# 15.1 Stoichiometry and composition  (Page 3/5)

 Page 3 / 5

## 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.

are nano particles real
yeah
Joseph
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
no can't
Lohitha
where we get a research paper on Nano chemistry....?
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
has a lot of application modern world
Kamaluddeen
yes
narayan
what is variations in raman spectra for nanomaterials
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
how did you get the value of 2000N.What calculations are needed to arrive at it
Privacy Information Security Software Version 1.1a
Good
Richard is sitting on his chair and reading a newspaper three (3) meters away from the door
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
Properties of longitudinal waves