what worked well. Here’s my method:
Procedure
1) Add a small amount of Propanone into the Mortar. Place a handful of nettle leaves into the Mortar
2) Grind the nettles in the propanone until you get a moderate amount of pigmented solution
3) Use the filter paper to filter the solution into a beaker.
4) Take a piece of Chromatography paper and draw a line 10mm from one of the ends. Mark a point in the centre of the line-this will be the pigment spot.
5) Use the micropipette to extract a sample of the solution and then place a drop onto the spot drawn as before. Let the drop dry, and then place a second small drop on the first. Repeat this process 5 times in order to build up a concentrated pigment in the small area.
6) Whilst preparing the pigment spot, pour the solvent into the boiling tube to a depth no more than 15mm.
7) Fold the opposite end of the Chromatography paper and suspend the Chromatography paper in the boiling tube.

Insurance Fraud
Let’s not base policy on inflated statistics.
By David Hogberg
Anyone who pays even the slightest attention to the health-care debate in this country probably knows that there are “44 million uninsured Americans.” The figure was all but shouted from the rooftops during the recent Cover the Uninsured Week. It is standard boilerplate for John Kerry’s stump speeches. Hillary Clinton, in her recent screed, was unwilling to round off the number: “Some 43.6 million Americans are uninsured, and the vast majority of them are in working families.”
The existence of the 44-million figure is a tribute to Benjamin Disraeli’s quip that “there are three kinds of lies: lies, damned lies, and statistics.” If one accepts the Current Population Survey’s numbers (the source for the 44-million statistic), there are in fact closer to 35 million uninsured Americans. Over 20 percent of the uninsured in this country are not citizens.
Yet there is good reason to be skeptical of the CPS’s numbers. The CPS is intended to measure the number of people who have been uninsured for an entire year. One problem with the CPS statistic is that it includes both those who are insured for a short time and those who are chronically uninsured (defined as being uninsured for at least a year). Many people go without insurance for a few months often as the result of being between jobs. The CPS statistic of 44 million does not make that distinction.
Another drawback is that CPS asks respondents to recall their insurance status over the last twelve months, increasing the probability of sampling error due to respondents’ memory lapses. Last year a paper from the Congressional Budget Office contrasted the CPS with two other surveys, the Medical Expenditure Panel Survey (MEPS) and the Survey of Income and Program Participation (SIPP). MEPS and SIPP track their respondents every few months, so the error due to memory lapse should be minimized. Interestingly, MEPS reported 31 million chronically uninsured, while SIPP reported only 21 million.
Yet even the numbers reported by the MEPS and SIPP surveys overstate the number of uninsured. Some respondents who receive Medicaid may say they are uninsured because of the stigma associated with the Medicaid program. Studies suggest that this may result in an undercounting of the insured by 12 to 15 percent. According to the CBO, “the number of non-elderly people who are enrolled in Medicaid at any time during the year could be undercounted in population surveys by about 4 to 5 million.”
Another wrinkle occurs in the definition of the uninsured. There are many people who are eligible for Medicaid but are not enrolled in the program. Some argue that they should be counted as uninsured, while others argue that they should not. The latter group seems to have the stronger case, since such people can receive Medicaid coverage retroactively for health-care expenses. At present, there is no exact data on the number of people who are eligible for Medicaid but not enrolled. The most recent study, from 1994, estimated that about 2.9 million children who were uninsured were eligible for Medicaid.
Finally, it is important to note that, according to the SIPP survey, over 18 percent of the chronically uninsured say that they have gone without insurance because either they have not needed it or do not believe in it. When the various factors are accounted for, it is possible that the true number of the chronically uninsured is 12 to15 million.
Does the actual number matter? Either way, one might object, there are still millions who lack health insurance. Actually, it matters a great deal, because those who are most likely to tout the 44-million-uninsured statistic also tend to be the advocates of wholesale reform of the health-care system, usually of the government-run variety. A larger number gives their arguments more weight.
Second, understanding the actual magnitude of the problem gives us better direction in terms of policy. Of those chronically uninsured, the vast majority are poor, but over 60 percent are under the age of 35. Thus, the uninsured may be a largely healthy population that could afford to purchase health-care in a more consumer-driven system. Indeed, many of those currently purchasing insurance with health-savings accounts were previously uninsured.
