# We can see that the molar mass of ch times 6 gives us

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We can see that the molar mass of CH times 6 gives us the molar mass of benzene. Example 14 A compound with an empirical formula of CH2is found to have a molecular weight of 42 g/mol. What is the true formula (molecular formula)? Empirical formula molar mass (CH2) = 12.01 + (1.008 x2) = 14.026 g x = 42 g = approx. 3 14.026 g Therefore 3 CH2units make up the true formula (molecular formula) which is C3H6.
In-Class Practice 7 (ICP7) A compound is 24.27% carbon, 4.07 % hydrogen and 71.65 % chlorine. The molar mass of the compound is 98.96 g/mole. Determine the empirical and molecular formulas for this compound.
Mole Worksheet Calculations with Moles, Mass and Molecules Answers are provided on the right. 1. How many moles of atoms are contained in the following? ANSWERS: a.22.5 grams of Zn 0.344 mol Zn 22.5 g Zn x 1 mole Zn = 0.344 moles of Zn 65.37 g Zn b.0.688 grams of Mg 0.0283 mol Mg c.4.5 x 1022atoms of Cu 0.075 mol Cu d.382 grams Co 6.48 mol Co e.0.055 grams Sn 0.00046 mol Sn 2. Calculate the number of grams in each of the following? a.4.25 x 10-4moles of H2SO4 0.0417 g 4.25 x 10-4mol H2SO4x 98.08 g H2SO4= 0.0417 g H2SO41 mol H2SO4 b.4.5 x 1022molecules CCl4 11 g c.0.00255 moles of Ti 0.122 g d.1.5 x 1016atoms of S 8.0 x 10-7g 3. How many molecules are contained in each of the following? a.1.26 moles of O2 7.59 x 10231.26 mole O2 x 6.022 x 1023molec = 7.59 x 1023molec O21 mole O2 b.0.56 moles of C6H6 3.4 x 1023c.16.0 grams of CH4 6.00 x 1023d.1000. grams of HCl 1.652 x 10254. How many oxygen atomsare contained in each of the following? a.16.0 grams of O2 6.02 x 102316.0 g O2 x 1 mol O2x 6.022 x 1023molec O2x 2 atoms O = 6.02 x 102332.00 g O21 mol O21 molec O2 b. 0.622 moles of MgO 3.75 x 1023c.6.00 x 1022molecules of C6H12O6 3.60 x 1023d.225 grams of MgCO3 4.82 x 10245. How many molecules would be in a sample of 250 grams of aluminum bromide, AlBr3? 5.6 x 1023molec 6. A sample of aluminum oxide, Al2O3, containing 4.5 x 1024molecules would have what mass? 760 g
Practice Assignment: Moles On a separate sheet of paper, show the setup and answer for each problem. Follow the formal problem solving method that is illustrated in the examples above. Please note that your answers may differ in the first or second decimal place due to use of a different periodic table. 1. What is the molar mass of Al(ClO4)3? 2. What is the molar mass of lead (IV) nitrate, Pb(NO3)4? 3. Find the molar mass of C2H2O42H2O. 4. How many carbon atoms are in two molecules of C12H22O11? 5.What number of hydrogen atoms are in 4.0 moles of (NH4)2HPO4? 6. 1.28 x 1023molecules of C10H22would have what number of carbon atoms? 7. How many moles are there in 39.6 g of S? 8. How many grams of HC2H3O2are there in 3.6 moles of HC2H3O2? 9. How many moles of CO2are contained in 42.0 x 1024molecules of CO2? 10. How many moles are contained in 106.2 g of CH4? 11. Find the mass (grams) of one Hg (mercury) atom. (use 4 s.f.) 12. How many grams of O2gas are there in 6.30 x l026molecules?
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