You've got a table of experimental data.
You've plotted the data on a graph.
Now, how do you draw a line of best fit?
Why should you draw a line of best?
AUS-e-TUTE has just added new resources that answers these questions and helps you draw the line of best for your data by giving you a tool to use which makes the whole process as easy as clicking a button!
Visit http://www.ausetute.com.au and click on the Line of Best Fit link.
Saturday, November 30, 2013
Thursday, November 28, 2013
Salts of Drugs a Health Risk
Many studies have shown that excess salt is harmful to heart health, but many commonly prescribed medicines have sodium added to improve their absorption into the body, but the effect of doing this has not been known. For example, 1 Alka-Seltzer tablet contains 324 mg of aspirin (the drug) and 445 mg of sodium.
University of Dundee and College of London researchers have found that a person taking the maximum, daily dose of some medicines would exceed the recommended daily dietary intake limits for sodium. In Australia, the total maximum recommended limit of sodium for adults should be less than 2300 mg per day (less for children). The label on the Alka-Seltzer tablets carries a warning that you should not take more than 8 tablets per day.
In the study, the researchers found that patients taking the sodium-containing medication had a 16% increased risk of a heart attack, were 7 times more likely to develop high blood pressure, and, were 28% more likely to die, compared with patients who took the non-sodium containing versions of the same drug.
So why do we add sodium to drugs if it is potentially harmful?
We do this because many drugs are actually insoluble in water. The cells in your body are made up mostly of water, so if you want to be able to transport a drug around the body, and have it absorbed into cells, it is beneficial if the drug is soluble in water.
How do we add sodium to drugs?
If the drug is, for example, a weak acid like aspirin, then it is not very soluble in water.
Being a weak acid, though, aspirin can undergo a proton transfer (neutralisation) reaction with a base such as sodium hydroxide. The product of a neutralisation reaction are salt and water.
acid + base → salt + water
aspirin + sodium hydroxide → sodium salt of aspirin + water
The sodium salt of aspirin readily dissolves in water by dissociating into positive sodium ions and negative "aspirin" ions.
Reference:
BMJ-British Medical Journal (2013, November 26). High salt levels in medicines increase risk of cardiovascular events. ScienceDaily. Retrieved November 28, 2013, from http://www.sciencedaily.com /releases/2013/11/131126191557.htm
Further Reading
aspirin
mass conversions
ppm
molarity
neutralisation
proton transfer reactions
acid dissociation constants
Suggested Study Questions:
University of Dundee and College of London researchers have found that a person taking the maximum, daily dose of some medicines would exceed the recommended daily dietary intake limits for sodium. In Australia, the total maximum recommended limit of sodium for adults should be less than 2300 mg per day (less for children). The label on the Alka-Seltzer tablets carries a warning that you should not take more than 8 tablets per day.
In the study, the researchers found that patients taking the sodium-containing medication had a 16% increased risk of a heart attack, were 7 times more likely to develop high blood pressure, and, were 28% more likely to die, compared with patients who took the non-sodium containing versions of the same drug.
So why do we add sodium to drugs if it is potentially harmful?
We do this because many drugs are actually insoluble in water. The cells in your body are made up mostly of water, so if you want to be able to transport a drug around the body, and have it absorbed into cells, it is beneficial if the drug is soluble in water.
How do we add sodium to drugs?
If the drug is, for example, a weak acid like aspirin, then it is not very soluble in water.
Being a weak acid, though, aspirin can undergo a proton transfer (neutralisation) reaction with a base such as sodium hydroxide. The product of a neutralisation reaction are salt and water.
acid + base → salt + water
aspirin + sodium hydroxide → sodium salt of aspirin + water
The sodium salt of aspirin readily dissolves in water by dissociating into positive sodium ions and negative "aspirin" ions.
