Metals and Acids: Chapter 3 (PDF)

## Chapter 3: Metals and acids ### 3.1 Acids and metals **Learning objectives** After this topic you will be able to: * compare the reactions of different metals with dilute acids * explain the test for hydrogen gas. **Key Words** acid, metal **Sulfuric similarities?** Plan an experiment to...

## Chapter 3: Metals and acids ### 3.1 Acids and metals **Learning objectives** After this topic you will be able to: * compare the reactions of different metals with dilute acids * explain the test for hydrogen gas. **Key Words** acid, metal **Sulfuric similarities?** Plan an experiment to answer these questions: Do metals that react vigorously with hydrochloric acid also react vigorously with sulfuric acid? Is hydrogen formed as a product? **Foul Fact** In the US, a person died from zinc poisoning after eating 461 pennies. American pennies are mainly zinc. **Zookeepers were worried.** A hyena was ill. Its foot was swollen. It refused to eat. What was wrong? Vets used X-rays to solve the mystery. The hyena had swallowed 20 zinc coins. In the stomach, zinc reacted with hydrochloric acid. The reaction made zinc chloride. zinc + hydrochloric acid → zinc chloride + hydrogen Zinc chloride dissolves in water. It mixes with blood and travels around the body. This causes zinc poisoning. **How do other metals react with acids?** Metals all have similar physical properties. They are shiny. They conduct heat and electricity. Metals have patterns in their chemical properties too. Anna pours dilute hydrochloric acid into a test tube. She adds magnesium ribbon. The mixture bubbles vigorously. The magnesium ribbon appears to get smaller, and disappear. A colourless solution remains. There has been a chemical reaction: magnesium + hydrochloric acid → magnesium chloride + hydrogen Anna repeats the experiment with different metals. Zinc and iron bubble steadily in acid. Lead reacts more slowly. All the reactions make a solution of a salt, and hydrogen gas: zinc + hydrochloric acid → zinc chloride + hydrogen iron + hydrochloric acid → iron chloride + hydrogen lead + hydrochloric acid → lead chloride + hydrogen **How do you test for hydrogen?** A reaction in a test tube makes bubbles. How can you tell if the bubbles contain hydrogen gas? 1. Collect the gas by holding an empty test tube above the reaction test tube. 2. Light a splint. 3. Hold the splint in the test tube that now contains the gas. 4. Listen. If the splint goes out with a squeaky pop, the gas is hydrogen. The squeaky pop happens because hydrogen and oxygen react explosively. The product is water. hydrogen + oxygen → water **Do all metals react with dilute acids?** Some metals do not react with dilute acids. Nothing happens if you add gold, silver, or copper to dilute hydrochloric acid. Here is a list of how vigorously different metals react with dilute hydrochloric acid: | Metal | Reactivity | | --------------- | ---------- | | Magnesium | Most reactive | | Zinc | | | Iron | | | Lead | | | Copper, silver | Do not react | | Gold | Do not react | **Gold does not react with dilute acids.** The reaction is in a test tube. How can you tell if the bubbles contain hydrogen gas? #### Summary Questions 1. Copy the sentences below, choosing the correct bold words. Some metals react with hydrochloric acid. The products are **a salt/an alkali** and **oxygen/hydrogen** gas. Iron reacts more vigorously than **magnesium/zinc/lead** and less vigorously than **magnesium/lead/copper**. Some metals, for example, **zinc/silver/magnesium**, do not react with dilute hydrochloric acid. 2. Some breakfast cereals contain small amounts of iron. Iron is an important mineral. a. Predict the products of the reaction of iron when it reacts with hydrochloric acid in the stomach acid. Explain your prediction. b. Describe how you could test if your prediction was correct. 3. Draw a visual summary of the reactions of metals and acids, making as many links as possible. ### 3.2 Metals and oxygen **Learning objectives** After this topic you will be able to: * compare the reactions of different metals with oxygen * use state symbols in balanced formula equations. **State a case** When you write state symbols, use lower case letters - it's (g), not (G). **Have you ever burned magnesium? What did you see?