Chemistry Edexcel iGCSE - Chapter 17 - Acids, Bases and Salt Preparations

To be continued

Formula of hydrochloric acid

HCl

Formula of nitric acid

HNO₃

Formula of sulfuric acid

H₂SO₄

Formula of ethanoic acid

CH₃COOH

Formula of phosphoric acid

H₃PO₄

How does the reactivity series affect how acids react with metals?

Metals below hydrogen on the reactivity series don’t react with dilute acids. Metals above hydrogen on the reactivity series react with dilute acid to produce a salt and hydrogen gas.

General equation for the reaction between a metal and acid

metal + acid → salt + hydrogen

If a metal is lower on the reactivity series (but still higher than hydrogen), how does that affect the reaction.

The lower it is on the reactivity series, the slower the reaction.

How do bases neutralise acids

They combine with hydrogen (H⁺) ions to produce water

General equation for the reaction between a metal oxide (base) and an acid

metal oxide + acid → salt + water

General equation for a reaction between a metal hydroxide and an acid

metal hydroxide + acid → salt + water

General equation for a reaction between a carbonate and an acid

carbonate + acid → salt + water + carbon dioxide

Name the soluble nitrates

All nitrates are soluble

Name the insoluble sulfates, the rest of the sulfates are soluble

Lead sulfate, barium sulfate and calcium sulfate are all insoluble

Name the insoluble chlorides, the rest of the chlorides are soluble

Silver chloride and lead chloride are insoluble

Name the soluble carbonates, the rest of the carbonates are insoluble

Sodium carbonate, potassium carbonate and ammonium carbonate are all soluble

Name the soluble hydroxides, the rest of the hydroxides are insoluble

Sodium hydroxide, potassium hydroxide and ammonium hydroxide are all soluble

How to make copper(II) sulfate crystrals? (this method works with any mixture)

1. Add dilute sulfuric to a beaker and warm it in a water bath/on a bunsen burner

2. Add copper(II) oxide in excess, stirring the mixture so that it all reacts. We add excess so that all the acid reacts.

3. Filter off the excess copper(II) oxide using filter paper and a funnel and transfer the solution to an evaporating basin.

4. Heat the solution of copper(II) sulfate so some of the water evaporates until crystals form

5. Once half of the water is evaporated and crystals have begun to form, stop heating the mixture and allow it to cool slowly so that the rest of the water can evaporate and the crystals can become larger

6. Filter the crystals out of the solution and leave them to dry in a warm place

Which elements/compounds don’t need to be heated to form crystals

Carbonates and magnesium

Why does this method not work with sodium, potassium and ammonium salts?

Sodium, potassium and ammonium salts are soluble in water.

How to make sodium sulfate crystals? (works for potassium and ammonium salts)

1. Add 25cm³ of sodium hydroxide into a conical flask using a pipette and add a few drops of an indicator such as methyl orange

2. Add dilute sulfuric acid into the flask using a burette until the indicator changes color.

3. The volume of acid needed is noted and then the same volumes of acid and alkali is are mixed together in a clean flask without indicator.

4. The solution is left to evaporate off some water until a saturated solution is formed. Then it is left to cool until crystals form.

5. The crystals are filtered out of the solution and then are left in a warm place to dry

How is the process different for simple ammonium salts?

Instead of evaporating them to dryness, you would let them crystallise slowly as they don’t have a water of crystallisation. Heating dry ammonium salts causes them to break up.

How do you make an insoluble salt?

Mix solutions of two soluble salts

How do you know what to mix together to make an insoluble salt?

All nitrates, all sodium and potassium salts are soluble. To make an insoluble salt, simply take the nitrate of the metal part and mix it with either a sodium or potassium non-metal part.
I.e. to make lead(II) iodide, use lead nitrate and sodium iodide

How to prepare a pure sample of lead(II) sulfate?

1. Take 25cm³ of lead(II) nitrate in a beaker and add 25cm³ of sodium sulfate.

2. Lead(II) sulfate will form, it’s a white precipitate

3. The precipitate is filtered but it’s not pure yet, it’s contaminated with solutions of sodium nitrate and the excess reactant.

4. Wash the residue with distilled water into the filter paper and allow it to pass through, this washes away everything except the insoluble lead(II) sulfate. Repeat this several times to ensure that the sample isn’t contaminated

5. Transfer the filter paper with the lead(II) sulfate to a warm oven and leave it to dry.

The Arrhenius theory of acids and bases is that acids produce H⁺ ions and that alkalis produce OH^- ions. The problem is that this isn’t widely applicable. What is the Brønsted-Lowry theory?

Acids are a proton (hydrogen ion) donor and alkalis are a proton (hydrogen ion) acceptor.