Copper

Copper is soft and easily bent and so is a good conductor of electricity, which makes it useful for wiring. Copper is also a good conductor of heat and it does not react with water. This makes it useful for plumbing, and making pipes and tanks.

Copper ores

Some copper ores are copper-rich – they have a high concentration of copper compounds. Copper can be extracted from these ores by heating them in a furnace, a process called smelting. The copper is then purified using a process called electrolysis.

Electricity is passed through solutions containing copper compounds, such as copper sulfate. During electrolysis, positively charged copper ions move towards the negative electrode and are deposited as copper metal.

Posted on 05:08 / 1 comments / Read More

Extracting metals and making alloys

Metals are very useful. Ores are naturally occurring rocks that contain metal or metal compounds in sufficient amounts to make it worthwhile extracting them: most everyday metals are mixtures called alloys.

Methods of extracting metals

The Earth's crust contains metals and metal compounds such as gold, iron oxide and aluminium oxide, but when found in the Earth these are often mixed with other substances. To become useful, the metals have to be extracted from whatever they are mixed with. A metal ore is a rock containing a metal, or a metal compound, in high enough concentration to make it economic to extract the metal.

Ores are mined. They may need to be concentrated before the metal is extracted and purified. The economics of using a particular ore may change over time. For example, as a metal becomes rarer, an ore may be used when it was previously considered too expensive to mine.

Reactivity and extraction method

Metals are produced when metal oxides are reduced (have their oxygen removed). The reduction method depends on the reactivity of the metal. For example, aluminium and other reactive metals are extracted by electrolysis, while iron and other less reactive metals may be extracted by reaction with carbon or carbon monoxide.

Reactivity and extraction method

Metals (in decreasing order of reactivity)	Method of extraction
potassium sodium calcium magnesium aluminium	extract by electrolysis
carbon
zinc iron tin lead	extract by reaction with carbon orcarbon monoxide
hydrogen
copper silver gold platinum	extracted in various ways

The method of extraction of a metal from its ore depends on the metal's position in the reactivity series.

Gold, because it is so unreactive, is found as the native metal and not as acompound. It does not need to be chemically extracted from its ore, but chemical reactions may be needed to remove other elements that might contaminate the metal.

Posted on 05:04 / 1 comments / Read More

Quarrying

You need to be able to evaluate some of the effects of the limestone industry.

The main advantages and disadvantages of the limestone industry

Advantages	Disadvantages
Limestone is a valuable natural resource, used to make things such as glass and concrete.	Limestone quarries are visible from long distances and may permanently disfigure the local environment.
Limestone quarrying provides employment opportunities that support the local economy in towns around the quarry.	Quarrying is a heavy industry that creates noise and heavy traffic, which damages people's quality of life.

Links

You may wish to read thisBBC News item (2006) about a public inquiry into a limestone quarry in the Peak District National Park. Consider the arguments for and against quarrying limestone in a national park.

Posted on 05:03 / 1 comments / Read More

Uses of limestone

Limestone is a type of rock, mainly composed of calcium carbonate. Limestone is quarried (dug out of the ground) and used as a building material. It is also used in the manufacture of cement, mortar and concrete.

Reactions with acids

Carbonates react with acids to produce carbon dioxide, a salt and water. For example:

calcium carbonate + hydrochloric acid → carbon dioxide + calcium chloride + water

CaCO₃ + 2HCl → CO₂ + CaCl₂ + H₂O

Since limestone is mostly calcium carbonate, it is damaged by acid rain. Sodium carbonate, magnesium carbonate, zinc carbonate and copper carbonate also react with acids: they fizz when in contact with acids, and the carbon dioxide released can be detected using limewater.

Calcium hydroxide

When limestone is heated strongly, the calcium carbonate it contains decomposes to form calcium oxide. This reacts with water to form calcium hydroxide, which is an alkali. Calcium hydroxide is used to neutralise excess acidity, for example, in lakes and soils affected by acid rain.

Cement, mortar and concrete

Cement is made by heating powdered limestone with clay. Cement is an ingredient in mortar and concrete:

• mortar, used to join bricks together, is made by mixing cement with sand and water
• concrete is made by mixing cement with sand, water and aggregate (crushed rock)

Advantages and disadvantages of various building materials

Limestone, cement and mortar slowly react with carbon dioxide dissolved in rainwater and wear away. This damages walls made from limestone, and leaves gaps between bricks in buildings. These gaps must be filled in or ‘pointed’. Pollution from burning fossil fuels makes the rain more acidic than it should be, and this acid rain makes these problems worse.

