O Level Revision : Integrated Science - Science in Industry - Nature and Behaviour of Matter

States of matter

• Matter is anything that occupies space and has mass.
• Matter can exist in three states: solids, liquids and gases.
• Whether a material is a solid, liquid and gas, depends the motion of the particles within it.

a) Solids

• Particles are very close together.
• The particles only vibrate about a fixed point.
• Have fixed mass, shape and volume.

b) Liquids

• Particles are only a little further apart than in a solid.
• Liquids can change their shape, but they have a fixed volume.
• Liquids can be poured.

c) Gases

• Particles are much further apart.

The kinetic energy in particles increases as matter changes state from solid to liquid and from liquid to gas.

• Gases change their shape and volume depending on their container.

Note: The state of matter can therefore change depending on whether energy has been supplied or taken away from the particles.

Changes in states of matter

Heating and cooling substance

1. Liquid water is left in deep freezer for 24 hours.
2. Crushed ice in beaker is heated gently.

A thermometer is used to take the temperature after every 2 minutes and results are recorded.

3. A crystal of iodine is placed in an evaporating basin and a filter funnel is placed upside down over the crystal. The crystal is warmed gently using a bunsen burner flame.
4. A lump of candle wax is heated and allowed to cool.

State the observations in the activity.

1. Results for activity 2 can be used to draw a graph of temperature against time.
2. The graph is called the heating curve of water.
3. A cooling curve can also be drawn.

Structure of atoms

• The smallest part of an element is called the atom.
• An atom is the smallest part of matter which can take part in a chemical reaction.
• The atom is made up of neutrons, protons  and electrons.
• The protons and neutrons are found in the nucleus of the atom.
• Electrons orbit (move around) the nucleus.
• The atomic particles have different charges protons (positively charged) and surrounding the nucleus are orbits containing electrons which are negatively charged. Neutrons have no charge hence they are neutral.
• A normal atom has equal numbers of protons and electrons. The positive and negative charges
• cancel each other out.
• Number of protons in an atom is called atomic or proton number.
• Number of protons and neutrons in an atom is called nucleon number.

Elements, mixtures and compounds

• Matter can be classified as elements, mixtures and compounds.
• An atom is the smallest particle of an element which can take part in a chemical change
• An element is a substance made up of atoms of the same type.
• A molecule is the smallest particle of a compound made up of two or more different atoms.
• A compound is a substance made up of two or more different elements chemically joined together.
• A mixture contains two or more different substances physically joined together.

 The characteristics of compounds and mixtures

Chemical reactions

•  In chemical reactions, new substances are formed.
• The properties of the substance formed will be different to the properties of the original substances which have been combined.
• What happens in a chemical reaction, can be represented using   a chemical equation.

Making a mixture and a compound

Materials

Magnesium ribbon, burner, sulphur, iron filings, aluminium foil, evaporation dish, magnet

Method

1. Burn a magnesium ribbon and observe.
2. Mix iron filings and sulphur in an aluminium foil. Run a magnet over the substances and observe.
3. Mix iron filings and sulphur in an aluminiurn foil. Wrap the substances in the foil and heat the parcel in an evaporating dish. Stop heating and allow the parcel to cool then open it up. Bring a magnet close to contents of parcel and observe.

Results

1. Magnesium burnt with a bright flame producing a white substance.
2. Iron filings were attracted by the magnet.
3. A greyish substance which could not be attracted by a magnet was produced.

Conclusion

• In 2, substances kept their properties. Iron was attracted by a magnet and the yellow sulphur could still be seen. The iron and the sulphur formed a mixture.
• Therefore : A mixture is made up of different substances mixed in any proportion and not chemically joined.
• In 1, the magnesium was no longer there at the end of the experiment. The white substance formed is magnesium oxide which is a result of a chemical reaction between magnesium and oxygen.

In a chemical reaction energy is either taken in or given out and a new substance is formed. The chemical reaction above can be represented by a chemical equation i.e.

Magnesium  +   oxygen   →  magnesium oxide

Magnesium oxide is a compound since the magnesium atoms and the oxygen atoms are chemically joined.

