6.1 Physical /Chemical changes. by Isabella Tan

A substance can be changed by heating, adding other substances, mixing and so on. The changes are either physical of chemical.

Signs of a Chemical Change; new substances are formed meaning the compound has its own set of properties; energy is used during the change, and is irreversible or very hard to reverse. An example of a chemical change is burning Magnesium Ribbon.

When heated the Magnesium reacts with Oxygen and magnesium oxide is formed (a new substance), heat and light - and very very bright light - is given out (energy being used) and once the ribbon is burnt you can’t change back into what it used to be (irreversible). Thechemical equation is 2Mg + O2 = 2MgO.

Other examples are fireworks, cooking of eggs, burning, roasting of marshmallows

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For physical changes; no new substances are formed meaning the mixture has characteristic of both particles and is easily reversible. An example is mixing iron and sulfur particles.

When you mix both of them together you do not get Iron(II) Sulphide but you get a mixture of iron and sulphide (no new substance) and to separate the mixture you just need to drag a magnet over it and it would attract all the iron (easily reversible)

Other examples are boiling water, melting iron, dissolving sugar in water, mixing mud in water.

The Environment - Oxygen ( By Shi Wen Hua , 3Y )

( Most commercially produced O2 is used to smelt iron into steel . )

( Low pressure pure oxygen is used in space suits )

Oxygen

Oxygen is obtained from the air. It can be compressed and stored in cylinders, or it can be kept as a liquid at its boiling point of -182 ℃ in insulated tanks .

Oxygen is third most abundant element in the universe by mass after hydrogen and helium and the most abundant element by mass in the Earth's crust.

Structure

At standard temperature pressure , oxygen is colorless , odorless gas with the molecular formular O2, in which the two oxygen atoms are chemically bonded to each other with a spin triplet electron configuration .

Oxygen is very important in our life !

Useso of Oxygen : ( applications )

Medical

In hospitals , Oxygen in cylinders is used to help people with breathing difficulties. Ambulances carry oxygen for the same purpose.

Life support and recreational use

A notable application of Oxygen as a low-pressure breahing gas is in modern space suits, Which surround their occupant's body with pressurized air. These devices use nearly pure oxygen at about one third normal pressure , resulting in a normal blood partial pressure of oxygen .

Industrial

Smelting of iron ore into steel comsumes 55% of commercially produced Oxygen .

Oxygen is used in industry for combustion. For example , in making steel , oxygen gas is passed into molten iron to burn off impurities .

What Is Air? Chapter 14.1 By Thiang Thai Ming Clss 3Z

The Earth's Atmosphere

The atmosphere is made up of a blanket of gases surrounding the Earth. We live in the troposphere. Weather occurs in this layer. When we fly in commercial jets, we're in the stratosphere. The mesosphere is where only astronauts have passed and the ionsphere is the highest layer which consists of mostly charged particles.

What Does Air Consist Of?

• Nitrogen - 79%



• Oxygen - 20%



• Others ( CO2, Other Noble gases, Water Vapour)
  

The Ozone Layer

Ozone has the formula O3, it consists of 3 oxygen atoms. It is formed when Ultraviolet Radidation from the sun breaks down the oxygen molecules into atoms. Thes atoms react with other oxygen atoms to form ozone.

Ozone molecules protect us by absorbing the harmful ultraviolet radiation and break down into oxygen atoms agin. The energy produced when new bonds are formed is heat, therefore the ozone layer is warmer than the air below it.

Measuring The Amount Of Oxygen In Air

Apparatus: A tube of hard glass rod is connected to two gas syringes A and B. The tube is packed with small pieces of coper wire. One syringe containes 100 cm3 of oxygen and the other is empty.

The Method:

1. The tube is heated by the bunsen burner. When A's plunger is pushed inwards, the ai is forced through th etube and into B. The oxygen reacts with the hot copper and turns it black. When A is empty, B's plunger is pushed in, forcing air back into A. Repeat the cycle a few ore times.


2. Heating is stopped after 3 minutes and the apparatus is allowed to cool. All the gas is then pushed into one syringe and its volume measured.


3. Steps one and two are repeated until the volume of the gas remains steady. This means that all the oxygen have been used and the final volume is recorded.

The results:

Starting volume: 100 cm3. Final Volume: 79cm3

Vol. of oxygen in 100cm3 of air will be 21cm3.

Percentage of oxygen in air is 21/100 x 100 = 21%

The Manufacture Of Ethanol Chapter 17.7 By Zach Sia Class 3Z

What is ethanol?
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a powerful psychoactive drug, best known as the type of alcohol found in alcoholic beverages and in modern thermometers It is also used as a fuel for cars. Ethanol is one of the oldest recreational drugs. In common usage, it is often referred to as alcohol or spirits. Ethanol is avolatile, colorless liquid that has a strong characteristic odor. It burns with a smokeless blue flame that is not always visible in normal light.