Reference:
BMJ-British Medical Journal (2013, November 26). High salt levels in medicines increase risk of cardiovascular events. ScienceDaily. Retrieved November 28, 2013, from http://www.sciencedaily.com /releases/2013/11/131126191557.htm
Further Reading
aspirin
mass conversions
ppm
molarity
neutralisation
proton transfer reactions
acid dissociation constants
Suggested Study Questions:
- Convert these masses in milligrams to masses in grams
- 324 mg
- 445 mg
- The label on the Alka-Seltzer packet recommends dissolving 2 tablets in water. For these two tablets, calculate the mass in milligrams of
- aspirin
- sodium
- If you were to take the maximum number of tablets, 8, in a day, how much of each of the following substances would you be ingesting?
- aspirin
- sodium
- Would you be exceeding the recommended daily dietary intake limits for sodium in Australia? Explain your answer.
- A low salt food is one that contains less than 120 mg of sodium per 100 g of food. If Alka-Seltzer were to be considered a low salt food, what would the mass of each tablet need to be?
- Aspirin has the molecular formula C9H8O4. What is the molar mass of aspirin?
- The sodium salt of aspirin has the molecular formula C9H7O4-Na+. What is the molar mass of the sodium salt of aspirin?
- Calculate the mass of sodium in 1 Alka-Seltzer tablet due to the sodium salt of aspirin.
- Compare the mass of sodium calculated above to the actual mass of sodium present in 1 Alka-Seltzer tablet according to the package. How would you explain the difference in the two masses?
- If a person dissolved 2 Akla-Seltzer tablets in 150 mL of water, what is the concentration of sodium ions in the water in
- mol/L
- mg/L
- ppm
- Recommendations for the daily intake of potassium are higher than those for sodium at 4700 mg day, so one way to alleviate the sodium problem in aspirin tablets might be to replace the sodium with potassium. Describe one way that you could produce the potassium salt of aspirin.
Tuesday, November 26, 2013
Structure of Benzene
AUS-e-TUTE has just uploaded new resources for the Benzene topic.
You will find the new Structure of Benzene tutorial, game and test under the Aromatic Compound heading when you log-in to the Test Centre.
Relevant syllabus study guides have also been updated to include these new links.
The key concepts can be found in the "free-to-view" tutorial at
http://www.ausetute.com.au/benzene.html
There is a clickable link on that benzene page which will take AUS-e-TUTE members straight to the complete new tutorial.
You will find the new Structure of Benzene tutorial, game and test under the Aromatic Compound heading when you log-in to the Test Centre.
Relevant syllabus study guides have also been updated to include these new links.
The key concepts can be found in the "free-to-view" tutorial at
http://www.ausetute.com.au/benzene.html
There is a clickable link on that benzene page which will take AUS-e-TUTE members straight to the complete new tutorial.
Sunday, November 24, 2013
Pthalate in Plastics
Researchers in the USA have found a link between premature births and the exposure of pregnant women to a group of organic (carbon based) chemicals known as phthalates.
Phthalates have been used for more than 50 years as plasticizers, substances which are added to plastics to increase their flexibility, transparency, durability and longevity. For example, adding phthalates to polyvinyl chloride (PVC) makes the PVC soft and flexible, ideal for flexible plastic tubing. You will find phthalates in many products you come into contact with every day, from vinyl upholstery and floor tiles, to plastic food containers and wrappers, to personal care products like perfumes, moisturizer, and liquid soap.
Phthalates have the general structural formula shown below:
R and R' represent alkyl groups.
If R and R' are both CH3 (methyl) groups, the molecule is known as dimethyl phthalate (abbreviated as DMP).
If R and R' are both C2H5 (ethyl) groups, the molecule is known as diethyl phthalate (abbreviated DEP).
When R and R' are very small alkyl groups, like methyl or ethyl groups, the phthalates are colourless, odourless liquids at room temperature and pressure.
The phthalates are added to molten plastic, allowing the phthalates to mix with with the polymer. The polar C=O groups in the phthalate molecules interact with partial positive charges on atoms in the polymer chain, for example, the Cδ+ of the C-Cl covalent bond in a polyvinyl chloride polymer.
When the plastic is cooled, the interactions between the phthalate and the polymer chains remain, and the alkyl groups of the phthalate screen the polymer chains from interacting with each other so that the polymer chains can slide over each other. This results in a more flexible plastic.
