Acids and Bases in the World - acid rain, chlorine in pools and cleaning products.

by juhosa (student)

AS and A Level Science

Acids and Bases in the World

Acid Rain

Cause

Caused by a chemical compound such as sulphur dioxide or nitrogen oxides being released into the air
These substances can rise very high in the atmosphere where they react with water, oxygen and other chemicals forming acidic pollutants
Are able to dissolve very easily in water and carried far by wind, becoming part of the rain, sleet, snow and fog

The source of the release of these chemical compounds occurs from the burning of fossil fuels and pollutants from auto mobiles and factories, mainly humans cause this pollution
Some natural pollution however in balance with the Earth so there isn't a huge rise in acidic level, humans change this and make it higher

Equations to show the formation of acidic pollutants

Sulphur Dioxide + Water forming sulphurous acid

SO2(g) + H2O(l) ↔ H2SO3(aq)

Sulphur Dioxide oxidises to Sulphur trioxide

2SO2(g) + O2(g) → 2SO3(g)

Sulphur Trioxide + Water forming sulphuric acid

SO3(g) + H2O(l) → H2SO4(aq)

Nitrogen oxides + Water form nitrous acid and nitric acid

2NO2(g) + H2O(l) → HNO2(aq) + HNO3(aq)

Consequences on environment

Acid rain has many consequences on the environment, impacting on surface waters, aquatic animals, soils, forest and other vegetation, human health effects and even effects on buildings

Acid rain causes the pH of the water to become lower, a majority of fish eggs won't hatch if the pH of the water is lower than 5 and adult fish can die if the pH becomes lower than this
As rivers and lakes become more acidic due to the acid rain, the less lifeforms that are able to live in those conditions, substantially reducing biodiversity

Acid rain can have huge effects on soil, the hydronium ions of acid rain mobilise toxins such as aluminium and leach away essential nutrients and minerals such as magnesium

Indirectly acid rain will also have an affect on forests and plant life, as the soil becomes damaged and loses a lot of its nutrients the plants and trees are no longer able to grow

The chemical compounds that make up acid rain can have adverse effect on human health, the increasing amount of fine particles in the air contribute to heart and lung problems such as asthma and bronchitis

Acid rain can destroy buildings as the make-up of acid rain reacts with calcium carbonate to create gypsum which then flakes off

Swimming Pools

The need for Chlorine in swimming pools

Chlorine is what is used to help keep a swimming pool clean, you could say that Chlorine is effectively a sanitiser.
When Chlorine is put into water, a reaction occurs forming hypchlorous acid and hydrochloric acid, how much of each depends on the water temperature and pH
Hypochlorous acid is what 'sanitises' the pool water, it does this by slashing through the cell walls and destroying the inner enzyme structures and processes
The reaction of Chlorine with water

Cl2(g) + H2O(l) ↔ HCl(aq) + HclO(aq)

Why it's important to maintain an appropriate pH

Water that is too acidic or too basic will cause undesirable reactions
If it is too acidic the water may corrode metal equipment, cause skin irritation, and etching on surface materials
Too basic can cause scaling on the pool surface and plumbing equipment and cloudy water
However both being too acidic or basic will have an effect on how well Chlorine will work, if its too acidic the Chlorine will dissipate too quickly, too basic and it wont destroy pathogen as well
Maintaining ...

This is a preview of the whole essay

Cl2(g) + H2O(l) ↔ HCl(aq) + HclO(aq)

Why it's important to maintain an appropriate pH

Water that is too acidic or too basic will cause undesirable reactions
If it is too acidic the water may corrode metal equipment, cause skin irritation, and etching on surface materials
Too basic can cause scaling on the pool surface and plumbing equipment and cloudy water
However both being too acidic or basic will have an effect on how well Chlorine will work, if its too acidic the Chlorine will dissipate too quickly, too basic and it wont destroy pathogen as well
Maintaining the pH within a set range enables Chlorine to work at its best and sanitise the pool as much as possible while also allowing for no undesirable effects to occur

Cleaning

Oven cleaners are as you can see, what cleans an oven when it gets dirty from cooking food in it. Many things make the oven dirty however the majority of it is fats and oils
Generally oven cleaners are basic in pH, this is because they react with the fats and oils. This term is also described as saphonification
The process by which produces soap, it involves base hydrolysis of triglyceride’s, which are esters (chemical compounds derived by an oxoacid reacting with a hydroxyl compound e.g. alcohol) of fatty acids to form the salt of a carboxylate
The hydroxide ion adds to the carbonyl (a compound containing metal combined with carbon monoxide – e.g. nickel carbonyl) group of the ester producing an orthoester
Orthoester can then reform the carbonyl, expelling of the hydroxide or alkoxide. The former leads to the starting materials making it unproductive, however if alkoxide is removed a carboxylic acid is formed.
The alkoxide is more basic than the conjugate base of the carboxylic acid and therefore proton transfer is rapid
Because there are high amounts of oils and fats in an oven due to cooking, an oven cleaner with a base in it is very effective as the process of saphonification removes these oils and fats leaving behind a nice and clean oven
An example equation would be NaOH as the oven cleaner reacting with HCl to form sodium chloride salt and water
NaOH + HCl -> NaCl + H20

Bleach is often used in household cleaning, in areas such as the bathroom and toilet. Why this is so however is discussed in more detail below
Bleach contains a number of chemicals that remove colour, whiten or disinfect often via oxidation
An example chemical would be the typical household chlorine bleach, NaClO
An example reaction for bleach being used to clean up say a vinegar spill would be

NaClO + CH3COOH -> HClO + CH3COONa

In which hypochlorous acid is released

Bleach is such a great disinfectant because of its ability to oxidise, when sodium chlorite comes in contact with germs etc. It oxidises the molecules, killing them
The hypochlorous acid that is also formed from this reaction causes certain proteins to build up in bacteria making their cells unable to function

