Indicators for Strong Acid - Strong Base Titrations

When a strong acid is added to a strong base the products are water and a salt.
Water is neutral, that is [H⁺(aq)] = [OH^-(aq)]
 (or [H₃O⁺(aq)] = [OH^-(aq)] if you prefer)

The salt of a strong acid and base is made up of a cation that will not react with water to any appreciable extent, and an anion that will not react with water to any appreciable extent, so this salt does not affect the  [H⁺(aq)] and [OH^-(aq)] in the water, that is, the aqueous solution remains neutral.
At 25°C, K_w = [H⁺(aq)] × [OH^-(aq)] = 10^-14
Since [H⁺(aq)] = [OH^-(aq)]
K_w = [H⁺(aq)]² = 10^-14
√[H⁺(aq)]² = √10^-14
[H⁺(aq)] = 10^-7 mol L^-1
 So, at 25°C the pH of this salt solution will be pH = -log₁₀[H⁺(aq)] = -log₁₀[10^-7 ] = 7.0
A suitable indicator is one that changes colour at around pH = 7.00
Suitable indicators, for example, are bromothymol blue (colour change between 6.7 and 7.6) or phenol red (colour change between 6.8 and 8.4)

Phenolphthalein changes colour between pH 8.3 and 10. Phenolphthalein is NOT an appropriate indicator for a strong acid - strong base titration.

If we add a drop of phenolphthalein indicator to an aqueous solution of strong acid, the pH will be less than 7 and the solution will remain colourless. As we add strong base, hydrogen ions react with excess hydroxide ions to produce salt and water, so the pH increases. At pH = 7.0 all the strong acid will have been neutralised by the addition of strong base, BUT the phenolphthalein indicator will not have changed colour!
Phenolphthalein will not change colour until an excess of strong base (hydroxide ions) has been added and we have overshot the equivalence point for the reaction. The volume of strong base we record in this experiment will be too large!.

In strong base such as an aqueous solution of sodium hydroxide, the pH will be high and a drop of phenolphthalein indicator will turn the solution pink.
As we add a strong acid such hydrochloric acid, we will be consuming some of the hydroxide ions, and decreasing the pH. Somewhere between pH 8.3 and 10 we will decide that all our base has been neutralised by the acid because the indicator is now colourless instead of pink. But the reality will be that there is still excess hydroxide ions in solution waiting to be neutralised by the addition of more acid, so the volume of acid we have added, as indicated by the colour change of the indicator will be too low!

Learn all about how to choose an appropriate indicator for different types of acid-base titrations ar
https://www.ausetute.com.au/indicata.html

Hydrolysis of Acids and Bases

If you want to find the value of the acid dissociation constant for a weak acid you look up tables of values. For example, the value of K_a for acetic acid (ethanoic acid) is always tabulated.
But what if you want the value of a base dissociation constant?  What if you want the value of K_b for the acetate ion (ethanoate ion)? You won't find this value in a table, you'll have to know how to calculate it!

AUS-e-TUTE has just added new resources to help you understand and apply the concept of acid and base hydrolysis including calculations. AUS-e-TUTE Members should log-in to access the new tutorial, game, test, exam (with worked solutions), and teacher members can access the worksheet wizard to make printable worksheets and quizzes (with answers).

If you are not an AUS-e-TUTE Member, the "free-to-view" tutorial is currently available at

https://www.ausetute.com.au/kakbkw.html

Glycaemic Index

Low GI food or high GI food?
What is GI?
How is it measured?
What does it mean?
These are many other questions are addressed in AUS-e-TUTE's new glycaemic index (GI) resources.
AUS-e-TUTE Members should log-in to access the new tutorial, game, test and exam.
If you are not an AUS-e-TUTE Member you can access a "free-to-view" tutorial for evaluation purposes at https://www.ausetute.com.au/glycaemic.html

Hydrolysis of Proteins

Lots of foods contain protein. When you eat them the proteins undergo hydrolysis reactions to break them down into their constituent amino acids.
AUS-e-TUTE has just added a new tutorial, game, test and exam to help you understand this.
AUS-e-TUTE Members should log-in to use these new resources (listed under Biochemical Reactions).
Non-members can currently access a "free-to-view" tutorial at
https://www.ausetute.com.au/hydrolysisprot.html