** Magnesium burns vigorously. It reacts with oxygen from the air. The product is magnesium oxide. magnesium + oxygen → magnesium oxide 2Mg(s) + O2(g) → 2MgO(s) In the balanced equation above, (s) and (g) are state symbols: * (s) means solid * (g) means gas Magnesium reacts with oxygen even when you do not heat it. If you leave magnesium in the air, its surface atoms react with oxygen. This forms a thin layer of magnesium oxide. Gold is unreactive. It does not burn. Its surface atoms do not react with oxygen. This explains why gold stays shiny. **How do reactions with acids and oxygen compare?** Magnesium reacts vigorously with dilute acids. It also burns in oxygen. Magnesium is a reactive metal. Gold does not react with dilute acids or with oxygen. It is unreactive. There is a pattern. Metals that react vigorously with dilute acids also react vigorously with oxygen. Metals that do not react with dilute acids do not react with oxygen. **How do other metals react with oxygen?** If you sprinkle zinc powder into a Bunsen flame, you see bright-white sparks. Zinc oxide forms: zinc + oxygen zinc oxide 2Zn(s) + O2(g) → 2ZnO(s) There is a similar reaction with iron filings. The product is iron oxide. Copper does not burn in a Bunsen flame. Instead, it forms black copper oxide on its surface. copper + oxygen → copper oxide 2Cu(s) + O2(g) → 2CuO(s) | Metal | Reaction with dilute acid | Reaction with oxygen | | --------------- | --------------------------- | ------------------------ | | Magnesium | Reacts very vigorously | Burns vigorously | | Zinc | Reacts steadily | Burns less vigorously | | Iron | Reacts steadily | Burns | | Lead | Reacts slowly | | | Copper | No reaction | When heated, form layer of oxide on surface. | | Gold | No reaction | | **Fair test?** Jamilla compares the burning reactions of metals. She wants to list four metals in order of how vigorously they react. She has magnesium ribbon, an iron nail, zinc filings, and a piece of copper pipe. She also has a Bunsen burner and tongs. With a partner, discuss how Jamilla can compare the burning reactions. How could she improve her investigation? #### Summary Questions 1. Copy and complete the sentences below. Some metals burn vigorously in air, for example, **_.** The products of the reactions **_.** Some metals form an oxide layer on their surface when heated, for example, **_.** Some metals, for example, **_** do not react with oxygen. 2. Write the balanced formula equation for the reaction of calcium with oxygen. Include state symbols. 3. Potassium reacts explosively with dilute hydrochloric acid. Predict how vigorously it reacts with oxygen, and the products of the reaction. Explain your answers. 4. Create a song or rap to describe patterns in the reactions of metals with acids and oxygen. ### 3.3 Metals and water **Learning objectives** After this topic you will be able to: * compare the reactions of metals with water * use the reactivity series to predict reactions. **Look at the metals around you.** Do they react with water? Stainless steel taps do not. Nor do copper water pipes or gold jewellery. **The state symbols include:** * (l) for the liquid state * (aq) for a substance dissolved in water. **How do metals react with steam?** Magnesium reacts slowly with cold water. But it reacts quickly with steam. magnesium + water → magnesium oxide + hydrogen Mg(s) + H₂O(g) → MgO(s) + H₂(g) **Some metals do react with water.** Calcium bubbles vigorously, then seems to disappear. The bubbles are hydrogen gas. calcium + water → calcium hydroxide + hydrogen **How do other metals react with water?** The Group 1 metals react vigorously with water. There is a flame when potassium reacts with water. Sodium and lithium react slightly less vigorously. There is a pattern in the Group 1 metal reactions with water. They all make soluble hydroxides and hydrogen gas. potassium + water → potassium hydroxide + hydrogen 2K(s) + 2H2O(l) → 2KOH(aq) + H2(g) Zinc and iron also react with steam. The products are hydrogen, and a metal oxide. Copper and gold are unreactive. They do not react with cold water or steam, just as they do not react with dilute acids and oxygen. **What is the reactivity series?