[nataliercoley]

hey i have to do a lab where i measure the pressure of H2 gas (with a pressure gauge) emmited during the reaction between a magnesium strip and 10ml of 0.4M HCL. this gave me a graph of H2 gas (on the y axis) and time on the x axis. using the ideal gas law (PV=nRT) to find n, i converted the graph to be moles of H2(y axis) vs. time(x axis). now the problem is, i have to move that to moles of HCL consumed, then mols of HCL remaining so that i can uses conc. = mol/L to find the concentration over time. i thought that if i doubled the moles of H2 i could get moles of HCL consume over time because the equation is: 2HCL + Mg ----- H2 + MgCL2 especially since my teacher said that would work and then the graph should be twice as big. but i dont know how to turn a graph of 'mol HCL consumed over time' to 'mol HCL remaining over time'.
PLEASE HELP?

[Borek]

Sum of consumed and remaining is constant, that's mass conservation.

[nataliercoley]

does this still apply if i didnt let the reaction go to completion?

[nataliercoley]

also..what exactly do you mean by 'constant'? do you mean that they are equal, and if not..how do i calculate the moles remaining? furthermore since the graph of moles consumed is getting higher as the reaction progresses, the graph of moles remaining would be getting equally lower. do you know what kind of equation i could use to flip the graph over?

[Borek]

does this still apply if i didnt let the reaction go to completion?

Doesn't matter, mass conservation holds all the time.

also..what exactly do you mean by 'constant'? do you mean that they are equal, and if not..how do i calculate the moles remaining? furthermore since the graph of moles consumed is getting higher as the reaction progresses, the graph of moles remaining would be getting equally lower. do you know what kind of equation i could use to flip the graph over?

moles of used + moles of remaining = moles at the beginning

Solve for moles of remaining, you know (or can calculate) two others.