Chemical Reactions and Essential Resources

Nothing arrives ready to use

Look at the list of things this topic covers and it reads like four separate subjects. Equations. Acids and bases. Metals and how we get them out of the ground. Water, air and sustainability. Most students revise them as four, and never notice they are one. ⚠️⚠️ NOT ONE THING IN THAT LIST ARRIVES ON EARTH READY TO USE. There is no iron lying about as iron. It is locked into rock, joined to oxygen. There is no drinkable water in the sea, or in a river. The gases we need from the air arrive mixed together with everything else. ⭐ EVERY USEFUL MATERIAL WE HAVE IS ALREADY JOINED TO SOMETHING, AND ALL OF THIS TOPIC IS THE BUSINESS OF GETTING IT APART AGAIN. Once you see it that way, one question runs through the whole unit: what will the separation cost? ⭐⭐ AND CHEMISTRY HAS AN ANSWER, WHICH IS WHY THE REACTIVITY SERIES SITS IN THE SAME TOPIC AS THE RESOURCES. THE SERIES IS A PRICE LIST. A reactive metal is one that combines eagerly and holds on hard. So the more reactive it is, the more determined it was to join up in the first place, and the more energy you have to spend forcing it back apart. ⚠️ THAT IS WHY SOME METALS COME OUT WITH CARBON AND HEAT, AND OTHERS NEED ELECTRICITY. IT IS NOT AN ARBITRARY RULE. IT IS A BILL. And here is the part that makes the rest of the unit fall into place. ⭐ NEUTRALISATION RUNS THE OTHER WAY. An acid and a base put together make a salt and water, readily, and giving out heat. ⚠️ THAT IS THE DOWNHILL DIRECTION. IT COSTS NOTHING AND HAPPENS BY ITSELF. ⭐⭐ WHICH IS EXACTLY WHY SEPARATION IS EXPENSIVE. THINGS COMBINE BECAUSE COMBINING IS DOWNHILL, AND EVERY RESOURCE WE WANT IS ALREADY SITTING AT THE BOTTOM OF THAT HILL. One question to carry through the rest of this module: is this reaction putting things together or pulling them apart, and which direction is uphill?

Three resources, one problem

The same problem three times over. Each column is a thing we need, the state it actually arrives in, and what getting it out costs.

Tap what the price-list idea claims

Tap the TWO statements that follow from every useful resource arriving already combined.

• How reactive a metal is predicts not only how it is extracted but how much that extraction costs
• Combining is the direction things go by themselves, which is why separating them has to be paid for
• Most useful materials can be found in a pure state if you look in the right place
• Whether a metal is extracted with carbon or with electricity is a matter of which is cheaper to build

Why one metal needs electricity

You may already know that some metals are extracted by heating with carbon while others need electrolysis. What does the price-list idea add to that rule?

• The reason behind it: a more reactive metal combined more eagerly and holds on harder, so more energy is needed to reverse it, and carbon is simply not a strong enough pull for the most reactive ones
• That the rule applies in the opposite order from the one usually taught
• That electrolysis is chosen because it is the cheaper of the two methods
• Nothing beyond the rule itself, which is all the exam requires

Five terms the whole topic leans on

Five terms, each defined by what it is. What each one costs, and which direction it runs in, is the work of the steps that follow.

Match each resource to what separating it costs

Two that follow from separation being uphill

Select the TWO statements that follow from combining being the direction things go by themselves.

• Neutralisation happens readily and gives out heat, which is what you expect of a reaction running downhill
• Recycling a metal is worth more than it first appears, because it skips the separation that was the expensive part
• Metals are hard to extract mainly because their ores are rare
• Potable water is water that has been made chemically pure

The long question, and the plan this topic gives you

You already know that this specification puts unusual weight on handling numbers, and that working set out line by line earns marks even when the final figure slips. ⚠️ THERE IS A SECOND THING ABOUT YOUR PAPERS THAT MATTERS JUST AS MUCH, AND IT IS NOT ABOUT NUMBERS AT ALL. ⚠️⚠️ UNITS 1 AND 2 CARRY A LONGER EXTENDED-WRITING QUESTION, THE QER QUESTION, AND IT IS MARKED ON HOW WELL YOU COMMUNICATE AS WELL AS ON THE CHEMISTRY. Organisation, clear sentences and correctly spelled chemical terms all count. ⭐ YOU CAN KNOW THE RIGHT CHEMISTRY AND STILL LOSE MARKS BY DELIVERING IT AS A HEAP. ⭐⭐ AND THIS TOPIC HANDS YOU A PLAN FOR FREE, BECAUSE THE SEPARATION CHAIN IS ALREADY AN ORDER. SAY WHAT STATE THE RESOURCE ACTUALLY ARRIVES IN. Joined to what, mixed with what. SAY WHAT HAS TO BE REMOVED, and whether it is merely mixed in or chemically joined, because those cost very different amounts. SAY WHICH METHOD WILL DO IT AND WHY THAT ONE. ⚠️ NAME THE REASON, NOT JUST THE METHOD. "Electrolysis is used" is a fact; "electrolysis is used because carbon cannot remove oxygen from a metal that holds it more tightly than carbon does" is an explanation. THEN GIVE THE CONSEQUENCE. What it costs, and what follows from that cost. Three or four paragraphs in an order the marker can follow, and the organisation marks are earned before the chemistry is even judged. ⚠️ TWO HABITS THAT COST MARKS ON THIS PAPER IN PARTICULAR. ⚠️ THE FIRST IS WRITING A WORD EQUATION WHERE A BALANCED ONE WAS ASKED FOR, OR LEAVING ONE UNBALANCED. An equation is the accounting for the separation: it shows that every atom that went in came out somewhere. An unbalanced one says atoms were created or destroyed, which is why it earns nothing. ⚠️ AND THE SECOND IS REACHING FOR A FIGURE YOU ARE NOT SURE OF. A temperature, an energy saving, a percentage: if you are not certain, explain the mechanism instead. The mechanism is what is being marked.