** The patterns of metal reactions with acids, oxygen, and water are similar. The reactivity series describes these patterns. It lists the metals in order of how vigorously they react. The metals at the top have very vigorous reactions. Going down the list, the metals get less reactive. | Reactive | | -------- | | Potassium| | Sodium| | Lithium| | Calcium| | Magnesium| | Aluminium| | Zinc| | Iron| | Lead| | Nickel| | Copper| | Silver| | Gold| | Unreactive | **Tim's tin** Tim wants to know the position of tin in the reactivity series. He does practical tests to collect the data in the table. | Metal | Observations on adding to dilute hydrochloric acid | Observations after leaving metal in water and air for one week | Observations on adding dilute sulfuric acid | | ---------------- | ------------------------------------------- | ---------------------------------------------------------- | ---------------------------------------------------- | | Magnesium | Bubbles slowly | No change | Bubbles form slowly | | Aluminium | Bubbles form, more vigorously than nickel | Makes red-brown flaky substance | Bubbles form, more vigorously than nickel | | Zinc | Bubbles form, more vigorously than nickel | No change | Bubbles form, more vigorously than nickel | | Iron | Bubbles form, more vigorously than nickel | No change | Bubbles form, more vigorously than nickel | | Lead | No change | No change | No change | | Nickel | | | | | Copper | No change | No change | No change | | Silver | No change | No change | No change | | Gold | No change | No change | No change | Talk about how Tim's data help answer his question. Discuss tests he could do to discover more about the position of tin. #### Summary Questions 1. Write six sentences from the sentence starters and enders below. Sentence starters | Sentence enders ------------- | ------------- Sodium... | ...is less reactive than copper. ...reacts very vigorously with water. Gold ...| ...does not react with oxygen, water, or acid. ...is unreactive. Iron... | ...is near the top of the reactivity series. ...is more reactive than copper. 2. Write a balanced equation for the reaction of sodium (Na) with water. The products are sodium hydroxide (NaOH) and hydrogen. 3. Use the evidence in the table below to predict the position of nickel in the reactivity series. Explain your prediction. ### 3.4 Metal displacement reactions **Learning objectives** After this topic you will be able to: * predict pairs of substances that react in displacement reactions * use the reactivity series to explain displacement reactions. **Key Words** displace, displacement, thermite reaction **What is copper used for?** Electric cables, water pipes, and computer parts all include the metal. Most copper comes from rock that contains copper compounds. Scientists get copper from rock by using chemical reactions. Here's how: Add sulfuric acid to the rock. Copper sulfate solution forms. Add waste iron to the copper sulfate solution. There is a chemical reaction. One of the products is copper: iron + copper sulfate → iron sulfate + copper Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s) Iron is more reactive than copper. It displaces copper from its compound, copper sulfate. The reaction is a displacement reaction. In a displacement reaction, a more reactive element displaces, or pushes out, a less reactive element from its compound. **Other displacement reactions** Elliott adds magnesium to copper sulfate solution. Magnesium is more reactive than copper. So magnesium displaces copper from its compound. magnesium + copper sulfate → magnesium sulfate + copper Mg(s) + CuSO4(aq) → MgSO4(aq) + Cu(s) If you add copper to magnesium sulfate solution, there is no reaction. Copper is less reactive than magnesium. So copper cannot displace magnesium from its compounds. **Do oxides take part in displacement reactions?** Aluminium is more reactive than iron. It displaces iron from its compounds. For example: aluminium + iron oxide → aluminium oxide + iron 2Al(s) + Fe₂O₃(s) → Al₂O₃(s) + 2Fe(1) This is the thermite reaction. It involves mixing the two powders, and heating them strongly. The reaction is exothermic. The reaction mixture gets so hot that the iron melts. Other metal-metal oxide pairs react. The metal on its own needs to be more reactive than the metal in the compound. For example: iron + copper oxide → iron oxide + copper 2Fe(s) + 3CuO(s) → Fe₂O₃(s) + 3Cu(s) Iron has displaced copper from copper oxide. Copper does not react with iron oxide. This is because copper is less reactive than iron. #### Planning paragraphs Make notes for a piece of writing to explain displacement reactions. Decide how to divide the information into paragraphs. Plan what to include in each paragraph. Then write your paragraphs. Swap with a friend. Can you suggest improvements? #### Summary Questions 1. Copy the sentences below, correcting the five mistakes. In a displacement reaction, a less reactive metal pushes out a more reactive metal from its compound. For example, iron displaces aluminium from aluminium oxide. 