I took a look on the website of the Royal Society of Chemistry some time back and found some resources that will help you to organise all the information that you have learnt about acids, bases and salts, and some helpsheets that you may find useful to classify reactions.
The ones that I think will be most useful are
Core
Acid revision map
Completing word equations
Types of Chemical Reaction
additional and extension
The periodic table
Explaining acid strength
Print and keep. Enjoy!
Friday, February 25, 2005
Mathematical interlude - The divine ratio, Phi
At the moment we are doing chemical calculations, an important part of the sylabus as these will lay the groundwork for much of the rest of your course, so we'll need to really understand what's going on here, hence why I am taking it so slowly to make sure that none of you get left behind.
In class the other day I mentioned the constant Phi, whose value is 1.618. This is a dimensionless constant as it is a ratio, and it's a ratio found so commonly in nature that it has it's own name: The Divine Ratio. More about the Divine Ratio in a minute.
When I say a "dimensionless ratio" I see a lot of you looking back at me blankly - let me clarify.
If we take a line and measure it we get back a measurement with units in, lets say for simplicity, metres. The unit of this measurement is metre. The dimension of this measurement is 1, as it's a straight line, which in theory takes up only one spatial dimension. It's one-dimensional or 1D.
If we then take the same line and move it "upwards" in space it traces out a new object. If we travel the same distance "up" as the length of the orignal line we get a new shape built, a square. The square now has units of metres-squared or metres to the power of 2. The shape exists now in a second dimension. This goes on and on by taking your new object and pulling it into the next dimension to create the next-dimensional object. *(see end notes for further comments on dimensional increase)
If we take a square and divide the area by the length of the line we arrive back at the original line length and the original unit, metre, and hence the original dimension.
If we however, take the square and divide it be another square, or take a square number and divide it by another square number, what do we get?
Something that has no units. A ratio. This tells us how many times our square can fit into the space occupied by the dividing square.
This ratio is dimensionless, as is the ratio of a line (1D) divided by a line (1D). In fact ALL ratios are dimensionless.
The point of the lesson on Wednesday was to point out that the RAM is nothing but a RATIO of masses, which compares the mass of the element you are looking at with another mass. The mass that was chosen was the mass of the carbon atom, or specifically part of a carbon atom. In order to give us a constant to compare to the mass of a standard Carbon-12 divided into 12 was chosen as the standard.
The name RELATIVE Atomic Mass tells us that it's not ACTUALLY an atomic mass, as that would have units of mass, namely the atomic mass unit or even grams if you wanted. But this tells us how many times more or less it's mass is compared to something else.
So Hydrogen has a mass equal to one twelth of a carbon-12, Lithium, 7 times etc. Note that the RAM is the Relative Atomic Mass of a number of atoms and hence it can be a non-integer number (not whole number) like Chlorine.
As this is only a ratio and has no units, in calculations it does not represent ACTUAL quantities, only it only tells us how much more one elements mass is than another. e.g. it's true to say "The mass of Oxygen is 16 times that of Hydrogen and 4 times that of Helium" - this statement would hold true if we were talking about any quantity of oxygen, hydrogen or helium. It's a COMPARISON. It's also true to say that "The same NUMBER OF ATOMS of oxygen would have a mass 16 times that of the SAME NUMBER of Hydrogen and 4 times that of the SAME NUMBER of helium"
Anyway back to the Divine Ratio. The divine ratio is dimensionless, as a ratio always is. It is the most beautiful example (in so many ways) of the dimensionlessness of ratios as it is seen in nature in the division of many different dimensions.
Plants, Animals and human beings all display proportions that follow the divine ratio. Try it next time you have a tape measure. Measure the distance between the top of your head and the floor. Then divide that length by the distance between your belly button to the floor. The number that comes out is 1.618. Phi.
Try this one - hip to floor divided by knee to floor. Or this one while you're sitting at your desk - finger joints. Toes. Spinal divisions. In fact the human being is such a testimony to Phi that Leonardo da Vinci himself drew his human figure, The Vitruvian Man in these proportions and this was long regarded as the most perfect human figure in art. The name of the painting derives from the Roman Architect Marcus Vitruvius who praised the Divine Proportion in his text De Architectura. You can read more about the Divine Ratio in Dan Browns "The Da Vainci Code"
Phi is everywhere - in shells, trees, mountains, coastlines, clouds and other fractals. Everywhere. The number of males to females in any bee colony is phi.