As it is described earlier bleach is very useful in many areas because of its ability to one disinfect and sanitise and two to remove colour from what it reacts with
By soaking cutlery in bleach, we are able to get the discolouration in any of the material present due to the oxidisation powers of bleach breaking the bonds that make up the chromosphere thereby making the material unable to absorb light or absorb light that is not on a visible spectrum
The bleach will also provide some disinfectant properties as described in the previous question
Rinsing the cutlery with water then will dilute any remaining bleach washing it away from the cutlery
Soaking the cutlery in vinegar is due to the fact that vinegar is acidic, because of this it can dissolve mineral deposits from smooth surfaces it is also effective against bacteria and mould providing that extra sanitisation with a clean and shiny finish to the cutlery.
Rinsing after will remove any residue and the remaining vinegar

Sulphuric acid (H2SO4) is a very strong acid, and also a very strong oxidising agent
Because of these properties and its high level of corrosiveness it is very efficient at cleaning drains
It is often found in many drain cleaners however it is recommended that it is only used by plumbers as it can be quite hazardous
Sulphuric acid is hygroscopic (a substances ability to trap and hold water molecules) and hence it is used as a drying agent. Mould generally likes dark and moist environments, add a bit of sulphuric acid and it is no longer going to be a moist environment, thereby killing the mould
Also because of this dehydrating quality it means that it has a highly exothermic reaction with water, meaning a lot of heat is realised when combined with water
We sometimes boil water in order to sterilise the water killing any germs in it, sulphuric acid can cause this effect as well in drains, sterilising them due to the high amounts of heat released along with its high levels of corrosiveness
Very efficient at removing hair, grease, mould and clogs in a drain
H2SO4 + H2O -> HSO4- + H3O+

Drinks

The soft drink coca-cola is actually in fact acidic, registering a pH value of 2.5 to 4.2, with 2.5 being the higher acidic rating
The reason that coke or any soft drink for that matter is acidic is due to carbon dioxide present in them in order to make them effervescent (bubbly)
A small amount of the carbon dioxide reacts in solution and forms carbonic acid (H2CO3)
CO2 + H2O → H2CO3
As the coke is left to sit for an hour some of the carbon dioxide is released from the coke and back into the air, thereby lowering the amount of carbon dioxide and in turn carbonic acid. This will bring the pH higher as there is less acid and it will go closer to the neutral pH of 7

Calculation for HCl

C2 = 10^-pH = 10^-2.8 = 1.58489319x10^(-3) mol L-1

C1V1 = C2V1 → 0.01 x 0.1 = 1.58489319x10^(-3) x V2

V2 = C1V1 / C2 = 0.6309573455L

V2 – 0.1 = 0.5309573455 → 0.531L

0.531L of water needs to be added in order to obtain a hydrochloric acid solution with a pH of 2.8
Method

Put safety glasses on
Measure and pour 100mL of 0.01M Hydrochloric acid into an uncontaminated 1L beaker
Measure and pour 0.531L of uncontaminated water into the 1L beaker

Equipment – 0.01M Hydrochloric acid, Safety Glasses, Clean 1L beaker, Measuring cylinder

This step is important as it removes as much contaminants as possible, the wire brush removes unwanted substances embedded into the tooth, washing of the tooth removes any bacteria or other substances present that may contaminate the experiment and washing with water removes any leftover detergent/residue

Water was only added to the first test tube as this is the 'controlled' part of the experiment, providing something to go back upon when comparing the effects of acid on teeth

The using of fresh acid each time was to ensure that statistically assuming no contamination the teeth will undergo the same conditions as the previous trial in the attempt to find a trend in the data

Dependant – The dependant variable in this experiment (the one we measure) would be the changing weights of the teeth over time
Controlled – The controlled variable would be the tooth in water, the amount of liquid used, concentration of the acid, amount of teeth per test tube and the use of fresh water/acid after each measurement
Independent – The independent variable is the time variance of which we measure the masses of the teeth

G & H you will find attached at the end of this paper

The general trend of the graph indeed indicates that the over time the mass of the teeth in acid is decreasing slowly
We can also deduct from the graph that the tooth in water actually gained weight
The reason the tooth in the water gained weight is most likely to be explained to be because of osmosis, where the tooth has absorbed water and thereby gained weight
The general decreasing trend over time of the weight of the teeth in acid indicates that the acid does indeed dissolve your teeth as the dentist had said
This would be due to the acid reacting with the teeth and the corrosive properties of an acid may also have had a part in reducing the mass of the teeth

In any experiment unless using equipment that can measure out quantities in exact amounts there is likely to be human error
These errors would include the actual amount of 0.01M HCl poured in may not have been an exact 100mL
As with the amount of water would not have been exactly 0.5309573455L
These errors would mean that the pH of the acid would not have been exactly 2.8 therefore changing the accuracy of the results
Another human error possibility is the pH of coke, as researched before cokes pH can actually vary per can

A way to improve the validity of the results would be to cover the test tubes with test tube stoppers to ensure no contamination occurs
To control the type of tooth used, ensuring they're all the same tooth (canine, molar, incisor etc.)
To control the temperature of the acid so as to not change the accuracy of the results
To ensure the conditions of the teeth are all the same, e.g. they all have fillings or none of them have fillings

Acids and Bases in the World - acid rain, chlorine in pools and cleaning products.

This is a preview of the whole essay

Document Details

Related Essays

Practical on Enthalpy changes between acids and bases.

In this experiment, you will investigate some of the important chemical pro...

Acid Rain

The Causes And Forms Of Acid Rain.