Unknown Gas Identity? Bootcamp question

[PerioDont]

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An unknown gas has a density of 1.79 g•L-1 at 273K and 1 atm. Identify the gas.

This is the answer they give. My question is does anyone know where they got the 20L/1 mol number from?

 

[whitepapertree]

You could do it that way, otherwise when given a density along with pressure, temp, etc. I like to use P(MW)=DRT

so MW=(1.79)(273)(0.082)

I am not sure where they got 20L per 1 mol, they probably just rounded down from 22.4

 

[catalysts]

1 mol of gas @ std conditions = 22.4 L. All they did was approximate the numbers.

It is one of the conversions that you certainly need to know. Look up the "all roads go through mol-ville" conversions.

 

[Ari Rezaei]

It's an approximation, since it's tough to multiply 1.79 * 22.4 without a calculator. So you round 1.79 -> 2, and 22.4 L/mol -> 20, and 2*20 = 40 g/mol

Definitely know 22.4 L = 1 mol at STP, it can help you skip a lot of stuff. This problem would be hard to solve with the formula P(MW)=DRT without a calculator.

 

[Artdent97]

Sorry, meant to post "Thanks". The app accidentally pasted it.

Sorry again.

 

[whitepapertree]

1 mol of gas @ std conditions = 22.4 L. All they did was approximate the numbers.

It is one of the conversions that you certainly need to know. Look up the "all roads go through mol-ville" conversions.

1 mol of gas @ std conditions = 22.4 L. All they did was approximate the numbers.

It is one of the conversions that you certainly need to know. Look up the "all roads go through mol-ville" conversions.

 

[Artdent97]

Sorry, meant to post Thanks Whitepapertree. The app accidentally pasted it.

Sorry again.

 

[BSharp]

I did this problem by taking 40g /22.4 L.
Answer is almost exact.