Hydrolysis of Carbohydrates

Carbohydrates like disaccharides and polysaccharides can be broken down into monosaccharides.
In the lab we use acid hydrolysis, but in your body you use enzymes to do this.
AUS-e-TUTE has just added a new tutorial, game, test and exam to help you understand these chemical reactions. Members should log-in to access these new resources (under Biochemical reactions).
If you are not an AUS-e-TUTE member you can access a "free-to-view" tutorial at https://www.ausetute.com.au/hydrolysiscarbs.html

Nanocellulose Foam

You have probably held polystyrene cups (styrofoam cups) in your hands. It is a wonderful material for making disposable cups because it is light-weight, holds it shape well, and is an excellent insulator. All this means that you can fill a polystyrene cup with hot tea and drink from it without having it burn your hands. High school chemistry teachers are very fond of using polystyrene cups as "cup calorimeters" in the school laboratory. Unfortunately, polystyrene is not an environmentally friendly polymer, it doesn't break down, it is chemically inert, so persists in the environment.
Plant-based polymers which degrade in time, such as cellulose, could replace polystyrene if we can make a cellulose-based material with same properties as polystyrene.
Cellulose is a polysaccharide. It is composed of many glucose units joined together by ether bonds (glycosidic links). During acid hydrolysis these ether bonds (glycosidic links) are attacked and broken so that the final product of a complete reaction is a lot of glucose molecules. The reaction mechanism for the acid hydrolysis of cellulose is shown below:


If only some of the ether bonds (glycosidic links) within a cellulose polymer chain are attacked, then you could end up with shorter chains of glucose polymer, still enough glucose units in the chain to be considered cellulose. If these chains are only 5-20 nanometres wide (even though they may be several micrometres long) they will be referred to as nanocellulose.
Researchers at Washington State University have added polyvinyl alcohol, shown below:

to nanocellulose. Polyvinyl alcohol binds to the nanocellulose which stabilises the foam that can be  produced. This light-weight material is reported to be a better insulator than polystyrene foam (styrofoam) and "can support up to 200 times its weight without changing shape. It degrades well, and burning it doesn't produce polluting ash."

Suggested Further Reading:
Nanotechnology

Suggested Study Questions:

1. Convert the following measurements to metres (m):
   • 5 nm
   • 20 nm
   • 100 μm
   • 1000 μm
2.  Convert the following measurements to nanometres (nm)
   • 5 × 10^-9 m
   • 2.5 μm
   • 5.2 mm
   • 0.75 cm
3. Draw a section of cellulose polymer containing 6 glucose units. Circle the ether bonds (glycosidic links) in red.
4. Draw the results of acid hydrolysis if all the ether bonds (glycosidic links) in this section of cellulose polymer were broken.
5. Draw the results of acid hydrolysis on the section of cellulose polymer you drew for question 3 if only 2 new "molecules" are produced. Is there only one possible answer? If more than one answer is possible, how many possible answers can you think of?
6. Consider the structure of cellulose and of polyvinyl alcohol. Explain how polyvinyl alcohol can "bind with" cellulose. 
7. Explain why a nanocellulose foam can be stabilised by adding polyvinyl alcohol.
8. Consider the combustion of cellulose. Give the products for
   • complete combustion of cellulose
   • incomplete combustion of cellulose
9. Wood is composed largely of cellulose. When a wood log burns on a camp fire it produces a sooty flame. Explain why.
10. Explain why nanocellulose is unlikely to produce a sooty flame when it burns.

