Chemical Earth
 

The Chemical Earth

 

1.     The living and non-living components of the earth contain mixtures

 

Construct word and balanced formulae equations of chemical reactions as they are encountered

 

Acquired skill

 

Identify the difference between elements, compounds and mixtures in terms of particle theory

 

Identify that the biosphere, lithosphere, hydrosphere and atmosphere contain examples of mixtures, elements and compounds

 

Biosphere: living matter on earth includes                            

·         Faeces

·         Plants

·         Algae

·         Animals

 

Lithosphere: crust plus the top proportion of mantle

·         Iron ore

·         Rocks

·         Sand

 

Hydrosphere: Liquid water components of the earth

·         Sea water

 

Atmosphere: layer of gas surrounding the earth

·         Air

 

Identify and describe procedures that can be used to separate naturally occurring mixtures of:

·         Solids of different sizes

·         Solids and liquids

·         Dissolved solids in liquids

·         Liquids

·         Gases

 

 

 

 

 

Solids of different sizes:

Mixtures in which the particles of the different substances have different sizes can be separated by sieving. For example at quarries the separation of fine sand and coarser material is done to make concrete.  

 

Also another way to separate two solids is based on solubility. If one solid is soluble in a liquid while the other is insoluble the liquid is added to give a solution and insoluble solid. The mixture is then filtrated and you are left with a solid. The other solid in the solution can then be attained via evaporation

 

 

 

 

 

 

 

 

 

 

 

Solids and Liquids:

Mixtures of solids and liquids are often separated using filtration. The liquid or solution passes through the paper while the suspended solid remains on the top of the filter paper. The liquid or solution that passes through the filter paper is called a filtrate. Sand can be separated from sea water using this method. Sometimes if the solid is coarse or has very dense particles, sedimentation and decantation can be used. Sedimentation is the process in which the solid settles to the bottom of the container and decanting is the process of carefully pouring off the liquid and leaving the solid undistributed at the bottom of the container.

 

 

 

 

 

 

 

 

 

 

 

Dissolved Solids in Liquids:

When a solid is dissolved in a liquid (solution) the solid and liquid can be separated through vaporising off the liquid (called the solvent). We can do this by boiling the solution or by just evaporating it. In evaporation the liquid is heated to a temperature below its boiling point so that some of the particles escape from the surface of the liquid into the air and get blown away. Evaporation to dryness is the process of heating the solution in the evaporating basin so no solvent (solution) remains. This process means that no liquid or solution remains which means we are only left with the solid component. If we wish to keep both we need to use distillation.

 

 

 

 

 

 

 

 

 

 

Distillation is the method of separating two or more liquids from one another or separating the liquid from the solids in a solution. It should be used for a great difference in boiling points. The substance (2 or more liquids or a solution) is heated until one liquid vaporises and moves up the neck and condenses in a different chamber.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Separating Liquids  

Distillation can also be used to separate to liquids with a great variance in their boiling points. When separating two liquids of similar boiling points fractional distillation is used. The arrangement allows for repeated condensations and vaporisations up the column, effectively giving many separate distillations causing it to be more accurate. This means that eventually a pure sample of the more volatile substance in the original mixture emerges from the top of the column. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Immiscible liquids (liquids when mixed do not form a homogeneous liquid e.g. water and kerosene) have their own method of separation. This is based on their solubility and often a separating funnel is used. The pear shape allows us to run out the bottom liquid without getting it contaminated with any of the top one.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Separating Gases

Gas mixtures are generally separated by using either differences in boiling points or differences in solubilities in liquids such as water. Fractional distillation can be used as well as with the use of U-tubes.

