S2i Sunday, September 23rd 1. Find the molar mass of the following: C5H12 72.146 Na2SO4 142.05 Ca3(PO4)2 310.18 VOCl3 173.29 P2W24O80H6 5760.148 2. Using the molar mass, calculate the number of moles of the following: 45.3 g C5H12 1 mol 72.146 g = 0.628 mol C5H12 56 mg Na2SO4 1 g 1 mol 1000 mg 142.05 g = 3.9 x 10-­‐4 mol Na2SO4 0.245 g Ca3(PO4)2 1 mol = 7.90 x 10-­‐4 mol Ca3(PO4)2 310.18 g 789 g VOCl3 1 mol 173.29 g = 4.55 mol VOCl3 4.5 g P2W24O80H6 1 mol = 7.8 x 10-­‐4 mol P2W24O80H6 5760.148 g 3. Mole Ratio Practice Find the moles of hydrogen in 45.3 g C5H12 0.628 mol C5H12 12 mol H 1 mol C5H12 = 7.54 mol H Part 4 = 7.60 g H 7.54 mol H 1.008 g 1 mol H Find the moles of sodium in 56 mg Na2SO4 = 7.8 x 10-­‐4 mol Na 3.9 x 10-­‐4 mol Na2SO4 2 mol Na 1 mol Na2SO4 Part 4 = 0.018 g Na 7.8 x 10-­‐4 mol Na 22.99 g 1 mol Na Find the moles of calcium in 0.245 g Ca3(PO4)2 = 2.37 x 10-­‐3 mol Ca 7.90 x 10-­‐4 mol Ca3(PO4)2 3 mol Ca 1 mol Ca3(PO4)2 Part 4 = 0.0950 g Ca 2.37 x 10-­‐3 mol Ca 40.08 g Ca 1 mol Ca Find the moles of chloride in 789 g VOCl3 = 13.7 mol Cl 4.55 mol VOCl3 3 mol Cl 1 mol VOCl3 Part 4 = 486 g Cl 13.7 mol Cl 35.45 g Cl 1 mol Cl Find the moles of oxygen in 4.5 g P2W24O80H6 = 0.062 mol O 7.8 x 10-­‐4 mol P2W24O80H6 80 mol O 1 mol P2W24O80H6 Part 4 = 0.99 g O 0.062 mol O 16 g 1 mol O 4. Adding on to your calculations above, find the number of grams of the element in the compound 5. Find the percent of the element in the compound % hydrogen in 45.3 g C5H12 7.60 𝑔 𝐻𝑦𝑑𝑟𝑜𝑔𝑒𝑛
𝑥 100 = 16.8% 45.3 𝑔 𝐶5𝐻12
% sodium in 56 mg Na2SO4 0.018 𝑔 𝑁𝑎
𝑥 100 = 32% 0.056 𝑔 𝑁𝑎2𝑆𝑂4
% calcium in 0.245 g Ca3(PO4)2 0.095 𝑔 𝐶𝑎
𝑥 100 = 38.8% 0.245 𝑔 𝐶𝑎3 𝑃𝑂4 3
% chloride in 789 g VOCl3 486 𝑔 𝐶𝑙
𝑥 100 = 61.6% 789 𝑔 𝑉𝑂𝐶𝑙3
% oxygen in 4.5 g P2W24O80H6 0.99 𝑔 𝑂
𝑥 100 = 22% 4.5 𝑔 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑
6. Putting it all together If you have 88.9 g P2O5, how many moles of phosphate do you have? = 1.25 mol P2O5 88.9 g P2O5 1 mol P2O5 2 mol P 141.94 g P2O5 1 mol P2O5 If you have a sample of 23.56 g of K3N, how many grams of potassium do you have in that sample? = 21.05 g K 23.56 g K3N 1 mol K3N 3 mol K 39.1 g K 131.31 g K3N 1 mol K3N 1 mol K If I have a sample of 56 g of NaCl, what percent of the sample is sodium, and what percent of the sample is chloride? = 22 g Na 56 g NaCl 1 mol NaCl 1 mol Na 22.99 g Na 58.44 g NaCl 1 mol NaCl 1 mol Na !!! !"
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𝑥 100 = 39% Sodium 100% total -­‐ 39% sodium= 61% Chloride Helpful Hints: To go from grams of a compound to the percent of just one element: 1) grams to moles: use molar mass of compound 2) moles of compound to moles of element: use mole ratio 3) moles of element to grams of element: use molar mass of element 4) to go to percent: (grams of element ÷ grams of compound) x 100