How is ethanol made?
There are two ways one is by using plant material and the other is with using ethene which is obtaining from oil.
Ethanol by fermentation
Ethanol fermentation is a biological process where sugars like glucose, fructose and sucrose get broken down into ethanol using yeast in the absence of air thus this happens:

enzymes
C₆H₁₂O₆ → 2C₂H₅OH + 2CO_{2 + Energy}
glucose in yeast ethanol carbon dioxide
Because it is in the absence of oxygen it is classified as anaerobic respiration.
Any substance that has sugar, starch or cellulose can be fermented. (Starch and cellulose break down into glucose.) So ethanol can be made from things like grass, corn, potatoes, wood or corn.

One experiment that can be done to produce ethanol is this.
1. grind the corn, treat it with enzymes to break its starch down into glucose and then add yeast.

2. Leave the material to ferment for 20 to 60 hours.

3. The fermented liquid contains a mixture of substances. Separate the ethanol from it by fractional distillation.
Ethanol from ethene
Ethanol can be made by hydration of ethene.

The ethene is obtained first by cracking long-chain alkanes from oil.

The hydration is exothermic and is reversible. High pressure and low temperature would give the best yield. But in practice it is carried out at 570 degrees Celsius to give a decent rate of reaction.
Difference in the two methods

Ethanol by fermentation

The advantages:

It is a renewable like sugarcane or corn.
It is a good way to use organic waste material

Disadvantages:
Need a lot of material to make even a single litre of ethanol.
Fractional distillation uses a lot of energy and money.
Fermentation is slow and tanks must shut down and restart between batches.
When ethanol reaches a certain concentration the yeast stops working.
This limits the amount of ethanol you can get per batch.

Ethanol from ethene

Advantages:
The reaction is fast.
The plant runs continuously. No time is wasted in shutting down and restarting.
It gives pure ethanol.

Disadvantages:
Ethene is made from oil a non-renewable rescource.
Energy is needed to make steam and get the right temperature and pressure for the reaction.
Under the reaction conditions a lot of the ethene remains unreacted. You have to keep recycling it.

Which method is more commonly used?
In countries where oil is cheap they would probably use ethene.
Countries where oil is expensive like the USA fermentation is more commonly used.

Most Common uses
Ethanol is now commonly used as a fuel for cars as it is more environmentally safe source of fuel, the government takes many measures to ensure people use ethanol as fuel like reducing taxes on it or making flexible-fuel cars that run on ethanol and petrol or the mixture of the two.

Ethanol is also used as a alcoholic drink. It is always made by fermenting for example, Grapes fermented for wine or barley fermented for beer. After it is fermented it is filtered and gotten ready to drink. The mixture of things in the liquid gives it its taste and smell.

http://www.youtube.com/watch?v=IRdOc7Mel28 Video of ethanol

Bibliography Wikipedia,
http://scifun.chem.wisc.edu/CHEMWEEK/PDF/Ethanol.pdf,
http://www.chemguide.co.uk/physical/equilibria/ethanol.html

Chapter 11.1 - Energy changes in reaction - by Yap Jun Xian 3Z

In Chemistry, two types of reactions can occur:
Physical
Chemical

From here, Chemical reactions can be split into two more groups:
Exothermic reactions and
Endothermic reactions.

In order to understand these reactions, we need to understand energy changes. When a chemical reaction occurs, the bonds between the atoms are broken, and new ones are formed. This requires energy. If the amount of energy required to form new bonds is higher than the amount of energy required to to break them, it releases energy. If the amount of energy required to form new bonds is lower than the amount of energy required to break them, it takes in energy. What determines the amount of energy taken in or given out is the difference in the amount of energy taken in subtracted by the amount of energy given out (Energy in-Energy out). If the answer if negative, it released energy, if the answer is positive, it takes in energy. The answer also provides us with the overall amount of energy that was used or released in the reaction.

---Exothermic reactions---
The word exothermic can be split into two. Exo, meaning 'out' in greek, and therm, meaning 'heat'. From this we can understand that exothermic reactions give out heat. Common examples of exothermic reactions include the neutralisation of an acid and alkali or combustion. In these examples, energy is taken in to break the molecular bonds, after which energy is released when new bonds are formed. Exothermic reactions occur when the amount of energy released is higher than the amount taken in, resulting in the release of heat. The graph above shows that the reactants require more energy to be broken down/formed while the product requires less to be broken down/formed.



A simple experiment on exothermic reactions can be done in a lab.

Apparatus:
Aqueous HCl
Aqueous NaOH
1 Test tube/boiling tube
2 Measuring cylinders

1) Add some aqueous HCl into a measuring cylinder, add an equal amount of aqueous NaOH into a seperate measuring cylinder.
2) Add the two solutions into the test tube.

What happens:
The reaction produced more energy forming bonds than it took in to break the bonds. Because of this, the overall amount of energy used is a negative, and the energy is released as heat.

---Endothermic reactions---
The word endothermic can be split up into two. Endo, which means 'in' in greek, and therm. From this we know that endothermic reactions take in heat, and is the opposite of an exothermic reaction. Examples of endothermic reactions are photosynthesis, the mixing of water with ammonium nitrate (NH4NO3) and decomposition of calcium carbonate into calcium oxide. In these reactions, energy is taken to break the molecular bonds, after which energy is released when new bonds form. Endothermic reactions occur when the amount of energy released is lower than the amount taken in, resulting in the loss of heat. The graph above shows that the reactants require less energy to form/break the molecular bonds than the products.