If you want to read about fractals but don't want to pick up a maths book I strongly recommend, Michael Crichtons Jurassic Park. If you do want to pick up a maths book then I would recommend popular science such as "From here to infinity" by Ian Stewart (A lecturer at my old university)
And of course there is a wealth of information to be found on the web too. Have fun!
Phoenix
*End notes - In Edwin A Abbot's classic mathematical novel "Flatland" he describes the process beautiully as "being pulled "up but not north". The story describes the encounter of A Square, an inhabitant of Flatland where all beings are 2-dimensional, who one day meets a divine being from the next dimension, A Sphere. Described with the fanaticism of a avid mathematician Abbott paints a witty and thought provoking picture of the narrowmindedness of society, through a discourse in geometry, and opens the minds eye to the possiblity, or should that be certainty of dimensions above the limits of our perception. Written in the 19th century, Abbotts novel predated Einsteins advances into the next dimension (relativity) by almost half a century.
- Extended -
At your present level of study, a thorough knowledge of dimensional analysis is not really important as you deal with so few variables in your equations. As your study increaseas it becomes much more important to check that the dimensions on either side of your equations balance, and this is why I feel it necessary to introduce you to the concept of dimensions, even though it's not on the sylabus as such. If you choose to take this knowledge on then that's great, if not then you'll learn it later anyway, it is your choice.
A point of note though - a dimensionless constant, though dimensionless, still can have a very profound effect on your final answer as these are ratios. Take Pi for example. This is but a ratio of the circumference over the diameter of a circle. Though dimensionless it appears in one of the first equations you will have ever learnt. The point here in chemistry is that the RAM is a dimensionless constant, a ratio of the mass of a given amount of an element against 1/12 of the mass of a carbon-12 atom.
Other dimensionless constants you may have met include Hubbles constant, e and now Phi. If it's a ratio it's dimensionless by it's very definition, because it is one quantity divided by another quantity of the same units. Hence, in actual fact, the big numbers in our balanced equations that we refer to as the number of moles are actually dimensionless ratios showing us proportions of reactants
In class the other day I mentioned the constant Phi, whose value is 1.618. This is a dimensionless constant as it is a ratio, and it's a ratio found so commonly in nature that it has it's own name: The Divine Ratio. More about the Divine Ratio in a minute.
When I say a "dimensionless ratio" I see a lot of you looking back at me blankly - let me clarify.
If we take a line and measure it we get back a measurement with units in, lets say for simplicity, metres. The unit of this measurement is metre. The dimension of this measurement is 1, as it's a straight line, which in theory takes up only one spatial dimension. It's one-dimensional or 1D.
If we then take the same line and move it "upwards" in space it traces out a new object. If we travel the same distance "up" as the length of the orignal line we get a new shape built, a square. The square now has units of metres-squared or metres to the power of 2. The shape exists now in a second dimension. This goes on and on by taking your new object and pulling it into the next dimension to create the next-dimensional object. *(see end notes for further comments on dimensional increase)
If we take a square and divide the area by the length of the line we arrive back at the original line length and the original unit, metre, and hence the original dimension.
If we however, take the square and divide it be another square, or take a square number and divide it by another square number, what do we get?
Something that has no units. A ratio. This tells us how many times our square can fit into the space occupied by the dividing square.
This ratio is dimensionless, as is the ratio of a line (1D) divided by a line (1D). In fact ALL ratios are dimensionless.
The point of the lesson on Wednesday was to point out that the RAM is nothing but a RATIO of masses, which compares the mass of the element you are looking at with another mass. The mass that was chosen was the mass of the carbon atom, or specifically part of a carbon atom. In order to give us a constant to compare to the mass of a standard Carbon-12 divided into 12 was chosen as the standard.
The name RELATIVE Atomic Mass tells us that it's not ACTUALLY an atomic mass, as that would have units of mass, namely the atomic mass unit or even grams if you wanted. But this tells us how many times more or less it's mass is compared to something else.
So Hydrogen has a mass equal to one twelth of a carbon-12, Lithium, 7 times etc. Note that the RAM is the Relative Atomic Mass of a number of atoms and hence it can be a non-integer number (not whole number) like Chlorine.
