Word equations:
Hydrogen + oxygen water
Reactants “give off” or “change into” Product
In water, there are two hydrogen atoms for every oxygen atom.
Chemical reactions and equations
Sulphur + oxygen Sulphur dioxide
The reactants are sulphur and oxygen. When you mix them, nothing happens until sulphur is heated. Then the reaction start, producing a blue flame in the gas jar full of oxygen. The product is the compound sulphur dioxide.
Carbon + oxygen Carbon dioxide
This is a chemical change because the reactant chemically bond to form the new substance.
Methane + oxygen water + carbon dioxide
In this process energy is also released, and in a methane molecule there are four hydrogen atoms to every carbon atom. This indicates that methane is a compound. To find out if something has reacted, you can check the masses or compare the properties.
The “ide” ending is a compound shows that two elements have combined. An oxide is formed in an oxidation reaction, when something reacts with oxygen and it is in the same way with other compounds as well. We can also split compounds into their original elements using reactions.
In the apparatus, electricity is passed through water. The water splits up to form its elements hydrogen and oxygen. This shows that water is made from hydrogen and oxygen. The below diagram shows the Hoffman Voltammeter that splits water into its elements using electrical energy.
Elements to Compounds
If you mix the elements iron and sulphur, you won’t see any change. However, if you gently heat the mixture with a Bunsen burner, the elements react. They change into a new substance called iron sulphide. Iron sulphide contains the elements iron and sulphur, but has very different properties.
Word Equations: iron + sulphur iron sulphide
The reaction
The reactants iron and sulphur change in appearance as the reaction takes place. This tells us that a chemical reaction has taken place. The reactants carry on glowing after the Bunsen burner is removed, showing that heat is given out as the new substance forms. We can also check the substance’s property to check if a reaction has taken place.
Iron- Magnetic
Sulphur- Not magnetic
Mixture- the iron in the mixture is magnetic
Compound- Not Magnetic
Reaction with hydrochloric Acid
Hydrochloric acid reacts with iron to produce hydrogen gas. It is given off in bubbles. Sulphur didn’t react with hydrochloric acid to give off hydrogen gas. The compound, iron sulphide did react with hydrochloric acid, but the bubbles of gas weren’t hydrogen. This shows that the chemical properties of iron change as it turns into iron sulphide.
Fe + S FeS
The atoms of iron and sulphur are chemically joined. They are in a fixed ratio. There is one iron atom for every sulphur atom.
Signs of a chemical reaction
- Colour Change
- Glows
- Gives off a gas
- Produces smoke
- Heats Up
- Flashes
- Produces a solid
- Cools Down
These observations tell us that a chemical reaction is happening. Sometimes it is extremely hard to spot is reaction. Some materials change colour when you warm them, but they are not actually undergoing a chemical reaction.
Mixtures
A pure substance is not mixed with anything else. A gas jar of oxygen is pure because it is not mixed with anything else. Compounds can also be pure. Copper oxide is pure if it doesn’t contain anything except copper oxide.
A material with more than one substance in it is impure. A mixture contains more than one substance mixed together, but not chemically joined. So mixtures are impure. A mixture can be made from any combination of substances with any composition. Compounds always have a fixed composition- they have a known ratio of elements which is shown in their formula. Because mixtures do not have a fixed composition, they do not have a formula.
Fractional Distillation of Liquid Air
Air is a mixture of gases. But if air is pressurised and then allowed to quickly expand, it cools and turns into a liquid. If this liquid air is then slowly warmed, the components of the mixture boil off at different temperatures. The gases can be collected and separated from each other. This is known as fractional distillation of liquid air.
Separating Mixtures
- Filtering to remove solid bits from a liquid
- Chromatography to separate substances with different solubilities.
- Distillation to separate a solvent from a solution.
Changing state
When pure water changes state, it always changes at the same temperature. All elements and compounds have a fixed melting and boiling point. Water has a melting point of 0 degrees and a boiling point of 100 degrees. If you have an impure substance (a mixture) , the melting and boiling points change depending on the composition, Impurities tend to raise the boiling point and lower the freezing point. To check if a substance is pure or not, we can melt the substance. If the substance melts quickly, then it is a pure substance. If it melts gradually, then it is an impure substance.
Type of Water Boiling point
Deionised 100.2
Tap 100.8
Salty 102.5
Pure 100
This shows that salty water has the most impurities, and even shows that our normal tap water has some impurities in it.
