How do I calculate the partial pressure of HCl?

Calculate the % by mass of AL & HCL?

• The entire question is : A 43.0 mg sample of aluminum reacts with an excess of 6M HCL. A58.3ml volume of hydrogen gas is collected over water @20degC. The pressure of the wet Hydrogen gas is adjusted to atmospheric pressure, (760torr) Calculate the percent by mass of aluminum in the sample. The vapor pressure of water @ 20degC is 17.5 torr I just need alittle help setting up the problem please! I can do the actual calculations, Thanks!

• Answer:

  Setting out the steps 1. You will need to know the pressure at which the gas was collected at as you need to correct for water vapour. So if the gas was collected at p mm Hg then the partial pressure of hydrogen is p - 17.5 2. Convert the gas volume to STP using PV/T = PV/T (I left off the subscripts but you get the picture) and divide by the molar gas volume (22.35 L at STP) to yield moles of hydrogen. 3. Convert to mass of aluminium by the stoichiometry 2Al + 6HCl ===> 2ALCl3 + 3H2 Note 1 mol of H2 requires 2/3 mol of Al and AW Al = 27 4. %Al = Al calc g / Sample size g x 100 Note All that is important in the last step is the units are consistent g and g, mg and mg etc 5. Not sure about % HCl You could certainly work out the mass of HCl required or how many litres of 6MHCl were needed by noting that 1 mol H2 requires 2 mol HCl. This would quickly give the mass of HCl or the volume of 6M HCl. Hey you did not want the calcs done or the answers. Hope this helps.