Answer
a.FM of $HNO_{2}$ = 47.0 amu
b. FM of CO = 28.0 amu
Work Step by Step
a. There are 2 atoms O, 1 atom H and 1 atom N in the figure, therefore we have to find formula mass for $HNO_{2}$.
FM of $HNO_{2}$ is the sum of atomic masses of all atoms in formula:
1 AM H = 1 x 1.007 amu = 1.007 amu
1 AM N = 1 x 14.006 amu = 14.006 amu
2 AM O = 2 x 15.999 amu = 31.998 amu
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FM of $HNO_{2}$= 1.007 amu + 14.006 amu + 31.998 amu
FM of $HNO_{2}$ = 47.011 amu
FM of $HNO_{2}$ = 47.0 amu ( to three significant figures)
b. a. There is 1 atom Cand 1 atom O in the figure, therefore we have to find formula mass for CO
FM of CO is the sum of atomic masses of all atoms in formula:
1 x AM = 1 x 12.01 amu = 12.01 amu
1x AM O = 1 x 15.99 = 15.99 amu
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FM of CO= 12.01 amu + 15.99 amu
FM of CO = 28.00 amu
FM of CO = 28.0 amu ( to three significant figures)