Concrete is easily formed into different shapes before it sets hard. It is strong when squashed, but weak when bent or stretched. However, concrete can be made much stronger by reinforcing it with steel. Some people think that concrete buildings and bridges are unattractive

Posted on 05:02 / 2 comments / Read More

Products from calcium carbonate

For your exam, you need to know how calcium hydroxide is obtained from calcium carbonate.

Making calcium oxide

If calcium carbonate is heated strongly, it breaks down to form calcium oxide and carbon dioxide. Calcium oxide is yellow when hot, but white when cold.

Here are the equations for this reaction:

calcium carbonate  calcium oxide + carbon dioxide

CaCO₃ CaO + CO₂

This is a thermal decomposition reaction.

Making calcium hydroxide

Calcium oxide reacts with water to form calcium hydroxide, which is an alkali. Here are the equations for this reaction:

calcium oxide + water → calcium hydroxide

CaO + H₂O → Ca(OH)₂

A lot of heat is produced in the reaction, which may even cause the water to boil.

Posted on 05:01 / 2 comments / Read More

Transition metals

The transition metals are placed in the periodic table in a large block between groups 2 and 3. Most metals (including iron, titanium and copper) are transition metals.

The transition metals

Common properties

The transition metals have these properties in common:

• they are metals
• they are good conductors of heat and electricity
• they can be hammered or bent into shape easily

The transition metals are useful as construction materials. They are also useful for making objects that need to let electricity or heat travel through them easily.

Posted on 05:05 / 1 comments / Read More

Calcium carbonate

Limestone is mainly calcium carbonate, CaCO₃, which when heated breaks down to form calcium oxide and carbon dioxide. Calcium oxide reacts with water to produce calcium hydroxide. Limestone and its products have many uses, including being used to make cement, mortar and concrete.

Thermal decomposition

Calcium carbonate breaks down when heated strongly. This reaction is calledthermal decomposition. Here are the equations for the thermal decomposition of calcium carbonate:

calcium carbonatecalcium oxide + carbon dioxide

CaCO₃CaO + CO₂

Other metal carbonates decompose in the same way, including:

• sodium carbonate
• magnesium carbonate
• copper carbonate

For example, here are the equations for the thermal decomposition of copper carbonate:

copper carbonate copper oxide + carbon dioxide

CuCO₃CuO + CO₂

Metals high up in the reactivity series (such as sodium, calcium and magnesium) have carbonates that need a lot of energy to decompose them. Indeed, not all the carbonates of group 1 metals decompose at the temperatures reached by a Bunsen burner.

Metals low down in the reactivity series, such as copper, have carbonates that are easily decomposed. This is why copper carbonate is often used at school to show thermal decomposition. It is easily decomposed and its colour change, from green copper carbonate to black copper oxide, is easy to see.

The thermal decomposition of copper(II) carbonate is easily demonstrated

Posted on 05:00 / 1 comments / Read More

The chlor-alkali industry

If an electric current is passed through concentrated sodium chloride solution, hydrogen gas forms at the negative electrode and chlorine gas forms at the positive electrode. A solution of sodium hydroxide forms.

You might have expected sodium metal to be deposited at the negative electrode. But sodium is too reactive for this to happen, so hydrogen is given off instead.

During electrolysis:

• Hydrogen ions H⁺ (from the water) are discharged at the negative electrode as hydrogen gas, H₂
• Chloride ions Cl^– are discharged at the positive electrode as chlorine gas, Cl₂
• Sodium ions Na⁺ and hydroxide ions OH^– (from the water) stay behind - they form sodium hydroxide solution, NaOH

Electrolysis of sodium chloride solution

The three products of electrolysis

The three products of the electrolysis of concentrated sodium chloride solution have important uses in the chemical industry:

• Hydrogen is used as a fuel and for making ammonia
• Chlorine is used to kill bacteria in water, and to make bleach and plastics
• Sodium hydroxide is used to make soap and bleach

Now try a Test Bite.

Read on if you're taking the higher paper.

Posted on 07:54 / 1 comments / Read More

Predicting the products of electrolysis

Ionic substances in solution break down into elements during electrolysis. Different elements are released depending on the particular ionic substance.

