4.15 g tungsten is burned in chlorine and 8.95 g tungsten chloride (WCl6) was formed.
Find the relative atomic mass of tungsten.
Please help haha thanks!
We begin with 4.15 g of pure tungsten, and finish with 8.95 g of tungsten chloride. All of the tungsten in the original sample is present in the tungsten chloride, so there must be 4.8 g of chlorine in the sample, as 4.15 g of the 8.95 g sample is tungsten.
4.8 g of chlorine is equivalent to 0.135 mol of chlorine. The ratio of tungsten to chlorine is 1 : 6, so the amount of tungsten is one sixth the amount of chlorine. Therefore, the amount of tungsten is 0.0225 mol.
We know that the amount of tungsten in the tungsten chloride is the same as the original amount of tungsten. Therefore, 0.0225 mol of tungsten has a mass of 4.15 g, and hence, by ratios, 1 mol of tungsten has a mass of 184.16 g, approximately 184.
Finally, the question asks for a relative atomic mass, so the answer must be in atomic mass units, so the relative atomic mass of tungsten is 184 atomic mass units.
We have 8.95g of WCl6.
n(WCl6) = 8.95/(6x35.5 + 183. =0.022555443 mol
There is one tungsten cation in tungsten chloride. Therefore n(WCl6) = n(W)
Therefore, Mr of W = 4.15 / 0.022555443 mol = 183.9910615, to 3 sig figs, is 184.
Your answer is 184. But, why would it ask you to find the atomic mass of tungsten when you already have it on your periodic table?
You can't use the value for the molar mass of tungsten in the calculation of the relative atomic mass of tungsten. It's similar to mathematics - if a question asks you to prove a relationship, you cannot assume the relationship is true.