Question

**(a) Calculate the number of oxygen molecules and the
number of oxygen atoms in 34.5 g of
O**_{2}**.**

**oxygen molecules =**

×

**10**

** oxygen atoms
=**

×

**10**

**Enter your answers in scientific notation.**

**(b) Calculate the mass of 8.99**

×

**10**^{14} **SO**_{3}
**molecules.**

×

**10**

**g**

**Enter your answer in scientific notation.**

Answer #1

**1)**

**Molar mass of O2 = 32 g/mol**

**mass(O2)= 34.5 g**

**number of mol of O2,**

**n = mass of O2/molar mass of O2**

**=(34.5 g)/(32 g/mol)**

**= 1.078 mol**

**number of molecules = number of mol * Avogadro’s
number**

**number of molecules = 1.078 * 6.022*10^23
molecules**

**number of molecules = 6.49*10^23 molecules**

**number of atoms = 2*number of molecules**

**= 2*6.49*10^23 atoms**

**= 1.30*10^24 atoms**

**2)**

**number of mol of SO3 = number of molecules / Avogadro’s
number**

**= (8.99*10^14) / (6.022*10^23)**

**= 1.493*10^-9 mol**

**Molar mass of SO3,**

**MM = 1*MM(S) + 3*MM(O)**

**= 1*32.07 + 3*16.0**

**= 80.07 g/mol**

**mass of SO3,**

**m = number of mol * molar mass**

**= 1.493*10^-9 mol * 80.07 g/mol**

**= 1.20*10^-7 g**

**Answer: 1.20*10^-7 g**

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________g

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