CHE1: ELEMENTS,COMPOUNDS AND MIXTURES

A mixture is a substance containing two or more substances that are not chemically combined.

If a mixture is separated by any of the above methods, a pure substance can be got.

What is the chemical nature of the pure substance obtained?

They are either elements or compound.

Elements

What is an element?

Is a substance which cannot be split up into simple substances by chemical means?

An element contains only one kind of atoms.

An atom is the smallest part of an element which can take part in a chemical reaction. An atom and therefore an element is represented by symbol. A symbol is a letter or two which represent an atom of an element.

For example

Oxygen           O,   Hydrogen          H, Sulphur          S

When two letter represent a symbol the first one is a capital letter and the other a small letter for example Cl for chlorine, calcium          Ca.

More symbols;-

Nitrogen          N

Aluminum           Al

Potassium          K

Iron          Fe

Gold      Au

Phosphorous      P

Tin      Sn

Mercury     Hg

Lead      Ph

Zinc      Zn

Magnesium     Mg

Carbon      C

Copper      Cu

Actinium     Ac

Uranium     U

Silver       Au

COMPOUNDS

What is a compound?

A compound is substance containing two or more elements that are chemically combined in definite ratio.

Image result for compounds chemistry

Examples of compounds

Water      H2O that is Hydrogen and Oxygen

Carbon dioxide      CO2 carbon and Oxygen

Copper (II) Oxide      Cuo…….Copper and Hydrogen

Ethanouodionic (CooH)2…….Carbon, Hydrogen and Oxygen

Chloroform CHCL3……Carbon, Hydrogen and Chlorine

Manganese (IV) Oxide MnO2

Sodium Hydrogen Carbonate NaHCO3

Sodium PeroxideNa2O2

Sodium Chloride NaCl

Compound are represented by a formula (sometimes an element is also represented by a formula)

What is a formula?

A formula is a combination of symbols and numbers. It shows the elements and ratio they combine to form a molecule of a compound.

What is a molecule?

A molecule is the smallest particle of an element or compound which can exist in a free or separate state. Oxygen, Carbon oxide

 

 

compounds

Exercise

Is water a mixture or a compound give reason for your answer?

Reasons:

  • It is not easy to separate the elements that make up water
  • Properties of a compound are different from those of an element
  • Cannot be separated by physical methods
  • A lot of energy is given off when water is formed

Physical and chemical changes

What is a physical change?

Is the change where no new substance formed?

For example:

  • Melting cheese
  • Freezing ice
  • Boiling water
  • Melting candle wax
  • Sublimation of ammonium
  • What is a chemical change?

A change in which a new substance is formed

Example:

-Rusting of metal

-Burning wood to ash

-Milk going sour

-An explosion

How do chemical changes differ from physical changes?

Physical (temporary) Chemical (permanent)
1.      Are reversible Usually irreversible
2.      No new substances is formed A new substance is formed
3.      To effect a physical change requires very little energy if any A chemical change requires or gives out a lot of energy
4.      No change in mass Always a change in mass

 

Investigating the effort different between mixtures and compounds

An experiment on mixture on mixtures and compounds. Appearance of iron is dark grey. Appearance of sulphur is yellow.

The mixture is

-Some of the mixture was heated in a test tube it turned dark and started glowing red hot. Another mixture was got and water was added.

-The iron settled and the sulphur made a suspension in the water

-Dilute hydro caloric acid was added to the mixture of iron and sulphur. The iron and sulphur separated the iron in the acid produced bubbles.

-A magnet was passed over the mixture

Observation

The iron attracted by the attracted by the magnet. When the mixture in experiment 1 was cooled, hydro choric acid was added to the mixture and the reaction between the acid and mixture formed a gas which smelt like rotten boiled egg. The cooled mixture was dark grey.

Investigating the effect of heat on substance?

Substance Appearance before heating Changes after heat
1.      Iodine Shiny grey solid Forms a purple
2.      Sulphur Yellow solid Melts to green then to brown and then to red to black forming a boiling liquid
3.      Potassium chloride White crystallized solid Remain white
4.      Zinc oxide White powder Turns yellow
Appearances after heating
1.      Forms grey shiny crystals
2.      Went back to yellow
3.      White crystallized solid
4.      Cools back to white after heating
5.      Turned permanently black

 

copper

When heated some substances do not change at all, others temporality and reverse to the original while others change permanently. Those which don’t change at all are not affected by heat e.g. potassium chloride. Those which change temporarily are said to undergo a physical change. For example Sulphur, Iodine

Those which change permanently are said to undergo a chemical change e.g Ammonium dichromate, Zinc carbonate, copper (II) nitrate, Zinc Nitrate.

In everyday life physical and chemical changes occur even when no heating has been done e.g. rusting, melting ice.

calcium hydroxide

A burning candles water and carbon dioxide

Observation

  1. Anhydrous copper (II) Sulphate turns blue
  2. Lime water turns milky

Explanation

Water and carbon dioxide are formed when a candle burns in air. The water turns anhydrous copper sulphate blue and carbon dioxide turns lime water milky

Is a candle burning in air a chemical or physical change?

It is a chemical change because a new substance is formed and it is irreversible

 

crystals

Observation

  1. A colorless vapor given off the heated crystals condenses to a colorless liquid in the empty test tube.
  2. The blue crystals form a grey residue
  3. If some of the colorless liquid is dropped on the grey powder, the powder turns blue
  4. Any liquid containing water for example dilute acid, top water etc also turn the grey residue blue.

Explanation

When copper (II) Sulphate crystal are heated they lose their water of crystallization and form an hydrous copper (II) sulpahte

Copper (II) sulphate crystals heat water + anhydrous copper (II) sulphate

grey powder

Water of crystallization is a definite amount of water with which some substances chemically combine to form crystals.

Anhydrous copper (II) sulphate is used to detect the presence of water.

ASSIGNMENT : MIXTURES MARKS : 10  DURATION : 1 week, 3 days

 

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