2. Predict which pairs of substances will react. Give reasons for your decisions. a. zinc and copper sulfate solution b. iron and zinc chloride solution c. aluminium powder and copper oxide powder d. iron filings and lead oxide powder 3. Draw a cartoon that explains how displacement reactions occur. ### 3.5 Extracting metals **Learning objectives** After this topic you will be able to: * use the reactivity series to decide which metals can be extracted from their ores by heating with carbon * calculate the amounts of metals in ores. **What links the pictures?** The items are made from steel. Steel is mainly iron. But where does iron come from? You cannot find the element on its own in the Earth's crust. **What is an ore?** In the Earth's crust, iron is joined to other elements, in compounds. In many of these compounds iron is joined to oxygen. These are iron oxides. Most iron oxide is mixed with other compounds in rock. A rock that you can extract a metal from is called an ore. * Iron ore is a mixture of iron oxide and other compounds. * Aluminium ore is a mixture of aluminium oxide and other compounds. **How are metals extracted from ores?** There are two main stages in extracting iron from its ore. These are: 1. Separate iron oxide from the compounds it is mixed with. 2. Use chemical reactions to extract iron from iron oxide. The chemical reactions involve heating iron oxide with charcoal. Charcoal is a form of carbon. It is cheap, and easy to get hold of. **Which metal oxides react with carbon?** Carbon is a non-metal. But we can place it in the reactivity series, between aluminium and zinc. Any metal that is below carbon in the reactivity series can be displaced from its compounds by carbon. You can heat carbon powder with copper oxide powder. Carbon displaces copper from copper oxide: carbon + copper oxide → copper + carbon dioxide C(s) + 2CuO(s) → 2Cu(s) + CO₂(g) You can also heat carbon with lead oxide. carbon + lead oxide → lead + carbon dioxide C(s) + 2PbO(s) → 2Pb(s) + CO₂(g) **Can carbon extract any metal from its compounds?** You cannot use carbon to get aluminium from aluminium oxide. This is because aluminium is more reactive than carbon. It is above carbon in the reactivity series. Gold always exists as the element itself. It does not form compounds because it is very unreactive. The gold just needs separating from the substances it is mixed with. **Ore waste** Iron ore from different places contains different amounts of iron. Companies extract iron from ores containing between 16% and 70% iron. Calculate the masses of waste from 1 tonne (1000 kg) of each of these ores: an ore that is 50% iron, an ore that is 16% iron, and an ore that is 70% iron. #### Summary Questions 1. Copy the sentences below, choosing the correct bold words. An ore is a **substance/rock** that you can extract metal from. Most metals exist in the Earth's crust as **compounds/elements**. These are **joined to/mixed with** other substances in ores. 2. An ore contains 6% copper. Calculate the mass of copper in 100 kg of this ore. Show your working. 3. Use the reactivity series to write the balanced symbol equation for the reaction of carbon with zinc oxide. Include state symbols. 4. Explain why some metals can be extracted from compounds by heating with carbon, and why some cannot. Include examples to illustrate your answer. ### 3.6 Ceramics **Learning objectives** After this topic you will be able to: * describe ceramic properties * explain why the properties of ceramics make them suitable for their uses. **Have you ever wondered what a toilet is made from?** Toilets are made from pottery. Pottery is an example of a ceramic material. A brick is a block of a ceramic material. Ceramic materials are compounds. They include metal silicates, metal oxides, metal carbides, and metal nitrides. **Why are ceramics useful?