 

Assess separation techniques for their suitability in separating earth materials, identifying the difference in properties which enable these separations

 

Properties of separations

 

Boiling and Melting points:

·         Pure substances  have characteristic boiling and melting points

·         Can be used to separate mixtures (e.g. distillation) and to verify the purity of a substance (impurities lower melting point of one substance can increase or decrease boiling and melting points)

·         Boiling point depends on pressure – usually at normal atmospheric pressure

 

Density:

·         Mass per unit of volume

·         Density is a known, specific characteristic of a pure substance e.g. water we can always work out the density as it is a pure substance (uniform throughout) whereas soil density can not be calculated as it is a mixture

·         Can be used to separate mixtures e.g. separating funnel (if immiscible), centrifuging (spinning), flotation

 

Solubility:

·         In various liquids e.g. water, alcohol, chloroform etc.

 

Chromatography:

·         Goes up filter paper – based on solubility

 

Magnetic:

·         Fe, Co, Mn

 

 

 

 

 

 

 

Separation Method

Property used in the separation

Separation of solids:

 

Sieving

Particle size

Adding a solvent, the filtration

Ones substance is soluble in the chose solvent while the others are insoluble

Separation of solids and liquids:

 

Filtration

One substance is solid, the other a liquid or solution

Separation of solid dissolved in liquid:

 

Distillation (also two liquids)

Big difference in boiling points

Evaporation

Liquid has much lower boiling point than the solid

Separating liquids:

 

Fractional distillation

Significant but relatively small difference in boiling points

Separation Funnel

Components are immiscible liquids. Based on DENSITY!

 

Describe situations in which gravimetric analysis supplies useful data for chemists and other scientists

 

Gravimetric analysis is determining the quantities (mass) of substances present in a sample. It could be presented by mass or by percentage of total mass. There are several reasons as to wanting to know the percent composition of a mixture:

·         To decide whether a newly discovered mineral deposit contains sufficiently high percentage of the required compound to make its extraction from that deposit economically viable

·         To determine the composition of soil in a particular location to see if it is suitable for growing a certain crop

·         To determine the amounts of particular substances present in water or air to decide how polluted the samples are

·         To decide whether a particular commercial mixture has the same percentage composition as a similar mixture being marketed by a rival company

 

 

 

 

 

 

 

Apply systematic naming of inorganic compounds as they are introduced in the laboratory

 

Compound of two elements (binary compound)

·         Determine which element goes first by looking at the periodic table, generally the metal more to the left goes first

·         The first elements name remains unchanged while the seconds elements name is chopped off and replaced with “ide”

·         It occurs that more information must be added to the name if the compound in not the only one possible between two elements. 

-        If both the elements are non metals, their proportions are given using prefixes: mono, di, tri, tetra, penta, hexa, hepta, oct, non, dec

-        If one element is a metal and the other is a non metal the proportions of the elements by giving the valency of the metal atom in roman numerals in brackets after is name. e.g.

Iron () Oxide (Fe 2+ + O2-) or Iron () Oxide (Fe 3+ + O2-  à   Fe2O3)

 

Ionic compounds with more than two elements

·         An ionic compound can be composed of more than two elements if it includes polyatomic ions. For example sodium hydroxide is Na+ + OH- which gives NaOH.

 

Acids

The names of the following acids must be known:

·         HCl – hydrochloric acid

·         HNO3 – nitric acid

·         H2SO4 – sulfuric acid

 

Special Names

Although the rules outlines above are normally used when naming inorganic compounds, some substances have special names for example:

·         H2O is water

·         NH3 is ammonia

 

 

 

 

 

 

 

 

 

 

 

2. Although most elements are found in combinations on Earth, some elements are found uncombined

 

Explain the relationship between the reactivity of an element and the likelihood of its existing as an uncombined element

 

90 or so elements exist on the earth as compounds. This is because most elements are chemically reactive, that is when they come into contact with certain elements they react to from compounds. The relationship between reactivity of an element and its likelihood of its existing as uncombined element is “the more reactive an element is, the less chance there if of finding it in the earth as an uncombined element”. For example sodium and potassium are very reactive elements which are never found as free elements where as gold and the noble gases are extremely unreactive and occur naturally as uncombined elements

 

