(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

"A student reacts an unknown mass of iron (Fe) in an excess of sulfuric acid

(H2SO4). The balanced equation is:

2 Fe(s) + 3sH2SO4(aq) → Fe2(SO4)3(aq) + 3 H2(g)

She records the following data:

23.0°C

Temperature

Pressure 98.4 kPa

Volume of dry hydrogen collected 47.3 mL

Find the mass of iron used in the experiment."

2. Relevant equations

PV = nRT and a ratio.

3. The attempt at a solution

The solution says (the formatting was ruined when I pasted this and I tried to fix it so if anything is left ruined by accident, sorry):

" Given: T = 23.0°C + 273 = 296 K; V = 0.0473 L; P = 98.4 kPa;

R = 8.31 kPa⋅L/mol⋅K, we can calculate the number of moles of hydrogen gas

produced by the ideal gas equation: n = PV/RT

n = (98.4 kPa)(0.0473 L)/(8.31 kPa⋅L/mol⋅K)(296 K)

n = 1.89 x 10^(-3) mol of H2

From the balanced equation:

2 Fe(s) + 3H2SO4(aq) → Fe2(SO4)3(aq) + 3 H2(g) hydrogen and iron

are in a ratio of 3:2 moles. There must, therefore, be 2/3(1.91 x 10^(-3) mol) of Fe

present, that is, 1.26 x 10^(-3) mol of Fe. Since the molar mass of Fe is 55.85g/mol,

this represents 0.0705 g of Fe."

but I don't see how 1.89 x 10^(-3) mol becomes 1.91 x 10^(-3) mol nor do I see why the ratio is 2/3 of approximately the number of moles of H_2; I think it should be 3/2 of exactly the number of moles of H_2 as shown in my work.

My attempt is attached. I'm feeling that I'm correct but could someone please confirm if I am right and the solution is wrong or tell me why I am wrong if I am wrong?

Any input would be greatly appreciated!

Thanks in advance!

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# Homework Help: Find the mass of iron used in the experiment.

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