# 0.9 Quantitative aspects of chemical change  (Page 3/10)

 Page 3 / 10
 Element Relative atomic mass (u) Molar mass ( $\mathrm{g}·\mathrm{mol}{}^{-1}$ ) Mass of one mole of the element (g) Magnesium 24,31 24,31 24,31 Lithium 6,94 6,94 6,94 Oxygen 16 16 16 Nitrogen 14,01 14,01 14,01 Iron 55,85 55,85 55,85

Calculate the number of moles of iron ( $\mathrm{Fe}$ ) in a $11,7\phantom{\rule{2pt}{0ex}}\mathrm{g}$ sample.

1. If we look at the periodic table, we see that the molar mass of iron is $55,85\phantom{\rule{2pt}{0ex}}\mathrm{g}·\mathrm{mol}{}^{-1}$ . This means that 1 mole of iron will have a mass of $55,85\phantom{\rule{2pt}{0ex}}\mathrm{g}$ .

2. If 1 mole of iron has a mass of $55,85\phantom{\rule{2pt}{0ex}}\mathrm{g}$ , then: the number of moles of iron in $111,7\phantom{\rule{2pt}{0ex}}\mathrm{g}$ must be:

$\frac{111,7\mathrm{g}}{55,85\mathrm{g}·{\mathrm{mol}}^{-1}}=2\phantom{\rule{2pt}{0ex}}\mathrm{mol}$

There are 2 moles of iron in the sample.

You have a sample that contains 5 moles of zinc.

1. What is the mass of the zinc in the sample?
2. How many atoms of zinc are in the sample?
1. Molar mass of zinc is $65,38\phantom{\rule{2pt}{0ex}}\mathrm{g}·\mathrm{mol}{}^{-1}$ , meaning that 1 mole of zinc has a mass of $65,38\phantom{\rule{2pt}{0ex}}\mathrm{g}$ .

2. If 1 mole of zinc has a mass of $65,38\phantom{\rule{2pt}{0ex}}\mathrm{g}$ , then 5 moles of zinc has a mass of: $65,38\phantom{\rule{2pt}{0ex}}\mathrm{g}×5\phantom{\rule{2pt}{0ex}}\mathrm{mol}=326,9\phantom{\rule{2pt}{0ex}}\mathrm{g}$ (answer to a)

3. $5×6,022×{10}^{23}=30,115×{10}^{23}$

## Moles and molar mass

1. Give the molar mass of each of the following elements:
1. hydrogen
2. nitrogen
3. bromine
2. Calculate the number of moles in each of the following samples:
1. $21,62\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of boron ( $\mathrm{B}$ )
2. $54,94\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of manganese ( $\mathrm{Mn}$ )
3. $100,3\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of mercury ( $\mathrm{Hg}$ )
4. $50\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of barium ( $\mathrm{Ba}$ )
5. $40\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of lead ( $\mathrm{Pb}$ )

## An equation to calculate moles and mass in chemical reactions

The calculations that have been used so far, can be made much simpler by using the following equation:

$\mathbf{n}\left(\mathrm{number of moles}\right)=\frac{\mathbf{m}\left(\mathrm{mass of substance in}\phantom{\rule{2pt}{0ex}}\mathrm{g}\right)}{\mathbf{M}\left(\mathrm{molar mass of substance in}\phantom{\rule{2pt}{0ex}}\mathrm{g}·{\mathrm{mol}}^{-1}\right)}$
Remember that when you use the equation $n=\frac{m}{M}$ , the mass is always in grams ( $\mathrm{g}$ ) and molar mass is in grams per mol ( $\mathrm{g}·\mathrm{mol}{}^{-1}$ ).

The equation can also be used to calculate mass and molar mass, using the following equations:

$m=n×M$

and

$M=\frac{m}{n}$

The following diagram may help to remember the relationship between these three variables. You need to imagine that the horizontal line is like a 'division' sign and that the vertical line is like a 'multiplication' sign. So, for example, if you want to calculate 'M', then the remaining two letters in the triangle are 'm' and 'n' and 'm' is above 'n' with a division sign between them. In your calculation then, 'm' will be the numerator and 'n' will be the denominator.

Calculate the number of moles of copper there are in a sample that weighs $127\phantom{\rule{2pt}{0ex}}\mathrm{g}$ .

1. $n=\frac{m}{M}$
2. $n=\frac{127}{63,55}=2$

There are 2 moles of copper in the sample.

You are given a 5 mol sample of sodium. What mass of sodium is in the sample?

1. $m=n×M$
2. M ${}_{\mathrm{Na}}=22,99\phantom{\rule{2pt}{0ex}}\mathrm{g}·\mathrm{mol}{}^{-1}$

Therefore,

$m=5×22,99=114,95\phantom{\rule{2pt}{0ex}}\mathrm{g}$

The sample of sodium has a mass of $114,95\phantom{\rule{2pt}{0ex}}\mathrm{g}$ .

how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Do somebody tell me a best nano engineering book for beginners?
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
what is nano technology
what is system testing?
preparation of nanomaterial
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
what is system testing
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
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
how did you get the value of 2000N.What calculations are needed to arrive at it
Privacy Information Security Software Version 1.1a
Good
Berger describes sociologists as concerned with
What makes metals better to use as wires than non-metals? (please link to bonding type)??? HELP