As this is only a ratio and has no units, in calculations it does not represent ACTUAL quantities, only it only tells us how much more one elements mass is than another. e.g. it's true to say "The mass of Oxygen is 16 times that of Hydrogen and 4 times that of Helium" - this statement would hold true if we were talking about any quantity of oxygen, hydrogen or helium. It's a COMPARISON. It's also true to say that "The same NUMBER OF ATOMS of oxygen would have a mass 16 times that of the SAME NUMBER of Hydrogen and 4 times that of the SAME NUMBER of helium"
Anyway back to the Divine Ratio. The divine ratio is dimensionless, as a ratio always is. It is the most beautiful example (in so many ways) of the dimensionlessness of ratios as it is seen in nature in the division of many different dimensions.
Plants, Animals and human beings all display proportions that follow the divine ratio. Try it next time you have a tape measure. Measure the distance between the top of your head and the floor. Then divide that length by the distance between your belly button to the floor. The number that comes out is 1.618. Phi.
Try this one - hip to floor divided by knee to floor. Or this one while you're sitting at your desk - finger joints. Toes. Spinal divisions. In fact the human being is such a testimony to Phi that Leonardo da Vinci himself drew his human figure, The Vitruvian Man in these proportions and this was long regarded as the most perfect human figure in art. The name of the painting derives from the Roman Architect Marcus Vitruvius who praised the Divine Proportion in his text De Architectura. You can read more about the Divine Ratio in Dan Browns "The Da Vainci Code"
Phi is everywhere - in shells, trees, mountains, coastlines, clouds and other fractals. Everywhere. The number of males to females in any bee colony is phi.
If you want to read about fractals but don't want to pick up a maths book I strongly recommend, Michael Crichtons Jurassic Park. If you do want to pick up a maths book then I would recommend popular science such as "From here to infinity" by Ian Stewart (A lecturer at my old university)
And of course there is a wealth of information to be found on the web too. Have fun!
Phoenix
*End notes - In Edwin A Abbot's classic mathematical novel "Flatland" he describes the process beautiully as "being pulled "up but not north". The story describes the encounter of A Square, an inhabitant of Flatland where all beings are 2-dimensional, who one day meets a divine being from the next dimension, A Sphere. Described with the fanaticism of a avid mathematician Abbott paints a witty and thought provoking picture of the narrowmindedness of society, through a discourse in geometry, and opens the minds eye to the possiblity, or should that be certainty of dimensions above the limits of our perception. Written in the 19th century, Abbotts novel predated Einsteins advances into the next dimension (relativity) by almost half a century.
- Extended -
At your present level of study, a thorough knowledge of dimensional analysis is not really important as you deal with so few variables in your equations. As your study increaseas it becomes much more important to check that the dimensions on either side of your equations balance, and this is why I feel it necessary to introduce you to the concept of dimensions, even though it's not on the sylabus as such. If you choose to take this knowledge on then that's great, if not then you'll learn it later anyway, it is your choice.
A point of note though - a dimensionless constant, though dimensionless, still can have a very profound effect on your final answer as these are ratios. Take Pi for example. This is but a ratio of the circumference over the diameter of a circle. Though dimensionless it appears in one of the first equations you will have ever learnt. The point here in chemistry is that the RAM is a dimensionless constant, a ratio of the mass of a given amount of an element against 1/12 of the mass of a carbon-12 atom.
Other dimensionless constants you may have met include Hubbles constant, e and now Phi. If it's a ratio it's dimensionless by it's very definition, because it is one quantity divided by another quantity of the same units. Hence, in actual fact, the big numbers in our balanced equations that we refer to as the number of moles are actually dimensionless ratios showing us proportions of reactants
Tuesday, February 22, 2005
Chill out year 9 it's a QUIZ
Maybe I didn't really make this clear enough. The quiz is designed to help you to LEARN and to try to STRETCH you. It's not a TEST as such in that the result is for you and me to know, no one else. It's for me to test your learning and for you to see what more you need to learn. It's NOT a test in the sense that it will not go on any official documents. It is there to HELP YOU.
Is that clear enough?
Is that clear enough?
Monday, February 14, 2005
Acids, bases and salts test now online
The test is uploaded and ready to take now until Feb 23 at the very very latest. I suggest though that you wait until after the Wednesday lesson before you take it.
It's very hard....
http://quizstar.4teachers.org and log on using the username and password you were given in class - if you have lost it please email me
good luck!
It's very hard....
http://quizstar.4teachers.org and log on using the username and password you were given in class - if you have lost it please email me
good luck!
