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F02_E1A - Chemistry 111 Page 1 out of 5 Exam I Fall 2002...

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Chemistry 111 Page 1 out of 5 Exam I / Fall 2002 Answer Key Bonus (01 pt): Imagine that the nuclide 14 O were to absorb an electron into the nucleus (rather than emit a beta particle). What nuclide would it form? Well, it is absorbs an electron, that is probably something very similar to the beta emission, except backwards. This means that a proton would be converted into a neutron. Therefore, the atomic number would decrease by one, while the mass number would remain the same . 7 14 N Show all your work in the space provided in order to receive any credit at all! 1. K 3 PO 4 What is the formula for potassium phosphate? (03 pts) 2. 1.56 mol Determine the number of moles of oxygen atoms (O) in 25.0 grams of oxygen gas (O 2 ). (06 pts) 25.0 g O 2 × 1 mol O 2 32.0 g O 2 × 2 mol O 1 mol O 2 = 1.56 mol O . 3. 7.63 × 10 23 How many hydrogen (H) atoms are there in 32.1 g of aluminum hydroxide, Al(OH) 3 , MW = 75.98 ? (10 pts) 32.1 g Al(OH) 3 × 1 mol Al(OH) 3 75.98 g Al(OH) 3 × 3 mol H 1 mol Al(OH) 3 × 6.022 × 10 23 atoms 1 mol H = 7.63 × 10 23 H atoms . 4. 17.4 % During a combustion of a 20.0 g sample of an unknown hydrocarbon (a compound that has carbon and hydrogen only), 31.0 g of water are formed. What is the mass percent of H in that hydrocarbon? (08 pts) Well, we need to figure out how many grams of hydrogen are in that water sample. 31.0 g H 2 O × 1 mol H 2 O 18.02 g H 2 O × 2 mol H 1 mol H 2 O × 1.008 g H 1 mol H = 3.47 g H.
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