Calculations for Strong Bases

AUS-e-TUTE has just added new resources!
As part of the update of our "Acids and Bases" topic, tutorials, games, tests, and exams have been added for the following:

• pOH Concepts
• Strength of Bases
• Calculating the pOH of Strong Bases (aqueous solutions)
• Calculating the Hydroxide Ion Concentration of Strong Bases (aqueous solutions)
• Calculating the pH of Strong Bases (aqueous solutions)
• Calculating the Hydrogen Ion Concentration of Strong Bases (aqueous solutions)

AUS-e-NEWS March 2013

Since the 1960's, superacids have become an essential tool in industry.

Without the powerful ability of superacids to react with, and break down, raw petroleum we would not have a supply of cheap, high-strength plastics.

But what is a superacid?

Read this super issue of AUS-e-NEWS to find out !

Links to the following new resources can be found in the Test Centre (http://www.ausetute.com.au/members/testcent.html)

                - Properties of Acids and Bases (tutorial, game, test)

                - Definitions of Acids and Bases (tutorial, game, tests, exams)

                - pH Scale (Tutorial, game, test, exam)

                - pH Calculations, introductory (tutorial, game, test, drill)

                - pOH Calculations, introductory (tutorial, game, test, drill)

                - Hydrogen Ion Concentration calcuations, introductory (tutorial, game, test, drill)

                - Hydroxide Ion Concentration Calculations, introductory (tutorial, game, test, drill)

                - Strength of Acids (Tutorial, game, test,exams)

                - Strong Acid pH Calculations (Tutorial, game, test, exam)

                - Strong Acid Hydrogen Ion Concentration Calculations (Tutorial, game, test, exam)

                - Strong Acid Hydroxide Ion Calculations Calculations (Tutorial, game, test)

                - Strong Acid pOH Calculations (Tutorial, game, test)

                - Oxidation of Alkenes (tutorial, game, test, exam)

If you have haven't received your issue of AUS-e-NEWS, please contact us.

pH of the Manning River

"A POISONOUS plume of acid 'comparable to car batteries' is forming in the Manning River, near Taree in northern NSW, researchers from the University of NSW say." reports Ben Cubby in his article "Acid plume poisons river after floods"  in the Sydney Morning Herald, Thursday 28^th February 2013.
Let's take a look at the chemistry behind the story.
Firstly, Taree, a town located about 3 hours north of Sydney, is surrounded by farm land, land reclaimed from the wetlands. The sulfate ion, SO₄^2-, is commonly found in fertilizers used in commercial farming. Recent rain, and flooding, has concentrated these acidic sulfates in the river.

A little later in the story we find that "Tests carried out by the university's water research laboratory show alarming amounts of acid, with a pH level of two - compared with a normal level of seven - meaning the Manning River water is roughly as acidic as lemon juice."
Chemistry students would realize that there are many factors that can effect the pH of river water, for example, if the river runs through limestone rocks the pH of the water will increase, but if the river runs through areas of peat the pH of the water will decrease.
The pH of river water typically lies within the range of about 6.5 to 8.5.  Water with a low pH is said to be acidic, water with a high pH is said to be basic or alkaline. Most organisms, with the exception of some bacteria, can not live in water with a pH less than 6.5. Similarly, a pH greater than 8.5 also presents problems for the survival of most organisms in rivers.
The juice of a lemon often has a pH of about 2, and the vinegar you buy from the shop will also have a pH around 2. Both lemon juice and vinegar are acidic substances.
On the other hand, oven cleaner has a pH of about 13 and soapy water has a pH of about 12. Both oven cleaner and soapy water are basic solutions (or alkaline solutions).

