Lehman College of the City University of New York 17.How many atoms are there in

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Lehman College of the City University of New York 17.How many atoms are there in 177g of magnesium chloride? b. 1.06 x 1026 atoms c 3.39 x 1024 atoms d. 1.81 x 104 atoms e. 1.13 x 1024 atoms 18. How many moles are there in 8.0 g of calcium phosphate? a. 0.022 moles b 0.026 moles C. 0.037 moles d. 0.046 moles e. 0.059 moles 19. What is the molecular formula of a compound if the molar mass of the compound is found to be 186.5 gram and the empirical formula is C2H,? a. CzH7 b. CoH21 C12H14 d.C12Hsz 20. When 12 g of methanol (CHsOH) was treated with excess oxidizing agent (Mn0.), 14 g of formic acid (HCOOH) was obtained. Using the following chemical equation, calculate the percent yield. (The reaction is much more complex than this; please ignore the fact that the charges do not balance.) a.100% b. 92% C. 82% d. 70% e. 55% 21. Napthalene (CoHe) is an organic molecule that has only LDF. How is it possil then that napthalene is a solid at room temperature, but water is a liquid? a. Molecules with IMF always have higher boiling points. b. Water molecules can form H-bonds so water must have stronger IMF than th napthalene. c. Napthalene is a large planar molecule and so its LDF's are stronger than the in water d. Molecules with IMF are more likely to be solids at room temperature

Explanation / Answer

Q17

atoms in 177 g of MgCl2

MW of MgCl2 = 95.211 g/mol

mol = mass/MW = 177/95.211 = 1.85902 mol of MgCl2

1 mol = 6.022*10^23 molecules

1.85902 mol = 1.85902*6.022*10^23 molecules = 1.1195018*10^24 molecules

1 molecules = 3 atoms

so 1.1195018*10^24 molecules = 3* 1.1195018*10^24 = 3.3585*10^24 atoms

Q18

Ca3(PO4)2

MW = 310.17 g/mol Ca3(PO4)2

mol = mass/MW = 8/310.17 = 0.0257923 mol of Ca3(PO4)2

nearest answer is b

Q19

molecular formual for:

MW of empirical = 2*12 + 1*7 = 31 g/mol

so... times of empiricla formula in total mass

x times = MW / MW empirical = 186.5/31 = 6.01612

so

C2H7)*6 = C12H42

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