• The greyish substance is iron sulphide, thus a new substance is formed.
• yellow sulphur can no longer be seen and the iron has lost its property of being attracted by a magnet.
• A chemical reaction occurred and the equation is:

Iron   +   sulphur  → iron sulphide

Metals and non-metals

• Materials can be classified into metals and non-metals.
• Metals have similar physical and chemical properties.
• The properties of metals are related to their use in industry and everyday life.

Comparison of the physical properties of metals and non-metals

Reactivity of metals

• Metals react with air i.e. oxygen, water and dilute acids.
• Some metals react more vigorously than others, while others do not react at all.

The reactions of some metals with air, water and dilute acids

Reaction with air

Magnesium     +    air (oxygen)   → Magnesium oxide

Reaction with water

Magnesium     +   water  → magnesium hydroxide

Reaction with acid

Magnesium   +   hydrochloric acid  → magnesium chloride + hydgrogen

• Metals can be placed in order of their reactivity forming a reactivity series.

Oxidation and reduction

Definition:

Oxidation can be defined as:

(i) gain of oxygen                              (ii)  loss of hydrogen

Reduction can be defined as

(i) loss of oxygen                               (ii)  gain of hydrogen

Oxidising and reducing agents

• An oxidising agent is a substance which oxidises something else.
• An oxidising agent gives oxygen to another substance or removes hydrogen from it.
• A reducing agent reduces something else.
• A reducing agent removes oxygen from another substance or gives hydrogen to it.
• A reaction where both oxidation and reduction is taking place is called a redox reaction.
• The purification of some metals from their ores involves redox reactions.

Some common oxidising and reducing agents

• All substances are divided into acids, bases and salts (neutrals).
• Acids, bases and salts have different properties.
• Acids will react with bases to form salts. This reaction is called neutralisation.

Acids

• Acids are formed when a non-metal burns in air or oxygen to form non-metallic oxide.
• When non- metallic oxides are added to water they form acids.

Examples are: (i)   carbon dioxide + water                                          carbonic acid

(ii)  nitrogen dioxide + water                                       nitric acid  +   nitrous acid

(iii) sulphur dioxide + water                                          sulphurous acid

• Acids have a pH of between 1 and 6.
• Many acids react with carbonates to give a salt, water and carbon dioxide.
• An example is hydrochloric acid and calcium carbonate.

Hydrochloric acid + calcium carbonate              calcium chloride  + water + carbon dioxide.

Bases

• Bases are formed by dissolving metal oxides or adding water to reactive metals.
• Bases contain metal or metal like ions and hydroxyl ions.

Examples are: (i)   sodium   +   water                       sodium hydroxide  +  hydrogen

(ii)  magnesium + water                         magnesium hydroxide  +  hydrogen

• Sodium hydroxide and magnesium hydroxide are bases.
• Bases have a pH of between 8 and 14.
• Bases react with acids to form salt and water.

 Comparison between acids and bases

Salts

• Salts are formed through the process called neutralisation.
• Neutralisation is whereby an acid reacts with a base to give salt and water.
• Salts are neutral and have a pH of 7.
• Many acids react with carbonates to give a salt, water and carbon dioxide.

Formation of salts

Method

1. Burn a piece of magnesium in air.
2. Collect the ash and dissolve it in distilled water.
3. Add acid to the magnesium hydroxide formed.
4. Dip (i) blue litmus paper, and

(ii) red litmus paper into the solution

Observations

The litmus papers do not change colours.

Conclusions

Salts are neutral.

Safety Precautions

1. Be sure you wear properly fitting goggles during a practical involving acids and bases.
2. Universal indicator is alcohol b a s e d  a n d     t h e r e f o r e flammable.
3. Dispose of this waste down the drain or according to local regulations.
4. Always wash your hands after the practical activity.

Speed of reaction

• Every reaction has a rate or speed at which it proceeds.
• There are various factors that affect the rate of reaction.

These are:

• Temperature                   •      Surface area
• Catalysts                        •      Concentration

 Factors affecting the rate of reaction

Reversible reaction

• A reversible reaction is a reaction which goes in both directions. This means the initial reactants react to form a product and the product can react in a reverse reaction to form the reactants.
• After some time equilibrium may be reached, where the backwards reaction will be equal to
• the forward reaction.
• Reversible reactions are indicated by double arrows facing different directions, e.g.
• Nitrogen+    Hydrogen →  Ammonia