Is river water with a pH of 2 "comparable to car batteries" as claimed in the story?
Lead-acid batteries, such as those found in cars, contain sulfuric acid, H₂SO₄. Sulfuric acid is a strong acid that undergoes dissociation in water so that an aqueous solution of sulfuric acid contains both hydrogen ions, H⁺, and sulfate ions, SO₄^2-. The acidic river water will contain both hydrogen ions, H⁺, and sulfate ions, SO₄^2-, if sulfate fertilizers have been used on the land where the river runs, so the acid in the car's lead-acid battery and the river water are comparable in that they contain the same ions.
The concentration of sulfuric acid in the lead-battery will usually be between 4 and 5 mol L^-1 (let's just assume its 4.5 mol L^-1 ).
If we assume the complete dissociation of sulfuric acid:
H₂SO₄ → 2H⁺ + SO₄^2-
Then the concentration of hydrogen ions, H⁺, in solution is 2 times the concentration of the sulfuric acid:
[H⁺] = 2[H₂SO₄ ] = 2 x 4.5 = 9.0 mol L^-1
We can calculate the pH of the battery acid, since pH = -log₁₀[H⁺] = -log₁₀[9.0] = -0.95
Battery acid is very, very acidic!
While you might be very happy to put vinegar on your chips (pH~2) and eat them, you  should most definitely NEVER put battery acid on your chips and eat them!

Reference:

 http://www.smh.com.au/environment/conservation/acid-plume-poisons-river-after-floods-20130227-2f6bh.html#ixzz2MA2XQ5AJ

Further Reading:
Calculating pH

Suggested Study Questions:

1. Draw up a table with two headings; acid and base. Place each of the following substances in  the correct column in the table : orange juice (pH =3), baking soda (pH = 9), milk (pH =6), tomato juice (pH =4),  drain cleaner (pH =14), black coffee (pH=5).
2. Calculate the concentration of hydrogen ions in each of the substances in the table, in mol/L
3. Assume a drinking glass has a total value of 250 mL, and that a "full glass" of a drink is actually only 225 mL. Calculate the moles of hydrogen ions found in a "full glass" of
   • orange juice
   • milk
   • black coffee
4. Consider 225 mL of the river water with a pH =2. Calculate the moles of hydrogen ions present.
5. Imagine you took 25 mL of orange juice (pH=3) and diluted it with water to a volume of 500 mL. 
   • Calculate the concentration of hydrogen ions in the diluted solution.
   • Calculate the pH of the diluted solution.
6.  Sometimes cooks heat ingredients to "release their flavour". Acids, like vinegar, tend to have a sour taste. A cook has 200 mL of vinegar (pH=2.2)  in a pan.
   • Calculate the concentration of hydrogen ions present in the solution.
   • On very gentle heating, the volume of the vinegar solution is reduced until it is only 50 mL. Calculate the pH of this concentrated solution.
7. We could prepare a solution of sulfuric acid with a pH of 2 using the acid out of the car's lead-acid battery.
   • Calculate the concentration of hydrogen ions present in 4.5 mol L^-1 sulfuric acid.
   • Calculate the concentration of hydrogen ions present in sulfuric acid with a pH of 2.
   • If you had 10 mL of battery acid, what volume of water would you have to add in order to prepare a sulfuric acid solution with a pH of 2?
8. Imagine the a dam with a volume of 250,000ML and a pH=2. How much water would have to be added to the dam in order for the dam to have a pH=7 ?

Drunken Fruit Flies

Wasps are a major killer of fruit flies. They inject their eggs inside fruit fly larvae, then, when the wasp egg hatches, the wasp larva starts eating the fruit fly lava from the inside!
Scientists at Emory University have found that fruit flies prefer to lay their eggs in an environment  with a "high" concentration of ethanol. The fruit flies have evolved a certain amount of tolerance to this toxic ethanol, but the wasps who inject their eggs inside fruit fly larvae find the ethanol level to be lethal. Furthermore, fruit fly lava that have been infected with wasp larva tend to prefer to eat food with a high ethanol content, this raises their blood alcohol level and helps kill the wasp larva.

The most common natural source of ethanol is rotting fruit. Yeasts on rotting fruit can ferment the fruit sugars, like fructose, to produce ethanol:

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

This fermentation reaction takes place in anaerobic environments, that is, environments in which oxygen is not present.
The concentration of ethanol in rotting fruits has been  found to be between 0.04 and 0.72 v/v%. By comparison, the ethanol content in beer is usually between 3 and 6 v/v%, while the ethanol content of wine is between 8 and 11 v/v%.
Volume/volume (or volume) percent is a common way to refer to the concentration of alcoholic solutions. It refers to the volume of solute divided by the volume of solution which is then multiplied by 100, that is:

v/v% = V(solute)/V(solution) x 100

Beer that is 3 v/v% ethanol contains 3 mL of ethanol in every 100 mL of beer.