Why recycling one metal beats recycling another

Recycling usually arrives in a lesson as something you ought to do. Here it is arithmetic, and the arithmetic is the interesting part. Follow two metals from the ground and the difference does itself. THE FIRST METAL SITS BELOW CARBON IN THE SERIES. It is dug out joined to oxygen, heated hard with carbon, and the carbon takes the oxygen away. That costs fuel and a great deal of heat, and it is not cheap. ⭐ BUT IT IS THE CHEAPER OF THE TWO ROUTES, BECAUSE CARBON IS DOING THE WORK. THE SECOND METAL SITS ABOVE CARBON. ⚠️ CARBON CANNOT TOUCH IT. IT HOLDS ITS OXYGEN MORE TIGHTLY THAN CARBON DOES, SO HEATING IT WITH CARBON ACHIEVES NOTHING AT ALL. The only thing that will pull it apart is an electric current, run through the molten compound continuously. ⭐ AND THAT IS AN ENORMOUS AMOUNT OF ENERGY, SPENT FOR AS LONG AS THE PROCESS RUNS. Now throw both metals away, and dig them both up again. You pay both bills again. But collect them instead, and melt them down. ⭐⭐ MELTING A METAL THAT IS ALREADY A METAL DOES NOT SEPARATE ANYTHING. IT ONLY CHANGES ITS SHAPE. You are paying for heat, and nothing else. ⚠️ THE ENTIRE SEPARATION STEP, WHICH WAS THE EXPENSIVE PART, IS SKIPPED. ⭐ SO THE SAVING FROM RECYCLING IS NOT THE SAME FOR EVERY METAL. IT IS LARGEST FOR THE METALS THAT WERE HARDEST TO GET APART IN THE FIRST PLACE. Recycling the one that needed an electric current avoids far more than recycling the one that only needed carbon. ⚠️ AND NOTICE WHAT THAT ARGUMENT DID NOT NEED. IT NEEDED NO FIGURES. It follows from where the two metals sit in the series, which you already know. The same reasoning runs through the rest of the unit. Cleaning a river is cheaper than treating the sea, because floating solids are only mixed in while salt is chemically joined. And separating a gas from the air is cheaper than breaking a compound apart, for the same reason. ⭐ IN EVERY CASE THE QUESTION IS THE SAME ONE: HOW TIGHTLY IS THE THING YOU WANT BEING HELD, AND BY WHAT?

Order how to work out what it will cost

Put these six steps into the order you would follow to decide how a resource must be separated and what that will cost.

• Establish what state the resource actually arrives in
• Decide whether the unwanted material is merely mixed in or chemically joined
• If it is joined, work out how tightly, using position in the reactivity series
• Choose the cheapest method strong enough to break that hold
• State the energy cost that method carries
• Ask whether collecting and reusing the material would skip that cost entirely

Build the sentence that names the reason

The difference between a fact and an explanation is one clause. Assemble it.

The separation run

Five questions on what it costs to pull things apart. Three lives.

Complete the reactions and resources facts

A rock containing enough of a metal compound to be worth extracting from is an _____. The use of an electric current to break a compound down into simpler substances is _____. The reaction of an acid with a base to produce a salt and water is _____. Water that is safe to drink, which is not the same as chemically pure water, is _____.

Three answers to strengthen

Three student answers on reactions and resources. In each case the mark is in the reason, not the verdict.

• An answer states, correctly, that one metal is extracted with carbon and another by electrolysis, and stops there. Why does it score poorly?
• Asked why recycling metals matters, a student writes that it saves resources and is better for the environment. How would you strengthen it?
• A student writes that potable water is water that has been made pure. What needs correcting?

Explain what separation costs

Two metals are both found joined to oxygen, but one sits above carbon in the reactivity series and the other below it. Explain how each is obtained, why the methods differ, and what that means for recycling them.

• Open by saying what state each metal actually arrives in, rather than starting with the method
• Explain how each is separated, and name the reason the method works rather than only the method
• Explain why carbon cannot be used on the metal above it in the series
• Compare the energy cost of the two routes, and say which is the more expensive and why
• Explain why recycling saves more for one of these metals than for the other
• Avoid any figure you are not certain of, and make sure any equation you write is balanced