At the negative electrode

At the negative electrode, positively charged ions gain electrons. This is reduction, and you say that the ions have been reduced.

Metal ions and hydrogen ions are positively charged. Whether you get the metal or hydrogen during electrolysis depends on the position of the metal in the reactivity series:

• The metal will be produced if it is less reactive than hydrogen
• Hydrogen will be produced if the metal is more reactive than hydrogen

The reactivity series of metal - carbon and hydrogen are not metals, but they are shown for comparison

So the electrolysis of copper chloride solution produces copper at the negative electrode. But the electrolysis of sodium chloride solution produces hydrogen.

At the positive electrode

At the positive electrode, negatively charged ions lose electrons. This is oxidation, and you say that the ions have been oxidised. The table summarises some of the elements you should expect to get during electrolysis.

 

Negative ion in solution	Element given off at positive electrode
Chloride, Cl–	Chlorine, Cl2
Bromide, Br–	Bromine, Br2
Iodide, I–	Iodine, I2
Sulfate, SO42–	Oxygen, O2

Putting it together

The table shows some common ionic compounds, and the elements released when their solutions are electrolysed.

 

Ionic substance in solution	Element at the negative electrode	Element at the positive electrode
Copper chloride, CuCl2	Copper	Chlorine
Copper sulfate, CuSO4	Copper	Oxygen
Sodium chloride, NaCl	Hydrogen	Chlorine
Hydrochloric acid, HCl	Hydrogen	Chlorine
Sulfuric acid, H2SO4	Hydrogen	Oxygen

Posted on 07:54 / 1 comments / Read More

Electroplating

Electrolysis is used to electroplate objects. This is useful for coating a cheaper metal with a more expensive one, such as copper or silver.

How it works

• The negative electrode should be the object that is to be electroplated
• The positive electrode should be the metal that you want to coat the object with
• The electrolyte should be a solution of the coating metal, such as its metal nitrate or sulfate

Here are two examples.

Electroplating with silver

The object to be plated, such as a metal spoon, is connected to the negative terminal of the power supply. A piece of silver is connected to the positive terminal. The electrolyte is silver nitrate solution.

Electroplating with copper

The object to be plated, such as a metal pan, is connected to the negative terminal of the power supply. A piece of copper is connected to the positive terminal. The electrolyte is coppersulfate solution.

This arrangement can also be used to purify copper during copper manufacture. In this case, both electrodes are made from copper. The negative electrode gradually gets coated with pure copper as the positive electrode gradually disappears. The animation shows how this works:

Posted on 07:53 / 5 comments / Read More

Making insoluble salts

Insoluble salts do not dissolve in water. They can be made by mixing appropriate solutions of ions together.

Soluble and insoluble salts

 

Soluble	Insoluble
All nitrates	None
Most sulfates	Lead sulfate, barium sulfate
Most chlorides, bromides and iodides	Silver chloride, silver bromide, silver iodide, lead chloride, lead bromide, lead iodide
Sodium carbonate, potassium carbonate	Most other carbonates
Sodium hydroxide, potassium hydroxide	Most other hydroxides

Notice that all nitrates and most chlorides are soluble. This is why many of the chemicals you use in the laboratory are nitrates or chlorides. If you want to make an insoluble salt, you can react together two soluble salts in a precipitation reaction.

Making an insoluble salt

Silver chloride is insoluble - you can see this from the table. You need a soluble silver salt and a soluble chloride salt to make it. Silver nitrate and sodium chloride are both soluble. When you mix their solutions together, you make soluble sodium nitrate and insoluble silver chloride:

• silver nitrate + sodium chloride → sodium nitrate + silver chloride
• AgNO₃(aq) + NaCl(aq) → NaNO₃(aq) +AgCl(s)

The silver chloride appears as tiny particles suspended in the reaction mixture - it forms a precipitate. The precipitate can be filtered, washed with water on the filter paper, and then dried in an oven.

Remember: if you want to make an insoluble salt XY, mixing X nitrate with sodium Y will always work. In the example above, X is silver and Y is chloride.

Using precipitation reactions

Precipitation reactions can be used to remove unwanted ions in solution. This is useful for treating drinking water and waste water.

Posted on 07:52 / 1 comments / Read More

Electrolysis

Electrolysis is the process by which ionic substances are broken down into simpler substances using electricity. During electrolysis, metals and gases may form at the electrodes.

What is electrolysis?