Classify elements as metals, non-metals and semi metals according to their physical properties

 

Metals

·         Solid at room temperature (besides mercury)

·         Have a shiny or lustrous appearance

·         Are good conductors of electricity and heat

·         Are malleable and ductile

 

Non-Metals

·         Do not conduct electricity

·         Gas or solid at room temperature

·         Not shiny

·         Lower melting and boiling points that metals

·         Very brittle if solid

 

Semi-metals

Properties of both classes

 

Account for the uses of metals and non-metals in terms of their physical properties

 

Metals

·         Tungsten is used for filaments in electric light bulbs because of its hight melting point

·         Copper is used for electrical wiring in houses because of its high electrical conductivity

 

Non-metals

Only a few in elemental (uncombined) forms are used and therefore the majority uses of non-metals are as compounds. Also the chemical properties are often more important for particular uses e.g. Helium is used to fill balloons instead of hydrogen as it is less chemically reactive. Physical uses of elemental non metals include:

·         Liquid nitrogen is used as a cooling agent (for extremely low temperatures) because of the suitability of its freezing (melting) and boiling points.

 

3. Elements in Earth materials are present mostly as compounds because of interactions at the atomic level

 

Identify that matter is made of particles that are continuously moving and interacting

 

Matter is made of particles that are continuously moving and interacting

 

Describe qualitatively the energy levels of electrons in atoms

 

Each energy shell can accommodate only a certain maximum number of electrons and its configuration is 2, 8, 18, 8.

 

Describe Atoms in terms of mass number and atomic number

 

The atomic number is the number of protons (and electrons) in the nucleus of an atom of an element

 

The mass number is the number of protons plus the number of neutrons

 

Describe the formation of ion in terms of atoms losing or gaining electrons

 

Ions form when a metal donates it outer shell electrons to a non-metal so both achieve full outer shells. Now that the metal has decreased in the number of electrons and knowing that number of protons equals number of electrons the metal is now a positively charged ion (cations). This happens in the opposite way with the non-metal, it has gained more electrons and now the number of electrons exceeds the number of protons and therefore it is a negatively charged ion (anions).

 

 

 

 

Apply the periodic table to predict the ions formed by atoms of metals and non-metals 

 

A general statement can be made about metals and non-metals. Metals will lose their electrons on their outer shell and become positively charged and non-metals will gain electrons and become negatively charged.

 

Apply Lewis electron dot diagrams to:

·         The formation of ions

·         The electron sharing in some simple molecules

 

 

 

 

Formation of Ions

 

 

 

 

 

 

 

 

 

 

 

 

 

Electron sharing

 

 

 

 

 

 

 

 

 

 

 

 

Describe the formation of ionic compounds in terms of the attraction of ions of opposite charge

 

Ionic compounds form due to the attraction of ions of opposite charge. The electron donation between a metal and a non-metal is the reason for it becoming a charged ion which then attracts each other.

 

Describe molecules as particles which can move independently of each other

 

Molecules are particles which can move independently of each other

 

 

 

 

 

Distinguish between molecules containing one atom (noble gas) and molecules with more than one atom

 

Diatomic molecule:

Is a pair of atoms permanently stuck together to form molecules e.g. oxygen gas (O2). They from a diatomic molecule as they have covalent bonds to attain full outer shells. Metals cannot form diatomic molecules as covalent bonds are needed for diatomic molecules.