Wine that is 11 v/v% ethanol contains 11 mL of ethanol in every 100 mL of wine.

This preference for eating rotting fruit containing ethanol displayed by the fruit flies seems to be uncommon. Most animals, including humans, seem to prefer ripe, but not rotting, fruit.

References:

1. B. Z. Kacsoh, Z. R. Lynch, N. T. Mortimer, T. A. Schlenke. Fruit Flies Medicate Offspring After Seeing Parasites. Science, 2013; 339 (6122): 947 DOI: 10.1126/science.1229625
2. Neil F. Milan, Balint Z. Kacsoh, Todd A. Schlenke. Alcohol Consumption as Self-Medication against Blood-Borne Parasites in the Fruit Fly. Current Biology, 2012; 22 (6): 488 DOI: 10.1016/j.cub.2012.01.045

Further Reading:
Fermentation
Carbohydrates
Naming Alcohols
Density

Suggested Study Questions:

1. Calculate the volume of ethanol in a stubby (375 mL) of full strength beer (ethanol concentration 4.8 v/v%).
2. An average standard wine glass has a volume of 150 mL. What volume of ethanol is present in a standard wine glass of white wine with an ethanol concentration of 11.5 v/v%?
3. Port is an example of a fortified wine, that is, a wine that has had an additional distilled beverage like brandy added to it to increase its alcohol content to about 17.5 v/v%. A standard port glass has  a volume of 60 mL. Calculate the volume of ethanol in a standard glass of port.
4. The specific gravity (density) of ethanol is 0.789 g/mL. Calculate the mass of ethanol present in a stubby (375 mL) of
   • full strength beer (5 v/v% ethanol)
   • light beer (2.7 v/v% ethanol)
5. Spirits such as rum and vodka, have an ethanol concentration of approximately 40 v/v%. A standard "nip" is 30 mL. Calculate:
   • the volume of ethanol in a nip of vodka
   • the mass of ethanol in a nip of vodka
6. The alcohol content of Marsala wine is increased by allowing water to evaporate off it. The concentration of ethanol in Marsala wine will reach about 18 v/v%. Calculate:
   • volume of ethanol in a 750 mL bottle of Marsala
   • mass of ethanol in this bottle of Marsala wine
7. A particular type of wine barrel holds 225 L of wine. Calculate the mass of ethanol present if the wine in the barrel is
   • red wine (13 v/v% ethanol)
   • white wine (11.5 v/v% ethanol)
   • champagne (12 v/v% ethanol)

Neutral pH?

We hear this term a lot, often in advertising. But what does it mean?

From a Chemist's point of view, there are two different concepts involved in this seemingly harmless "neutral pH" expression. These two different concepts are:

• neutral
• pH

Let's take a look at the Chemist's definition of neutral first.
A solution is neutral if the concentration of hydrogen ions, [H⁺], is equal to the concentration of hydroxide ions, [OH^-].
Chemists often use square brackets to denote concentration, the concentration of  hydrogen ions can be written as [H⁺] and the concentration of hydroxide ions can be written as [OH^-].
So, for a neutral solution:

[H⁺] = [OH^-] = neutral solution 

Pure water is an excellent example of a neutral substance.

Some of the water molecules, actually very few of them, dissociate to form hydrogen ions and hydroxide ions:

H2O

H+ + OH-

Every time a water molecule dissociates, it produces one hydrogen ion, H⁺, and one hydroxide ion, OH^-, so that the concentration of hydrogen ions is always the same as the concentration of hydroxide ions.
Therefore, pure water is always neutral!

The pH of a solution is a measure of the hydrogen ion concentration in the solution. pH can be defined as:

pH = -log₁₀[H⁺]

This equation can be used to calculate the pH of our neutral water, but only if we know the concentration of  hydrogen ions in the water.

The concentration of hydrogen ions in water is not constant!

