Quiz+3-+Answer+Key - 3 4 How many atoms are in 70 g of...

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Quiz #3 Chem 130 Sec 208 GSI: Andrea Geyer Please show all work or no credit will be given Name:______________________ 1) What is the difference between formula weight and molecular weight? The molecular weight is the sum of atomic weights of all atoms in a molecule of a substance. The formula weight is the sum of atomic weight of all atoms in a formula unit (not an entire molecule). The formula weight can be used to describe something that is not a molecule and hence does not have a molecular weight. 2) Balance the following equation: 3Sr(NO 3 ) 2 + 2Na 3 PO 4 6NaNO 3 + Sr 3 (PO 4 ) 2 3) Circle all answers that are a correct description of the following reaction: N 2 + 3H 2 → 2NH 3 i. 1 mol N 2 reacts with 3 mol H 2 to produce 2 mol NH 3 ii. 1 molecule N 2 reacts with 3 molecules H 2 to produce 2 molecules NH 3 iii. 1 g N 2 reacts with 3 g H 2 to produce 2 g NH 3 iv. 14 g N 2 reacts with 3.02 g H 2 to produce 17.02 g NH
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Unformatted text preview: 3 4) How many atoms are in 70 g of hydrogen gas? 70 g H 2 * (1mol H 2 / 2.016g H 2 ) * (2mol H / 1mol H 2 ) * (6.02*10 23 atoms/ 1mol H) = 4.18*10 25 atoms H Quiz #3 Chem 130 Sec 109 GSI: Andrea Geyer Please show all work or no credit will be given Name:______________________ 1) What more explicitly defines a substance a. The molecular formula b. The empirical formula 2) Balance the following equation: 2NBr 3 + 3NaOH --> N 2 + 3NaBr + 3HOBr 3) What is the mass percentage of chromium in lead (II) chromate? PbCrO 4 (52g/mol Pb)/ (323.2g/mol PbCrO 4 ) * 100 = 16 % 4) What is the molecular formula that corresponds to the empirical formula CH for a compound with the formula weight of 78.11 g/mol. C = 12.011 g/mol H = 1.008 g/mol CH = 13.019 g/mol (78.11 g/mol) / (13.019 g/mol) = 6 Answer: C 6 H 6...
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