Chemistry - Section 2

More about the periodic table

Arranged in periods (rows) - properties change quite dramatically as you go along, and groups (columns)- elements in the same group have similar properties as they have the same number of electrons in the outer shell.

The periodic table can be split into metals and non metal.
Metals- left of the zig zag , they conduct electricity. Metal oxides are bases meaning they will neutralise acids and when dissolved will form a solution with a pH of more than 7.
Non metals- right of the zig zag, poor comductors of heat and electricity, non metal oxides are normaly acidic, when dissolved they will form a pH of less than 7.

Group 0 are called the noble gases and they are inert. They are inert because they have a full outer shell.

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Group 1- the alkali metals

Group 1 elements all react in similar ways. For example when litiphium sodium and potassium are out in water they all react vigorously. The reaction produces a metal hydroxide which is alkaline. The reaction also produces hydrogen (fizzing).
Sodium (s)+ water (l)— sodium hydroxide (aq)+ hydrogen (g)

Group 1 elements ger more reactive as the atomic number increases. You can see this in the rate of reaction with water.Lithium takes the longest time and potassium takes less time.
LITHIUM- moves slowly above the surface until it disappears, water = alkaline
SODIUM- fizzes rapidly and moves quickly, may ignite.
POTASSIUM- reacts vigorously, burns with a lilac flame and sometime explodes.

All group 1 metals have 1 electron in their outer shell, as you go down the outer shell is further from the nucleus so the attraction is less. The atom is more easily lost so the metals are more reactive.

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Group 7- The Halogens

Element- Atomic number-colour-state at RT-boiling point
Chlorine- 17- green- gas- -34
Bromine- 35- red brown - liquid -59
Iodine- 53-dark grey-solid-185
In group 7 the fewer number of electrons the more reactive, as the outer shell is closer to the nucleus and the force of attraction is stronger.

Halogens can combine with hydrogen to for, hydrogen halides . When hydrogen chloride dissolves in water the molecules split up this is called dissociation. The solution formed is called hydrochloric acid and its acidic.

...if HCl is dissolved in an organic solvent like methylbenzene meaning it doesn't dissociate so it's not acidic. Make sure that if you test it will litmus paper that there is no moisture as if there is it will dissociate and it will behave like an acid.

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Displacement Reactions

Elements in group 7 take part in displacement reactions- a more reactive element displaces a less reactive element from a compound.
KCL colourless + Cl2 colourless/ Br2 orange/ I2 brown = no reaction
KBr colourless +Cl2 colourless/ Br2 orange/ I2 brown= Orange Br2/ NR/ NR
Kl colourless + Cl2 colourless/ Br2 orange/ I2 brown = brown I2/brown I2/ NR

EQUATION FORM: Cl2 + 2KI —• I2 + 2KCl
Each chlorine gains an electron to form chlorine ions.
Iodine lose an electron to form neutral iodide.
Loss of electron = oxidation Gain of electron= reduction (OIL RIG)
In displacement reaction oxidation and reduction happen simultaneously. An oxidising agent get reduced and a reducing agent gets oxidised.
This is known as a redox reaction.

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Reactions of Metals

Acid + metal - salt + hydrogen
The more reactive the metal the faster the reaction will go, the speed is indicated by the rate at which bubbles are given off, which is detected by the burning splint test. Ex. Magnesium big squeaky pop, produces a lot of bubbles with cold dilute acids. Al- fair old squeaky pop with warm dilute acid produces a lot of bubbles. Zn and Fe- react slowly , more strongly if you heat them up.
The name of the salt depends on the metal and the acid used. HCl will always form a chloride salt and H2SO4 will produce a sulfate salt.

Metal + Water -metal hydroxide + hydrogen (reactive metals will react very vigorously)
(Less reactive metal) + steam - metal oxide + hydrogen

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The reactivity Series

K, Na, Li, Ca, Mg, Al, (carbon), Zn, Fe, Tin, Pb, (hydrogen), Ag, Au

A more reactive metal will displace a less reactive metal from its oxide as it will bond more strongly with the oxygen.
If you put a reactive metal into a solution of a less reactive metal the reactive metal will displace the less reactive metal in the salt. But if the more reactive metal is already in the compund the the added natal won't be able to displace it .

Reactivity series can be used to work out where in the reactivity series the metal is.

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Iron

Iron corrodes easily , it happens when iron is in contact with both oxygen and water= oxidation reaction. ( as the iron gains water ). Water becomes loosely bonded to the iron oxide forming hydrated iron oxide =rust.
Iron + oxygen + water - hydrated iron oxide.
Rust is a soft solid that flakes off to leave more iron available to rust.

Prevent rust:
Barrier method: painting / coating with paint (big structures) , oiling/ greasing (moving parts involved.

Sacrificial method: placing a more reactive metal with iron, the water and oxygen will then bond more tightly with the sacrificial metal than with the iron.
Zinc is often used as the sacrificial method as its more reactive and will be oxidised instead. A coating of zinc can be sprayed onto the object - galvanising. Or big blocks can be bolted to the iron - can be used on ships hulls or underground pipes.

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Oxygen in the Atmosphere

Composition of the atmosphere: 21% oxygen, 71% nitrogen, 1% argon and 0,04% CO2.