The concentration of hydrogen ions in water depends on the temperature of the water!
The dissociation of water molecules requires energy:

H2O + energy

H+ + OH-

If you put more energy into the system by heating it, then more water molecules dissociate, the concentration of hydrogen ions increases and the concentration of hydroxide ions also increases.
If you take energy away from the system by cooling it, then fewer water molecules dissociate, the concentration of hydrogen ions decreases and the concentration of hydroxide ions also decreases.
If we were to measure the concentration of hydrogen ions in pure water at various temperatures, we would find the following values:

Water temperature	[H+] x 10−7 M	pH
0°C	0.32	7.50
10°C	0.55	7.26
18°C	0.84	7.08
25°C	1.10	6.96
30°C	1.34	6.87
50°C	2.82	6.55
60°C	3.55	6.46
70°C	4.60	6.34
80°C	5.92	6.23
90°C	7.28	6.14
100°C	8.54	6.07

So what is the pH of water?
The pH of water is dependent on the temperature of the water.
Water is neutral for every value of pH because the concentration of hydrogen ions is always equal to the concentration of the hydroxide ions.
We can ONLY talk about the pH of water IF we state the temperature of the water.
For example, we can talk about water having a pH of approximately 7 at 25^oC, or we could say that the pH of water is approximately 6 at 100^oC.
Pure water is always neutral.
Pure water is neutral at 25^oC.
Pure water is neutral at 100^oC.

As Chemistry students, what we can't say is that water has a pH of 7, or that a neutral aqueous solution has a particular pH, unless we state the temperature of the system.

Further Reading:
Definitions of Acids and Bases
pH
Dissociation Constant for Water

Suggested Study Questions:

1. Plot a graph of temperature versus concentration of hydrogen ions in water. Describe the shape of the line, and write a generalization that links hydrogen ion concentration and temperature.
2. Plot a graph of temperature versus pH of water. Describe the shape of the line and write a generalization linking the  temperature of water and its pH.
3. Use your graph to find the pH of water at:
   • 12^oC
   • 22^oC
   • 32^oC
4. Construct a table giving the concentration of hydroxide ions in water at each of the temperatures shown above.
5. Plot a graph of temperature versus concentration of hydroxide ions in water. Describe the shape of the line, and write a generalization linking hydroxide ion concentration in water and temperature.
6. Use your graph to find the concentration of hydroxide ions in water at:
   • 12^oC
   • 22^oC
   • 32^oC
7. Explain why water is neutral at all temperatures.
8. Explain why the pH of water varies with temperature.

What is a Search Engine?

If you want to find information, what is the first thing you do?

You will probably use your smartphone, tablet, laptop, notebook, netbook, or some other "computer", to connect to the internet and then type your question into a search engine.
You've probably used one of the popular search engines such as google, yahoo or bing, but there are hundreds of search engines to choose from (you can visit http://www.thesearchenginelist.com if you would like a lengthy list of search engines).

A search engine can be a useful tool for helping you find information, as long as you enter an appropriate search term. In other words, if you ask a silly question you will get lots of silly responses (known as garbage in, garbage out, or GIGO).

It is important to realize that a search engine is NOT a person, a search engine can not answer your questions.
A search engine is NOT an encyclopedia, it does not give you specific information related to your question. Search Engines do not write their own pages of information.
A search engine is NOT a dictionary, it can not define a term for you and give you examples of usage. Search engines do not write their own definitions or examples.

So, what is a search engine?
A search is just a computer program that acts like a library catalogue or the index of a book.
Pages on the internet containing information are categorized by the search engine, just like in a library catalogue or the index of a book.
When you type in your search term, or question, the search engine matches your term, or question, as closely as possible to the pages of information on the internet that it has catalogued or indexed.

So what? Who cares?
You should!
In order to successfully use a search engine to find what you want, you need to understand what it is (and what it is not) in order to understand what it can do (and what it can't do).
Let's take a look at some examples.

