GSCE Science - Chemistry - C4

Topics

• Oxidation and Reduction
• The Reactivity Series
• Methods of Extraction
• Displacement Reactions
• Metals and Acids
• Metal Salts
• Neturalisation
  
• Uses of Alkalis and Acids
  
• General Equations for Reactions
• Electrolysis

Oxidation and Reduction

• Oxidation - gain of electrons - or gain of oxygen 
• Reduction - loss of electrons  - or loss of oxygen

When a metal reacts with oxygen it becomes oxidised and becomes a metal oxide. For example, when copper reacts with oxygen it becomes copper oxide. This process is known as oxidation.

However, over time all metals will become oxidised. But it depends on the reactivity of a metal.

Metal + Oxygen → Metal Oxide

When a metal reacts with a compound containing hydrogen, it becomes reduced and becomes a metal once again, with a form of hydrogen as a by-product.  For example, when copper reacts with hydrogen it becomes copper and water. This process is known as reduction. 

Metal Oxide + Hydrogen → Metal + Hydrogen 

The Reactivity Series

The Reactivity Series orders the reactivity of metals. Their reactivity is dependent on how easily they lose their electrons when forming positive ions. Therefore the higher up the list, the more easily, the metal loses their electrons. When metals react with water and acids, they lose electrons to form positive ions. So the higher up the list, the more easily it reacts with water and acids. The order is the relative reactivity of different metals with either acids and metals, and then ordered, that is the series

The Reactivity Series - starting with the most reactive down to the least

• Potassium - K
• Sodium - Na
• Calcium - Ca 
• Magnesium - Mg
• Carbon - C
• Zinc - Zn
• Iron - Fe
• Hydrogen - H
• Copper - Cu

The gases are there to compare the methods of extraction.

Methods of Extraction

Common metals, like iron and aluminum react with oxygen to form oxides and need to be reduced and become pure, to be used in many industries. Therefore, since metals don't all occur in their native states, different methods of extractions are needed to remove the compound which has reacted with the metal. They are known as metal ores, metals containing rocks. All the methods use different processes but the product is the same, a pure metal. The materials are concentrated, and the other rocks are removed, then it is reduced and the metal itself is extracted from its compound. 

The reactivity of a metal determines the process of extraction that is used. The postion of it related to carbon is very important. 

Metals above carbon have to be extracted using electrolysis. These metals include potassium, sodium, lithium, calcium and magnesium. 

Metals below carbon can be extracted using reduction by carbon since they are less reactive than carbon. These metals include, zinc, iron and copper. 

However, some metals which do occur in their native don't need to be extracted and purified at all. These include, gold and silver. They are mined as an elemental form. 

Methods of Extraction

• Copper

Copper has a low reactivity, it doesn't occur in a native state as it reacts over time to form copper compounds. After being purified using reduction by carbon, it still has impurities and needs to be processed using electrolysis to remove any further impurities. The reason copper is taken through two methods of extraction, is to improve its conductivity, During electrolysis, pure copper forms at the cathode and impurities form at the anode making anode mud.

• Plantinum

Plantium is a rare and expensive metal and is used in jewellery and the plating on engines. Plantinum like gold and silver does occur in its native state and it has an incredibly low reactivity. This metal is very similar to gold. 

• Aluminum

Aluminum is a very reactivity metal and as it is likely to corrode is coated with oxygen atoms to prevent it. Because of its low density it is most commonly used in the aerospace industry as it doesn't add unneccesary weight to the aircraft. It is also used for aluminum foil as it is mallable. Finally it is used for containers as it can keep its contents under high pressures.

Displacement Reactions

When you react, a metal (a) with a metal oxide (b), the product will either be a oxidised with b reduced or the other way round depending on the reactive of a metal. You can use the reactivity series to predict these reactions. The element or an ion is displaced and moves to another element creating a compound. Since the other element or ion is stronger and more reactive it is able to move the element/ion to join their compound. 

Carbon and Hydrogen can also be used to oxidise a substance. However, both of them are negative and on a wider scale are bad for the environment. Carbon reactions produces carbon dioxide which is a greenhouse gas and is damaging for the environment. Hydrogen releases steam in its reactions which is technically a greenhouse gas. 

