16/04/2015 C3 Chemicals in our Lives – Risks and Benefits W Richards The Weald School (OCR 21 st Century)

16/04/2015 C3.1 – The origins of Minerals

16/04/2015 The Structure of the Earth A thin crust km thick A mantle – has the properties of a solid but it can also flow A core – made of molten nickel and iron. Outer part is liquid and inner part is solid The average density of the Earth is much higher than the crust, so the inner core must be very dense

16/04/2015 Movement of the Lithosphere The Earth ’ s LITHOSPHERE (i.e. the _______) is split up into different sections called ________ plates: These plates are moving apart from each other a few centimetres every _______ due to the ________ currents in the mantle caused by the ________ decay of rocks inside the core. Words – radioactive, crust, convection, tectonic, year

16/04/2015 Plate Movements Oceanic Crust Mantle Magma Earthquakes and volcanic eruptions can be common here Igneous Rock Convection Currents

16/04/2015 Magnetic Patterns in Sea Floor Spreading The Earth ’ s magnetic field swaps poles every million years. The above picture shows those changes recorded over time in rocks on the sea floor and provides evidence for long-term sea floor spreading.

16/04/2015 Continental Drift Look at the coastlines of South America and Africa. I wonder of they used to fit together… Alfred Wegener I ’ m going to call this my Theory of Continental Drift

16/04/2015 Tectonic theory Because of this movement, a lot of the rocks that are in the UK would have originally formed in different climates. Fascinating!

16/04/2015 What are rocks? Rocks are made from a combination of minerals and can be hard or soft depending on how the minerals are arranged. Rocks can be found here… …and here… …and here

16/04/2015 Forming rocks When rocks are transported by a river they are eroded: Rocks can be broken off the side of mountains Rock shape up here Rock shape down here “ Sediment ”

16/04/2015 Sedimentary rocks and salt Limestone Processes like mountain building followed by erosion and sedimentation have led to the formation of valuable resources in the UK, like sedimentary rocks and salt: Rock salt Where deposits of such natural resources were large, chemical industries quickly appeared, for example, this coal mine in Yorkshire:

16/04/2015 Studying Sedimentary Rocks This rock contains fossils, giving useful clues about the development of life Scientists study sedimentary rocks to get useful information about the Earth, such as: This rock contains ripple marks to show where water was present in the past This rock contains shells and other fragments of life

16/04/2015 C3.2 – Where does Salt come from?

16/04/2015Salt Salt is an important substance for many reasons… Flavouring and preservation Treating icy roads Chemical uses

16/04/2015 Ways to get Salt Salt mines – large scale underground mining will produce salt with impurities so its useful for roads but not food. This approach has a rish of mines collapsing or causing subsidence. Water solutions – a solution of salty water (like seawater) can be left so that the water evaporates and the salt crystallizes. This will produce purer salt.

16/04/2015 Government Departments Government departments such as the Department of Health and the Department for Environment, Food and Rural Affairs have a role in food and health, including carrying out risk assessments on foods and advising the public on healthy eating. A lot of statistics point to a link between salt and conditions such as high blood pressure and heart disease.

16/04/2015 C3.3 Why do we need chemicals like alkalis and chlorine?

16/04/2015Alkalis Alkalis are chemicals that have been used for centuries. Some examples: Other uses included making glass and binding dyes to cloth. Alkalis were made from burnt wood or from stale urine!!

16/04/2015 Neutralisation reactions A neutralisation reaction occurs when an acid reacts with an alkali. An alkali is a metal carbonate or metal hydroxide dissolved in water. ACID + ALKALI SALT + WATER Na Cl H H O H Na O H Copy and complete the following reactions: 1)Sodium hydroxide + hydrochloric acid 2)Calcium hydroxide + hydrochloric acid 3)Sodium hydroxide + sulphuric acid 4)Magnesium hydroxide + sulphuric acid

16/04/2015 Reactions of metals carbonates with acid A metal carbonate is an alkaline compound containing a metal, carbon and oxygen. METAL CARBONATE + ACID SALT + CARBON DIOXIDE + WATER Copy and complete the following reactions: 1)Magnesium carbonate + hydrochloric acid 2)Calcium carbonate + hydrochloric acid 3)Sodium carbonate + sulphuric acid Mg H Cl Mg Cl H H H C O O O O O O C

16/04/2015 Making alkalis Large-scale industrialisation caused a shortage of alkalis in the 19 th century, so a new method had to be found: I’m an old scientist. I used to make alkalis from limestone and salt using coal as a fuel. The only problem was that it made a lot of pollution – hydrogen chloride (an acidic gas) and large piles of toxic hydrogen sulfide. What’s the solution? One solution could be to turn the waste products into something useful – for example, oxidation can convert hydrogen chloride into chlorine, which can be used to kill germs and as an ingredient in bleach.

16/04/2015 Chlorine in Drinking Water Since chlorine was introduced in drinking water in the early 1900s the incidences of water-borne diseases has decreased dramatically: However, there other problems caused when chlorine reacts with organic materials in the water.

16/04/2015 Positive electrode Negative electrode Electrolysis of Salt Water Sodium chloride solution (salt water) NaCl (aq) Sodium hydroxide (NaOH (aq) ) – useful for making soaps and manufacture of paper Salt water (e.g. seawater or brine) can be electrolysed using an electric current to produce chlorine and other useful products: Chlorine gas (Cl 2 ) – useful for making bleach and plastics Hydrogen gas (H 2 ) – useful as a potential fuel source or manufacture of HCl

16/04/2015 C3.4 What can we do to make our use of chemicals safe and sustainable?

16/04/2015 Harmful Chemicals There are a large number of industrial chemicals with many widespread uses. The problem is, there can be a lack of evidence that these chemicals might be harmful. Consider the example of asbestos: Asbestos was widely used in buildings but banned in 1986 due to its effects on the respiratory system. There are other chemicals in the environment that can persist for many years and be carried over large distances. Eek!

16/04/2015 Uses of PVC Poly(chloroethene), PVC PVC stands for polyvinylchloride and has many uses: PVC contains carbon, hydrogen and chlorine. The problem with PVC is that it has “plasticizers” in it that modify its properties and make it stronger – these plasticizers can leak out of the PVC into the environment.

16/04/2015 Life Cycle Assessments (LCAs) Step 1: Manufacture What resources are needed? What effect will this have on the environment? Step 2: Use How much energy will be needed? What is the effect on the environment? Step 3: Disposal How is the product disposed of? What is the effect on the environment?