1. A Search Engine is NOT a Person
a) The term with multiple meanings
Example : mole
Your chemistry teacher will tell you that a mole is defined as 6.02 x 10²³ "things", or as the molecular mass of a substance expressed in grams.
If you type mole into your favourite generic search engine (eg, google, yahoo, bing) you will end up with a list of links to pages of information on the internet about various types of moles including the chemical definition of a mole, the mole as an animal, the mole as skin blemish (moles and freckles), mole as a Mexican sauce.
The search engine is not capable of interpreting your question and putting it into context like a person can.
If you ask your chemistry what a mole is, the chemistry teacher assumes you are talking about a chemical mole.
If you ask your biology teacher what a mole is he or she will probably ask you for more information (what sort of mole do you mean).
If you ask a medical doctor, he/she will probably tell you about skin blemishes.
As a cook about mole, they'll start talking about sauces.
A search engine cannot guess what type of mole you are interested in because a search engine is not a person.

b) "The homework answer"
If you ask a person what a + 2a is if a is equal to 2, they will probably 6, and your maths homework is probably done.
Now, type a + 2a if a is equal to 2 into your favourite search engine. What do you get? You get a list of pages on the internet, probably maths related, which include reference to a, +, and 2a.
The search engine cannot answer your homework question if you treat the search engine like a person.

c) "The homework question"
If you stand in front of someone and ask, "happy?", they will probably assume you are asking them if they are happy and respond to the implied question by saying something, "Yes. I'm happy."
A search engine cannot interpret the question, so a search engine does not know if you asking for a definition of the word happy, or if you are asking it if it is happy, or if you are asking about movies that have happy in the title etc. You can prove this to yourself just by opening up 2 windows with your favourite search engine open in each and typing "happy" into one and "are you happy?" into the other.

d) Spelling Mistakes and Typos
Spelling is important in science, and it can be critical in chemistry.
If you have been asked to find out about ethene, but you type ethane into your search engine, your search engine will list resources dealing with ethane NOT ethene. The search engine does not know you have made a spelling mistake or typo because both ethane and ethene exist.

e) Asking Nonsense
You type nonsense into a search engine's textbox it will provide you with a list of links to resources on the internet that make reference, in some way, to the nonsense you have typed in. A person would know you are asking nonsense, but a search engine is not "intelligent", it can't decide that what you are asking is nonsense.
For example, if you ask a person  how old Jo is if John is Jane's brother they'll tell you this is nonsense, but if you type how old is Jo if John is Jane's brother into the textbox of a search engine, you'll end up with millions of links to pages that reference Jo, John, Jane, brother, old, etc.

2. A Search is NOT an Encyclopedia nor is it a Dictionary
A search engine is not a "resource", it is only a tool.
An encyclopedia is a resource, it provides information that you can use.
In order to find the information you want in the encyclopedia you can use its index, the index is a tool.
Pages on the internet contain information, these pages are the resources.
A search engine is a tool you can use to find the resources.
If you have been asked by your chemistry teacher to find out about quicksilver, and you type "quicksilver" into your favourite search engine, the search engine gives you millions, of links to pages on the web that make reference to quicksilver. In order to get the information you will need to click each link.

There are ways to ensure that you don't put garbage into a search engine, which should reduce the amount of garbage the search engine gives you, but we'll deal with that another day.

Practice Questions
Which of the following questions are most likely to be appropriate search terms or questions (things you could type into a search engine that would result in links to web pages that contain similar sorts of useful information)? Explain your decision in each case.

1. What is the red dot in the diagram?
2. multiplication
3. mathematical multiplication
4. What is induction?
5.  mathematical induction
6. What is the answer to question 4 on page 91?
7. How many moles are in x grams of NaCl?
8. How long does it take to melt ice?
9. What is the chemical composition of ice?
10. What is the chemical composition of solid water?

The examples below are actual search terms that real people have typed into a search engine
In each case, explain why it is NOT an appropriate search term.