** Ceramics have many uses. Their uses depend on their properties. * Bricks are strong when forces press on them. They are also durable and attractive. This makes them suitable for buildings. * Ceramics do not conduct electricity. They are not damaged by water. This makes them useful for electrical power-line insulators. * Ceramics have high melting points. This makes them suitable for jet-engine turbine blades, which get very hot. * Ceramics do not react with water, acids, or alkalis. You can decorate them. This makes them useful for plates, bowls, mugs, and jugs. **Splendid ceramics** You work for a ceramics company. Your boss wants you to write an article for a newspaper, explaining why ceramics are useful. Start by making notes on what to include. Then decide how to organise your ideas into paragraphs. Next, work out how to get readers interested. Finally, write your article. **What are the properties of ceramics?** All ceramic materials have similar physical properties. They are: * hard - you can only scratch them with harder materials * brittle - they break easily * stiff - they are difficult to bend * solid at room temperature, with very high melting points * strong when forces press on them * break easily when stretched * electrical insulators. Ceramics also have similar chemical properties to each other. They do not react with water, acids, or alkalis. **Why do ceramics have these properties?** In ceramic materials, a huge number of atoms join together in one big structure. There are strong forces between the atoms. This structure explains the properties of ceramic materials. * You need a great amount of energy to break forces between atoms. This explains why ceramics have high melting points. * The bonds between atoms are very strong. This is why they are hard. You break some bonds when you scratch ceramic materials. #### Summary Questions 1. Copy and complete the following sentences using the words below. insulators silicates compounds high brittle oxides hard Ceramics are **_.** They include metal **_** and metal **_.** Ceramics are **_** and **_.** They have **_** melting points. They are electrical **_.** 2. Look at the data in the table. Decide which materials could be ceramics. Explain your choices. | Material | Relative hardness | Melting point (°C) | | -------- | ----------------- | ----------------- | | A | 2.0 | 321 | | B | 9.0 | 3532 | | C | 3.0 | 825 | | D | 9.0 | 2930 | | E | 5.8 | 2800 | 3. Summarise the information about ceramics in a table, including how and why they are useful. ### 3.7 Polymers **Learning objectives** After this topic you will be able to: * describe polymer properties * explain how polymer properties make them suitable for their uses. **Do you know what umbrellas, beach balls, and carrier bags have in common?** They are made from polymers. A polymer is a substance with very long molecules. A polymer molecule has identical groups of atoms, repeated many times. There are many polymers. Different polymers have different properties. Their properties make them suitable for their uses. **Why are natural polymers useful?** Plants and animals make natural polymers, including wool, cotton, and rubber. * Sheep make wool. Wool fibres trap air between them. This means that wool traps heat, making it useful for jumpers and socks. * Cotton plants make cotton fibres. Cotton fabric is strong, durable, and absorbs sweat. It is useful for summer clothing like t-shirts. * Rubber trees produce rubber. Rubber is flexible, waterproof, and durable. These properties make it suitable for tyres. **Why are synthetic polymers useful?** Synthetic polymers do not occur naturally. They are made in chemical reactions. There are hundreds of synthetic polymers. #### Summary Questions 1. Copy and complete the sentences below. A polymer has **_** molecules. Each molecule has identical groups of **_**, repeated many times. There are two types of polymer: **_** polymers and **_** polymers. Synthetic polymers include PVC and **_.** Poly(ethene) is **_** because its molecules slide over one another. 2. The list gives some properties of poly(styrene). Choose properties from the list that explain why polystyrene is suitable for: a. packaging b. disposable cups. Properties: low density; does not conduct electricity; poor conductor of heat; white colour. 