Chemistry Dot Points- Module 2 - Metals

Chemistry Dot Points Tyson Xu

METALS

Metals have been extracted and used for many thousands of years1.1 Outline and examine some uses of different metals through history, including contemporary uses, as uncombined metals or as alloys

AGE TIME METALS USED USED FORStone Age From ancient to

times to about 3000BC

Gold/Silver-Looked good-Found uncombined (Native)-Malleable-Resistant to rust

- Ornaments- Decoration

Copper Age 3200BC – 2300BC Copper-Sometimes found uncombined-CuO heated with charcoal copper

CuO(s) + C(s) Cu(s) + CO(g)

-Tools-Weapons

Bronze Age 2300BC – 1200BC Bronze (Alloy of Copper)-Copper + Tin = Bronze

-Tools -Weapons

Iron Age 1200BC – 1AD Iron-Haemetite - Fe2O3 mixed with charcoal and heated in furnaces by blowing air constantly for sufficient heat

Fe2O3(s) + 3C(s) 2Fe(s) + 3CO(g)

-Easily corroded; Alloys of iron were used

-Tools-Weapons

Modern Age 1AD - Present Aluminium/Tungsten/Chromium/Titanium etc.

-Electronics (Computers, telephones)-Buildings

1.2 Describe the use of common alloys including steel, brass and solder and explain how these relate to their properties

Alloy- A homogenous mixture between a metal and one or more other elements; often metalsAlloy Properties UsesBrass50-60% Cu 40-50% Zn

-Lustrous gold appearance-Hard but easily machined

-Plumbing fittings-Musical Instruments-Decorations

Bronze80-90% Cu10-20% Sn

-Hard-Resists corrosion-Easily cast

-Ship’s propellers-Casting statues

Solder30-60% Sn40-70% Pb

-Low melting point-Adheres firmly to other metals when molten

-Joining metals together (plumbing/electronics)

Steels (Fe + C)Mild Steel< 0.2% CStructural Steel0.3-0.6% CHigh-carbon Steel0.6-1.5% CStainless Steel10-20% Cr5 – 20% Ni

-Soft Malleable

-Hard, high tensile strength

-Very hard

-Hard, resists corrosion, lustrous

-Car bodies/pipes/nuts and bolts/roofing

-Beams and girders/railways

-Knives/Drill bits/Chisels/Hammers

-Kitchen sinks/Cutlery/Surgical instruments


1.3 Explain why energy input is necessary to extract a metal from its ore- Strong ionic bonding within compounds in metal ores require lots of energy to break- More reactive metals = strong bonds- Energy is also required to mine the ore- Energy required to purify the metal/form it into useful alloy

1.4 Identify why there are more metals available for people to use now than there were 200years ago

- Advances in commercial extraction processes has led to many new metals being available for use, e.g. Electrolysis- Al

- Lack of such extraction technology resulted in only limited amounts of metals being able to be used 200 years ago

- Some metal ores had melting points that were much too high to be used in the past. Advancement in chemistry has allowed them to form useful alloys with much lower melting points

- Advancement in chemistry has also led to the discovery of new metals

Metals differ in their reactivity with other chemicals and this influences their uses

2.1 Describe observable changes when metals react with dilute acid, water and oxygenMetal Type Water Acid OxygenMost Reactive E.g. Potassium

K(s) + 2H2O(l) Mg(OH)2(aq) + H2(g)

With COLD water

Mg(s) + HCl(aq) MgCl2(aq) + H2(g)

-Vigorous Bubbling-Metal disappears-Container gets hot

2Mg(s) + O2(g) 2MgO(s)

-Burns readily with very bright flame

Medium ReactiveE.g. Zinc

Zn(s) + H2O(g) ZnO(aq) + H2(g)

With HOT steam

Zn(s) + HCl(aq) ZnCl2(aq) + H2(g)

-Few bubbles-Metal doesn’t disappear-Slower reaction

2Zn(s) + O2(g) 2ZnO(s)

