Middlesex County College Dept of Chemistry and Physics Chemistry 121 64 Spring 2

Question

Middlesex County College Dept of Chemistry and Physics Chemistry 121 64 Spring 2017 Exam 2 Duration 90 min Name Mot J Answer all the questions. Please show all the work to receive full credit. i) Write the chemical formula and calculate the molecular mass of each of the following substances (8 points) a)Sulfuric acid b)Perchloric acid c)Dinitrogen pentoxide d)Chromium(III) sulfate ii) Calculate the number of K atoms in 77.4 gofK (3 points) iii) Calculate the number of moles of KCI03 in 46.0 gof KCIO3 (3 points)

Explanation / Answer

Q1.

for:

a) sulfuric acid --> HSO4

MW = H+S+4*O = 1+32 + 4*16 = 97 g/mol

b)

perchloric acid, "per" means plenty of oxygens so

HClO4 --

MW = 1 + 35.5 + 16*4 = 100.5 g/mol

c)

Dinitrogen = N2, pentoxide = O5

so

N2O5 --> 2*14 + 5*16 = 108 g/mol

d)

Chromium --> Cr+3 and Suldate = SO4-2 so:

Cr2(SO4)3

MW = 52*2 + (32+16*4)*3 = 392 g/mol

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