AI and chemistry

 How good are AI generated responses to typical chemistry questions?

No better than the source material used for the answer ... which can include common misconceptions.

One such question is "What is the pH of water?". To a chemist this is a nonsense question (comparable to asking what colour an apple is or what shape a building is) yet it is often asked in school science classrooms around the world. 

I asked ChatGPT "What is the pH of water?" This was the answer ...

The pH of pure water at 25 degrees Celsius (77 degrees Fahrenheit) is considered neutral and is defined as 7. A pH value below 7 indicates acidity, while a pH value above 7 indicates alkalinity. It's important to note that the pH of water can be influenced by dissolved substances, and natural water sources may have varying pH levels due to the presence of minerals and other compounds.

I asked perplexity.ai "What is the pH of water?" This was the answer ...

The pH of water is 7, which is considered neutral. A pH of 7 is neither acidic nor basic. It is important to note that the pH of pure water can change due to the presence of impurities or the absorption of carbon dioxide from the air, which can make it slightly acidic. However, under normal conditions, the pH of pure water is 7, indicating neutrality

2

Surprise, surprise, both answers are inaccurate and riddled with common misconceptions (although, to its credit, perplexity.ai does provide sources, but to its discredit it does not refer to a specific temperature which is critical!). ChatGPT emphasizes "pure water", while perplexity.ai is content with just "water". To a chemist, both terms are the same, "water" is a pure substance. If water has substances dissolved in it it is no longer "water" it is an "aqueous solution". Perplexity.ai's referral to "normal conditions" is baffling, perhaps it refers to standard conditions for aqueous solutions? After these issues, both AIs seem to perpetuate the misconception that acidity, basicity (alkalinity) and neutrality are defined by a pH value. This is not true. They are two entirely different concepts (although both are based on an Arrhenius description of aqueous solutions). pH is a measure of aqueous hydrogen ion concentration, independent of whether the aqueous solution has been designated acidic, basic or neutral. Acidic, basic, neutral are terms to describe a the relative amounts of hydrogen ions and hydroxide ions in an aqueous solution.

So, let's start by talking about the neutrality of "pure water". Pure water is always neutral (regardless of its pH). This is because the concentration of acidic protons in the water, H⁺(aq) or H₃O⁺(aq), is always equal to the concentration of basic hydroxide ions in the water, OH^-(aq), that is [H⁺(aq)] = [OH^-(aq)]

An acidic aqueous solution is one in which the concentration of acidic protons is greater than the concentration of basic hydroxide ions, that is, [H⁺(aq)] > [OH^-(aq)]

A basic aqueous solution is one in which the concentration of acidic protons is less than the concentration of basic hydroxide ions, that is, [H⁺(aq)] < [OH^-(aq)] 

So "pure water" is always neutral, but what is its pH? pH is a measure of the concentration of aqueous hydrogen ions in solution, the greater the concentration of hydrogen ions in aqueous solution, the lower the pH. The concentration of these hydrogen ions is very much dependent on the water temperature. The pH of pure water at 10^oC is approximately 7.27 but the water is still described as neutral because [H⁺(aq)] = [OH^-(aq)]. The pH of pure water at 50^oC is about 6.63 but the water is still neutral because [H⁺(aq)] = [OH^-(aq)].

 The pH of water at 25^oC is approximately 7 and is based, NOT on it being defined this way, but on a calculation of the hydrogen ion concentration of water at this temperature.

So, what happens to pH if other substances are dissolved in water to form aqueous solutions at 25^oC? Using an Arrhenius definition of acids and bases (and a pH of 7 which has 1 significant figure but even that digit is uncertain), if an aqueous solution has pH < 7  at 25^oC it could be described as acidic, but if the temperature is greater than 25^oC the solution may be neutral, it may even be basic, we simply do not have enough information to decide. Similarly, If an aqueous solution has pH > 7  at 25^oC it could be described as basic, but if the temperature is less than 25^oC it is not a justifiable conclusion.