Reference:
http://www.abc.net.au/news/2013-11-19/common-plastics-chemical-linked-to-pre-term-births/5101828
Further reading:
Esters and Esterification
Bond Polarity
Intermolecular Forces
Suggested Study Questions:
Phthalates have been used for more than 50 years as plasticizers, substances which are added to plastics to increase their flexibility, transparency, durability and longevity. For example, adding phthalates to polyvinyl chloride (PVC) makes the PVC soft and flexible, ideal for flexible plastic tubing. You will find phthalates in many products you come into contact with every day, from vinyl upholstery and floor tiles, to plastic food containers and wrappers, to personal care products like perfumes, moisturizer, and liquid soap.
Phthalates have the general structural formula shown below:
R and R' represent alkyl groups.
If R and R' are both CH3 (methyl) groups, the molecule is known as dimethyl phthalate (abbreviated as DMP).
If R and R' are both C2H5 (ethyl) groups, the molecule is known as diethyl phthalate (abbreviated DEP).
When R and R' are very small alkyl groups, like methyl or ethyl groups, the phthalates are colourless, odourless liquids at room temperature and pressure.
The phthalates are added to molten plastic, allowing the phthalates to mix with with the polymer. The polar C=O groups in the phthalate molecules interact with partial positive charges on atoms in the polymer chain, for example, the Cδ+ of the C-Cl covalent bond in a polyvinyl chloride polymer.
When the plastic is cooled, the interactions between the phthalate and the polymer chains remain, and the alkyl groups of the phthalate screen the polymer chains from interacting with each other so that the polymer chains can slide over each other. This results in a more flexible plastic.
Reference:
http://www.abc.net.au/news/2013-11-19/common-plastics-chemical-linked-to-pre-term-births/5101828
Further reading:
Esters and Esterification
Bond Polarity
Intermolecular Forces
Suggested Study Questions:
- Draw the structural formula for
- dimethyl phthalate
- diethyl phthalate
- Give the molecular formula for
- dimethyl phthalate
- diethyl phthalate
- On the structural formula for dimethyl phthalate, circle a benzene ring.
- On the structural formala for diethyl phthalate, circle an ester functional group.
- Dimethyl phthalate can be prepared in an esterification reaction using phthalic acid and methanol. Draw the most likely structural formula for phthalic acid.
- In chemistry, what is meant by a polar bond?
- On the structural formula of diethyl phthalate, show the partial charges of the atoms in the polar areas of the molecule.
- Draw a diagram to show the interaction between dimethyl phthalate and a section of the polyvinyl chloride polymer.
Friday, November 22, 2013
HPLC
AUS-e-TUTE has just added new resources for the High Performance Liquid Chromatography (HPLC) topic.
The new resources include a tutorial, game, test and exam.
Go to http://www.ausetute.com.au and log-in to start using these new resources.
The Chemistry Syllabus Study Guides for Queensland, New South Wales, Australian Capital Territory, Victoria, South Australia, and, AP Chemistry (USA and undergraduate) have been updated to include these new resources.
Links to the new resources have also been added from the Class/School Group index page.
The new resources include a tutorial, game, test and exam.
Go to http://www.ausetute.com.au and log-in to start using these new resources.
The Chemistry Syllabus Study Guides for Queensland, New South Wales, Australian Capital Territory, Victoria, South Australia, and, AP Chemistry (USA and undergraduate) have been updated to include these new resources.
Links to the new resources have also been added from the Class/School Group index page.
Wednesday, November 20, 2013
Gas Chromatography Resources
AUS-e-TUTE has added new resources for the Gas Chromatography (GC) topic.
You will find links to the new tutorial, game, test and updated exams included in
You will find links to the new tutorial, game, test and updated exams included in
- Test Centre index page (all members)
- Queensland syllabus study guide for chemistry (Australia)
- New South Wales syllabus study guide for chemistry (Australia)
- Australian Capital Territory syllabus study guide for chemistry (Australia)
- Victorian syllabus study guide for chemistry (Australia)
- South Australian syllabus study guide for chemistry (Australia)
- AP syllabus study guide for chemistry (USA and undergraduate chemistry)
- Class/School Group index page
Saturday, November 9, 2013
A little MatheMagic is needed!