3. The table gives data about three synthetic polymers. Use the data to compare the polymers. | Polymer | Strength when pulled (N/mm²) | Relative hardness | Density (g/cm³) | | ------------------------ | --------------------------- | ------------------- | --------------- | | low-density poly(ethene) | | | 0.92 | | high-density poly(ethene) | | | 0.96 | | poly(propene) | 48 | 20 | 0.90 | | poly(vinyl chloride) | 60 | 10 | 1.30 | | nylon | | | 1.16 | | acrylic | 74 | 34 | 1.30 | ### 3.8 Composites **Learning objectives** After this topic you will be able to: * describe composite properties * explain why composite properties make them suitable for their uses. **In constructing a new building, builders use reinforced concrete.** What makes this material so strong? Reinforced concrete consists of steel bars with concrete around it. Concrete is not damaged when forces press on it. But it breaks easily when stretched. Steel is not damaged by stretching forces. Together, steel and concrete put up with strong squashing and stretching forces. Reinforced concrete is a composite material. A composite is a mixture of materials. Each material has different properties. The composite has properties that are a combination of the properties of the materials it is made up of. Scientists experiment with different mixtures. They develop composites with the best properties for particular uses. **Other composites** **Carbon-fibre-reinforced plastic** This bicycle frame is made from carbon-fibre-reinforced plastic (CFRP). The composite consists of two materials: * carbon fibres, which are thin tubes of carbon. The fibres are woven into a fabric. * a gluelike polymer, which is moulded into different shapes when soft. Some cyclists prefer CFRP bicycles to steel ones. Reasons for this are: * CFRP has a lower density, making bicycles lighter * CFRP does not rust * CFRP is very strong * you can mould CFRP into any shape. CFRP has some disadvantages. Bicycles made from CFRP are expensive. If crashed, they are badly damaged. **Glass-fibre-reinforced aluminium** The aeroplane Airbus A380 contains around 20% composite materials. One of these composites is glass-fibre-reinforced aluminium. The materials in this composite include: * thin layers of aluminium * layers of glass fibre * a gluelike polymer to join the layers. **Comparing composites** Callum makes three blocks of a composite material from mud and straw. He puts different amounts of straw in each block. The mud dries. Discuss how Callum could use the apparatus in the diagram to compare the strengths of the blocks. Write down the variables, and suggest how to make the investigation fair. #### Summary Questions 1. Copy the sentences below, choosing the correct bold word. A composite material is a **mixture/compound** of two or more materials. Each of these materials has **different/the same** properties. The composite material has properties that are a **combination of/exactly the same as** these properties. 2. Fibreglass is a composite material. It is made from a polymer called polyester resin, and glass fibres. Use the data in the table to explain why fibreglass is a better material for canoes than polyester resin alone. | Material | Density (g/cm³) | Strength when pulled (MPa) | Strength when squashed (MPa) | | ----------- | ----------------- | --------------------------- | ---------------------------- | | polyester resin | 1.3 | 55 | 140 | | fibreglass | 1.6 | 250 | 150 | 3. Draw a visual summary of the information on composites. ### 4.1 The Earth and its atmosphere **Learning objectives** After this topic you will be able to: * compare the layers of the Earth * describe the composition of the atmosphere. **What goes into a packet of crisps?** The potatoes come from plants. The plants use water, carbon dioxide from the air, and nutrients from the soil to grow. The salt comes from the sea, or from a mine. Aluminium for the bags comes from bauxite rock. The crisps are packed in nitrogen, which was separated from the air. Everything for the packet of crisps - and everything we use - comes from the Earth, the air, or the oceans. **What is the structure of the Earth?