Whatever the solution, we should not let inflated statistics lead us into adopting misguided health-care policies.

different samples of aluminum(Al):
a. along a thin Al wire
b. they are placed on a sheet of Al metal, like a cookie sheet.
c. They are connected to a solid Al paper weight in the shape of a cube.
All samples are made of the same material, but one will have more resistance, another less. Explain! Try to give an answer in technical terms, such as “fan out,” “1-,2-. And 3- dimensional,”etc

I’m writing my essay on gastritis (inflammation of the stomach lining) and my teacher gave me this format which i do not understand. Here’s how my teacher wants us to write it:
Chapter 1- introduction
a)introductory paragraph
b)statement problem
c)purpose
d)significance of the study
e)research questions and/or hypothesis
Chapter 2- Background
a) literature review
b) definition of terms —> in a sentence, in the flow of the paper
Chapter 3- Methodology
a) restate your purpose/research questions
b) population and sampling
c) validity
d) analysis
e) assumptions
Yea so this is the format and i dont understand it at all! Especially chapter 2, what does he mean by literature review and definition of terms? Im so lost. How can i write a problem and everything else on gastritis.

Question 2. (5.2.2, 5.4.2, 5.5.1) 17
a) Name and describe two reasons for the application of surface finishes to timber. 2
b) Explain the steps involved in preparing the surface of timber for the application of a finish. 3
c) Explain with the aid of sketches how to apply a wax finish and a one pot plastic finish. 6
d) Provide three reasons for the use of timber stains. 3
e) Explain with the aid of sketches how to apply a spirit stain. 3
Question 3. (5.2.2, 5.4.2, 5.5.1) 6
a) Explain the following terms and describe their uses. 4
• closed coat abrasive
• open coat abrasive
b) Name two common abrasive materials used in the manufacture of abrasive paper. 2
Question 4. (5.4.1, 5.5.1) 5
a) Prepare a report outlining the steps required to mark out and cut a rebate joint using hand tools. Use diagrams in your answer.
Question 5. (5.2.1, 5.5.1, 5.6.1) 10
a) Prepare a report outlining five issues that need to be considered during the design of the Trinket Box. Explain why each is important.
Question 6. (5.7.1, 5.7.2) 7
a) Identify three renewable and three non-renewable resources used in the timber industry. 3
b) Explain the importance of sustainability to the timber industry and how it can be achieved. 4
Question 7. (5.2.2, 5.4.2, 5.5.1) 8
a) Prepare a properties table for the following adhesives: Contact Adhesive, PVA, Epoxy, Urea Formaldehyde.
The table could look like the sample below.
Type Preparation Shelf Life Assembly Time Time to develop maximum strength Gap Filling Qualities Weather Resistance Typical Uses
Hot Melt heat in gun 1 year 50 seconds, less if cold. 30 minutes to 1 hour good moderate bonds most materials with no clamping needed.
Contact Adhesive

Richard Sample is taking this assessment.
Decide whether or not the topic is too narrow or needs to be narrowed more.
1. Movies in the 1930s. (1 point)
too narrow
not narrow enough
Refer to the topic from above.
2. Choose a appropriately narrowed topic. (1 point)
The technological advancements in movies in the 1930s.
Film stars of the 1930s.
Movie production companies in the 1930s.
Film equipment used in the 1930s.
3. Using the topic technological advancements in the movies in the 1930s, decide what type of purpose this research paper will have.
(1 point)
to inform
to entertain
to criticize/to denounce
to show cause and effect
4. Using the same topic from the previous question, choose a preliminary research question or questions that would be suited to the topic. (2 points)
What sort of actors appeared in the movies in the 1930s?
What sort of advancements in color film were made in the 1930s?
What were production companies’ profits in the 1930s?
What sort of advancements were there in sound in the 1930s?
5. Why is it important to keep in mind your audience when you write? Choose all that apply. (2 points)
It is a good idea to keep your audience in mind so you match your topic goals appropriately.
