-1
$\begingroup$

$\pu{112 ml}$ of hydrogen combines with $\pu{56 mL}$ of oxygen to form water. When $\pu{224 mL}$ of hydrogen is passed over heated cupric oxide, the cupric oxide loses $\pu{0.160 g}$ of its weight. All volumes are measured at STP. Show that the result agrees with the law of constant composition.

Although I solved the question, I came across a very interesting step in the procedure of doing so:

Weight of $\pu{112 mL}$ of $\ce{H2}$ at STP is calculated as $\frac{112 \times 2}{22400}$

Does this mean density of a gaseous substance at STP can be given as

$$\text{density} = \dfrac{\text{Mass}}{\text{Volume}} = \dfrac{\dfrac{\text{Volume(mL)}\times\text{Molar Mass}}{22400}}{\text{Volume(mL)}} = \dfrac{\text{Molar Mass}}{22400} $$

Can we say that this holds true?

Improve this question
$\endgroup$
2
  • $\begingroup$ There have been different values for STP in the past. Currently at STP the molar volume is 22.7 liters. $\endgroup$ – MaxW Jun 27 '18 at 17:45
  • $\begingroup$ Yes...Just knowing T, P and its identity, you can derive a density formula. [for an ideal gas] $\endgroup$ – user43021 Jun 27 '18 at 18:34
2
$\begingroup$

This is true for ideal gases at standard temperature and pressure. The Volume of an ideal gas is 22.4 L/mol at 298.15 K and 1 bar. You can check this yourself by rearranging the ideal gas equation and solving for the molar volume at STP.

Edit: Make sure you always use correct units, preferably SI in your equations. And use them in all equations.

Improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.