-Burns slowly as solid-Burns readily as powder

Least Reactive E.g. Gold

No Reaction No Reaction No reaction


2.2 Describe and justify the criteria used to place metals into an order of activity based on their ease of reaction with oxygen, water and dilute acidsActivity Series of Metals

-The more violent the reaction = higher position in activity series-Degree of reaction with oxygen – Less reactive metals don’t react-Highly reactive metals react with cold water, very reactive metals react with hot water, moderate activity metals react with hot steam, less reactive metals don’t react- Metals that are relatively unreactive can be determined by their reactivity with dilute acids (less reactive metals do not react)

2.3 Identify the reaction of metals with acids as requiring the transfer of electrons- Acid molecules break up when they react with metals- Metals form positive ions, thus they give away electrons- These electrons are attracted to hydrogen protons from the decomposed acid molecules- Resulting is the metal combining with the non-hydrogen element of the acid to form stable

metal salt compounds while hydrogen atoms combine in twos to form stable diatomic molecules

2.4 Outline examples of the selection of metals for different purposes based on their reactivity, with a particular emphasis on current developments in the use of metals

Metal Use PropertiesLithium -Pace makers

-Cameras-Button cells

Energy of electrons transferred from lithium anode and the high reactivity of lithium

Magnesium -Fireworks-Military/Emergency Purposes (Flares)-Inside Boilers

Relatively high reactivity and the fact it burns bright when heated with air

Aluminium -Cans-Aircraft bodies

Relatively low reactivity doesn’t corrode

Titanium -Artificial joints-Aircraft/ship bodies-Pipes

Low reactivity stable, resistance to corrosion, Chemically inert nature in human body

2.5 Outline the relationship between the relative activities of metals and their positions on the Periodic Table

- Most reactive = Alkali Metals- The most reactive metals are those at to the bottom of the vertical groups and to the left

side of the periods, thus the alkali metals is the most reactive metals of the periodic table. The least reactive metals are found at the bottom of the transition metal block


2.6 Identify the importance of first ionisation energy in determining the relative reactivity of metals- First ionisation energy: the minimum energy required to form one mole of uni-positive ions

from isolated gaseous atoms under standard conditions- The lower the first ionisation energy of a metal, the more reactive it is likely to be- By reducing the ionisation energy of a metal, the overall amount of energy given out

increases, thus the reaction becomes more violent

As metals and other elements were discovered, scientists recognised that patterns in their physical and chemical properties could be used to organise the elements into a Periodic Table

3.1 Identify an appropriate model that has been developed to describe atomic structureModel of atomic structure: Bohr’s model – features:

- Electrons move around the nucleus in a circular orbit- Atom is composed of a small, central nucleus made up of protons and neutrons- Electrons occupy stationary levels

3.2 Outline the history of the development of the Periodic Table including its origins, the original data used to construct it and the predictions made after its construction

1. Ancient Greeks – All matter is made up of 4 main elements; earth, fire, wind, water2. Lavoisier in 1787 classified known elements into metals and non-metals based on their

physical and chemical properties3. Dalton in 1808 proposed Atomic Theory; that elements are made up of atoms4. Dobereiner in 1829 found similarities in physical/chemical properties of groups of 3

elements. The Triadse.g.

Na Ca ClLi Sr BrK Ba I

5. Newlands in 1863 put forward Law of Octaves; If elements are placed in order of increasing atomic mass, there is a repetition of similar properties after every 8th element; correct for first 20elements but not after Calcium.