Breaking Triglycerides up into Fatty Acids

Triglycerides are found in the fats and oils you eat. They are produced in a condensation reaction between a glycerol and 3 fatty acids. So, is it possible to reverse this reaction? Can we add water to a triglyceride to break it up into glycerol and 3 fatty acids?
Good question!
AUS-e-TUTE has new resources to help you understand the hydrolysis of triglycerides.
Members should log in to access the new tutorial, game, test and exam (with worked solutions).
If you are not an AUS-e-TUTE Member, you can access the "free-to-view" tutorial at
https://www.ausetute.com.au/hydrolysistg.html

Methanol and the Home-Brewer

In June 2013, a young man in Queensland died as a result of drinking homemade liquor. It is believed that the liquor contained a toxic level of methanol (also known as wood alcohol). Drinking 10 mL of pure methanol can cause permanent blindness, drinking 30 mL of methanol can kill you.

The first step in the production of homemade liquors, is the fermentation of sugar.
Methanol, CH₃OH,is formed during fermentation.
When fermenting 6 kg of sugar dissolved in water for the production of distilled spirits such as whiskey or vodka, the home-brewer (and home-distiller) will typically find that the concentration of methanol in their brew is about 3 parts per million.

Many fruits are used by the home-brewer as the source of sugar to be fermented. Each fruit will lend a distinctive flavour to the final product. But fruits that are high in pectin will produce greater concentrations of methanol. Apples, apricots, guavas, quinces, plums, gooseberries, and citrus fruits like oranges, all contain high levels of pectin, typically more than 1% by mass pectin. Grapes, cherries and strawberries contain low levels of pectin, less than 1% by mass pectin.

Pectin contains  galacturonic acid which has the structural formula shown below:

In pectin, about 80% of the carboxyl groups in galacturonic acid are esterified with methanol. The remaining non-esterified carboxyl groups exist as the acid, or as salts with sodium, potassium or calcium. When pectin is broken down by enzymes during the brewing process, the methyl esters react with water to produce methanol.

The second step in the production of homemade liquor is the distillation step.
This is the crucial step in removing as much of the toxic methanol as possible.
The boiling point of methanol is about 65^oC, but the boiling point of ethanol (the desired product) is about 78^oC. During the distillation process, the first fraction collected should contain the methanol. This fraction should be collected and discarded. The next fraction should contain the desired liquor. It is highly recommended that any distillate collected after about 96^oC also be discarded.


Reference:
http://www.couriermail.com.au/news/queensland/ballandean-man-bill-lynam-who-lost-his-son-joel-to-homemade-liquor-poisoning-is-thankful-that-other-son-joshua-survived/story-fnihsrf2-1226664893229

Further Reading
http://ausetute.com.au/members/alkanolp.html (members only tutorial on alkanols)
http://ausetute.com.au/members/carboxyl.html (members only tutorial on alkanoic acids) 
http://ausetute.com.au/partspm.html 
http://ausetute.com.au/density.html 

Suggested Study Questions:

1. Draw the structural formula for methanol.
2. Locate the functional group present in methanol on the structural formula above. Name the functional group. 
3. At 25^oC methanol has a density of  0.79 g mL^-3. Calculate the mass of methanol present in a lethal dose of pure methanol .
4.  Convert the concentration of methanol given for homemade whiskey into a concentration in g mL^-1.
5. Assume the young man who died drank homemade whiskey. What minimum volume of homemade whiskey did he drink?
6. For galacturonic acid given the:
   • molecular formula
   • molar mass
7.  On the structural formula for galacturonic acid identify and name the functional groups present.
8. Draw the structure for the sodium salt of galacturonic acid.
9. Draw the structure for galacturonic acid esterified with methanol.
10. Give the molecular formula and molar mass for the structure above.
11. Apples contain about 1% by mass pectin. 10 kg of apples are to be used in the production of a homemade liquor. What mass of pectin will be present?
12. Assume exactly 100% of the carboxyl groups in galacturonic acid are esterified with methanol. How many moles of the ester are present in 10 kg of apples?
13. Write an equation representing the reaction between this ester and water to form methanol  and galacturonic acid.
14. How many moles of methanol could be produced by the break down of pectin in 10 kg of apples?
15. Assuming the young man who died had drunk this apple concoction without distilling and removing the methanol, what minimum volume of fermented apple-drink would he have had to have drunk?
16. Why do you think most countries have outlawed home-distilling?