction. We get Clearing the Fractions If after dividing each ratio by the smallest you get a fraction and... The last two decimals are approximately.33,.67,.25,.50,.75 or.20, then multiply all the ratios as follows = 1/3 multiply by.67 = 2/3 multiply by.25 = 1/4 multiply by.50 = 1/2 multiply by.75 = 3/4 multiply by.20 = 1/5 multiply by Clearing the Fractions Example, get to X 4 Y 1.67 Z 2 Multiply each ratio by what? You get what? so now you have to multiply by what? to get Now you try it Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. What is its empirical formula?

7 Molecular Formula 1. Find the formula. 2. Find the empirical formula. 3. Divide the mass by the mass. 4. Multiply each by the answer from step 3. Molecular Formula Show your work below The empirical formula for ethylene is CH 2. Find the molecular formula if molar mass is 28.1 g/mol. Empirical to molecular Caffeine has a molar mass of 194 g. what is its molecular formula? Steps... Remember, we previously figured out that caffeine s empirical formula was C 4 H 5 N 2 O. So, it s empirical mass is about 97 g. 194/97 = 2, so there are two empirical formulae in one molecular formula. Multiply the empirical ratios by 2 to get Example A compound is known to be composed of % Cl, 24.27% C and 4.07% H. Its molar mass is known (from gas density) is known to be g. What is its molecular formula? Show your work below

8 Chapter 7 WS #1 Name: Ch. 7-1 pg. 228 pp#1-3 Moles Particles 1. How many ions in mol of Na + ions? Ans.: 1.13 x10 23 ions Na How many atoms in 1.45x10-17 mol of arsenic? Ans.: 8.73 x10 6 atoms As Ch. 7-1 pg How many moles do 5.66x10 25 lithium ions, Li + equal? Ans.: 94.0 mol Li + 4. How many moles in 3.161x10 21 molec. of CO 2? Ans.: mol CO 2 Ch. 7-1 pg. 231 pp#1-3 Mass Particles 5. What is the mass of 2.11x10 24 atoms of copper? Ans.: 223 g Cu 6. What is the mass of 3.01x10 23 formula units of NaCl? Ans.: 29.2 g NaCl Ch. 7-1 pg. 232 pp# Find the number of atoms in 237g Cu. Ans.: 2.25 x10 24 atoms Cu 8. Find the number of ions in 20.0g Ca 2+. Ans.: 3.00x10 23 ions Ca 2+

9 USE THSE TABLES TO HELP YOU COMPLETE THE CHAPTER 5.3 WORKSHEETS

10 5 3 1 Chapter 7 WS #2 Name : Ch. 7-2 pg. 236 pp#1-2: Average Atomic Mass 1. Find avg at mass Ga if 60.00% has mass amu & 40.00% a mass of amu. Ans.: = amu 2. Do O 2 if 99.76% is amu, 0.038% mass amu, & 0.20% mass of amu. Ans.: = amu Ch. 7.2 p. 253, 42. Find avg at mass Ag if 51.35% is amu and the rest is amu. Ans. = amu. 44 Find avg at mass Fe if 5.90% is amu, 91.72% is amu, 2.10% is amu and 0.280% is amu. Ans. = amu CH. 7-2 pg. 239 pp#1 Molar Mass Find the molar mass for each of the following compounds: CsI g/mol C 12 H 22 O 11 g/mol I 2 g/mol Mg 3 (PO 4 ) 2 g/mol CH. 7-2 pg. 239 pp#2 Write the formula and then find the molar mass for the following cerium hexaboride CeB 6, g/mol iron (III) hydroxide, g/mol tetraphosphorus decoxide, aluminum sulfate, g/mol tin(ii) chloride, g/mol g/mol Ch. 7-2 SR pg. 240 pp#11 Determine the formula, the molar mass, and the number of moles in 2.11g of each of the following compounds. a. strontium sulfide Ans.: SrS, g/mol, mol SrS (try to get 1.76x10-2 ) b. phosphorus trifluoride Ans.:, g/mol, mol (2.40 x10-2 ) c. zinc acetate Ans.:, g/mol, mol (1.15x10-2 )

11 Chapter 7 WS #3 Name : Ch. 7-3 p. 253 Empirical formulas and percent composition 49. A silver compound is 63.50% Ag, 8.25% N and 28.25% O. Find its empirical formula (ans. AgNO 3 ) 50. A phosphorous oxide is 56.24% P and the rest is oxygen. Find the empirical formula (ans. P 2 O 3 ) 51. The empirical formula of altretamine is C 3 H 6 N 2. Molar mass is 210 g/mol. What is its molecular formula? Ch. 7-3 pg. 248 pp #4: Calculate the percent composition of each of the following: SrBr2 Ans.: 35.41% Sr, 64.59% Br CaSO4 Ans.: 29.44% Ca, 23.55% S, 47.0% O Mg(CN)2 Ans.: 31.83% Mg, 31.46% C, 36.70% N Ch. 7-3 pg. 248 pp#2 Calculate the % of both elements in sulfur dioxide. Ans.: 50.05% S, 49.95% O Ch. 7-3 pg. 248 pp#3 Calc. the % comp. of ammonium nitrate. Ans.: 35.00% N, 5.05% H, 59.96% O

12 Chapter 7: Review Graded Assign. Name: Period: 1 mol of any substance equals particles. The base unit for 1 mole is / Which will have the greater number of ions, 1 mol of Cu 3 (PO 4 ) 2 or 1 mol of Si 3 N 4? As the atomic mass of elements increases going down the periodic table, what happens to the number of atoms in 1 mole of the element? Use your periodic table to find the molar mass of Au: Te: V: Be: What element has a molar mass of g/mol?, g/mol, and g/mol The molar mass of an element = the mass of mole(s) The molar mass of an element is to its atomic weight In the chemical formula C 2 H 6, the subscripts indicates there are atoms of C and atoms of H in the compound Determine the molar mass for the following: Al 2 S 3 Mg 3 (PO 4 ) 2 Potassium Dichromate Calculate the following (Use bar = bar): 1 atom of Ca = grams 5.67 grams of Ga = moles 23 moles of C 2 H 6 = grams 453 grams of Pb(NO 3 ) 2 = molec. 234 atoms of As = moles moles of C 2 H 4 O 2 = molec. The percent of O in Fe(OH) 3 = The percent composition of K 2 Cr 2 O 7 =