It is a good idea to keep your audience in mind so that you define terms and ideas that your audience may not know.
It is not necessary to keep your audience in mind when you write.
It is necessary to keep your audience in mind so you cite your sources properly.

I have to write a fairly large paper on this subject, and wanted to get some input from what promises to be a diverse group of people. So far, Oregon is the only state that has a law that permits assisted suicide, called the “Death With Dignity” act. My question is, how do you personally feel about it? That is, if somebody is terminally ill, with no hope of recovery, and has lost control of their body and every other aspect of their life, do you see any harm in them deciding to end their life on their own terms? Should they have to suffer until they die a “natural” death or is it morally permissible for them to decide when they go, when the rest of their life is going to be filled with pain and agony? I would really like some thought put into your answers, since “The bible says that suicide is wrong” is not going to help me understand the actual opinions and views of a sample of the public. Thank you all!!

apearently this study says no.
Study clears cannabis of schizophrenia rap – No greater risk than general non-tokers
By Tim Worstall
Posted in Policing, 6th November 2008 13:19 GMT
Regular readers will recall the confused mess
(http://www.theregister.co.uk/2008/05/08/cannabis_law_analysis/)
that is this government’s cannabis policy. There has been a drop in cannabis consumption since it was downgraded from Class B to C, but nevertheless they want to put it back up to Class B again. Yes, we know all about the argument that what you ingest is entirely your business, it being your body and all that but morals are always trumped by politics.
In the comments section to our last piece the general consensus was that the policy was driven either by a craven servility to the Murdoch press or, as a daring alternative, a bending to Daily Mail woo woo. The general consensus however was that it was Puritanism, that awful fear that someone, somewhere, might be enjoying themselves and that this situation cannot be allowed to continue. We’re arguing over whose Puritanism, not whether.
There was one vaguely respectable argument that could be put forward on the prohibitionist’s side, that of cannabis induced schizophrenia. This has been increasing even as the general incidence of schizophrenia has been stable (or even falling, depending upon who you ask). That the rise was on the order of 500 people a year means it’s not a very important point, not when compared to 3 million regular tokers, but there are still those who will buy the argument that people should be stopped from harming themselves, even if the risks are very low.
There is certainly a correlation, but we should still want to know about causation before we take any further action. For it is possible, and it is a view advanced by some (like myself last time), that those who are about to become schizophrenic dose themselves on cannabis as they are known to on alcohol and any other substance that comes to hand to still the voices. Or perhaps there’s a milder version, that cannabis induced psychosis isn’t in fact cannabis induced at all, but is simply coincidental: that it’s an early marker of schizophrenia rather than something brought on by cannabis itself.
When we try to test this we also want to be very careful indeed about our sample groups. We really don’t want to be making the mistake that the World Health Organisation has been making with HIV testing in sub-Saharan Africa. Testing pregnant women to give you the incidence of a sexually transmitted disease in the general population really ain’t all that clever: you’re testing the one group of the population where you have actual proof that they’ve been partaking in unprotected sex. It might be useful to get an idea of scale, but it’s just not going to be all that accurate.
Fortunately, all of this is just what some scientists have done
(http://www.reuters.com/article/healthNews/idUSTRE4A26JV20081103?feedType=RSS&feedName=healthNews&rpc=22&sp=true)
(sadly, the full paper
(http://archpsyc.ama-assn.org/cgi/content/short/65/11/1269)
is not online for free access). We know that there is a genetic predisposition to schizophrenia (more accurately to three different conditions that we’ll, for convenience sake, group together here). If we’re lucky we can also find a decent data set which we have indeed got, some 2.25 million Danes born between 1955 and 1990, and we know both their own treatments for either cannabis induced psychosis or for those varied schizophrenic type diseases. We can also track their familial relationships and see which of them did or didn’t suffer in these manners. Excellent, we can now try to test our correlation. Do people who have had cannabis induced psychotic episodes then go on to develop schizophrenia at a higher rate than their genetic predisposition (as evidenced by their familial incidence of schizophrenia) would lead us to believe they would?
