Question

Calculate the mass of the following gas sample at STP. 172 mL CO2

Answer 1

At STP, we have the following data:

`pV=\text{nRT}\begin{cases}p(\text{pressure)}=1\text{ atm} \\ V(volume)=172mL=0.172L \\ T(temperature)=0C=273\text{ K} \\ R=0.082(L\cdot atm)/(mol\cdot K) \\ n=mol\end{cases}`

To find the mass, we need to find the mol. Based in the formula, we clear the n (mol) and replace the STP values there:

`n=(pV)/(RT)=(1atm\cdot0.172L)/(0.082(L\cdot atm)/(mol\cdot K)\cdot273K)=0.00768molCO_2\text{.}`

Finally, to find the mass, we use the molar mass where you can find it in the periodic table (C = 12 g/mol and O = 16 g/mol)

For CO2, we do the following calculation :

`CO_2=1\cdot12\text{ g/mol }+2\cdot16\text{ g/mol=44 g/mol.}`

Doing the conversion from mol to mass (grams):

`0.00768molCO_2\cdot(44gCO_2)/(1molCO_2)\approx0.33792gCO_2.`

The mass of CO2 in this sample is 0.34 g.