Learners

Learners What is an acid? How do acids behave? Behaviour of acids in solution in respect of indicators, reaction with active metals, neutralisation of bases. Use dilute solutions of inorganic and organic acids, including fruit acids, for this activity. Indicators can include litmus solution, fruit teas (make the really concentrated), alcoholic extractions of coloured plant materials (leave petals infusing in ethanol for a couple of weeks). Robert Boyle used syrup of violets - try this. [|Lesson plan for indicators] [|You Tube videos for indicator testing using red cabbage] Watch for the fizz if an acid solution is used. calcium carbonate is not so good here because it gets coated with the insoluble salt very quickly, preventing further reaction. [|Carbonate tests for acids] Magnesium and zinc are useful metals to use. Watch for the fizz. Some of the reactions may be every rapid, with the solution getting very warm. Some may be very slow, especially with zinc foil. [|Metal acid reactions] [|Sodium reacts with four acids] [|Faraday lectures] || This section is about being clear what an acid is. ** Safety **: acids are potentially dangerous, corroding skin and clothing. Alkalis also react with skin. Goggles at least must be worn.
 * **Topic** || **Concept** || **History** || **Philosophy** ||
 * **Area 1**
 * Lesson 1**
 * //Characterising acids and alkalis using indicators//**
 * Lesson 2**
 * Characterising acids using sodium carbonate and calcium carbonate (marble)**
 * Lesson 3**
 * //Characterising acids using reactive metals//**


 * Lesson 1** is a reenactment of Boyle's use of indicators.


 * Lesson 2** is a part use of acids for detecting carbonates in mining in medieval times.

Indicators (e.g. Boyle and Lemery); Information on [|litmus] [|Article about red cabbage indicator, some parts very tough going.] [|'How stuff works' article on red cabbage] [|Wikipedia violets]
 * Lesson 3** is normally taught as a reaction of acids but can be seen as a method of characterising an acidic solution. || **History:**

Instruments; [|Boyle paper on elements] [|Joe Peatrovsky's history of acidity] [|Another history of acids and alkalis]

This [|history site] gives recipes for various syrups of plant materials including syrup of violets said to be used by Robert Boyle in 1665 as a practical indicator. Boyle claimed to be the first to note that alkalis turned syrup of violets to green in his book 'The Experimental History of Colours'. Of course, cloth dyers also knew a great deal about colour changes of plant indicators and used this knowledge in their work. Syrup of violets had a long medicinal history before Boyle used it for indicating an acid.

[|Ancient medical uses of syrup of violets.]

[|Medieval lead mining]

[|Contents page of German mining in 13th and 14th century]

The place of coinage in medieval times is part of the culture of establishing a civilization and of trading within that civilization. This is one of the interactions of society and science/technology.

Extraction of metals is also part of military history as tribes/nations battled for territory and resources and developed weapons to do so.

Extraction of metals is also part of machinery development, in the move from wood and stone to stronger materials. This is nowhere more obvious than in the development of the plough.

[|History of acid-base ideas], rather tough going in parts.

[|Antiquity: Article on French Alps mining]

[|Polish carbonate rocks in medieval times]

[|History of etching] || There are two ways of making sense of concepts. One is induction, which means taking lots of examples and working out what they have in common, or what they are all trying to say. the second is deduction which means saying what the idea is and then looking at examples to see if they fit.

The following examples show deduction in action. Scientists know about the effect of acidity on carbonate rocks, as you do from your practical work. See how they think about deducing this from their general understanding of acids on carbonate rocks.

[|Carbonate rocks discovered on Mars]