1. if the density is 4.70 g/cm3, then calculate the metal's atomic weight
2.  chemical bond energy in steel
3. how to calculate kj per mole
4. N2- on conceptual level
5. 100 parts a to 3 parts b by weight
6. 35.    how would the following elements become chemically stable?  (which ion would they form?) a.cl b. na c. al
7. how to find empirical formula by making table
8. how to calculate masses of reactants and products
9. which of the following is the best estimate of the percent abundance of the two isotopes of copper?
10. for each of the following balanced reactions calculate how many moles of each product would be produced by complete conversion of 0.50 mol of each reactant

Arsenic Tests

Somewhere around the 8th century, an Arab alchemist produced white arsenic trioxide (As₂O₃) from realgar, a naturally occurring arsenic sulfide mineral, As₄S₄:
As₄S₄ + 7O₂ → 2As₂O₃ + 4SO₂ Arsenic trioxide became one of the most widely administered poisons in history, and therefore, it became necessary to find reliable tests to show whether or not arsenic was present in a sample of food or drink, or whether it was present in a corpse.

In 1775, Carl Wilhelm Scheele treated arsenic trioxide with nitric acid and zinc which resulted in arsine gas (AsH₃), zinc nitrate and water:
As₂O₃ + 6Zn + 12HNO₃ → 2AsH₃ + 6Zn(NO₃)₂ + 3H₂O Arsenic was said to be present if an odour of garlic was produced because arsine gas smells a lot like garlic.

In 1787, Johann Metzger used a carbon reduction method to produce carbon dioxide gas and solid arsenic from arsenic trioxide and carbon:
2 As₂O₃ + 3 C → 3 CO₂ + 4 As As the arsenic trioxide is heated with charcoal, an "arsenic mirror" forms on the charcoal.

In 1785, Samuel Hahnemann produced a bright yellow precipitate of arsenic trisulfide, As₂S₃, by passing a stream of hydrogen sulfide gas, H₂S, through an acidified arsenic solution.

In 1836, James Marsh designed an apparatus that would detect and measure arsenic.
The sample is placed in a flask with arsenic-free zinc and sulfuric acid.
Arsine gas forms:

As₂O₃ + 6 Zn + 6 H₂SO₄ → 2 AsH₃ + 6 ZnSO₄ + 3 H₂O

The arsine gas is fed through a drying tube to a glass tube which is heated.
Arsine deomposes on heating, forming elemental arsenic which is a shiny black substance:

2 AsH₃ → 3 H₂ + 2 As

By placing a cold surface at the end of the heated tube it is possible to condense this arsenic, which forms a black "mirror".

http://www.youtube.com/watch?v=-vUZdAwgl2g

Today, these "wet" methods of chemical detection have been superceded by instrumental analysis. e Atomic absorption spectroscopy (AAS)  can now be used to determine not only the presence of arsenic, but also how much arsenic is present.

Further Reading:
Solubility Rules
Writing Precipitation Equations
Gravimetric Analysis
AAS
Oxidation and Reduction 
Carbon Reduction Methods

Suggested Study Questions:

1. Give the oxidation state (number) for arsenic in each of the following:
   • As₂O₃
   • As₄S₄
   •  AsH₃
   • As
2. For the reaction: As₄S₄ + 7O₂ → 2As₂O₃ + 4SO₂ which element, or elements, have been oxidized?
3.  Consider the reaction: 2 As₂O₃ + 3 C → 3 CO₂ + 4 As
   Is arsenic likely to be more or less active than carbon?
4. Write a possible net ionic equation for the reaction in which arsenic ions react with  hydrogen sulfide gas to produce a precipitate of arsenic trisulfide.
5. Consider the reaction: 2 AsH₃ → 3 H₂ + 2 As which results in the formation of a shiny black "mirror" of arsenic.
   • Has arsenic been oxidized or reduced?
   • Has hydrogen been oxidized or reduced?
   • If 1 mole of arsine gas decomposes completely, how many moles of hydrogen gas would be produced?
   • At 0^oC and 100 kPa, what volume of gas would be produced by the thermal decomposition of 25 moles of arsine?
   •  At 0^oC and 100 kPa, what mass of arsenic would be deposited after  the thermal decomposition of 150 mg of arsine.
   • At 25^oC and 100 kPa, what mass of arsine will decompose to produce 0.05 L of hydrogen gas?
   • A sample of gas containing arsine produces an "arsenic mirror" containing 0.02 g of arsenic. What mass of arsine was present in the gas sample?