It is important to note that if there are dissolved "substances", including "impurities", "minerals" or "carbon dioxide", then the "water" is not "pure water", it is an aqueous solution, and the AI discussions are not relevant. Furthermore, some solutes dissolve in water at 25^oC and increase its pH  (aqueous solution of sodium hydroxide), some decrease its pH  (aqueous solution of hydrogen chloride), and some may have no effect at all on its pH (aqueous solution of sodium chloride).

There is no simple, correct answer for the question "What is the pH of water?". The question does not contain enough information in order for it to be answered. IF the AIs simply stated that the pH of water at 25^oC is approximately 7, that would be a pretty good response, however, by providing additional information in the answer they are repeating, and encouraging, common misconceptions about the nature of "pure water", "pH", "acidity", "basicity" (or "alkalinity") and "neutrality". 

For a discussion on why pure water is always neutral and why its pH varies, see https://www.ausetute.com.au/kw.html

For a discussion on what determines whether an aqueous solution is acidic, basic or neutral, see https://www.ausetute.com.au/abneutral.html

What is an indicator?

What is an acid-base indicator?

What does it do?

Where do we use acid-base indicators?

These and other questions about acid-base indicators can be answered at 

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

AUS-e-TUTE Members also have access to the game, test and exam with worked solutions on this topic.

Join AUS-e-TUTE Today!

Arrhenius Acids and Bases

What is an acid?

What is a base?

These are both good questions and there is no simple answer.

It all depends on how you decide to define the terms "acid" and "base".

More than 100 years ago, a clever chemist by the name of Arrhenius proposed the first really useful definitions of acids and bases and AUS-e-TUTE has just added a new tutorial, game, test and exam (with worked solutions!), and even some flash cards o help you understand and apply the Arrhenius definition of an acid and of a base.

Not an AUS-e-TUTE Member? You can go to a free-to-view tutorial at 

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

Brønsted-Lowry Theory of Acids and Bases

 Ammonia, NH₃, is a base right?

Well, yes it is sometimes... but it can also be an acid.

Welcome to the wonderful world of Brønsted-Lowry acids and bases.

At AUS-e-TUTE, we've just added a new tutorial, game, tests and exam to help you understand Brønsted-Lowry acids, bases and their conjugates.

If you are not an AUS-e-TUTE Member you can view a tutorial on this subject for free at https://www.ausetute.com.au/bronstedlowry.html

pH of Aqueous Salt Solutions

If you titrate acetic acid with sodium hydroxide, what is the pH at the equivalence point?

If you dissolve ammonium chloride in water, what is the pH of the solution?

To answer these questions you will have to calculate the pH of an aqueous salt solution!

AUS-e-TUTE has just added new resources to help you do just that!

Members should log-in to use the new tutorial, game, test, drill, worksheet wizard, and problem solving template.

If you are not an AUS-e-TUTE Member, you can access the "free-to-view" tutorial at https://www.ausetute.com.au/phsaltcalcs.html

pH of a Solution When Weak Acid and Strong Base are Mixed

What happens to the pH of a weak acid as you add strong base to it?

For example, aqueous sodium hydroxide solution (NaOH_(aq)) is a strong base and acetic acid (CH₃COOH_(aq)) is a weak acid.

If you add 10 mL of 0.20 mol/L NaOH_(aq) to 25 mL of 0.10 mol/L CH₃COOH_(aq), what is the pH of the resultant solution?

Find out how to work this out, and work through other examples with worked solutions at AUS-e-TUTE.

A "free-to-view" tutorial is available at https://www.ausetute.com.au/phmixwasb.html

AUS-e-TUTE Members should log-in to play the new game, do the test and get repetitive endless practice with the new drill.

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

acid + base

When an acid and a base are mixed together they react to produce a salt and water.
The general word equation for this type of acid-base reaction is:

acid + base → salt + water

But can you write the word equation for the reaction between a specific acid, for example hydrochloric acid , and specific base, say sodium hydroxide?