Lead Oxide + Carbon = Lead + Carbon Dioxide

In this equation, the lead is reduced and the carbon is oxidised. Heat is needed and is applied to speed up the process,

Tungsten Oxide + Hydrogen = Tungsten + Hydrogen Oxide (steam)

In this equation, the tungsten is reduced and the hydrogen is oxidised, Heat is needed and is applied to speed up the process.

As, carbon and hydrogen are more reactive that these metals, they reduce the other product.

Metals and Acids

All acids are of different strengths and therefore when they react with other elements, compounds or mixtures, the results will vary because they will either be weak or strong. Acid strength tells you what proportion of acid molecules ionise in water and hence how strong the reaction will be; this is very different to the concentration of an acid which is the ratio of acid to the solution. Strong acids, like sulfuric, hydrochloric and nitric acid, ionise completely. All the acid particles dissociate (split apart) to release positive hydrogen ions. Weak acids, like ethanoic, citric and carbonic acids, do not fully ionise therefore only a small amount of acid particles are dissociated, to release less positive hydrogen ions. The ph of any substances is the concentration of hydrogen ions. So this means a strong acid will have a larger concentration of hydrogen, will a stronger alkali will have a smaller concentration of hydrogen.

When you react an acid with a metal oxide or metal hydroxide it produces a metal salt and water. While if you react an acid with a metal carbonate it produces a metal salt, water and carbon dioxide. When an acid and a pure metal react, it produces a metal salt and hydrogen. 

Acid + Metal Oxide → Metal Salt + Water

Acid + Metal Hydroxide → Metal Salt + Water

Acid + Metal Carbonate → Metal Salt + Water + Carbon Dioxide

Acid + Pure Metal → Metal Salt + Hydrogen

Metals and Acids

When you perform a reaction with a metal and an acid, there can be several risks. The handling of the acid can be a risk as it hurt the person conducting the experiment. To solve this, make sure to read the label and then take the right precautions. During metal and acid reactions, heat energy can be used to speed up the reaction. If you don't tie back your hair and keep the bunsen burner on a safety flame, so it is easier to see. Finally, if a test tube smashes, it could cut someone or land in someone's eye. Take care and wear safety specs.

In this experiment, you will need, test tubes, a test tube stand, metals, acids, and optional a bunsen burner, heat proof mat and a test tube holder, hand-held. First, measure out 5cm^3 of acid and metal and add the acid to the test tube. Then add the metal and record the reaction. Then repeat for all the other metals and acids. If required you could test for hydrogen by placing a lit splint into the test tube and if hydrogen is present you will hear a 'squeaky pop'.

Metals and Acids

In this investigation, we used copper, iron, zinc and magnesium. We also used sulfuric acid. The reactivity of the metal will change what the reaction is, and how 'violent' it is. 

When you react copper with sulfuric acid, there is no reaction because copper has a low reactivity. During the reaction, hydrogen was not present. 

When you react iron with sulfuric acid, the solution turns cloudy and fizzes. During the reaction, hydrogen was present.

When you react zinc with sulfuric acid, the solution turned blue, and bubbles formed. During the reaction, hydrogen was present.

When you react magnesium with sulfuric acid, the solution went white. During the reaction, hydrogen was present.

Metal + Sulfuric Acid → Metal Sulphate + Hydrogen

Metal Salts

The name of a metal salt is the compound of the metal and the acid. For example, when you react copper which hydrochloric acid you get copper chloride. The last piece of the name varies with each acid. 

A + Hydrochloric Acid → A Chloride

B + Sulphuric Acid → B Sulphate 

C + Nitric Acid → C Nitrate

Bases are chemicals which neutralise acids to make salts and water, they usually have a ph higher than seven. An example of a base is a metal oxide or metal hydroxide.

Most are soluble, but it depends on their salt. With this information, we can know whether we can separate them using electrolysis. 

Neutralisation

Neutralisation is a chemical reaction where a base and an acid interact. Acids and bases neutralise each other. Acids have a ph lower than seven and bases have a ph higher than seven. Therefore the salt and water produced by the reaction will have. a ph of seven.