The University of Queensland's Faculty of Engineering held a networking forum for teachers on 5th November 2013. They expressed a number of concerns regarding the High School graduates entering the first year engineering course, and I think it's worthwhile highlighting one of those concerns here.
The main academic concern is that High School graduates do not have an adequate background in mathematics to cope with engineering. Now, they were very upfront about this, admitting that part of the problem was that they reduced the prerequisite from Maths C to Maths B in order to attract more school graduates to engineering. For those not familiar with the Queensland education "system", students present 6 final subjects, Maths B is one subject and Maths C is a separate , more advanced subject. Previously, engineering hopefuls would study Physics, Chemistry, Maths B, Maths C, English + 1 other subject. Now, they can present Physics, Chemistry, Maths B, English + 2 other subjects. The assembled teachers weren't very sympathetic to start with, why don't you just raise the prerequisite to Maths C again? Until we were presented with examples of the kind of maths some of the students seemed to be struggling with.
One of the examples we were given was that there were students who believed that if
a + b = -1 then that means that a = -b
and that is a huge concern! But raising the prerequisite wouldn't help, simply because any Maths student in senior high school should have no trouble realizing that a = -1 - b
I've had a similar discussion with a friend of mine who is a lecturer in nursing (at a different university). Her complaint is that High School graduates entering first year nursing often have difficulty with calculations involving drug doses. For instance, students have to decide how many tablets to give a patient given that a doctor has prescribed 100 mg of drug A four times a day, and that the hospital supplies brand X tablets each containing 50 mg of drug A.
High School chemistry and physics teachers are very familiar with this problem. There always seem to be atleast a few students in each class who appear to be quite good at maths judging by their report cards, but who don't seem able to handle fairly simply algebra when they leave the maths class.
Now, before the maths teachers start feeling indignant, let me say that this problem is not restricted to maths, and, unfortunately, it isn't even restricted to students. After the Engineering Faculty's presentation, I was chatting to a science teacher who was telling me about developments in the silicon chip industry that required "water that is so pure it is acidic".Curious, I followed up with a few questions, thinking that this teacher may have been using a definition of acid that I wasn't familiar with, but no, this teacher seemed to be using a Bronsted-Lowry definition.
So, the problem in a nutshell is that we are graduating students from schools with reasonable grades in maths who are not capable of rearranging an equation (and the much worse problem that there are teachers teaching science who don't seem to understand the concept of equilibrium and neutrality).
Clearly, any "learning" that has taken place is only at a very superficial level. How can we address this problem?
The main academic concern is that High School graduates do not have an adequate background in mathematics to cope with engineering. Now, they were very upfront about this, admitting that part of the problem was that they reduced the prerequisite from Maths C to Maths B in order to attract more school graduates to engineering. For those not familiar with the Queensland education "system", students present 6 final subjects, Maths B is one subject and Maths C is a separate , more advanced subject. Previously, engineering hopefuls would study Physics, Chemistry, Maths B, Maths C, English + 1 other subject. Now, they can present Physics, Chemistry, Maths B, English + 2 other subjects. The assembled teachers weren't very sympathetic to start with, why don't you just raise the prerequisite to Maths C again? Until we were presented with examples of the kind of maths some of the students seemed to be struggling with.
One of the examples we were given was that there were students who believed that if
a + b = -1 then that means that a = -b
and that is a huge concern! But raising the prerequisite wouldn't help, simply because any Maths student in senior high school should have no trouble realizing that a = -1 - b
I've had a similar discussion with a friend of mine who is a lecturer in nursing (at a different university). Her complaint is that High School graduates entering first year nursing often have difficulty with calculations involving drug doses. For instance, students have to decide how many tablets to give a patient given that a doctor has prescribed 100 mg of drug A four times a day, and that the hospital supplies brand X tablets each containing 50 mg of drug A.
