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Unformatted text preview: choudhury (fac489) – Post-lab 3 Chemical Formula – lyon – (51155) 1 This print-out should have 23 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points What is the name of Na 2 CO 3 · 10 H 2 O? 1. sodium carbon trioxide decahydrate 2. sodium carbonate decahydrate correct 3. sodium carbonate nonahydrate 4. sodium (II) carbonate decahydrate Explanation: Salt hydrates are named by naming the anhydrous salt formula unit and adding the name of the water of hydration. The name of the hydrate includes a prefix, indicating of the number of water molecules attached to the formula unit. 002 10.0 points What is the name of CoCl 2 • 2H 2 O? 1. cobalt (I) chloride dihydrate 2. cobalt (II) chloride dihydrate correct 3. copper (I) chloride dihydrate 4. copper (II) chloride dihydrate 5. cobalt chloride dihydrate Explanation: Write the name of the ionic compound then write the corresponding prefix, which indi- cates the number of attached water molecules, in front of the word “hydrate”. (See “naming hydrates” in the reading section of experiment 2.) 003 10.0 points An element X combines with oxygen to form a compound of formula XO 2 . If 24.0 grams of element X combines with exactly 16.0 grams of O to form this compound, what is the atomic weight of element X? 1. 16.0 amu 2. 24.0 amu 3. 12.0 amu 4. 284 amu 5. 48.0 amu correct Explanation: m X = 24.0 g m O = 16.0 g We know from the formula XO 2 that one mole of X combines with exactly 2 moles of oxygen atoms. We can convert 16 grams of oxygen to moles using the atomic weight of oxygen from the periodic table: ? mol O = 16 g O × 1 mol O 16 g O = 1 mol O 1 mol O would combine with exactly 1 / 2 mol of X: ? mol X = 1 mol O × 1 mol X 2 mol O = 0 . 5 mol X We were given that 16 g of O combines exactly with 24 g X. We calculated that 16 g of O (1 mol O) would combine with 0 . 5 mol X. From this we can conclude that 0 . 5 mol X has a mass of 24 g. We can calculate the grams per mole: ? molar mass X = 24 g X . 5 mol X = 48 g X mol X The molar mass of an element in g/mol is numerically equal to the atomic mass in amu. Therefore, the atomic mass of X is 48 amu. 004 10.0 points 14 g of Si reacts with 16 g of O to produce SiO 2 , the only product, with no reactant left over. How much SiO 2 would be produced from 39 g of Si and excess O? choudhury (fac489) – Post-lab 3 Chemical Formula – lyon – (51155) 2 1. 0.0120 g 2. 44.6 g 3. 83.6 g correct 4. 55 g 5. 73.1 g Explanation: m ini , Si = 14 g m ini , O = 16 g m Si = 39 g By the law of conservation of mass, 14 g of Si and 16 g of O would produce 30 g of SiO 2 , if no Si and O are remaining at the end of the reaction. By the law of definite propor- tions then, the mass ratio of product SiO...
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This note was uploaded on 12/13/2011 for the course CH 204 taught by Professor Leytner during the Fall '08 term at University of Texas at Austin.
- Fall '08