Solve Eudiometry Problem: NH3 & H2 Mixture, 40 ml Oxygen Added

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konichiwa2x
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Hi, can someone please explain how to do this problem? I don't even understand the question properly.

50 ml of a mixture of NH3 and H2 was completely decomposed by sparking into nitrogen and hydrogen. 40 ml of Oxygen was then added and the mixture was sparked again. After cooling to room temperature, the mixture was shaken with alkaline pyrogallol and a contraction of 6ml was observed. Calculate the percentage of NH3 in the original mixture. (Assume that nitrogen does not react with Oxygen)

thanks.
 

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50 ml of a mixture of NH3 and H2 was completely decomposed by sparking into nitrogen and hydrogen.--> This means that NH3 will decompose into N2 and H2. And H2 will remain as H2.

40 ml of Oxygen was then added and the mixture was sparked again.--> O2 added will react with H2 to form H2O. Since given in question is that N2 does not react with O2.

After cooling to room temperature, the mixture was shaken with alkaline pyrogallol and a contraction of 6ml was observed.--> Alkaline pyrogallol will absorb O2. This means that 6ml of the gas is O2.

Then, you can use the information 6ml of O2 to work backward to calculate the percentage of NH3 in the original mixture.
 
thanks fopr explaining that!