High School chemistry and physics teachers are very familiar with this problem. There always seem to be atleast a few students in each class who appear to be quite good at maths judging by their report cards, but who don't seem able to handle fairly simply algebra when they leave the maths class.
Now, before the maths teachers start feeling indignant, let me say that this problem is not restricted to maths, and, unfortunately, it isn't even restricted to students. After the Engineering Faculty's presentation, I was chatting to a science teacher who was telling me about developments in the silicon chip industry that required "water that is so pure it is acidic".Curious, I followed up with a few questions, thinking that this teacher may have been using a definition of acid that I wasn't familiar with, but no, this teacher seemed to be using a Bronsted-Lowry definition.
So, the problem in a nutshell is that we are graduating students from schools with reasonable grades in maths who are not capable of rearranging an equation (and the much worse problem that there are teachers teaching science who don't seem to understand the concept of equilibrium and neutrality).
Clearly, any "learning" that has taken place is only at a very superficial level. How can we address this problem?
Wednesday, November 6, 2013
6 Random Questions Answered
Every so often, AUS-e-TUTE randomly selects 6 questions that have been asked in the last few hours by people who are not AUS-e-TUTE members.
Today's selection is:
1/ Question from Canada, "ammonia gas undergoes a combustion to produce nitrogen dioxide gas and water vapour. write and balance the equation"
Answer: 2NH3 +7/2O2 → 2NO2 + 3H2O
2/ Question from USA, "How do you convert weight percent to mass fraction?"
Answer: percent by mass (weight) = mass (weight) fraction x 100
reference: http://www.ausetute.com.au/weightpc.html
3/ Question from USA, "what are the physical properties of metals due to metallic bonding?"
Answer: The physical properties of solid metals are:
4/ Question from USA, "Can air be separated by physical means?"
Answer: Yes. Air is a mixture so it can be separated by physical means.
Reference: http://www.ausetute.com.au/chemphys.html
5/ Question from USA, "How do you calculate atomic mass from relative abundance?"
Answer: Given the relative atomic mass (r.a.m.) of an element and the mass of each of its isotopes, the relative abundance of each isotope can be calculated:
let y/100 = abundance of isotope 1
and (100 - y)/100 = abundance of isotope 2
then, r.a.m = [y/100 x mass isotope 1] + [(100 - y)/100 x mass isotope 2]
and solve for y
Reference: http://www.ausetute.com.au/atomicmass.html
6/ Question from USA, "How do you turn empirical formula into molecular formula?"
Answer: molecular formula = whole number x empirical formula
Reference: http://www.ausetute.com.au/empirical.html
Today's selection is:
1/ Question from Canada, "ammonia gas undergoes a combustion to produce nitrogen dioxide gas and water vapour. write and balance the equation"
Answer: 2NH3 +7/2O2 → 2NO2 + 3H2O
2/ Question from USA, "How do you convert weight percent to mass fraction?"
Answer: percent by mass (weight) = mass (weight) fraction x 100
reference: http://www.ausetute.com.au/weightpc.html
3/ Question from USA, "what are the physical properties of metals due to metallic bonding?"
Answer: The physical properties of solid metals are:
- conduct heat
- conduct electricity
- generally high melting and boiling points
- strong
- malleable (can be hammered or pressed out of shape without breaking)
- ductile (able to be drawn into a wire)
- metallic lustre
- opaque (reflect light)
4/ Question from USA, "Can air be separated by physical means?"
Answer: Yes. Air is a mixture so it can be separated by physical means.
Reference: http://www.ausetute.com.au/chemphys.html
5/ Question from USA, "How do you calculate atomic mass from relative abundance?"
Answer: Given the relative atomic mass (r.a.m.) of an element and the mass of each of its isotopes, the relative abundance of each isotope can be calculated:
let y/100 = abundance of isotope 1
and (100 - y)/100 = abundance of isotope 2
then, r.a.m = [y/100 x mass isotope 1] + [(100 - y)/100 x mass isotope 2]
and solve for y
Reference: http://www.ausetute.com.au/atomicmass.html
6/ Question from USA, "How do you turn empirical formula into molecular formula?"