AUS-e-TUTE is here to help!

We've just added new learning resources; a tutorial, game, test and exam to help our members write acid + base word equations. We even have a worksheet wizard that lets teachers make their own printable worksheet or quiz on this topic.

You can join AUS-e-TUTE today at https://www.ausetute.com.au/register.html

If you would like to a view a read-only tutorial for free, you can at https://www.ausetute.com.au/weacidbase.html

What is the pH of a Strong Base After You Dilute It?

The problem with strong bases like sodium hydroxide and potassium hydroxide are that they absorb moisture from the air making it difficult to accurately weigh them. So we rely heavily on obtaining an accurately known concentration for an aqueous solution of a strong base (using titration techniques for example) and then diluting this stock solution to produce new, dilute solutions of known concentration and pH.
When you dilute an aqueous solution of a strong base :

• hydroxide ion concentration decreases (towards 10^-7 M)
• pOH increases (towards 7)
• hydrogen ion concentration increases (towards 10^-7 M)
• pH decreases (towards 7)

Visit AUS-e-TUTE's new tutorial to understand why, then log-in to the Members ONLY area to play the game, answer test and exam questions (which give you instant feedback), take the quiz, or, just for teachers, you could make a printable worksheet or quiz.

pH after mixing acid and base

If you add enough strong base to a strong acid you can neutralise the solution and its pH will be 7.
But what if you don't add enough base to the acid.
Will the solution be neutral?
Will the pH of the solution be 7?
These are all very good questions which is why AUS-e-TUTE has just added a new tutorial, game, test and exam on this topic.
AUS-e-TUTE Members should log-in to use these resources.

If you are not an AUS-e-TUTE Member yet, you can view the tutorial for free at https://www.ausetute.com.au/phmixsab.html

Sodium Bicarbonate

One of the single most useful and versatile chemicals I have in my kitchen pantry is a box of sodium bicarbonate, also known as baking soda or bicarbonate of soda.
Read the March 2018 issue of AUS-e-NEWS to find out what makes this compound so special.

Subscribe for free at http://ausetute.com.au/ausenews.html

Acid-Base Equilibria and Beginner Teachers

Cathy is a Year 12 student in a Brisbane school (capital city of Queensland, Australia). Last week she had a chemistry exam, the topic was equilibrium which included acids, bases and acid-base titrations. I met her on her way to school on the morning of this exam. When I asked her if she felt confident about her exam, I was horrified by her response,
"Sort of. I've got a new teacher this year and she's not any better than the one I had last year. We did an experiment, she said it took too long so we didn't do any more."
Seasoned teachers are used to:

• student claims that their teacher is "no good" (especially if the student is performing poorly)
• student exaggeration (only 1 experiment in a whole term of equilibrium, surely not!)

"Oh come on", I said in my best 'you're kidding me' voice, "you studied equilibrium for a whole term and only did one experiment?"

"Yeah", she confirmed, "we watched a video on titration though".

"Didn't you do a titration experiment?"

"Nah. She said we didn't have time."

Even allowing for the possibility of student exaggeration, the thought that you would play a video showing someone else performing a titration rather than giving your own students the opportunity to carry out even a simple titration, is, quite frankly, appalling. 

From Cathy's description of the teacher I assume this is the teacher's first year out teaching (beginner teacher). Reflecting on my own first year of teaching (a long, long time ago), I remember struggling to meet the requirements of the chemistry syllabus in the time-frame allowed, and, I also remember that while teaching the techniques of titration was time consuming, the students learned more in a few practical sessions than they learned during the whole of the preceding theoretical lessons, and once they have mastered the techniques they can be put to use in real-world problems.