** The Earth is made up of four layers. * The outer layer is the rocky crust. It is between 8 km and 40 km thick. * Beneath the crust is the mantle. This is made mostly of solid rock, but it can flow. Very slowly, hotter rock rises and cooler rock sinks. About halfway to the centre of the Earth is the core. This is mainly iron and nickel. The outer core is liquid. The inner core is solid. Of course, no-one has dug to the centre of the Earth. Scientists learn about its structure by studying shock waves from earthquakes. They also examine rocks on the surface and under oceans, and materials that volcanoes bring to the surface. **What's in the crust?** Most rocks are mixtures of compounds. The pie chart shows the elements that make up these compounds. | Element | Percentage | | ------------------- | ----------- | | Oxygen | 46.4 | | Silicon | 28.2 | | Aluminium | 8.3 | | Iron | 5.6 | | Calcium | 2.4 | | Sodium | 2.3 | | Magnesium | 4.2 | | Potassium, titanium, | 2.1 | | and hydrogen | | **What is the atmosphere?** The atmosphere is a mixture of gases that surrounds the Earth. The part of the atmosphere nearest the Earth is the troposphere. This layer goes up to about 10 km above of the Earth. The troposphere is mainly a mixture of two elements, oxygen and nitrogen. There are smaller amounts of other substances, including argon and carbon dioxide. #### Summary Questions 1. Copy and complete the sentences below. Surrounding the Earth is a mixture of gases called the **_.** The Earth itself is made up of four layers. On the outside is the **_.** Next is the mantle. The substances of the mantle are mostly in the **_.** The **_** core consists mainly of two elements - iron and **_.** The substances of the outer core are in the **_** state. 2. The list below gives the names of the four most common substances in the atmosphere. Draw a ring around the name of the most abundant element. Underline the name of the most abundant compound. argon nitrogen oxygen carbon dioxide 3. Write a paragraph to compare the properties and composition of the Earth's crust, mantle, and core. ### 4.2 Sedimentary rocks **Learning objectives** After this topic you will be able to: * explain two properties of sedimentary rocks * explain how sedimentary rocks are made. **The pictures show three different types of rock.** How are they similar and how are they different? * Limestone. * Granite. * Marble. There are hundreds of rock types. Scientists classify them into three groups: * sedimentary rocks * igneous rocks * metamorphic rocks **What are the properties of sedimentary rocks?** Sedimentary rocks are made up of separate grains. You can see these with a hand lens. Sedimentary rocks are porous. They have gaps between their grains. Air or water can get into these gaps. Most sedimentary rocks are soft. You can scratch them easily. **How are sedimentary rocks made?** Sedimentary rocks are made up of pieces of older rocks. The process has several stages. **Weathering** Weathering breaks up all types of rock into smaller pieces called sediments. There are different types of weathering: * **Physical weathering** happens because of temperature changes. In **freeze-thaw weathering**, water gets into a crack in a rock. When the temperature is very cold, the water freezes. This forms ice. Ice takes up more space than liquid water. It pushes against the sides of the crack. This happens many times. Eventually, the rock breaks. * **Chemical weathering** happens when rain falls on rocks. Acids in the rain react with substances in the rock. * **Biological weathering** happens when plants and animals break up rocks. Weathering makes sediments but does not move them away from the original rock. **Erosion and transport** Next, sediments move away from their rock. Together, the breaking of rock into sediments and their movement away, is called erosion. Transport processes move sediments far from the original rock. Water, ice, wind, and gravity can all move sediments. **Deposition** Eventually, sediments stop moving. They settle in one place. This is deposition. Layers of different types of sediment may settle on top of each other. **Compaction and cementation** Over many years deposited sediments join together to make new rocks. This happens by: * compaction - the weight of sediments above squashes together the sediments below or * cementation - another substance sticks the sediments together. **How are sedimentary rocks useful?