Question. 1. what is the mass of a piece of magnesium which produces29.1ml of hy

Question

Question. 1. what is the mass of a piece of magnesium which produces29.1ml of hydrogen gas collected over water at 22.5 celsius and atpressure of 749 torr when dissolved in excess hydrochloricacid? b). How many moles of hydrogen is present in 38.6ml of Hcollected over water at 25.0 celsius and at a pressure of 748torr? Thanks Question. 1. what is the mass of a piece of magnesium which produces29.1ml of hydrogen gas collected over water at 22.5 celsius and atpressure of 749 torr when dissolved in excess hydrochloricacid? b). How many moles of hydrogen is present in 38.6ml of Hcollected over water at 25.0 celsius and at a pressure of 748torr? Thanks

Explanation / Answer

for both of these you use the ideal gas law, but you need topick a basis of consistent units.
lets use Litre-torr-Kelvin.
for this, the ideal gas constant R=62.636 L*Torr/(K*mol)

1.
first we convert. 29.1 mL=0.0291 L and 22.5 C = 293.6 K
(you should definitely be able to understand these unitconverstion)
2.
Now we use the ideal gas law PV=nRT where P is pressure, V isvolume, n is number of moles, R is ideal gas constant, and T istemperature. or rearrange n=PV/RT to solve for moles
3.
n=PV/RT= (749 Torr)*(0.291L)/(62.636 L*Torr/(K*mol)*293.6 K) this will you give an answer in moles
4.
Now we employ the stoichiometry. Write out (or figure out) thebalanced equation,
the balanced equation is
Mg + H2O--> MgO + H2
and you'll see that one mole of Mg gives you one mole ofH2.
so n is both the number of moles of H2 and the number of moles ofMg metal. (because the number of moles are equal)
Multiply the number of moles by the molar mass of Magnesium (24.31g/mol) to get your answer in grams.
so
your answer will be n (which you figured out from plugging in thenumbers and doing out the math above) in moles * 24.31 g/mol andyour answer will be in grams
i hope this is more clear. i still left the math for you to crunchyourself because its good practice, but at this point its just amatter of plugging these numbers into your calculator

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