 

Monatomic molecule:  

The noble gases are atoms which exist as independent atoms and don’t need to join with another atom to become diatomic as they have a full outer shell. Examples are neon and helium

 

Describe the formation of covalent molecules in terms of sharing of electrons

 

Covalent bonds form between atoms where they share electrons to achieve a full outer shell (stable configuration)

 

Construct formulae for compounds formed from:

·         Ions

·         Atoms sharing electrons

 

Acquired

 

 

 

 

 

 

4. Energy is required to extract elements from their naturally occurring sources

 

Identify the differences between physical and chemical change in terms of rearrangement of particles

 

Physical Change: No new substance is created

·         Easily reversible

·         Usually involves small amount of energy

·         Separation of mixtures

 

Chemical change: At least one new substance is formed

·         Difficult to reverse

·         Generally a large input of energy

·         Indications of chemical change:

-        Precipitate formed

-        Colour change

-        Significant change in temperature

-        Disappearance of solid

-        Odour is produced

 

Summarise the differences between the boiling and electrolysis of water as an example of the difference between physical and chemical change

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Boiling water: Physical change

Boiling water is a physical change as no new substance is produced but instead water is being boiled (physical property) and simply changing state. Also, little energy is required and the procedure is easy to reverse.

 

Electrolysis of water: Chemical change

The electrolysis of water is a chemical change as two new substances (hydrogen gas, oxygen gas) are produced. Also compared to boiling large energy is required and the procedure is hard to reverse.

 

Identify light, heat and electricity as the common forms of energy that may be released or absorbed during the decomposition or synthesis of substances and identify examples of these changes occurring in everyday life

 

Decomposition reactions:

A decomposition reaction is a chemical reaction in which a compound is broken down into simpler substances. Light, heat and electricity is absorbed and released.

·         Electricity is used in the process of electrolysis to separate water into hydrogen and oxygen gas

·         Light decomposes silver chloride into silver solid and chlorine gas

·         Heat from a Bunsen burner decomposes Copper Carbonate solid into Copper oxide solid and carbon dioxide gas

 

Everyday uses:

·         Aluminium is decomposed by electrolysing molten aluminium oxide

·         Calcium carbonate (limestone) is decomposed to calcium oxide and carbon dioxide by heating it to make lime, cement and glass

 

 

Synthesis reactions:

A synthesis reaction is a chemical reaction in which simple substances combine to form a more complex substance. Light, heat and electricity is absorbed and released.

·         When magnesium is heated it combines with the oxygen in the air exposing a bright light and it forms magnesium oxide

·         Iron and sulphur is heater without oxygen to form iron sulphur

 

Everyday uses:

·         The rusting of iron/steel to form iron oxide

·         The burning of coke (carbon) which releases much heat energy is used in many different ways

 

5. The properties of elements and compounds are determined by their bonding and structure

 

Identify differences between physical and chemical properties of elements, compounds and mixtures

 

 

Describe the physical properties used to classify compounds as ionic or covalent molecular or covalent network

 

Physical property

Ionic

Covalent Molecular

Network Covalent

Melting and Boiling Points

Generally high as there are strong electrostatic forces between ions

Low as weak intermolecular forces

Very high as all held together by covalent bonds

State at room temperature

Solid as high melting and boiling point (usually crystalline) (NaCl)

Gases, liquids and some solids (O2, H20)

Solid as very high melting point. (SiO2, diamond)

Hardness

Hard, brittle powders. (NaCl)

Solids are soft or waxy (candle was is a hydrocarbon)

Very Hard (diamond)

Solubility in water

Most are soluble (NaCl)

Some are soluble if molecule is polar other are not (non polar)

NO

Electrical conductivity:

·         Solid

·         Molten

·         In solution (aqueous)

 

 

·         No

·         Yes

·         Yes (as become ions (+) and (-)

 

 

·         No (poor)

·         NO (poor)

·         NO (poor)

 

 

·         No (except graphite as free electron)

·         No

·         N/A

 

 

 

 

 

 

Distinguish between metallic, ionic and covalent bonds

 

Ionic:

Contain oppositely charged ions held together by electrostatic attraction. They form 3 dimensional lattices with regularly repeating arrangements of ions. Metal donates electrons to non-metal for both to gain a full outer shell. An electrostatic force of attraction between – and + ions. DOES NOT FORM A MOLECULE, IT IS ALWAYS IN A 3D CRYSTALINE LATTICE

 

 

 

 

 

 

 

 

 

 

 

 

Covalent Molecular:

Consists of small molecules (groups of atoms joined by covalent bonds). Forces between individual molecules (intermolecular) are usually weak but the actual covalent bonds (intramolecular) are strong. Atoms share electrons to get full outer shell.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Covalent Lattice (networks, macromolecules):

Form a 3 dimensional network of strong covalent bonds between atoms. Focus on carbon and silicon (Silicon dioxide, silicon carbide)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Metallic Bonds:

Metals exist as 3 dimensional lattices of positive metal ions surrounded by a sea of mobile outer electrons. There electrons are said to be delocalised.