Uses of Alkalis and Acids

Acids - a substance with a ph lower than seven that produce H+ ions in solution, all acids contain H atoms since they contain it in their chemical composition, and produce it when they react, they are also corrosive

Alkali - a substance with a ph higher than seven that produce OH- ions in solution, all alkalis contain OH atoms since they are hydroxides and produce it when they react, they are also irritant 

Both acids and alkalis can be used in a variety of household products because of their properties. Citrus fruit contains critic acid which gives it its distinctive taste. Ethanoic acid produces the strong smell in table vinegar, the smell is down to the chemical compounds in the substance. Sodium Hydroxide is incredibly powerful and corrosive so is used in oven cleaning products. 

General Equations for Reactions

acid + metal → salt + hydrogen

The type of salt produced is the name of the metal and the name of the acid that is also used. Hydrogen is produced because it is displaced from the acid's atoms.

acid + metal carbonate → salt + water + carbon dioxide

The carbonate has carbon atoms which are displaced to produce the gas. Hydrogen is formed by reacting with the metal from the acid and since the metal has oxygen from the carbonate, water is formed.

acid + metal oxide → salt + water

The reactivity of the metal changes the extremity of the reaction. Water is produced from the hydrogen in the acid.

In these reactions, the metal is usually the alkali and when you reach the two together a base is formed. This base is neutral. You usually don't react alkali metals and acids together as they neutral and a base, and a hydroxide. 

Electrolysis

Electrolysis is the process of breaking down an ionic compound, as this compound which is known as the electrolyte has to be molten or dissolved in water so the ions are free to move. 

Electrolysis is an oxidation and a reduction reaction occurring at the same time so an ionic compound is split into two atoms. 

• Anode - positive electrolyte
• Cathode - negative electrolyte 
• Electrolyte - broken down compound

Electrolysis

During electrolysis, several steps occur to make the reaction occur:

• 1. The positively charged ions move to the negative cathode (covered with electrons)
• 2. The negatively charged ions move to the positive anode (lacks electrons)
• 3. Both of these are powered by a power pack
• 4. The cathode is supplied by the negative side and the anode is powered by the postive side
• 5. The positive ions and the negative ions are attracted to either electrode because opposite charges attract 
• 6. These ions move through the solution because heat is added giving them energy
  
• 7. The positive ions gain electrons to form an atom, this is reduction - x^+ + e^- → x
• 8. The negative ions lose electrons to form an atom, this is oxidation - y^- + e^- → y

Electrolysis

Aluminium is found as the compound, aluminium oxide so electrolysis is used to create pure aluminium. The first stage is to melt the compound to break down the bonds, but aluminium has a high melting point so cryolite is added lowering the temperature and the cost of production. Graphite is used at the electrolyte as it can withstand high temperatures and is a good conductor of electricity. 

Aluminium ions are attached to the cathode and gain three electrons to form an aluminium atom, this is reduction. Oxide ions are attached to the anode and lose two electrons to form an oxygen atom, this is oxidation.

During this process, the anode must be replaced regularly as graphite/carbon and oxygen react forming carbon dioxide.

• Cathode - Al^3+ + 3e^- → Al 
• Anode - O^2- → O + 2e^-

Electrolysis

• Copper Sulphate Solution

Aqueous solutions are dissolved in water. Water ionises forming hydrogen and hydroxide ions. When you perform electrolysis of copper sulfate solution, you need to bear in mind that there are two ions for each electrode. 

• Anode - 4OH^- → Ov2 + 2Hv20 + 4e^-
• Cathode - Cu^2+ + 2e^- → Cu

• Sodium Chloride Solution 

During electrolysis of sodium chloride solution the postive sodium and postive hydrogen are both attrached to the cathode. And both the negative chloride and the negative hydroxide. 

• Anode - 2Cl^- → Clv2 + 2e^-
• Cathode - 2H^+ + 2e^- → Hv2

Hydrogen is only produced if it is more reactive than hydrogen. So in this reaction, copper is produced at the cathode and the oxygen is produced at the anode. The halogen is produced if the solution contains halide ions.