Answer: molecular formula = whole number x empirical formula
Reference: http://www.ausetute.com.au/empirical.html
Monday, November 4, 2013
Azobenzene: cis-trans isomers
A new soluble, light sensitive polymer has been created at the University of Helsinki. The polymer partially dissolves in water or certain alcohols, and, when exposed to light, the polymer switches to its cis isomer and dissolves completely.
This new polymer chain is known to contain azo compounds, and azo compounds are known for this ability to switch between cis and trans isomers using light.
Azo compounds are organic molecules in which two benzene rings (known as phenyl groups) are linked by two nitrogen atoms.
Azobenzene has the IUPAC name diphenyldiazene and is the simplest of the azo compounds.
When the 2 benzene rings (phenyl groups) are on the same side of the N=N bond this is known as the cis isomer. The structural formula for cis-azobenzene is shown below:
When the 2 benzene rings (phenyl groups) are on different sides of the N=N bond this is known as the trans isomer. The structural formula for trans-azobenzene is shown below:
The cis isomer is less stable than the trans isomer. In the presence of light (hν) , the trans isomer will convert to the cis isomer:
but because the cis isomer is less stable, it will relax back to the trans isomer over time:
Cis-azobenzene is more polar than trans-azobenzene so cis-azobenzene is more water soluble than trans-azobenzene.
Reference:
Szymon Wiktorowicz, Heikki Tenhu, Vladimir Aseyev. Using Light To Tune Thermo-Responsive Behavior and Host–Guest Interactions in Tegylated Poly(azocalix[4]arene)s. Macromolecules, 2013; 46 (15): 6209 DOI: 10.1021/ma4011457
Further Reading:
Cis-trans (geometric) Isomers
Suggested Study Questions:
This new polymer chain is known to contain azo compounds, and azo compounds are known for this ability to switch between cis and trans isomers using light.
Azo compounds are organic molecules in which two benzene rings (known as phenyl groups) are linked by two nitrogen atoms.
Azobenzene has the IUPAC name diphenyldiazene and is the simplest of the azo compounds.
When the 2 benzene rings (phenyl groups) are on the same side of the N=N bond this is known as the cis isomer. The structural formula for cis-azobenzene is shown below:
When the 2 benzene rings (phenyl groups) are on different sides of the N=N bond this is known as the trans isomer. The structural formula for trans-azobenzene is shown below:
The cis isomer is less stable than the trans isomer. In the presence of light (hν) , the trans isomer will convert to the cis isomer:
|
hν → |
|
but because the cis isomer is less stable, it will relax back to the trans isomer over time:
|
→ | |
Reference:
Szymon Wiktorowicz, Heikki Tenhu, Vladimir Aseyev. Using Light To Tune Thermo-Responsive Behavior and Host–Guest Interactions in Tegylated Poly(azocalix[4]arene)s. Macromolecules, 2013; 46 (15): 6209 DOI: 10.1021/ma4011457
Further Reading:
Cis-trans (geometric) Isomers
Suggested Study Questions:
- Give the molecular formula for cis-azobenzene and trans-azobenzene.
- Explain why azobenzene displays cis-trans (geometric) isomerism.
- If the N=N bond in azobenzene was replaced with N-N, would the resulting molecule display cis-trans (geometric) isomerism? Explain your answer.
- On a drawing of the structural formula of trans-azobenzene, circle a phenyl group.
- Diazene (diimine) has the molecular formula (NH)2 . It contains the same N=N bond as azobenzene or diphenyldiazene. Diazene also displays cis-trans (geometric) isomerism. Draw both cis-diazene and trans-diazene.
- Hydrazine has the molecular formula N2H4. Draw a possible structural formula for hydrazine.
- Do you expect hydrazine to display cis-trans (geometric) isomerism? Explain your answer.
- Draw the molecular formula for the molecule trans-dibutyldiazene.
- Dibutyldiazene undergoes an addition reaction with hydrogen gas. Draw the structural formula for the product of this reaction.
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