# 15.1 Stoichiometry and composition  (Page 3/5)

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## Molar volumes of gases

Molar volume of gases
1 mole of gas occupies $22,4{\mathrm{dm}}^{3}$ at S.T.P.

## Molar concentrations of liquids

A typical solution is made by dissolving some solid substance in a liquid. The amount of substance that is dissolved in a given volume of liquid is known as the concentration of the liquid. Mathematically, concentration (C) is defined as moles of solute (n) per unit volume (V) of solution.

$C=\frac{n}{V}$

For this equation, the units for volume are $\mathrm{dm}{}^{3}$ . Therefore, the unit of concentration is $\mathrm{mol}·{\mathrm{dm}}^{-3}$ . When concentration is expressed in $\mathrm{mol}·{\mathrm{dm}}^{-3}$ it is known as the molarity (M) of the solution. Molarity is the most common expression for concentration.

Do not confuse molarity (M) with molar mass (M). Look carefully at the question in which the M appears to determine whether it is concentration or molar mass.
Concentration

Concentration is a measure of the amount of solute that is dissolved in a given volume of liquid. It is measured in $\mathrm{mol}·{\mathrm{dm}}^{-3}$ . Another term that is used for concentration is molarity (M)

If $3,5\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of sodium hydroxide (NaOH) is dissolved in $2,5\phantom{\rule{2pt}{0ex}}{\mathrm{dm}}^{3}$ of water, what is the concentration of the solution in $\mathrm{mol}·{\mathrm{dm}}^{-3}$ ?

1. $n=\frac{m}{M}=\frac{3,5}{40}=0,0875\phantom{\rule{2pt}{0ex}}\mathrm{mol}$
2. $C=\frac{n}{V}=\frac{0,0875}{2,5}=0,035$

The concentration of the solution is $0,035\phantom{\rule{2pt}{0ex}}\mathrm{mol}·{\mathrm{dm}}^{-3}$ or $0,035\phantom{\rule{2pt}{0ex}}\mathrm{M}$

You have a $1\phantom{\rule{2pt}{0ex}}{\mathrm{dm}}^{3}$ container in which to prepare a solution of potassium permanganate ( $\mathrm{KMnO}{}_{4}$ ). What mass of $\mathrm{KMnO}{}_{4}$ is needed to make a solution with a concentration of $0,2\phantom{\rule{2pt}{0ex}}\mathrm{M}$ ?

1. $C=\frac{n}{V}$

therefore

$n=C×V=0,2×1=0,2\phantom{\rule{2pt}{0ex}}\mathrm{mol}$
2. $m=n×M=0,2×158,04=31,61\phantom{\rule{2pt}{0ex}}\mathrm{g}$

The mass of $\mathrm{KMnO}{}_{4}$ that is needed is $31,61\phantom{\rule{2pt}{0ex}}\mathrm{g}$ .

How much sodium chloride (in g) will one need to prepare $500\phantom{\rule{2pt}{0ex}}{\mathrm{cm}}^{3}$ of solution with a concentration of $0,01\phantom{\rule{2pt}{0ex}}\mathrm{M}$ ?

1. $V=\frac{500}{1 000}=0,5\phantom{\rule{2pt}{0ex}}{\mathrm{dm}}^{3}$
2. $n=C×V=0,01×0,5=0,005\phantom{\rule{2pt}{0ex}}\mathrm{mol}$
3. $m=n×M=0,005×58,45=0,29\phantom{\rule{2pt}{0ex}}\mathrm{g}$

The mass of sodium chloride needed is $0,29\phantom{\rule{2pt}{0ex}}\mathrm{g}$

## Molarity and the concentration of solutions

1. $5,95\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of potassium bromide was dissolved in $400\phantom{\rule{2pt}{0ex}}{\mathrm{cm}}^{3}$ of water. Calculate its molarity.
2. $100\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of sodium chloride (NaCl) is dissolved in $450\phantom{\rule{2pt}{0ex}}{\mathrm{cm}}^{3}$ of water.
1. How many moles of NaCl are present in solution?
2. What is the volume of water (in ${\mathrm{dm}}^{3}$ )?
3. Calculate the concentration of the solution.
4. What mass of sodium chloride would need to be added for the concentration to become $5,7\phantom{\rule{2pt}{0ex}}\mathrm{mol}·{\mathrm{dm}}^{-3}$ ?
3. What is the molarity of the solution formed by dissolving $80\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of sodium hydroxide ( $\mathrm{NaOH}$ ) in $500\phantom{\rule{2pt}{0ex}}{\mathrm{cm}}^{3}$ of water?
4. What mass (g) of hydrogen chloride ( $\mathrm{HCl}$ ) is needed to make up $1000\phantom{\rule{2pt}{0ex}}{\mathrm{cm}}^{3}$ of a solution of concentration $1\phantom{\rule{2pt}{0ex}}\mathrm{mol}·{\mathrm{dm}}^{-3}$ ?
5. How many moles of $\mathrm{H}{}_{2}\mathrm{SO}{}_{4}$ are there in $250\phantom{\rule{2pt}{0ex}}{\mathrm{cm}}^{3}$ of a $0,8\phantom{\rule{2pt}{0ex}}\mathrm{M}$ sulphuric acid solution? What mass of acid is in this solution?

## Stoichiometric calculations

Stoichiometry is the calculation of the quantities of reactants and products in chemical reactions. It is also the numerical relationship between reactants and products. In representing chemical change showed how to write balanced chemical equations. By knowing the ratios of substances in a reaction, it is possible to use stoichiometry to calculate the amount of either reactants or products that are involved in the reaction. The examples shown below will make this concept clearer.

anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
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
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
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
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
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
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many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
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I'm interested in nanotube
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what is nanomaterials​ and their applications of sensors.
how did you get the value of 2000N.What calculations are needed to arrive at it
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The fundamental frequency of a sonometer wire streached by a load of relative density 's'are n¹ and n² when the load is in air and completly immersed in water respectively then the lation n²/na is
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