This question is about iron. Steel consists mainly of iron. Iron rusts when it reacts with water and oxygen. Fig. 6.2 shows magnesium blocks attached to the bottom of a steel boat. The magnesium does not completely cover the steel. The magnesium blocks provide sacrificial protection for the steel. Fig. 6.2 (i) Explain, in terms of electrons, why magnesium is used for sacrificial protection. ......................................................................................................................................... . ................................................................................................................................... (ii) Name a metal that cannot provide sacrificial protection for steel. ...................................................................................................................................

Chemistry

IGCSE&ALevel

CAIE

Exam No：0620_s24_qp_43 Year：2024 Question No：6(c)

Answer:

Knowledge points:

7.3.1.1. an alkali by titration

7.3.1.2. excess metal

7.3.1.3. excess insoluble base

7.3.1.4. excess insoluble carbonate

7.3.2.1. sodium, potassium and ammonium salts are soluble

7.3.2.2. nitrates are soluble

7.3.2.3. chlorides are soluble, except lead and silver

7.3.2.4. sulfates are soluble, except barium, calcium and lead

7.3.2.5. carbonates are insoluble, except sodium, potassium and ammonium

7.3.2.6. hydroxides are insoluble, except sodium, potassium, ammonium and calcium (partially)

7.3.3. Define a hydrated substance as a substance that is chemically combined with water and an anhydrous substance as a substance containing no water

7.3.4. Describe the preparation of insoluble salts by precipitation

7.3.5. Define the term water of crystallisation as the water molecules present in hydrated crystals

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