Chemical Forums

Chemistry Forums for Students => High School Chemistry Forum => Topic started by: beethove on November 18, 2014, 09:51:10 PM

Title: Density problem
Post by: beethove on November 18, 2014, 09:51:10 PM

At 136°C and atmospheric pressure, the density of TiCl₄ is 5.6 g L^-1. Under the same conditions, the density of gaseous N is 0.83 g L^-1. Determine the molecular formula of TiCl₄.

ANSWER: TiCl₄

How? And the reasoning?  Thanks!

Title: Re: Density problem
Post by: Hunter2 on November 19, 2014, 01:02:38 AM

Express the density by using ideal gas equation. Calculate molecular mass with it.

Title: Re: Density problem
Post by: mjc123 on November 19, 2014, 04:47:41 AM

And remember that gaseous nitrogen is N₂, not N!

Title: Re: Density problem
Post by: beethove on November 19, 2014, 07:07:38 AM

I did and the mole ratio is 1:1, which I guess is why the answer is TiCl4...but why do I even need to know the mole ratio between them figure out the molecular formula TiCl₄?

Title: Re: Density problem
Post by: Hunter2 on November 19, 2014, 07:24:57 AM

What mole ratio do you mean.

Confirm the molare mass from N₂

You have pV = nRT, n =m/M and Rho = m/V

convert this to M =?

The same you do with the Titanium chloride. The calculated molar mass you have to split in x Ti and y Cl^-.

Title: Re: Density problem
Post by: beethove on November 19, 2014, 09:21:51 AM

I just got it.  Your method works.  Another way (and I think what the chapter was trying to test) was that density is proportional to molar mass. So, this also solves it:

5.6 g L^-1/0.83 g L^-1(28.0 molar mass N₂) = 189g of TiCl₄

Therefore, TiCl₄ is molecular formula.

Title: Re: Density problem
Post by: Hunter2 on November 19, 2014, 09:30:18 AM

Yes correctly.

Title: Re: Density problem
Post by: Borek on November 19, 2014, 09:57:23 AM

Quote from: beethove on November 19, 2014, 09:21:51 AM

Another way (and I think what the chapter was trying to test) was that density is proportional to molar mass.

Both approaches are perfectly equivalent and based on the same basic principles.