Well, looking at the 609 who had treatment for such pot induced freakouts and those 6,476 who were treated for the full blown nastiness, well, umm, no. Formally:
In terms of estimated rate ratios, persons who develop cannabis-induced psychosis are as predisposed to schizophrenia spectrum disorder and other psychiatric disorders as those who develop schizophrenia spectrum disorder without a history of cannabis-induced psychosis.
So at this point we can say that, no, that bad trip on some heavy **** does not lead on to schizophrenia. There’s no difference in incidence.
But the paper’s authors go much further:
Altogether, these findings, in addition to those of previous studies, indicate that cannabis-induced psychosis may not be a valid diagnosis but an early marker of schizophrenia.
That is, that the very idea of that bad trip is itself wrong. The disease is already there, simply wrongly diagnosed as being cannabis induced. And finally we get:
Rather, the degree of hereditar

If you guys can find as much as you can it would be very, very, VERY helpful. =D
1. 6.02 x 1023 of anything. Calculations required.
2. A cube made of sturdy material with a total volume of 1.0 L. On the note card include the dimensions of each side of the cube. Calculations required. (no work, no credit, no kidding)
3. A cube made of sturdy material with a total volume of 1.0 mL. On the note card include the dimensions of each side of the cube. Calculations required. (no work, no credit, no kidding)
4. An acid base indicator from nature other than one you have previously made for this class. The indicator can not be a substance sold as an indicator. State the source of the indicator, what color the indicator is with an acid and what color it is with a base.
5. A weak Arrhenius acid. Define Arrhenius acid. State the common and chemical names and chemical formula.
6. A weak Arrhenius base. Define Arrhenius base. State the common and chemical names and chemical formula.
7. A physical equilibrium system containing two or more phases. Define equilibrium. Identify the common name phase of the substances at equilibrium.
8. A chemical equilibrium system containing at least two phases. Define equilibrium. Write a balanced equation representing the equilibrium.
9. A chemistry cartoon cut from a news paper or magazine. Photocopies are not acceptable. On the back of the note card include a brief statement about the concept that the cartoon is satirizing.
10. A 0.05 M solution of a substance. Include the calculations you did (no work, no credit, no kidding) a description of how you made the solution, the common and chemical name of the compound, and chemical formula.
11. A heterogeneous mixture and a homogeneous mixture. Label each sample with the mixture it represents. On the back of your note card, identify the ingredients in each mixture.
12. The mass of sodium chloride that would be produced when 2.3 g of sodium reacts with 0.56 L of chlorine gas. Assume STP and 100 % yield. Calculations and balanced equation required. (no work, no credit, no kidding)
13. A list of all the winners of the Noble Prize in Chemistry for the last 10 years. Include what year they won the prize, the scientist(s) name(s), what country they are from, and a brief statement about the nature of their research.
14. A substance with a density greater than one. State the common name, chemical name and chemical formula of the substance.
15. Iron (III) oxide. Common name and chemical name required.
16. A homogeneous substance with exactly 29 protons in the nucleus of the atoms it is composed. Common name and chemical name required.
17. An inert gas. Common name and chemical name required.
18. A Bronsted Lowery Base. State the common name, chemical name and chemical formula for this substance. Define Bronsted-Lowery Base.
19. A product of an oxidation-reduction reaction. Chemical formula, common name and chemical name required.
20. An ionically bonded substance and a covalently bonded substance. Label each with the substance it represents. Chemical formulas, common names and chemical names required.
21. Dilute acetic acid. Common name and chemical formula required.
22. SiO2; Common name and chemical name required.
23. Polar molecules. Common name, chemical name, chemical formula required.
24. A metalloid. Common name, chemical name, chemical formula required.
25. Something to lower the freezing point of water. Common name, chemical name, chemical formula required.
26. A substance that dissolves endothermically. Common name, chemical name, chemical formula required.
27. A hydrocarbon with a molecular weight of > 100. Common name, chemical name, chemical formula required.
28. Nonpolar molecules. Common name, chemical name, chemical formula required.
29. An amount of water whose temperature would change by 15 oC when it absorbed 630 calories of heat energy. Calculations required. (no work, no credit, no kidding)
30. An equilibrium system containing carbonic acid, bicarbonate ions, and carbonate ions. Define equilibrium. Explain why, in terms of carbonic acid, bicarbonate ions, and carbonate ions, the system you are submitting is at equilibrium.
