How can using moles be useful in doing calculations in stoichiometry? Give at least two reasons.In this unit you have been reminded that the mole is a useful counting unit in chemistry, just as a...

How can using moles be useful in doing calculations in stoichiometry? Give at least two reasons.

In this unit you have been reminded that the mole is a useful counting unit in chemistry, just as a dozen may be easier to use to count groups of twelve. How can using moles be useful in doing calculations in stoichiometry? Give at least two reasons.

Asked on by tdj4325

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bandmanjoe's profile pic

bandmanjoe | Middle School Teacher | (Level 2) Senior Educator

Posted on

Stoichiometry is the study of ratios of elements or compounds and the way they react with each other in specific ratios or quantities.  Oftentimes, moles are used in describing these releationships between elements and/or compounds.  Moles are useful because they describe the number of a specific element required to react with a specific number of another element.  Consider the formation of water:

2H2  +  O2  --->  2H20

There are 2 moles of hydrogen required to react with one mole of oxygen which will produce 2 moles of water.  So you would need twice as much hydrogen as oxygen to produce water.  Another way moles come into play is describing the quantitative relationhips of the structure of compounds.  Consider a mole of glucose, C6H12O6.  What this means is there are 6 moles of carbon, 12 moles of hydrogen, and 6 moles of oxygen required to make one mole of glucose.

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sanjeetmanna's profile pic

sanjeetmanna | College Teacher | (Level 3) Assistant Educator

Posted on

Moles means avogadro number of molecules or atoms etc.,

Moles of a molecule = mass/ molar mass

Moles of a atom = mass/ atomic mass.

in Stoichometry moles is used at various places like 

finding mass.

mass = moles * molar mass

Finidng moles is the first step in finding limiting reactant.

 

Example

find the moles of 10 grams of Sodium hydroxide (NaOH)

moles = 10/40      [ Molar mass of NaOH = 40]

         = 0.25

Example

find the mass of 0.5 moles of calcium carbonate

moles = mass / molar mass

0.5 = mass/ 100   [ molar mass of Calcium carbonate = 100]

mass = 0.5 * 100

         = 50 grams.

 

Finding moles is also used at different stages, depending upon the problem need

 

chaobas's profile pic

chaobas | College Teacher | (Level 1) Valedictorian

Posted on

Let consider the reaction :

2 H2 + O2 ====> 2 H2O

Now we have 16 g of O2 which is being used in the reaction and wants to know the amount of product formed. 

First let's convert 16 g of O2 to moles

 

Moles = mass/molar mass 

Molar mass of O2 is 32g/mol

Moles of O2 = (16 g)/(32g/mol) = 0.5 mol O2

If we look at the reaction we can see that 1 mole of O2 gives 2 moles of water That is the molar ratio is 1 mol O2 : 2 mol H2O

 

So the amount of H2O formes would be

0.5 mol O2 * (2 mol H2O/1 mol O2) * ( 18 g H2O/1 mol H2O)

[molar mass of H2O is 18 g/mol]

18 g H2O.

So 16g of O2 will gives 18 grams of water.

 

Lets try anbother one:

CH4 + 2 O2 ======> CO2 + 2 H2O

this the the combustion reaction of methane. Let us consider 32 g of CH4 is burned(in presence of oxygen). Now let's find the amount of CO2 formes.

 

Moles of CH4 = 32 g/ 16 g/mol [molar mass of CH4 is 16g/mol]

moles of CH4 is 2 moles

 

Now in the reaction 1 mol of CH4 forms 1 mole of CO2. So the amount of CO2 formes would be

 

2 mol CH4 * (1 mol CO2/1 mol CH4)*(44 g CO2/1 mol CO2)

[molar mass of CO2 is 44g/mol)

88 g of CO2 is formed.

 

 

Hope it has helped you.:)

 

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