Ionic substances contain charged particles called ions. For example, lead bromide contains positively charged lead ions and negatively charged bromide ions.

Electrolysis is the process by which ionic substances are decomposed (broken down) into simpler substances when an electric current is passed through them.

For electrolysis to work, the ions must be free to move. Ions are free to move when an ionic substance is dissolved in water or when melted. For example, if electricity is passed through molten lead bromide, the lead bromide is broken down to form lead and bromine.

Electrolysis

Here is what happens during electrolysis:

• Positively charged ions move to the negative electrode during electrolysis. They receive electrons and are reduced.
• Negatively charged ions move to the positive electrode during electrolysis. They lose electrons and are oxidised.

The substance that is broken down is called the electrolyte.

Posted on 07:52 / 0 comments / Read More

Half-equations - Higher tier

A half-equation shows you what happens at one of the electrodes during electrolysis. You should be able to complete and balance half-equations for the reactions that happen during electrolysis.

Writing a half-equation

Electrons are shown as e^- in half-equations. A half-equation is balanced by adding, or taking away, a number of electrons equal to the total number of charges on the ions in the equation.

For example, here is how you would write the balanced half-equation for chloride ions forming chlorine gas:

 

Step	Result
1. Write the formulae of the reactant and product.	Cl- → Cl2
2. Adjust the number of ions, if needed.	2Cl- → Cl2
3. Count the number of charges. Add enough electrons so that both sides have the same total number of charges.	2Cl- → Cl2 2e-

You may also see this half-equation written as: 2Cl^- – 2e^– → Cl₂

The table shows some examples of half-equations before and after balancing.

 

Unbalanced	Balanced
Al3+ + e– → Al	Al3+ + 3e– → Al
Cl2+ + e– → Cu	Cu2+ + 2e– → Cu
H+ + e– → H2	2H+ + 2e– → H2
Br- → Br2 + e-	2Br- → Br2 + 2e-
O2- → O2 + e-	2O2 → O2 + 4e-

Posted on 07:55 / 0 comments / Read More

Aluminium extraction

Aluminium is the most abundant (found in large quantities) metal on Earth. But it is expensive, largely because of the amount of electricity used up in theextraction process.

Aluminium ore is called bauxite. The bauxite is purified to yield a white powder -aluminium oxide - from which aluminium can be extracted.

The extraction is done by electrolysis. But first the aluminium oxide must be melted so that electricity can pass through it. Aluminium oxide has a very high melting point (over 2000°C) so it would be expensive to melt it. Instead, it is dissolved in moltencryolite - an aluminium compound with a lower melting point than aluminium oxide. The use of cryolite reduces some of the energy costs involved in extracting aluminium.

Diagram showing cell for aluminium extraction

The diagram shows an aluminium oxide electrolysis tank. Both the negative electrode (cathode) and positive electrode (anode) are made of graphite, a form of carbon.

Aluminium metal forms at the negative electrode and sinks to the bottom of the tank, where it is tapped off.

Oxygen forms at the positive electrodes. This oxygen reacts with the carbon of the positive electrodes, forming carbon dioxide, and they gradually burn away. As a result, the positive electrodes have to be replaced frequently. This adds to the cost of the process.

Posted on 07:53 / 0 comments / Read More

Atoms

Atoms consist of electrons surrounding a nucleus that contains protons and neutrons. Neutrons are neutral, but protons and electrons are electrically charged: protons have a relative charge of +1 and electrons have a relative charge of -1.

Atoms and elements

All substances are made of tiny particles called atoms. An element is a substance that is made of only one sort of atom. There are about 100 different elements. These are shown in the periodic table, which is a chart with all the elements arranged in a particular way. The horizontal rows in the periodic table are called periods and the vertical columns are called groups. The elements in a group have similar properties to each other.

Metals and non-metals

The metals are shown on the left of the periodic table, and the non-metals are shown on the right. The dividing line between metals and non-metals is shown in red on the table below. You can see that most of the elements are metals.

The periodic table divided into non-metals and metals

Chemical symbols

The atoms of each element are represented by a chemical symbol. This usually consists of one or two different letters, but sometimes three letters are used for newly discovered elements. For example, O represents an oxygen atom, and Na represents a sodium atom.

The first letter in a chemical symbol is always an UPPERCASE letter, and the other letters are always lowercase. So, the symbol for a magnesium atom is Mg and not mg, MG or mG.

Posted on 07:56 / 0 comments / Read More