31. A substance that will change hydroxyapatite, Ca5(PO4)3OH, to fluorapatite, Ca5(PO4)3F.
32. A weak organic acid. Define weak organic acid. Common name, chemical name, chemical formula required.
33. Something containing titanium (IV) oxide.
34. An alkaline earth hydroxide. Chemical formula, common name and chemical name required.
35. A compound composed of an alkali metal and a halogen. Common name, chemical name, and chemical formula required.
36. A mixture which could be separated using paper chromatography. Define paper chromatography. Common name required.
37. Something containing a transition element from period 4. Identify the transition element on the back of the note card.
38. A nonmetal. Define nonmetal. Common name and chemical formula required.
39. An electrolyte. Define electrolyte. Common name, chemical name, chemical formula required.
40. Something containing L-carvone or D-carvone. Identify which one you have. What characteristic does it impart to the substance which distinguishes it from the item you did not bring in.
41. The solid product of the reaction between aqueous solutions of calcium chloride and sodium carbonate. Balanced equation, chemical formula and common name required.
42. An aqueous solution of a nonelectrolyte. Identify the solute and solvent by common name.
43. A molecule with bonding that follows the octet rule. Common name, chemical name, chemical formula required.
44. A hydrated crystal. Chemical formula, common name and chemical name required.
45. 2-propanol. Common name and chemical formula required.
46. 0.30 mol of sodium carbonate. Calculations, chemical formula and common name required. (no work, no credit, no kidding)
47. A polymer of vinyl chloride. Define polymer. Identify the specific subunits of this polymer. Common name required.
48. An oxide of an element. Common name, chemical name, chemical formula required.
49. The salt produced when magnesium hydroxide reacts with sulfuric acid. Balanced equation, chemical formula, chemical name, and common name required.
50. The amount of NaCl produced from 10.0 g of sodium hydrogen carbonate reacting with an excess of hydrochloric acid. Assume 75 % yield. Balanced equation and calculations required. (no work, no credit, no kidding)

In science there is a lot of changes in matter, There are two types, Physical
and Chemical…
Matter is anything that has mass and volume.
To understand changes in matter, you need to know what the sample of matter was like before the change and what it is like after the change. You also need to be able to describe and classify matter.
States of Matter:
Solid
Liquid
Gas
Any kind of matter can be classified as a
mixture or a pure substance.
Mixture–matter that has two or more kinds of particles and thus may have different properties in different samples
Pure substance–a substance that has the same properties in any sample you choose. There are two kinds of pure substances: elements and compounds.
A physical change in a substance doesn’t change what the
substance is. In a chemical change where there is a chemical reaction, a new substance is formed and energy is either given off or absorbed.
For example, if a piece of paper is cut up into small pieces it still is paper. This would be a physical change in the shape and size of the paper. If the same piece of paper is burned, it is broken up into different substances that are not paper.
Physical changes can be reversed, chemical changes cannot be reversed with the substance changed back without extraordinary means, if at all. For example, a cup of water can be frozen when cooled and then can be returned to a liquid form when heated.
If one decided to mix sugar into water to make sugar water, this would be a physical change as the water could be left out to evaporate and the sugar crystals would remain. However, if one made a recipe for a cake with flour, water, sugar and other ingredients and baked them together, it would take extraordinary means to separate the various ingredients out to their original form.
When heat is given off in a chemical change or reaction, it is called an exothermic reaction. When heat is absorbed in a chemical change or reaction, it is called an endothermic reaction. The speed at which chemical reactions take place depend on the temperature pressure and how concentrated the substances involved in the chemical reaction are. Sometimes substances called catalysts are used to speed up or help along a chemical reaction. Light is helpful in the processing of film.
Magicians are not the only ones who can change one material into something completely different. Did you know that scientists, nature and even you can change one material into another? We call this “magic” a chemical reaction.
In a chemical reaction matter is changed from one substance from one to another.
Burning wood changes the wood into ash. Water will react with iron to form a new product. Do you know what it is? If you have ever left your bicycle in the rain you probably know it is called rust.