Amphoteric Shmamphoteric
Why was I so blase about the amphoteric definition? I have never EVER seen a test question on amphoteric properties. Just know it as a definition and I'm sure you will be fine. Can be a H+ donor or acceptor. That's it. Boring.
Don't stress over it.
Don't stress over it.
IGCSE too easy for you...?
Greetings happy campers! Not one for keeping this class at IGCSE levels I have been looking through work that could extend those really bright ones amongst you. Which I must add is most of you actually.
In response to some of your questions I have answered "The answer to that question you will meet at A-level" and I know that some of you probably think "what a cop-out he just doesn't know" Well actually here is what I mean.
At A-level we study the same thing in more detail in a topic called acid equilibria. If you read the first few pages of an A-level textbook you can see that it's identical to what you have already learnt. They start off with details of acid reactions, tell you about indicators and tell you about the pH scale.
Then they start to tell you in depth about the numbers involved in making the pH scale, which are based on a logarithmic scale of H+ ions. And in answer to your question at the beginning of the acids and bases course this leads to the definiton of the letters pH which stands for Partial Pressure of Hydrogen ions hence the small p (sometimes written as a sort of double p letter).
After that you will learn about indicators and how they work over a really small range (remember that universal indicator is a mixture of indicators) and you will go more in depth with acids, understanding why some acids are strong.
Already you know that it's to do with hydrogen ions and the definiton of strong and concentrated should be well understood. At A-level we talk about something called the disociation constant (remember that the "strength" of an acid depends on all the H+ ions disociating in water) - this puts disociation into numbers that can be compared.
Here, solubility comes into the picture again.
So what you learn at IGCSE follows directly on from year 8 acids and alkalis goes to IGCSE Acids, bases and salts, then leads to Acid equilibria.
If you're interested in learning more the following uploaded files will really push you hard but I promise that if you can do them you will find ALL the answers to all your IGCSE questions on this topic and the IGCSE acids, bases and salts topic will seem like a walk in the park.
If you want to do the exercises in your book then feel free.
At present not all the files have been uploaded on this topic and I will have to take them down after a while to avoid infringing too many copyright laws.
You may find it helpful to know how to use logarithms before you start on these though...
(Don't worry too much about the filenames it's just automatic filenames I put on my scanner)
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00001.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00002.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00003.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00004.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00005.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00006.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00007.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00008.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00009.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00010.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00011.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00012.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00013.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00014.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00015.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00016.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00017.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00018.jpg
Give them a try - just challenge yourself.
In response to some of your questions I have answered "The answer to that question you will meet at A-level" and I know that some of you probably think "what a cop-out he just doesn't know" Well actually here is what I mean.
At A-level we study the same thing in more detail in a topic called acid equilibria. If you read the first few pages of an A-level textbook you can see that it's identical to what you have already learnt. They start off with details of acid reactions, tell you about indicators and tell you about the pH scale.
Then they start to tell you in depth about the numbers involved in making the pH scale, which are based on a logarithmic scale of H+ ions. And in answer to your question at the beginning of the acids and bases course this leads to the definiton of the letters pH which stands for Partial Pressure of Hydrogen ions hence the small p (sometimes written as a sort of double p letter).
After that you will learn about indicators and how they work over a really small range (remember that universal indicator is a mixture of indicators) and you will go more in depth with acids, understanding why some acids are strong.
Already you know that it's to do with hydrogen ions and the definiton of strong and concentrated should be well understood. At A-level we talk about something called the disociation constant (remember that the "strength" of an acid depends on all the H+ ions disociating in water) - this puts disociation into numbers that can be compared.
Here, solubility comes into the picture again.
So what you learn at IGCSE follows directly on from year 8 acids and alkalis goes to IGCSE Acids, bases and salts, then leads to Acid equilibria.
If you're interested in learning more the following uploaded files will really push you hard but I promise that if you can do them you will find ALL the answers to all your IGCSE questions on this topic and the IGCSE acids, bases and salts topic will seem like a walk in the park.
If you want to do the exercises in your book then feel free.
At present not all the files have been uploaded on this topic and I will have to take them down after a while to avoid infringing too many copyright laws.
You may find it helpful to know how to use logarithms before you start on these though...
(Don't worry too much about the filenames it's just automatic filenames I put on my scanner)
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00001.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00002.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00003.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00004.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00005.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00006.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00007.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00008.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00009.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00010.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00011.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00012.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00013.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00014.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00015.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00016.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00017.jpg
http://www.geocities.com/sally500uk/CGPFoundationGCSEPhys00018.jpg
Give them a try - just challenge yourself.
