QUANTITATIVE CHEMISTRY TEST INTO Answer all questions. There are 15 multiple cho

Question

QUANTITATIVE CHEMISTRY TEST INTO Answer all questions. There are 15 multiple choice questions and 2 longer answer questions. NAME: Grade: 1. How many neutrons does an atom of oxygen-15 (O) have? A 15 B 16 C 7 2. The table below shows the mass number and abundance of the isotopes of krypton. Mass number 82 83 84 86 Relative abundance 1212 50 26 The relative atomic mass, Ar, of this sample of krypton is: A 84.0 B 84.1 C 84.2 D 84.3 3. Calculate the empirical formula of an oxide of nitrogen which contains 25.9% of nitrogen and 74, 1% of oxygen by mass. A NO B NO C NO D NO

Explanation / Answer

Q1

Oxygen 15 --> 15 is the mass number

Oxygen will have 8 electrons/8protons when neutral

so

neutrons = mass number - proton = 15-8 = 7 neutrons

choose C

Q2.

for Argon:

MW -avg = x1*MW1 +  x2*MW2 + ..  xn*MWn

MWavg = (12/100) * 82 + 12/100*83 + 50/100*84 + 26/100*86

MWavg = 84.16

choose C since rounding up will give this

Q3

assume 100 g of sample

25.9 g of N and 74.1 g of O

change to moles

mol of O = mass/MW = 74.1/16 = 4.63

mol of N = mass/M W= 25.9/14 = 1.85

raito

4.63/1.85= 2.5

or 5 mol of N per 2 mol o fO

N2O5

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