Chemical reactions may also produce heat, light, bubbles or color changes. When the bike rusted, the metal turned a different color so we know that a chemical reaction occurred between the bike and the water. Please remember that not all color changes prove that a chemical reaction has taken place.
A physical change is different than a chemical change. Things that are changed physically do not turn into something else.
Breaking a match in two pieces is an example of a physical change. Lighting a match and letting is burn is an example of a chemical change.
Matter undergoes certain changes as a result of the application of energy. Glaciers melt in summer and rivers freeze in winter. Water from saltpans on the sea coast dry up, leaving behind salt. Water from the sea evaporates to from water vapor, which form into clouds and then condense to form rain. A candle upon burning gives light, heat, water vapor and carbon dioxide. Hydrogen burns in air to form water.
Physical Change
A physical change is one in which the shape, size, appearance or state, of a substance may alter, but its chemical composition remains same. No new substance is formed. It is usually a change, which is reversible. By reversing the process, the original substance can be obtained.
Chemical Change
A change in which the composition of a substance is altered is called as chemical change. As a result, the original properties get changed and one or more new substances are formed.
Main Features of Physical and Chemical Changes
Energy Changes in a Chemical Reaction
Chemical reactions are often accompanied by evolution or absorption of energy.
Types of Chemical Changes
Decomposition It is a chemical reaction in which molecules of a substance break down to form simpler molecules of two or more new substances. Decomposition of a substance, due to heat is called thermal decomposition, while decomposition due to electricity, is called electrolytic decomposition.
Action of Heat on Substances
Heat is a very powerful form of energy. Although there are other forms of energy like light and electricity, heat is the most commonly used agent for initiating all chemical changes.
Summary
In a physical change the shape, size, appearance or state of a substance may alter, but it is a temporary change, which is usually reversible. There is no new substance formed, no change in the mass of the substance and no energy changes are involved.
Matter is the Stuff Around You
Mixtures on Earth Matter is everything around you. Matter is anything made of atoms and molecules. Matter is anything that has a mass. Matter is also related to light and electromagnetic radiation. Even though matter can be found all over the universe, you usually find it in just a few forms. As of 1995, scientists have identified five states of matter. They may discover one more by the time you get old.
You should know about solids, liquids, gases, plasmas, and a new one called Bose-Einstein condensates. The first four have been around a long time. The scientists who worked with the Bose-Einstein condensate received a Nobel Prize for their work in 1995. But what makes a state of matter? It’s about the physical state of molecules and atoms.
Changing States of Matter
Sun has more matter than all planets Elements and compounds can move from one physical state to another and not change. Oxygen (O2) as a gas still has the same properties as liquid oxygen. The liquid state is colder and denser but the molecules are still the same. Water is another example. The compound water is made up of two hydrogen (H) atoms and one oxygen (O) atom. It has the same molecular structure whether it is a gas, liquid, or solid. Although its physical state may change, its chemical state remains the same.
So you ask, “What is a chemical state?” If the formula of water were to change, that would be a chemical change. If you added another oxygen atom, you would make hydrogen peroxide (H2O2). Its molecules would not be water anymore. Changing states of matter is about changing densities, pressures, temperatures, and other physical properties. The basic chemical structure does not change.
The properties of a substance are those characteristics that are used to identify or describe it. When we say that water is “wet”, or that silver is “shiny”, we are describing materials in terms of their properties. Properties can be divided into the categories of physical properties and chemical properties. Physical properties are readily observable, like; color, size, luster, or smell. Chemical properties are only observable during a chemical reaction. For example, you might not know if sulfur is combustible unless you tried to burn it.
Another way of separating kinds of properties is to think about whether or not the size of a sample would affect a particular property. No matter how much pure copper you have, it always has the same distinctive color. No matter how much water you have, it always freezes at zero degrees Celsius under standard atmospheric conditions. Methane gas is combustible, no matter the size of the sample. Properties, which do not depend on the size of the sample involved, like those described above, are called intensive properties. Some of the most common intensive properties are; density, freezing point, color, melting point, reactivity, luster, malleability, and conductivity.
