Question

Gas Calculations Help!!

Mass of magnesium Strip (grams): 0.032 g
Volume of gas collected (mL): 30 mL
Barometric pressure (atm): 1.1 atm
Room temperature: 22C
Vapor pressure of the water (torr): 19.8 torr

Answer 1

1. Write the balanced equation for the reaction conducted in this lab, including appropriate phase symbols. Mg (s) + 2 H20 (l) --> H2 (g) + Mg (OH)2 (aq)

2. Determine the partial pressure of the hydrogen gas collected in the gas collection tube. 1.1atm = P1 + 0.0395atm
1.1atm – 0.0395atm = 1.0605

3. Calculate the moles of hydrogen gas collected. n = 1.0605atm * 30L / .0821 * 297 = 31.815 / 24.3837 = 1.1 mol

4. If magnesium was the limiting reactant in this lab, calculate the theoretical yield of the gaseous product. Show all steps of your calculation.

5. Determine the percent yield of this reaction, showing all steps of your calculation.

Answer 2

Can you check my answers for 1-3 and help me with 4 and 5? Please and thank you

Answer 3

1-3 looks good to me.

If you know the Mg is the limiting reactant, then use stoichiometry to find the volume of H2 gas that SHOULD HAVE BEEN made. There's your theoretical yield

Answer 4

Number 3 should be 1.3 mol instead of 1.1 mol

Answer 5

did you convert your volume properly from mL to L?

Answer 6

Yes

Answer 7

@wolfe8 can you please help with this?

Answer 8

0.08235g/L is the density of H2 gas

30mL = 0.030L of H2 Gas

(0.08235g/L) = x/0.030L

where, x = grams of hydrogen gas

once you have grams convert to moles using,

Mole = grams/molecular mass

Answer 9

As for partial pressure I assume you are suppose to use,

PV=nRT
and solve for P so,
P = nRT/V

I got a partial pressure of about 1.08

Answer 10

4. If magnesium was the limiting reactant in this lab, calculate the theoretical yield of the gaseous product. Show all steps of your calculation.

Use the moles of magnesium to find the moles of H2 gas,

Mg (s) + 2 H20 (l) --> H2 (g) + Mg (OH)2 (aq)

since it is 1 to 1 moles of hydrogen gas = moles of magnesium

Answer 11

Use the moles formula again I showed you above, that will give you the theoretical yeild

Answer 12

Percentage yield = (Actual Yield/Theoretical Yield)*100

Answer 13

Any questions?

Answer 14

For the gas constant R since you are dealing in atmospheres you will want to use the Gas constant with units, atm*L/K*mole so that you get atm for your units of pressure, saves you a conversion

Answer 15

So for number 2 the partial pressure should be 1.08?

Answer 16

We are using the ideal gas model so it is fine.

Answer 17

You know volume of gas is 30mL, even if there was atmospheric pressure present it wouldn't matter. I'm crazy for thinking otherwise

Answer 18

Hence daltons law blah

Answer 19

Yeah,

V = 0.030L
T = 295K
R = 0.0082 or something gas constant units with Latm
n = Moles determined using volume

Answer 20

I'm making the assumption that the container size = the amount of hydrogen gas collected

Answer 21

https://en.wikipedia.org/wiki/Eudiometer

Answer 22

I'm confused now.

Answer 23

Well if you can wait till later this afternoon I can try to dig up my old lab manual and help you with this, or you can search for calculations involving eudiometer,

Try this,
http://depts.gpc.edu/~dunchelb/1152L/Sampl_report.pdf

Or type in google,

eudiometer calculations

Answer 24

The atmospheric pressure effects the reading of the eudiometer so you have to use it in your calculation it is still ideal gas law but there is a step before it

Answer 25

This is a first year chem experiment though so I'm sure you can find out how to solve it properly, if there was no mention of an ediometer you can probably just negate the barometric pressure though and stick with the way I calculated it.

Answer 26

Hope this was helpful I need to get back to the grind

Answer 27

Oh and if you do it the eudiometer way you will not be converting volume to moles using density you will be using the ideal gas law to solve for moles

Answer 28

I still don't get it

Answer 29

what was the answer?