** There are many types of sedimentary rock. They have different properties and uses. #### Summary Questions 1. Write five correct sentences from the sentence starters and enders. Sentence starters | Sentence enders ------------- | ------------- Weathering......involves the weight of sediment above making sediments below stick together. Limestone is made from shells and skeletons that sank to the bottom of the sea. It is an attractive building material. Erosion... | ...moves sediments far away from the original rock. Transport...| ...breaks rock into smaller pieces. Deposition... | ...is the settling of sediments. Compaction... | ...breaks rock into smaller pieces and moves them away from the original rock. 2. Describe two properties of sedimentary rocks, and explain why they have these properties. 3. Create a flow diagram to explain how sedimentary rocks are formed. ### 4.3 Igneous and metamorphic rocks **Learning objectives** After this topic you will be able to: * compare the ways that igneous and metamorphic rocks form * explain how igneous and metamorphic rocks form. **What type of rock does the picture on the right show?** The rock is basalt. Basalt is an example of an igneous rock. Igneous rock forms when liquid rock cools and freezes. Igneous rock consists of crystals. There are no gaps between the crystals. This explains why igneous rocks are not porous. **How are igneous rocks useful?** Igneous rocks are hard. They are also durable, which means they are difficult to damage. These properties mean that igneous rocks are useful for pavements and underneath railway tracks. **Different sized crystals** Underground, liquid rock is called magma. Granite forms from magma. Underground, the magma cools and freezes slowly. The particles have time to arrange themselves into big crystals. Basalt forms when liquid rock cools and freezes quickly. This happens under the sea, or on the surface of the Earth when volcanoes erupt, for example. On the surface, liquid rock is called lava. There isn't enough time for large crystals to grow so basalt crystals are smaller than granite crystals. You need a hand lens to see them. **What are metamorphic rocks?** The pictures show metamorphic rocks. * Marble * Gneiss * Slate Metamorphic rocks form when heat, high pressure, or both change existing rock. For example: * Marble starts out as limestone. Marble forms when limestone below the Earth's surface heats up. The limestone does not melt, but its particles are rearranged. * Slate starts out as a type of sedimentary rock called mudstone. Slate forms when high pressure underground squashes the mudstone. This squeezes out water, and makes layers of new crystals. **How are metamorphic rocks useful?** Metamorphic rocks are made up of crystals. They are not porous. Marble is not porous. Many people like how it looks. This explains why it is suitable for kitchen worktops. Slate is not porous. It is made up of layers, so it can be split into thin sheets. This is why it makes good roofing tiles. **Granite quarry** Rubislaw Quarry, near Aberdeen, is probably the biggest hole in Europe. Between 1740 and 1971 quarry workers dug 6 million tonnes of granite from the quarry. Calculate the mean mass of granite dug out of the quarry each week during this time period. #### Summary Questions 1. Copy and complete the sentences below, choosing the correct bold words. High pressure underground may change any rock type into **igneous/metamorphic** rock. When liquid rock cools and freezes, **igneous/metamorphic** rock forms. Granite and basalt are examples of **igneous/metamorphic** rocks. Slate and marble are examples of **igneous/metamorphic** rocks. Igneous and metamorphic rocks are **porous/non-porous** because they are made up of **grains/crystals**. Igneous rocks are **hard/soft**. 2. Explain why some igneous rocks have small crystals, and others have bigger crystals. 3. Compare the ways in which igneous and metamorphic rocks form. Include examples in your answer. ### 4.4 The rock cycle **Learning objectives** After this topic you will be able to: * use the rock cycle to explain how the material in rocks is recycled. **Imagine you came back to Earth a million years after your death.** How would the rocks around you be different? All the time, rocks are changing. Weathering breaks down rock. Sediments make new rock. Volcanoes erupt, and their lava freezes. And, deep within the crust, heating and high pressure change rocks of all types. **What is the rock cycle?** Different rock types, and the processes that change one rock type into another, are linked in the rock cycle. The rock cycle