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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.

Guest Nov 2, 2018

#1**+2 **

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

ElectricPavlov Nov 2, 2018

#2**+2 **

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 O**2** 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

ElectricPavlov Nov 2, 2018

#3**+2 **

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

ElectricPavlov Nov 2, 2018