# Mole concept  (Page 3/4)

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Problem : Find the number of moles in 500 grams of pure Calcium carbonate?

Solution : The numbers of moles is given by :

$n=\frac{g}{{M}_{o}}=\frac{500}{100}=5$

Problem : Which represents greatest mass among 100 gm of calcium, 3 g-atoms of calcium , 1 mole of calcium oxide, ${10}^{25}$ molecules of oxygen?

Solution : We convert each of the given quantity in grams for comparison :

$100\phantom{\rule{1em}{0ex}}\text{gm of calcium}=100\phantom{\rule{1em}{0ex}}\text{gm}$

$3g-\text{atoms of calcium}=3X{A}_{Ca}=3X40=120\phantom{\rule{1em}{0ex}}\text{gm}$

$1\text{mole of calcium oxide}={M}_{CaO}\phantom{\rule{1em}{0ex}}\text{gm}=40+16=56\phantom{\rule{1em}{0ex}}\text{gm}$

${10}^{25}\phantom{\rule{1em}{0ex}}\text{molecules of oxygen}=\frac{{10}^{25}}{6.022X{10}^{23}}\phantom{\rule{1em}{0ex}}\text{moles}=0.166X{10}^{2}\phantom{\rule{1em}{0ex}}\text{moles}$

$⇒{10}^{25}\phantom{\rule{1em}{0ex}}\text{molecules of oxygen}=16.6\phantom{\rule{1em}{0ex}}\text{moles}=16.6X{M}_{{O}_{2}}\text{gm}=16.6X32=531.2\phantom{\rule{1em}{0ex}}\text{gm}\phantom{\rule{1em}{0ex}}$

Clearly, ${10}^{25}$ molecules of oxygen represents greatest mass.

## Number of entities

The number of moles in a given mass of a molecule is given by :

$\text{moles(n)}=\frac{g}{{M}_{o}}$

Since each mole has ${N}_{o}$ entities, the total numbers of entities in “n” moles is :

$\text{Total number of molecules}\left(N\right)=n{N}_{0}=\frac{g}{{M}_{o}}X{N}_{0}$

If we are interested to count atoms in a sample of an element, then we use “gram atom” as :

$\text{Total number of atoms}\left(N\right)={n}_{a}{N}_{0}=\frac{g}{A}X{N}_{0}$

Problem : If ${10}^{22}$ water molecules are removed from 100 mg of water, then find the remaining mass of water.

Solution : Here we need to find the mass of ${10}^{22}$ water molecules. We know that numbers of molecules is related to mass in gram as :

$N=n{N}_{0}=\frac{g}{{M}_{o}}X{N}_{0}$

$⇒g=\frac{N{M}_{o}}{{N}_{0}}=\frac{{10}^{22}{X}_{18}}{6.022X{10}^{23}}=2.989X0.1=0.2989\phantom{\rule{1em}{0ex}}\text{gm}=2.989\phantom{\rule{1em}{0ex}}\text{mg}$

$⇒\text{remaining mass of water}=100-2.989=97.011\phantom{\rule{1em}{0ex}}\text{mg}$

## Mole concept

Chemical reactions involve dissociation and association at atomic/molecular/ionic level. The measurements of constituent entities of a reaction can be carried out using conventional mass measurements in grams or kilograms. What is the need to carry out analysis in terms of moles?

Let us have a look at the chemical reaction :

$2{H}_{2}+{O}_{2}\to 2{H}_{2}O$

Let us further consider that there are 2 gms of hydrogen involved in the reaction. Can we interpret the given balanced equation to predict the mass of oxygen involved in the reaction? Clearly, it would not be possible unless we know the molecular mass. In terms of molecular mass, we see that 4 a.m.u of hydrogen reacts with 32 a.m.u of oxygen. This mass correlation, however, is slightly incomprehensible to our measurement sense as a.m.u is very minute mass almost incomprehensibly too small for our perceptible laboratory measurements in grams.

We can though extend the molecular mass proportion to grams. We note that the mass ratio of two elements in the reaction is 4:32 i.e. 1:8. Hence, 2 grams of hydrogen reacts with 16 grams of oxygen. This completes the picture. But, slight discomfort is that the correspondence of mass is not directly related with the numbers of molecules (coefficients of balanced chemical equation) involved in the reaction.

Mole concept simplifies the mass relation among reactants and products such that we can base our calculation on the coefficients (numbers of molecules involved in the reaction). At the same time, mass or the quantity of substance is on lab scale in grams. Looking at the equation, we can say that 2 molecules of hydrogen react with one molecule of oxygen. Extending this understanding of reaction to the moles of the substance, we come to the conclusion that “2 moles of hydrogen reacts with 1 mole of oxygen”. Here, we have simply scaled the molecular relation ${N}_{o}$ times.

#### Questions & Answers

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
yes
Asali
I'm not good at math so would you help me
Samantha
what is the problem that i will help you to self with?
Asali
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
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Yasmin
what is the function of carbon nanotubes?
Cesar
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Stoichiometry. OpenStax CNX. Jul 05, 2008 Download for free at http://cnx.org/content/col10540/1.7
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