# 0.8 Reactions in aqueous solutions  (Page 3/10)

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## Interesting fact

The simplest way to check whether water is hard or soft is to use the lather/froth test. If the water is very soft, soap will lather more easily when it is rubbed against the skin. With hard water this won't happen. Toothpaste will also not froth well in hard water.

A water softener works on the principle of ion exchange . Hard water passes through a media bed, usually made of resin beads that are supersaturated with sodium. As the water passes through the beads, the hardness minerals (e.g. calcium and magnesium) attach themselves to the beads. The sodium that was originally on the beads is released into the water. When the resin becomes saturated with calcium and magnesium, it must be recharged. A salt solution is passed through the resin. The sodium replaces the calcium and magnesium and these ions are released into the waste water and discharged.

## Acid rain

This section is not examinable and is included as an example of ions in aqueous solution.

The acidity of rainwater comes from the natural presence of three substances ( $\mathrm{CO}{}_{2}$ , $\mathrm{NO}$ , and $\mathrm{SO}{}_{2}$ ) in the lowest layer of the atmosphere. These gases are able to dissolve in water and therefore make rain more acidic than it would otherwise be. Of these gases, carbon dioxide ( $\mathrm{CO}{}_{2}$ ) has the highest concentration and therefore contributes the most to the natural acidity of rainwater. We will look at each of these gases in turn.

Acid rain

Acid rain refers to the deposition of acidic components in rain, snow and dew. Acid rain occurs when sulphur dioxide and nitrogen oxides are emitted into the atmosphere, undergo chemical transformations and are absorbed by water droplets in clouds. The droplets then fall to earth as rain, snow, mist, dry dust, hail, or sleet. This increases the acidity of the soil and affects the chemical balance of lakes and streams.

1. Carbon dioxide Carbon dioxide reacts with water in the atmosphere to form carbonic acid ( ${\mathrm{H}}_{2}{\mathrm{CO}}_{3}$ ).
${\mathrm{CO}}_{2}+\mathrm{H}{}_{2}\mathrm{O}\to {\mathrm{H}}_{2}{\mathrm{CO}}_{3}$
The carbonic acid dissociates to form hydrogen and hydrogen carbonate ions. It is the presence of hydrogen ions that lowers the pH of the solution making the rain acidic.
${\mathrm{H}}_{2}{\mathrm{CO}}_{3}\to {\mathrm{H}}^{+}+{\mathrm{HCO}}_{3}^{-}$
2. Nitric oxide Nitric oxide ( $\mathrm{NO}$ ) also contributes to the natural acidity of rainwater and is formed during lightning storms when nitrogen and oxygen react. In air, $\mathrm{NO}$ is oxidised to form nitrogen dioxide ( ${\mathrm{NO}}_{2}$ ). It is the nitrogen dioxide which then reacts with water in the atmosphere to form nitric acid ( ${\mathrm{HNO}}_{3}$ ).
$3\mathrm{NO}{}_{2}\left(\mathrm{g}\right)+\mathrm{H}{}_{2}\mathrm{O}\left(\mathrm{l}\right)\to 2\mathrm{HNO}{}_{3}\left(\mathrm{aq}\right)+\mathrm{NO}\left(\mathrm{g}\right)$
The nitric acid dissociates in water to produce hydrogen ions and nitrate ions. This again lowers the pH of the solution making it acidic.
$\mathrm{HNO}{}_{3}\to {\mathrm{H}}^{+}+{\mathrm{NO}}_{3}^{-}$
3. Sulphur dioxide Sulphur dioxide in the atmosphere first reacts with oxygen to form sulphur trioxide, before reacting with water to form sulphuric acid .
$2\mathrm{SO}{}_{2}+\mathrm{O}{}_{2}\to 2\mathrm{SO}{}_{3}$
$\mathrm{SO}{}_{3}+\mathrm{H}{}_{2}\mathrm{O}\to \mathrm{H}{}_{2}{\mathrm{SO}}_{4}$
Sulphuric acid dissociates in a similar way to the previous reactions.
$\mathrm{H}{}_{2}{\mathrm{SO}}_{4}\to \mathrm{H}{\mathrm{SO}}_{4}^{-}+{\mathrm{H}}^{+}$

Although these reactions do take place naturally, human activities can greatly increase the concentration of these gases in the atmosphere, so that rain becomes far more acidic than it would otherwise be. The burning of fossil fuels in industries, vehicles etc is one of the biggest culprits. If the acidity of the rain drops to below 5, it is referred to as acid rain .

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
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
Berger describes sociologists as concerned with
What makes metals better to use as wires than non-metals? (please link to bonding type)??? HELP