A typical sequence that is often taught for (monoprotic) acid-base equilibria assumes prior knowledge of solutions, concentration (molarity) and equilibrium concepts and calculations (including self-dissociation of water, K_w ):

1. What are the properties of acids and bases?
2. How do we define an acid and a base?
3. What is meant by the terms "strong acid"  and "strong base"?
4. How do we measure the strength of an acid or a base (pH scale)?
5. What happens when you add an (Arrhenius) acid to a (Arrhenius) base (neutralisation)?
6. How much (Arrhenius) acid do we need to add to a known amount of (Arrhenius) base in order to neutralise it (acidic, basic, neutral solutions)?
7. Discussion of titration techniques, including preparation of a standard solution.
8. Performing a strong acid - strong base titration.
9. Using the results of the experiment to calculate the concentration of the unknown acid or base.
10. Perform calculations for each 1 mL addition of strong acid to strong base in the titration experiment and graph the results (strong acid - strong base titration curve)
11. Discussion of weak acids (K_a).
12. Discussion of other acid-base reactions (proton transfer reactions) and other titration curves
13. What indicator should you use for a particular acid-base reaction? (optional, how does an indicator work)
14. Titration of weak acid - strong base (such as determination of acetic acid in vinegar)

If you see your students 4 or 5 times a week, this teaching program for acid-base equilibria will take about 4 weeks using a traditional, structured approach. If you have the luxury of being able to time your practical work so that it occurs in the correct sequence, and take time to link the practical work to the theoretical concepts, your students have a good chance of understanding and being able apply the concepts to unfamiliar problems.

If you don't do any experimental work, you could probably bowl it over in 2 to 3 of weeks, and be faced with a lot of bored students wondering why they ever took a course in chemistry.

If you take a student-centered constructivist approach (for example, start with the questions  like "what gives vinegar its tangy taste?",  "if acids are corrosive and burn skin, how come you can drink vinegar?",  "how can you measure the strength of an acid?", "how can we determine which brand of vinegar has the greatest concentration of acetic acid?"), be prepared to add another week (unless you give the students a lot of reading/research for homework). The benefits, however, are enormous. Your students are more likely to be engaged with the content and "on task", they will have to be able to justify decisions they make in order to design and perform experiments thereby linking concepts and practical work, and because they "invest" in the whole learning process they are more likely to be apply the understanding and knowledge gained to other problems.

So, if you are new to teaching acid-base equilibria, here a few suggestions:

1. Even if you firmly believe that constuctivist approaches to teaching are the most effective way to teach chemistry, be prepared to spend your first year of teaching chemistry taking a more traditional approach, using guided questioning to lead students towards the experiment(s) you need them to do (syllabus requirements) while still giving them "ownership" of the experiment and its results. Keep a list of the misconceptions you come across when you teach, this will help you be better prepared for next year. As you feel more confident in your ability to meet the syllabus requirements within the time you have, and you have a better feel for the misconceptions you will meet, you can start "loosening your hold" and give more time to truly constructivist approaches.
2. Let the students do as much practical work as possible (students not only need to be exposed the practical techniques of chemistry, they need to do the experiments in order to fully appreciate the significance of what you are trying to teach them). You also need to devote time to discussing the results of their experiments with them, and reinforcing the concepts, calculations, techniques etc involved. 
3. Spend time discussing the self-dissociation of water (that is, it is a lesson in its own right, not just a passing reference before you discuss acid-dissociation). Students will have been exposed to an "acids and bases" topic sometime between Years 7 and 10, but even so, many of them may still think that an acid has a pH less than 7, a base has a pH greater than 7, and that a neutral substance has a pH of 7. Believe me, it can be an uphill struggle to separate the two concepts of "acid, base, neutral" from the concept of "pH" in a student's mind (and if you don't believe me, think about the number of times you have seen/heard advertisements for products which talk about the "neutral pH" of skin/hair etc). If the students do not have a good grasp of the self-dissociation of water then they will not understand the pH of  aqueous solutions. (And a word of caution, just because a student can calculate the pH of an aqueous solution of base at 25^oC, it doesn't mean they understand the relevance of pH + pOH = 14, or [H⁺][OH^-] = 10^-14, and if you want to test this statement, ask you students to calculate the pH of 0.001 M NaOH(aq) at 50^oC, or ask them to find the pH of 0.01 moles of HCl(g) dissolved in 1 L of ethanol and see what happens, because the chances are they will simply do a pH + pOH = 14 calculation without even thinking about it!)
4. Spend time making the distinction between "strong acids", "weak acids", "dilute aqueous solutions of acids" and "concentrated aqueous solutions of acids" (similarly for bases) because once again, you are likely to have an uphill struggle to separate the two concepts "strength of an acid/base" and "concentration of an acid/base". Remember, they have already been exposed to statements such as, "I need a cup of strong coffee", or, "this cordial is a bit strong" which, in chemical terms should be "I need a cup of concentrated aqueous solution of coffee (or cordial as the case may be)". On the other hand, they have also been exposed to ads which say things like "concentrated laundry detergent" which is a slightly more appropriate use of the technical term "concentrated" (although I do remember one example that used "concentrated laundry liquid" which introduces the other problem of the loose usage of the word "liquid" instead of "solution"). One way to do this is to give each pair of students a bottle of acetic acid labelled with its concentration, and have them measure its pH with a pH meter. Also provide them with volumetric flask of HCl(aq) of known concentration (say 0.1 M) and have them measure its pH, then have them perform sequential 1:10 dilutions and measure the pH at each stage say they can see that pH is dependent on the concentration of the strong acid and that you can reach a point at which the pH, and therefore the concentration, of a strong acid is the same, and even greater than, the concentration of an aqueous solution of weak acid. When you tabulate the class results and ask them for an explanation be prepared for many of them to believe you somehow "tricked them", it can take time for them to break the strength/concentration misconception and replace it with a more appropriate separation of the two concepts. If the students do this activity themselves, it will easily take a lesson, if you do it as a demonstration it will take about 10 minutes, BUT, it is better for the students to do it themselves partly because it reduces the instances of "there must be a trick in this" thinking, but mostly because they can see the pH change with the concentration and they are going to have to justify that all the way to the point at which the pH of the strong acid is  greater than the pH of a weak acid.
5. Related to point 2 is the common misconception students may have that when you add an acid to a base you end up with a neutral solution that has a pH of 7. Personally, I think the best way to deal with this is to let the students work it out for themselves before you attempt to explain it to them. For example. give each pair of students a bottle of methyl orange indicator (you will need a fair degree of tolerance in establishing the end-point so don't use a pH meter) and a conical flask and have them add a 10.00 mL aliquot of standardised 0.1 M NaOH to the flask and record what happens to the indicator colour. Have them calculate the moles of hydroxide ions in the flask, as well as calculate the pH of the solution (so they are convinced the indicator is giving a true reading). Then give each pair a 100 mL volumetric flask containing 0.1 M monoprotic acid (some will get a strong acid such as HCl(aq), some will get a weak acid such as acetic acid). . Have them calculate the volume of acid they will need to add to the NaOH(aq) to neutralise it. Have them add this volume (straight from the pipette to the flask), give it a swirl, and record the colour of the indicator. Tabulate the results on the board (yellow vs red). Ask them why some changed colour and some didn't (be prepared to let the students with weak acids try adding more acid, many will believe they made a mistake in the calculations or in adding the solutions), if the students do not come to the realisation that only students with strong acids got a colour change at neutralisation, you can use questions to help guide them. I have found this is a far more effective method than just "telling them" and it need only take 15 minutes if all the solutions and equipment are prepared before hand AND you don't expect them to write it up as a prac (a demonstration takes even less time, but may not be quite as effective, that is, some students will believe you have somehow "tricked" them).
6. Have the students perform the calculations that will enable them to draw a strong monoprotic acid - strong base titration curve. If you have a class of 20 students, they only need to do one of the calculations each, you can tabulate the results and then they can graph the class results. There are a number of reasons for this, it reinforces the nature of the neutralisation reaction, stoichiometry, and of "limiting reagents" and "reactants in excess". It is also enables them to come to a greater understanding of the shape of the curve than if you just present it to them and discuss key points. Finally, if the students do not have a good grasp of why titration curves are the shapes they are, they will have a much harder time coming to terms with the nature of different indicators and why some indicators are more appropriate than others for particular titrations.
7. Do use "real-world" examples. The acetic acid concentration of brands of vinegar is not hard to do, and empowers them (if you have mothers whinging that their daughter will now only let them buy brand X because its better value because it has a higher concentration of acetic acid than other brands, then pat yourself on the back for a job well done!) If you are in a position to be able to safely determine the concentration of sulfuric acid in a lead-acid battery, then this is also not hard to do (but check whether it can be done at your school). Similarly, you will find concentrated HCl(aq) available at you local hardware store (for cleaning bricks) or pool suppliers (for addition to pools) and, if your safety guidelines allow, you can determine the concentrations of these.If you are prepared to take your students through back titrations (indirect titrations) then a wealth of new "real-world" opportunities is open to you.
8. Finally, do not deceive yourself. It is NEVER about what you "teach", it is ALWAYS about what the students "learn". YOU can make up time by giving the students notes you have prepared for them, making them read stuff for homework, making them watch a 30 minute video instead of doing a 2 or 3 day prac, then you can happily tick this off on your list of things to teach, BUT, you must also find out what the students have learned, because you may very well find out that you have been a bit hasty in ticking something off your list! 