Investigating the proportion of oxygen in the atmosphere: Copper:
When its heated copper reacts with oxygen in the air to make copper oxide - using up the oxygen. If you heat an excess of copper and pass air using two sealed syringes you can use the markers to tell how much oxygen has been used.
2Cu + O2 - 2CuO

Iron or phosphorus:
Iron reacts in the air to form rust. Soak iron wool in acetic acid- catalyse the reaction, and push the wool to the test tube, invert the test tube into a beaker. Over time the level of water in the test tube will rise as the iron is reacting with the oxygen . To work the percentage you have to mark the starting and finishing position of water and work the difference of volume. You can do a similar experiment with white phosphorus as when it reacts with oxygen it produces phosphorus oxide.

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Oxygen in reactions

You can make oxygen by using hydrogen peroxide, as it will decompose into water and oxygen : 2H2O2 - 2H2O + O2.
This reaction is rlly slow but it can be increased by addin manganese oxide (catalyst). You can collect the oxygen that's produced over water or by using a gas syringe
Collecting over water: using a delivery tube to bubble the gas into an upside down measuring cylinder or a gas syringe.

When you burn something it reacts with oxygen in the air to form an oxide which can have acidic or basic character.
Magnesium: burns with a bright white flame in air and the white powder is magnesium oxide. It is slightly alkaline. : 2Mg + O2 - 2MgO

Carbon: it will burn if its very strongly heated, orangey yellows flame and produces carbon dioxide. It is acidic: C + O - CO2

Sulfur: burns with a pale blue flame and produces sulfur dioxide, it is slightly acidic. S+ O2 - SO2

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Preparation of Carbon Dioxide

You can collectgases in a test tube, as the gas you are collecting displaces the air in the test tube. You can do this by upward delivery : to collect gases that are lighter than air , downward delivery: to collect gases denser than air.

Calcium carbonate are put in the bottom of a flask and dilute hydrochloric acid is added. This reaction produces calcium carbonate , water and carbon dioxide gas: 2HCl + CaCO3 - CaCl2 + H2O + CO2
Teñhe carbon dioxide is collected in a gas syringe or using downward delivery.

Thermal decomposition:
Heating a metal carbonate also produces CO2, this is an example of thermal decomposition, which is when a substance breaks down into simpler substances when heated. Copper carbonate is a green powder that will easily decompose to form carbon dioxide and copper oxide.
CuCO3 - CuO + CO2.
Carbon dioxide is then collected by downward delivery method.

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Carbon dioxide - the good and the bad

CO2 is used to make fizzy drinks, as its slights soluble in water and dissolves when under pressure which produces carbonic acid: CO2 + H2O - H2CO3
When you open a bottle the bubbles escaping are CO2. It is also used in fire extinguishers, as its denser than air so it sinks into the flames and stops the oxygen the fire needs to burn.

Carbon dioxide is also a green house gas. The temperature of the earth is a balance between the heat from the sun and the heat radiated back out into space. Some gases act like a natural insulating later (greenhouse gases) , they absorb most of the heat that would be radiated out into space, and re radiate it back to earth. Human activity affects the amount of carbon dioxde:
Deforestation: fewer trees means less CO2 is removed vía photosynthesis
Burning fossil fuels: carbon that was locked up in these fuels is being released.
It is because of these activities the concentration has been increasing

Increasing levels of CO2 and the gradual heating of the atmosphere is correlated. Global warming is a type of climate change that causes other types of climate change - changing rainfall patterns = severe flooding due to polar ice caps melting and sea level rising.

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Tests for Cations

Lithium- crimson red flame, Sodium- yellow orange flame, Potassium- lilac flame, Calcium- brick red flame
To do these tests you need a clean platinum loop, to know its clean add HCl and then burn it until the flame is transparent, then you can dip it into the sample.

Many metal hydroxides are insoluble and precipitate out of solution when formed- they have characteristic colours. So you add a few drops of NaOH forming a insoluble hydroxide.
Cu + 2OH - Cu(OH)2 = Blue
(II)Fe + 2OH - Fe(OH)2 = Studgy green
(III)Fe + 3OH - Fe(OH)3 = reddish brown

You can check fro ammonia gas (NH3) using a damp piece of red litmus paper, if there is ammonia present it will turn blue. Ammonia gas is also smelly but it's not a good idea to smell it as its very harmful to your eyes

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Tests for Anions

To test for carbonates add HCl and if there is carbonate present CO2 will be released, you can't test for CO2 using lime water. CO3 (2-) + 2H(+) - CO2 + H2O

To test for sulfates add HCl and barium chloride solution BCl2, if a white precipitate of barium sulfate is produced it means that the original substances was a sulfate-the HCl is added to get rid of any traces of carbonate or sulfite. Ba + SO4 - BaSO4

To test for halides add HNO3 and silver nitrate solution.
Ag + Cl - AgCl : a chloride ion gives a white precipitate of silver chloride.
Ag + Br - AgBr : a bromide ion gives a cream precipitate of silver bromide.
Ag + I - AgI : a iodide ion gives a yellow precipitate of silver iodide.

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Tests for gases and water

Chlorine-bleaches damp litmus paper, turning it white
Oxygen - relights a glowing splint
CO2- turns like water cloudy
Hydrogen- makes a squeaky pop with a lighted splint, it comes from hydrogen burning with the oxygen in the air to form H2O
Ammonia- turns damp red litmus paper blue, smells really bad.

Copper sulfate crystals can be used to test water: when its bound to water it forms blue crystals, by heating it yo it drives the water off which leaves white anhydrous copper sulfate powder. If you then add a couple drops of water to the white powder you get the blue crystals again.

When a sample has pure water it means its only made up of one substance , meaning it has a set defined physical properties like boiling and freezing point.
Pure water will boil at 100C and boil at 0C.

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