[|New Scientist article on effect of acidity on finding carbonate rocks on Mars] || The magic ingredient in acids Burn some sulphur in oxygen, in a combustion spoon (in a fume cupboard) and shake the new gas formed with water. Test the solution with indicator paper. Some of the non-metals can be very dangerous, or difficult to burn so your teacher may have done this beforehand and dissolved the non-metal oxide in water. You may also have other solutions labelled phosphorus oxide solution, and carbon dioxide solution. This [|picture table] may help you to see whether sulphur, phosphorus and carbon are metals or non-metals. (the picture table is full of interesting and highly visual stuff about elements) [|Sequence of burning non-metals in oxygen] Characterising oxides of metals Burn some metal, in a combustion spoon (in a fume cupboard) and shake the new material with water. Some of the metals can be rather dangerous to use so you your teacher may have done this beforehand and dissolved the metal oxide in water, if the metal oxide is soluble. Test the solutions with indicator paper. If the metal oxide is insoluble in water, see if it can react with dilute hydrochloric acid solution (**safety** - the acid solution is corrosive, so wear goggles and take care). [|Comparing metals and non-metals] || **Lesson 4** helps to identify acids as oxides of non-metals.
 * **Area 2**
 * Lesson 4**
 * Characterising acids as oxides of non-metals**
 * Lesson 5**


 * Lesson 5** has the challenge of induction, plus the challenge that many metal oxides are insoluble in water, so can not make solutions to be tested with indicators. The extra test with acid is an alternative in these cases but is more difficult for young chemists to understand.

[|Video burning sulphur]
 * //Burning non metals//**

[|Burning phosphorus]

[|Burning red phsophorus]

[|Video burning sodium]
 * //Burning metals//**

[|Video burning potassium]

[|Burning lithium]

[|Burning magnesium]

[|YouTube burning magnesium]

[|Burning iron]

[|How hard is it to set fire to a magnesium computer case? Very hard!]

[|Another video of burning magnesium] || Looking for the magic ingredient that is the cause of acidity would not have been strange in medieval times. [|Alchemy] was an occult activity and chemistry in the 16th and 17th centuries was not far from that link to the past. Firstly, Lavoisier was a great proponent of the idea that oxygen was the magic constituent. Secondly, Liebig proposed that hydrogen was the major ingredient. they are both coming from the same viewpoint, that is, the idea that there is something in all acids that gives them its character. || Looking for a cause that would have a clear effect is part of the nature of explaining. Searching for a cause in this way is a philosophical activity. The debate over [|phlogiston] did not take long. Johann Joachim Becher in 1667 created the idea. Mikhail Lomonosov, in 1753, weighed the metal before and after burning and concluded that phlogiston was not a helpful idea, especially when it did not change its mass when air was excluded, contrary to Robert Boyle's prediction. Joseph Black's student Daniel Rutherford discovered nitrogen in 1772. [|Antoine-Laurent Lavoisier]'s painstaking work confirmed Lomonosov's results. However, it is good to note that Lavoisier's results were turned down for publication and that he had to estblish his own journal to get them into print!

The characterisation process uses the philosophical process of induction, i.e. collecting lots of examples to see what they have in common. || Acids pass on their acidic character [|Ideas about acids in chronological order] Draft: test conductivity of citric acid in dry propanone, and in water. If you wish, you could bubble dry HCl gas into the two solvents, and test them with **dry** indicator paper, magnesium ribbon, sodium carbonate powder, and conductivity. the results can be explained by HCl--> H+ + Cl - It may be best to write the Arrhenius paper in intermediate English and set a comprehension exercise || || [|Arrhenius biography] [|Advanced history of Arrhenius] [|A personal history of Arrhenius by Hubert Alyea]
 * **Area 3**
 * Lesson 6**

[|Arrhenius paper on dissociation in solution]

[|pH] [|Interactive pH chart]

|| || 1. Mix aqueous solutions of hydrogen chloride and ammonia. 2. Mix dry gases of hydrogen chloride and ammonia Explain using Bronsted-Lowry ideas. The acid messenger is the hydrogen ion
 * **Lesson 7**

Arrhenius proposed that the role of the water was to assist in the separation of the ions. The hydrogen ion is the positive ion in all acidic solutions.

Bronsted and Lowry proposed that when an acid is put into water, it donates a hydrogen ion to the solvent. the water acts as a base in accepting this hydrogen ion. In gases, the same explanation can be used for the ammonia hydrogen chloride reaction. || || [|Bronsted-Lowry's ideas about acids]

[|Wikipedia on Bronsted Lowry ideas] || || Acids make bonds with bases
 * **Area 4**

The lesson practical content is similar to that in Lesson 7 The students should explain using Lewis acids ideas. || [|Wikipedia on Lewis acids] || || ||
 * Lesson 8**