 

 

Physical Property

Metal

Melting and Boiling Point

High as ions are held together strongly

Malleable and Ductile

As protons shift they do not repel.

Conductor of electricity

Good as the delocalised electrons can be made to move along to metal lattice if voltage is applied

Density

High as ions are packed closely together

 

 

 

 

 

Describe metals as three-dimensional lattices of ions in a sea of electrons

 

A metal is a 3D lattice of positive ions engulfed by delocalised electrons.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Describe Ionic compounds in terms of repeating 3 dimensional lattices of ions

 

An ionic compound is a repetition of 3 dimensional lattices of ions

 

 

 

 

 

 

 

 

 

 

 

 

 

Explain why the formula for an ionic compound is an empirical formula

 

The formula for an ionic compound is an indication of the RATIO of each element present in the compound. This is called the empirical formula. For example: NaCl has the ratio 1:1 so it could be Na2Cl2 or Na3Cl3. The empirical formula which relates to ionic compounds differs from molecular formula which relates to covalent compounds as it gives the EXACT number of each atom per molecule. Example: H2O must remain as two hydrogen to one oxygen.

 

Identify common elements that exist as molecules or as covalent lattices

 

Covalent Molecules:

·         O2 (oxygen)

·         H2O (water)

 

Covalent Lattices:

·         SiO2 (silica, silicon dioxide or quartz)

·         C (in form of diamond)

·         C (in the form of graphite)

 

Explain the relationship between the properties of conductivity and hardness and the structure of ionic, covalent molecular and covalent network structures

 

Ionic:

An ionic bond is initially an attraction of electrostatic forces between negative and positive ions. The ionic compound is therefore a hard brittle solid as the electrostatic forces hold the ions strongly together. An ionic compound will not conduct electricity when it is in a solid state as there are no free electrons to carry the charge. It will however conduct electricity when molten and dissolved in a solution (aqueous). This occurs as the charged ions separate from each other and become free to move and carry charge when in solution of in a molten state.

 

Covalent Molecular:

Covalent molecular compounds are small molecules (groups of atoms joined by covalent bonds). As the electrons are shared in covalent bonding there are no free electrons to carry a charge. Although the Intermolecular forces holding the molecules together are weak the intramolecular forces are strong which keeps the compound together. Therefore the compound will still not conduct electricity when molten or in an aqueous state as the intermolecular forces are strong. Covalent molecular compound are soft and waxy as they have weak intermolecular forces.

 

Covalent Lattices:

A covalent lattice is a 3 dimensional network of ions connected together by only by strong intramolecular forces. As these forces are extremely strong and no electrons are free covalent lattices do not conduct electricity in a solid state. It does not conduct electricity when molten as the intramolecular forces remain and neither in a solution as covalent lattices does not dissolve.

 

Choose resources and process information from secondary sources to construct and discuss the limitations of models of ionic lattices, covalent molecules and covalent lattice and metallic latices

 

Model Advantages

·         May help us to understand/explain an idea

·         Provide a visual picture when the real thing cannot be seen

·         Can be used to predict and explain properties

·         Summarise what we know

 

Model Disadvantages

·         Not exactly like the real thing

·         May not be objective e.g. church affecting model of solar system

·         Many not completely explain behaviour, based on incomplete data

·         May confuse model with real situation, often over simplified (e.g. DNA)

·         Assumptions behind models may not be correct