6. Mendeleev in 1869 proposed Periodic Law; If elements are placed in order of increasing atomic mass, elements with similar physical/chemical properties occur at regular/periodic intervals – Enabled him to place known elements, and leave gaps for undiscovered elements. He then predicted the properties of the unknown and his estimates were very close to the actual results. Known as “father of periodic table”

7. Ramsay from 1893-1898, discovered noble gases additional group 8. Moseley in 1914 stated Modern Periodic Law; When elements are placed in order of

increasing atomic number they show a periodicity of repeating pattern of properties. This solved problems made by atomic mass such as K (39.1) would be in Group VIII and Ar(39.95) would be in Group I


3.3 Explain the relationship between the position of elements in the Periodic table, and:- Electrical conductivity- Ionisation energy- Atomic radius- Melting point- Boiling point- Combining power (valency)- Electronegativity- Reactivity

Groups (Vertical columns)- 8 Main Groups (Excluding transition metals)- Group I – Alkali Metals- Group II – Alkaline Earth Metals- Group VII – Halogens- Group VIII – Noble gases

Periods (Horizontal rows)- 7 main periods

Transition Metals

Metals/Non Metals/Semi Metals

Lanthanide and Actinide Series

- Electrical conductivity: usually metals lying to the left and bottom of the periodic table are the best conductors of electricity; graphite (top, right) is an exception to this

- Ionisation energy : elements to the top and right part of the table have the largest ionisation energies

- Atomic radius : with the exception of the Noble Gases, the elements lying to the left and bottom of the periodic table have the largest atomic radii

- Melting/boiling point : with the exception of the Alkalis, the elements lying to the left and bottom of the table have the highest melting and boiling points

- Combining power (valency): group 1 and 7 have valency of 1, group 2 and 6 have valency of 2, group 3 and 5 have valency of 3, group 4 has valency of 4 – transition metals have variable valencies

- Electronegativity : a measure of an atom’s ability to attract a bond pair of electrons. Highest electronegative values are smallest atoms with highest nuclear charges


For efficient resource use, industrial chemical reactions must use measured amounts of each reactant

4.1 Define the mole as the number of atoms in exactly 12g of carbon-12 (Avogadro’s Number)

1 mole = 6.022 x 1023 particles = Avogadro’s Number = No. of atoms in 12g of carbon-12

- E.g. How many atoms are there in a pure copper coin weighing 2.56g? (Atomic weight of copper = 63.6)Number of moles of copper = 2.56/63.6 = 0.0403 molNumber of atoms of copper = 0.0403 x (6.02x10^23) – Avogadro’s constant

= 2.43 x 10^22 atoms

4.2 Compare mass changes in samples of metals when they combine with oxygen- When metals combine chemically with oxygen they gain mass. The oxide formed during the

reaction has a mass equal to the metal and oxygen – Law of Conservation of Mass (mass of reactants = mass of products)

4.3 Describe the contribution of Gay-Lussac to the understanding of gaseous reactions and apply this to understanding of the mole concept

- Gay-Lussac’s Law: At the same temperature and pressure, the volume of 1 mole of gas A is equal to the volume of 1 mole of gas B

- The number of particles in any given volume is therefore independent of the size and mass of the particles

- The mass of identical volumes of different gases could therefore be measured and the relative masses of different gases could be determined

-4.4 Recount Avogadro’s law and describe its importance in developing the mole concept

- Avogadro’s law: “equal volumes of gases at the same temperature and pressure contain the same number of molecules regardless of their chemical nature and physical properties”

- The number of particles in any given volume is therefore independent of the size and mass of the particles

- The mass of identical volumes of different gases could therefore be measured and the relative masses of different gases could be determined

- No. of moles = mass/molar mass

n = mM

- Limiting reagent: the reactant that limits how much of the product is produced, while the others are reagents present in excess because they have remained unreacted after the reaction

- To find the limiting reagent, calculate the number of moles of both reactants, then compare the stoichiometric ratio (ratio in formula) and actual. If stoichiometric ratio > actual mole ratio, then the top reagent (numerator) is the limiting reagent

- Note: use the limiting reagent to find the number moles- Ideal Gas : 22.71L @ T = 0C or 273 K, P = 100kPa or 1 atmosphere

24.79L @ T = 25C or 298K, P= 100kPa or 1 atmosphere


- Theoretical yield: the quantity of product (in grams) predicted from the chemical equation when known quantities of reactants undergo the reaction