Extensive properties are those that do depend on the size of the sample involved. A large sample of carbon would take up a bigger area than a small sample of carbon, so volume is an extensive property. Some of the most common types of extensive properties are; length, volume, mass and weight.
Pieces of matter undergo various changes all of the time. Some changes, like an increase in temperature, are relatively minor. Other changes, like the combustion of a piece of wood, are fairly drastic. These changes are divided into the categories of Physical and Chemical change. The main factor that distinguishes one category form the other is whether or not a particular change results in the production of a new substance.
Physical changes are those changes that do not result in the production of a new substance. If you melt a block of ice, you still have H2O at the end of the change. If you break a bottle, you still have glass. Painting a piece of wood will not make it stop being wood. Some common examples of physical changes are; melting, freezing, condensing, breaking, crushing, cutting, and bending. Special types of physical changes where any object changes state, such as when water freezes or evaporates, are sometimes called change of state operations.
Chemical changes, or chemical reactions, are changes that result in the production of another substance. When you burn a log in a fireplace, you are carrying out a chemical reaction that releases carbon. When you light your Bunsen burner in lab, you are carrying out a chemical reaction that produces water and carbon dioxide. Common examples of chemical changes that you may be somewhat familiar with are; digestion, respiration, photosynthesis, burning, and decomposition
A physical change is reversible, a chemical change is not. For example, the freezing of water would be a physical change because it can be reversed, whereas the burning of wood is a chemical change – you can’t ‘unburn’ it, A physical change is a change in which no new substance is formed; a chemical change results in the formation of one or more new substances. Again, consider the previous examples: Freezing water into ice just results in water molecules which are ’stuck’ together – it’s still H2O. Whereas burning wood results in ash, carbon dioxide, etc, all new substances which weren’t there when you started
Is there a difference?
Yes, is a big difference! If you change something physically you still have what you started with. For example, if you tear a piece of paper you still have paper. If you change something chemically you end up with something very different than what you started with. For example if you burn a piece of paper you end up with carbon and no more paper.
But, these are obvious examples. Is it always that simple? What if you put sugar into water? Is that a physical or a chemical change? How about if you freeze water? Is that physical or chemical? For these examples we have to examine what it would take to get the original substances back after wo have made the change. With the sugar and the water we could evaporate the water and find that the sugar is left and there is no change, except in how it looks. It is still sweet and it can be remixed in water. The frozen water can be melted and we have the same water we started with.
If we take that same sugar and water and mix it with flour and eggs and vanilla and chocolate chips and cook it we will have performed a chemical change making cookies. No matter what you do to the cookies you will never get the sugar and the water out of them as before.
All substances have properties that we can use to identify them. For example we can idenify a person by their face, their voice, height, finger prints, DNA etc.. The more of these properties that we can identify, the better we know the person. In a similar way matter has properties – and there are many of them. There are two basic types of properties that we can associate with matter. These properties are called Physical properties and Chemical properties..
Physical properties: Properties that do not change the chemical nature of matter
Chemical properties: Properties that do change tha chemical nature of matter
Examples of physical properties are: color, smell, freezing point, boiling point, melting point, infra-red spectrum, attraction (paramagnetic) or repulsion (diamagnetic) to magnets, opacity, viscosity and density. There are many more examples. Note that measuring each of these properties will not alter the basic nature of the substance.
Examples of chemical properties are: heat of combustion, reactivity with water, PH, and electromotive force.
The more properties we can identify for a substance, the better we know the nature of that substance. These properties can then help us model the substance and thus understand how this substance will behave under various conditions.
Physical properties:
Colour
Melting Point
Boiling Point
Solubility
Hardness
Strength
Elasticity
Heat Conductivity
Electrical Conductivity
Ability to transmit light
Lustre (’shininess’ or dullness)
Magnetic attraction
Chemical Properties are:
pH
Reaction with oxygen (flammability or corrosion)
Reaction with water
Reaction with acids and bases
Reaction with metals
So, in summary, there are really only two criteria for whether a change is chemical or physical: After the change does it look the same and Can you change it back? If the answer is yes, the change is physical every time.If the answer is no the change is chemical every time.