Hello!
Let's first find the molecular mass of nitrogen dioxide, knowing that by Avogadro's Law for each mole of a substance we have 6.02 * 10²³ molecules.
N = 1*14 = 14 amu
O = 2*16 = 32 amu
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molecular mass of nitrogen dioxide = 14 + 32 = 46 g/mol
How many molecules of nitrogen dioxide are in 1.28 g of nitrogen dioxide NO2?
46 g ---------------- 6,02*10²³ molecules
1,28 g ------------- y molecules
[tex]46*y = 1,28*6,02*10^{23}[/tex]
[tex]46y = 7,7056*10^{23}[/tex]
[tex]y = \dfrac{7,7056}{46}*10^{23} [/tex]
[tex]y = 0,167513043*10^{23}
[/tex]
[tex]\boxed{\boxed{y = 1,6751304*10^{22}\:molecules\:of\:nitrogen\:dioxide}}\end{array}}\qquad\checkmark[/tex]