AlP Rat Poison

Dozens of mysterious sealed silver canisters containing aluminium phosphide have washed up on Australian beaches between 2012 and 2015. The Australian Maritime Safety Authority (AMSA) suspects all the canisters have come from the same ship which dumped or lost its cargo in the Pacific Ocean. Aluminium phosphide is used as a fumigant to poison rats on ships.

When solid aluminium phosphide, AlP, is exposed to water, it releases highly toxic phosphine gas, PH₃, which smells like rotting fish. The chemical reaction can be represented by the balanced chemical equation shown below:
AlP_(s) + 3H₂O_(l) → PH_3(g) + Al(OH)_3(aq)

This is a proton-transfer reaction in which water is acting as Brønsted-Lowry acid by donating a proton to phosphorus. Phosphorus is therefore acting as a Brønsted-Lowry base by accepting a proton from water. Aluminium phosphide will react with acids according to the following chemical
AlP_(s) + 3H⁺_(aq) → PH_3(g) + Al³⁺_(aq)

These reactions make aluminium phosphide a good choice for ridding a ship of rats.
Firstly, as a solid, AlP can easily be stored as pellets in air-tight, water-tight, containers until it is ready to be used. When required, the pellets can be scattered in the effected area . In the humid air aboard ship, the AlP will start reacting to produce toxic phosphine gas, that is, the area will be fumigated. But it is also possible to entice rats to eat AlP pellets mixed with food, in which case it will act as pesticide, because on entering the acidic stomach of the rat, it will produce the toxic phosphine.

Aluminium phosphide is  a very effective way to get ride of rats, so much so, that is widely used in agriculture to remove rats from grain silos.

References:
"Toxic canisters washing up on Australian beaches pose serious health risk"
 http://www.smh.com.au/environment/toxic-canisters-washing-up-on-australian-beaches-pose-serious-health-risk-20150917-gjp5se.html

"Controlling rabbits with aluminium phosphide tablets"
 http://agriculture.vic.gov.au/agriculture/farm-management/chemical-use/publications/chemical-industry-news/chemical-industry-news-no.-75-summer-autumn-2013

"Phosphine fumigation"
https://www.worksafe.qld.gov.au/injury-prevention-safety/hazardous-chemicals/specific-hazardous-chemicals/phosphine-fumigation

Further Reading
Definition of Acids and Bases
Proton-transfer Reactions
Mass-mole Calculations
Molar Volume of Gases

Suggested Study Questions:

1. The symbols of some elements are listed below. Name each element.
   • Al
   • P
   • H
   • O
   • K
   • He
   • At
2. Calculate the amount of aluminium phosphide in moles given the masses of AlP given below:
   • 10 g
   • 10 kg
   • 10 mg
   • 10 μg
3. Calculate the moles of phosphine gas produced when each mass of AlP below reacts with excess water in a ship's hull:
   • 10 g
   • 10 kg
   • 10 mg
   • 10 μg
4. Based on your answers to question 3 above, calculate the mass of phosphine produced for each mass of AlP used.
5. Your ship is sailing towards eastern Australia and has just crossed the Tropic of Capricorn. You have been asked to estimate the volume of phosphine gas that will be produced when you release AlP pellets into the ships hold. Which molar gas volume will you use; 22.71 L or 24.79 L ? Explain your answer.
6. Rats are currently infesting a small part of your ship, about 150 m³. How much solid AlP would be required to fumigate this area, but not leave any AlP residue left over?
7. The Cook has already tried to fumigate the pantry and is sure there is a silver canister around that still contains some AlP, it could be in the pile of empty canisters, or, it could be in the pile of full canisters. No-one wants to kill themselves by opening the canisters to find out, so can you suggest a method that could be used on board ship to determine how much AlP is present in each canister.
8. Explain why the reaction between aluminium phosphide and water is described as a proton-transfer reaction and not as a redox reaction.
9. Explain why, even though aluminium phosphide and phosphine are toxic, it is considered safe to use these to fumigate silos containing grain which will be eaten by humans.
10. The silver canisters that have washed up on Australian beaches have no labels, presumably these have come off while they were in the ocean. You have been asked to design new labels for the canisters. The labels must include suitable safety and handling information.

Which of the following is an acid-base indicator?

Question: Which of the following is an acid-base indicator?

1. hydrochloric acid 
2. sodium hydroxide 
3. water 
4. phenolphthalein

Answer: Phenolphthalein is an acid-base indicator

1. Hydrochloric acid is an acid
2. Sodium Hydroxide is a base
3. Water is neutral

What is the best indicator for titration?

Question: What is the best indicator for titration?
Answer: That all depends on what you are titrating!

If you doing an acid-base titration, then you will need to know the relative strengths of the acid and base you going to be using.
Once you have determined an approximate pH for the equivalence point of the neutralisation reaction, you use this as the pH of the endpoint of the titration in order to determine the best acid-base indicator to use.

Sulfuric Acid - Sodium Hydroxide Titrations

Why does a titration of sulfuric acid using sodium hydroxide have only one equivalence point?
Why isn't the pH 7 at the equivalence point?

These are both excellent questions.

So, we've written a set of resources to help you understand!

AUS-e-TUTE Members should log-in and go to the new tutorial at:
http://www.ausetute.com.au/members/titrh2so4.html
and you can follow the links to the game and test from this page.

Not an AUS-e-TUTE member?
Part of this tutorial is currently available free to non-members for evaluation purposes at
http://ausetute.com.au/titrh2so4.html

Introduction to Buffers

AUS-e-TUTE has just uploaded two new sets of resources:

• Buffer Concepts (tutorial, game, test, exam)
• pH of Salt Solutions (tutorial, game, test, exam)

There has also been a significant update to the tutorial on Titration Curves (Graphs) with improved graphs and explanations.

Members should log-in and go to the Acid and Base section to find these new resources.

AUS-e-TUTE Update

The following resources have been added to AUS-e-TUTE:

• Neutralisation Reactions (tutorial, game, test)
• Acidic, Basic, Neutral Solutions (tutorial, game, test)
• Properties of Alkanes (tutorial, game, test, exam)
• Properties of Alkanols (alcohols) (tutorial, game, test, exam)
• Properties of Alkanoic (carboxylic) acids (tutorial, game, test, exam)
• Properties of Amines (tutorial, game, test, exam)

Syllabus Study Guides have also been updated.