Ionic Equations
Following Sundays lesson on ionic equations here are the notes promised regarding technique for dealing with them.
When you write an equation down of an acid reaction it’s obviously going to be in a solution as acids HAVE to be in solution right. And therefore it follows that there will be ions roaming about waiting to react.
Lets take for our example NaOH reacting with H2SO4, a common reaction
Worked Example 1
Step 1 – work out compounds involved
NaOH + H2SO4 --> H2O + Na2SO4
The 2 after the Na comes from the fact that SO4 has a valency of 2-
Step 2 – balance equation
2NaOH + H2SO4 --> 2H2O + Na2SO4
Notice again that it takes 2 OH- to neutralise that H2SO4 – this was Question 5c earlier
Step 3 – Break into ions
(2Na+)(2OH-) + (2H+)(SO4-) --> (2H2O) + (2Na+)(SO4-)
At this point note – there are 2 reasons that H2O is not written as ionsIt is NOT an ionic bond that links itIt is the solvent – it’s not actually IN solution and hence we can’t say it breaks up in solution because it IS the solution!
Step 4 – Which ones are no longer in solution?
We can tell which ones are still in solution because they are still ionic and dissociated. Because they started off dissociated and in solution then they appear the same on both sides so you can cross them off on either side because they are identical. After all, all these reactions can only take place IN water so if they are not soluble in water no further reactions can take place. What is left over will be either covalent, water or insoluble.
There are 2 ways to spot the ones that are no longer in solution
Step 5 – Write out the ones left
This is done by crossing out the ions that are identical on both sides (for the reasons described above) (2Na+)(2OH-) + (2H+)(SO4-) --> (2H2O) + (2Na+)(SO4-) This gives us the final equation 2OH- + 2H+ --> 2H2O Hope this makes more sense now.
When you write an equation down of an acid reaction it’s obviously going to be in a solution as acids HAVE to be in solution right. And therefore it follows that there will be ions roaming about waiting to react.
Lets take for our example NaOH reacting with H2SO4, a common reaction
Sodium Hydroxide + Sulphuric Acid à Water + Sodium Sulphate
To create an ionic equation and understand how it works we need to follow some simple steps, as follows- Work out the compounds involved (They will be ionic obviously so we may need to use our ionic cross trick)
- Balance the equation (once you’ve flipped the numbers from top to bottom it usually unbalances the equation so you need to make sure that the equation is balanced – otherwise the charges will later come back and bite you!)
- Break the equation into individual ions and bracket them off
- See which ones come out of the solution and hence are no longer reactive
- Write out the ions that are left still IN solution
Worked Example 1
Step 1 – work out compounds involved
NaOH + H2SO4 --> H2O + Na2SO4
The 2 after the Na comes from the fact that SO4 has a valency of 2-
Step 2 – balance equation
2NaOH + H2SO4 --> 2H2O + Na2SO4
Notice again that it takes 2 OH- to neutralise that H2SO4 – this was Question 5c earlier
Step 3 – Break into ions
(2Na+)(2OH-) + (2H+)(SO4-) --> (2H2O) + (2Na+)(SO4-)
At this point note – there are 2 reasons that H2O is not written as ionsIt is NOT an ionic bond that links itIt is the solvent – it’s not actually IN solution and hence we can’t say it breaks up in solution because it IS the solution!
Step 4 – Which ones are no longer in solution?
We can tell which ones are still in solution because they are still ionic and dissociated. Because they started off dissociated and in solution then they appear the same on both sides so you can cross them off on either side because they are identical. After all, all these reactions can only take place IN water so if they are not soluble in water no further reactions can take place. What is left over will be either covalent, water or insoluble.
There are 2 ways to spot the ones that are no longer in solution
- They will tell you that the product is insoluble The list on page 98 under the heading formation of salts gives you rules for which salts are and are not soluble.
- They ARE the solvent - water.
Step 5 – Write out the ones left
This is done by crossing out the ions that are identical on both sides (for the reasons described above) (2Na+)(2OH-) + (2H+)(SO4-) --> (2H2O) + (2Na+)(SO4-) This gives us the final equation 2OH- + 2H+ --> 2H2O Hope this makes more sense now.
Subscribe to:
Posts (Atom)
