MHB Calculate Oxygen Mass at RT & Pressure: 78 cm3

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To calculate the mass of 78 cm³ of oxygen at room temperature and pressure, the molar volume of gas is used, which is 24 liters. The number of moles is determined by dividing the volume by the molar volume, leading to 78/24000 moles of oxygen. Each mole of oxygen (O₂) has a molar mass of 32 g, as it consists of two oxygen atoms, each with a mass of 16 g. There is confusion regarding whether to use 32 or 16 for calculations, particularly in relation to the decomposition of hydrogen peroxide (H₂O₂), which produces half a mole of O₂. Ultimately, the correct mass calculation for 78 cm³ of oxygen is confirmed to be 0.104 g.
markosheehan
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Calculate the mass of 78 cm3 of oxygen at room temperature and pressure .

Im trying to work out the number of moles and then multiply by 32.
 
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markosheehan said:
Calculate the mass of 78 cm3 of oxygen at room temperature and pressure .

Im trying to work out the number of moles and then multiply by 32.

$n(O) = \dfrac{V(O)}{V_m(O)}$

$m(O) = n(O)M(O)$.

$V_m$ is the molar gas volume.
 
Im sorry I am still confused. I know the right answer is .104g
 
markosheehan said:
Im sorry I am still confused. I know the right answer is .104g

The molar volume of a gas ($V_m$) at room temperature and standard pressure is $24$ liter.
That is, $1$ mole is $24$ liter.
How many moles does that make in $78\text{ cm}^3$?
 
Thanks.
I feel the answer is wrong. 78/24000 ×32 is what gives the answer at the back of the book. Should it not be multiplied by 16 though because in the balanced equation for the reaction it's a half mile of oxygen is formed.?
 
markosheehan said:
Thanks.
I feel the answer is wrong. 78/24000 ×32 is what gives the answer at the back of the book. Should it not be multiplied by 16 though because in the balanced equation for the reaction it's a half mile of oxygen is formed.?

Not sure what you mean. Was there a reaction involved?

We have 78/24000 moles of oxygen molecules ($O_2$).
Each molecule consists of 2 oxygen atoms, and an oxygen atom has mass 16u.
Therefore we multiply the moles with $2\times 16=32$.
 
sorry i forgot to mention it was calculate the mass of 78 cm3 of oxygen produced by the the composition of hydrogen peroxide.
h202 goes to h20 +.5o2
so does this not mean you would multiply it by 16 instead of 32
 
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