 The Open Door Web Site |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Chemistry Section C : A Closer Look at Metals D. Acids and Alkalis There are many different substances that are classified as acids or alkalis. There are alos different types of acids and alkalis so it is important that we can do simple chemical tests to identify whether a substance is an acid, alkali or neutral. The substances used to test for acids and alkalis are called INDICATORS. These are substances that change colour to show if a substance is acid, alkali or neutral. Red litmus goes Blue in alkalis and Blue litmus goes Red in acids A very useful indicator called universal indicator (a mixture of several indicators) or pH indicator gives many different colours, it not only tells us if a substance is an acid alkali or neutral, but also its strength. We have a scale of colours called the pH scale.
E. A closer look at the oxidation of iron. Iron when left in air produces a substance that causes great problems. This substance is called RUST. Unlike other corroded metals rust is porous and causes the iron to be eaten away. What causes iron to rust? We need to have a closer look at the composition of air so that we can have a better idea as to what causes iron to rust.
For iron to rust it needs both oxygen and water. Rust is hydrated iron oxide.
iron(II)oxide and iron(III)oxide. Can you write the chemical reactions for each? Iron is such a useful metal, that we need to find methods to protect it from rusting. There are some very simple and cheap methods such as painting or oiling which are short term protection methods or there are more long term methods that are more expensive such as galvanising and alloying. pdf download on the protection of iron and steel F. Chemical formula and equations. We have already seen from section B (Atoms and Ions) how we can represent a chemical compound using a formula and how work out the formula of a chemical compound. We can also write a chemical equation representing the chemical reaction, using chemical formula. Rules:
Example:
Go to Internet site link G. Calculations from equations. When a chemical reaction occurs:
The mass of reactants is equal to the mass of products. This is known as the Law of Conservation of Mass. Example: When 2.4g of magnesium is fully combusted in oxygen it produces 4.0g of magnesium oxide. How much oxygen does it react with? Write the equation:
From the Law of conservation of mass we know that:
2. H. % composition If we know the formula of a compound we can find the percentage composition of the elements present in that compound. Example: Calculate the percentage oxygen in copper(II)sulphate
|
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