- Percentage composition : 1. Find number molar mass of compound2. Find moles of compound3. Find molar mass of element4. Write as percentage

4.5 Distinguish between the empirical and molecular formula- Empirical formula: ratio of number of each type of atom to each other- Molecular formula: actual number of each type of atom in a molecule of the compound

(elements)- Empirical formula questions:

1. Find number of moles2. Divide both by smaller number3. Round off to nearest whole number4. Use to write formula

The relative abundance and ease of extraction of metals influences their value and breadth of use in the community

5.1 Define the terms mineral and ore with reference to economic and non-economic deposits of natural resources

- Mineral - a naturally occurring compound of a metal found in the Earth’s crust- Ore - a deposit of minerals considered to be worth mining for extraction of one or more

metals- Gangue - unwanted/waste substances in ore

5.2 Describe the relationship between the commercial prices of common metals, their actual abundances and relative costs of production

- The higher the abundance the lower the price commercial of a metal. Thus, as the scarcity of a metal increases, so does the commercial price (as it becomes a rarity).

- The higher the production costs (i.e. costs of extraction and processing) the higher the commercial price of a metal. In this sense, the lower the production costs the lower the commercial price.

- The ease of transport also plays a role: the easier it is to transport the more likely it is to be cheaper to purchase, vice-versa.

5.3 Explain why ores are non-renewable resources- Ores are non-renewable resources because they are limited in quantity and are not being

formed in the earth’s crust at a rate that is meaningful in terms of human existence once all the accessible ore bodies of a particular metal have been mined, that metal will no longer be produced

ORE

Mineral Gangue

Metals


5.4 Justify the increased recycling of metals in our society and across the worldMetals are running out cost of production increasesIn the future, when ore supplies diminish, recycling will be necessary to replenish metal supplies for society

Recycling:- Is cheaper- Non-renewable natural sources of metals are conserved- Less waste disposal Less pollution

5.5 Describe the separation processes, chemical reactions and energy considerations involved in the extraction of copper from one of its ores

- Mining and crushing: mined copper ore is ground to separate copper ore from other useless material (PHYSICAL)

- Froth floatation: Crude ore is concentrated by froth floatation air is bubbled through mixture of pulverised ore in water containing an oil-detergent floatation agent copper mineral particles float and skimmed off in the froth (PHYSICAL)

- Roasting: Concentrated ore is roasted in air, which oxidises the FeS to FeO but leaves Cu2S unaffected (CHEMICAL)

2CuFeS2(s) + 4O2(g) Cu2S(s) + 2FeO(s) + 3SO2(g)

- Smelting: Product heated at high temp. with ground limestone, sand and additional concentrated ore converts FeO to a molten slag (CHEMICAL) and converts Cu2S from solid to liquid form

FeO(s) + SiO2(S) FeSiO3(l)

Cu2S(s) Cu2S(l)

- Roasting: Copper(I) sulfide is roasted in air Cu2S(s) + O2(g) 2Cu(s) + SO2(g)

This process requires a significant input of energy to maintain the temperatures required for this reaction

To obtain 100% pure copper, electrolysis is required this requires the MOST energy!

5.6 Recount the steps taken to recycle aluminium1. Collect scrap metal from society, i.e. shopping malls, recycling bins etc2. Transport to processing plant3. Separate metal from impurities4. Re-smelt and refining of metal5. Transport to product manufacturers

5.7 Analyse information to compare the cost and energy expenditure involved in the extraction of aluminium from its ore and the recycling of aluminium

Recycling of aluminium is much cheaper than extraction from its ore, i.e. bauxite.

Refining of bauxite requires about 15000MJ of energy per tonne of alumina produced, plus 50000MJ more for smelting, leading to 65000MJ.


Melting recycled aluminium requires 800MJ only, less than 5% of extraction. Therefore much cheaper and more efficient.

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Chemistry Dot Points- Module 2 - Metals