CORE Chemistry (Short Course) - 9222 OxfordAQA

Preparation Of Salts

Aperçu

Somewhere in the building you are sitting in there is almost certainly a tub of Epsom salts, a bottle of iron tablets, a bag of blue crystals for treating a pond or a sack of micronutrient for a field. Every one of them is a salt, and every one of them was made on purpose by a chemist who began with a bottle of acid and had to answer one practical question before anything else: what am I going to let that acid attack? The answer chooses the apparatus, decides how long the afternoon takes, and settles whether the product arrives as a dish of grown crystals or as a contaminated mess.

This lesson gives you the whole decision and then walks each branch of it in detail. You will learn the three partners an acid can be offered, why a route that works beautifully for copper would be dangerous for sodium, the reason chemists deliberately add too much of one reactant and then throw the leftovers away, why an indicator has to be used once and then carefully left out, and the patient technique that turns a colourless solution into a dish of grown crystals. By the end you will be able to plan a preparation for a salt you have never made, which is precisely what the examiner asks you to do.

Objectifs

  1. Soluble salts can be made from acids by reacting them with: metals - not all metals are suitable; some are too reactive and others are not reactive enough; insoluble bases - the base is added to the acid until no more will react and the excess solid is filtered off; alkalis - an indicator can be used to show when the acid and alkali have completely reacted to produce a salt solution. Students should be able to suggest methods to make a named soluble salt.
  2. Salt solutions can be crystallised to produce solid salts.

Carte mentale

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Note de cours

A salt is what remains when the hydrogen of an acid has been handed over to a metal and something else has carried the hydrogen away. Sodium chloride is a salt. So are the calcium sulfate in a plaster cast, the magnesium sulfate sold as Epsom salts, the iron(II) sulfate in an anaemia tablet, and the copper(II) sulfate that stains a school beaker blue. The name of any one of them is assembled from two parts, and both parts are chosen for you by your starting materials: the metal at the front comes from whatever you neutralise the acid with, and the family name at the back comes from the acid itself.

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Évaluation de la leçon

Félicitations, vous avez terminé la leçon sur Preparation Of Salts. Maintenant que vous avez exploré le concepts et idées clés, il est temps de mettre vos connaissances à lépreuve. Cette section propose une variété de pratiques des questions conçues pour renforcer votre compréhension et vous aider à évaluer votre compréhension de la matière.

Vous rencontrerez un mélange de types de questions, y compris des questions à choix multiple, des questions à réponse courte et des questions de rédaction. Chaque question est soigneusement conçue pour évaluer différents aspects de vos connaissances et de vos compétences en pensée critique.

Utilisez cette section d'évaluation comme une occasion de renforcer votre compréhension du sujet et d'identifier les domaines où vous pourriez avoir besoin d'étudier davantage. Ne soyez pas découragé par les défis que vous rencontrez ; considérez-les plutôt comme des opportunités de croissance et d'amélioration.

  1. Which salt is produced when copper(II) oxide reacts with dilute nitric acid? A. copper(II) nitrate B. copper(II) sulfate C. copper(II) chloride D. copper(II) hydroxide Answer: A
  2. A student adds excess magnesium oxide to warm dilute hydrochloric acid, then filters the mixture. What is present in the filtrate? A. magnesium oxide only B. magnesium chloride solution C. hydrochloric acid only D. solid magnesium chloride Answer: B
  3. Which metal cannot be used with dilute sulfuric acid to prepare its sulfate, because it is not reactive enough to react with the acid? A. magnesium B. zinc C. iron D. copper Answer: D
  4. Why is an indicator used when potassium nitrate is prepared from potassium hydroxide solution and dilute nitric acid? A. Potassium nitrate is insoluble in water. B. Potassium hydroxide dissolves, so an excess of it cannot be filtered off. C. Nitric acid does not react with potassium hydroxide. D. The reaction produces a gas that must be measured. Answer: B
  5. A salt solution is to be crystallised. What should be done to it? A. Boil it until it is completely dry. B. Filter it and keep the residue. C. Evaporate some of the water, then leave it to cool slowly. D. Add more water and leave it to cool slowly. Answer: C

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