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ENG045_SMT1

# ENG045_SMT1 - DATE Solution to MidTerm Exam#1 ENG45 Fall...

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DATE: October 19, 2011 Solution to MidTerm Exam #1 ENG45 Fall 2011 – Open Book / Open Notes. No cell phones or WiFi devices present. Do not leave the room without permission from the proctor. Address the proctor if you suspect the problem formulation is erroneous, but do not ask the proctor to interpret either the question or your answer. The exam will be evaluated as a whole, but the numbered questions are intended to weigh equally. The exam starts at 11:00am and ends at 11:50am. Write clearly your complete name, page number, and number of pages on each sheet of paper you turn in. 1. What is the Molecular formula and the charges of the ions for Magnesium Chloride ? Mg 2+ Cl - 2 . 2. Given that the mass density of Sodium Telluride is ρ = 2 , 900 kg/m 3 , how many mols of Sodium and Telluride atoms are there in a 1cm cube of Sodium Telluride? The formula with charges is Na + 2 Te 2 - ; thus we have two Na for each Te. The total mass of Na 2 Te is m = 1cm 3 ρ = 2 . 9 g. The periodic table gives the molar mass of Na 2 Te to be 173.58g/mol. We therefore have 0.0167 mol Te and 0.0334 mol Na.
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