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# Stoichiometry Help!

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1. How many grams of copper metal are needed to react with 0.150 moles HNO3 to produce copper(II) nitrate and hydrogen gas?

Cu + 2HNO3--> Cu(NO3)2 +  H2

2. How many moles of magnesium oxide are produced when 96 grams of oxygen gas react with magnesium metal?

2 Mg + O2 --> 2 MgO

3. How many moles of oxygen gas would be needed to react with 155 grams of propane gas, C3H8, in the combustion reaction, producing carbon dioxide and water?

C3H8 + 5O2 -->  3CO2 +  4H2O

I don't understand how to solve stoichiometry problems! Please help because it involves math and I don't know where else to go to get help with these.

off-topic
Nov 2, 2018

#1
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First one:

ONE mole of Cu is required for TWO moles of HNO3

You have  .150 mole of HNO3     so you need  .075 mole of Cu (copper) (half as much)

Copper mole weight 63.546 gm/mole

63.546 gm/mole x .075 mole = 4.766 gm of Cu required

Nov 2, 2018
#2
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Second one:

Oxygen mole weight 15.999 gm/mole           96 gm / 15.999 gm/mole = 6 moles of O

from the equation you are using O2 so there is only THREE moles of O2

each mole of O2 produces TWO moles of MgO from the equation

so you will get SIX moles of MgO

Nov 2, 2018
edited by ElectricPavlov  Nov 2, 2018
#3
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Third one:

(realize that oxygen gas is O2   not elemental oxygen O )

Propane gas

C3 H8  has a mole weight of     C x 3 + H x 8  =   12.011 x 3 + 1.008  x 8 = 44.097 gm/mole

155 gm / 44.097 gm/mole =3.515 moles

From the equation EACH mole of C3H8 requires FIVE moles of oygen gas

3.515 x 5 = 17.575 moles of O2 required

Nov 2, 2018
#4
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You are fantastic!! Thank you so very much for your help! I truly appreciate it. Have a wonderful day/night!

Guest Nov 2, 2018
#5
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You're welcome !   Hope you can figure them out now..... ElectricPavlov  Nov 2, 2018
#6
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Yes, I can! I just did another one that I have been stuck on and I finally got the correct answer!

Guest Nov 2, 2018
#7
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Very nice, EP.....I didn't know you were so well-versed in Chemistry!!!

[ I used to be able to do this stuff in High School, but....I've slept since then......]   CPhill  Nov 2, 2018