A simple experiment can be done on endothermic reactions.

Apparatus:
2g of ammonium chloride
Distilled water
1 test tube/boiling tube

1) Add 10ml of distilled water into the test tube.
2) Add the ammonium chloride into the water.

What happens:
The reaction took in more energy than it produced when forming bonds. Because of this, the overall amount of energy used was positive, and therefore, took in heat.

Thank you for reading.
*note* I couldn't find examples of experiments so I created them in hopes of them being correct.

Bibliography:
http://chemistry.about.com/b/2006/03/22/cold-packs-endothermic-reactions.htm
http://chemistry.about.com/od/lecturenotes13/a/endorxns/htm
Complete Chemistry for IGCSE page 160-163

Chapter 14.3 Pollution alert! by Jasmine 3Y

AIR Pollution!

A pollutant is a waste material that pollutes air, water or soil. Three factors determine the severity of a pollutant: its chemical nature, the concentration and the persistence.

What is the Air Pollution?
It is the release of chemicals and particulates into the atmosphere. Common gaseous air pollutants include Carbon monoxide, Sulphur dioxide, Nitrogen oxides and Lead compounds produced by industry and motor vehicles. Photochemical ozone and smog are created as nitrogen oxides and hydrocarbons react to sunlight.

Fossil Fuels!
Fossil fuels are fuels formed by natural resources such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years. Fuels contain a high percentage of carbon and hydrocarbonns.

The main air pollutants

Carbon monoxide (colourless gas,insoluble,no smell)
Its formed when the carbon compounds in fossil fuels burn in too little air. For example inside car engines and furnaces. It is poisonous even in low concentrations. It reacts with the haemoglobin in blood and prevents oxygen around the body...So you can die from oxygen starvation.

Sulphur dioxide (colourless acidic gas,sharp smell,soluble)
Its naturally in the fossil fuels mainly from oil and coal and forms sulphur dioxide when it burns. It gives us the eyes irritate and throat and causes respiratory problems.


Nitrogen oxide (acidic gas)
Its formed when the nitrogen and oxygen in air react together inside car engines and in hot furnaces. It causes respiratory problems and it dissolve in rain to form acid rain.

Lead compounds
A compound called tetra-ethyl lead was added to petrol to help it burn smoothly in engines. On burning,it produced particles of the lead compounds, mainly lead halides such as PbBrCl. Lead damages children's brains. It damages the kidneys and nervous system in adults.

Chptr 8.1: Acids and Alkalis by Baron J. Yan 3U

Acids: Acids are solutions of pure compounds in water that must be handled carefully, especially the concentrated solutions as they are corrosive,which means that it can burn through skin, clothes and even metal.
To see how hydrochloric acid burns through a penny then click the link here: http://www.youtube.com/watch?v=afjG8ahhi8U

But not all acids are this dangerous, for example take Coca Cola, it is make up of carbonic acids which gives it the bubbles and the power to rush out of the can, making the perfect prank to play on your unsuspecting friend. Acid turns blue litmus paper red and is from 1 to 7 on the pH scale with 1 being the strongest and 7 being the weakest, they have a sour taste but i would recommend NOT to taste them. The more common acids that are known are:
Hydrochloric acid (HCL)
Sulfuric acid (H2SO4)
Nitric acid (HNO3)
Ethanoic acid (CH3COOH)


Alkalies: Alkalies are another group of chemicals that affect litmus paper just like acid but in a different way. Just like acids they must be handled carefully as they too can burn really badly. Pure Alkalies are in solid form, except for ammonia which is in gas form. Alkalies are 7 to 14 on the pH scale and have a bitter taste to them and like acids, are NOT recommended to be tasted. Alkalies are used in cleaning products like soap and detergent as well as batteries.

pH :an acidic solution has a pH number less than 7 while a alkaline solution has a pH number greater than 7.
a neutral solution has a pH of exactly 7

THE BIG EXPERIMENT: MAKING YOUR OWN INDICATOR OUT OF RED CABBAGE LEAVES AND TESTING IT OUT ON DIFFERENT SOLUTIONS.

What is needed???: Red cabbage, test tubes, goggles, test tube rack, different chemical solutions, beaker tripod stand, wire gauze, Bunsen burner, syringe

Steps:
1. boil the red cabbage in water for about 20 minutes
2. after boiling allow to cool and remove cabbage
3. boil off excess water to obtain indicator
4. prepare test tubes with the various chemical solutions
5. using a syringe, add a few drops of the red cabbage solution into the test tubes
6. observe the colors that the indicators have turned into.
7. use the information you collected to see what the pH levels of the different acids are.

This is a video by a man showing what the experiment should look like: http://www.youtube.com/watch?v=6Tuv6noAgtY

As you can see that when the indicator turns reddish it is an acid but when it turns bluish it is an alkaline.


Thank You for bothering to read this blog you have not wasted 10 minutes of your life


good for you :)