EXPERIMENT 1.4 S C I E N C E. Making silver. 14 Heinemann Science Links 4. Aim To observe the formation of pure silver by a chemical reaction.

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1 The reactants are zinc and The products are hydrogen and hydrochloric acid. They contain: zinc chloride. They contain: 2 H, 2 Cl and 1 Zn atoms. 2 H, 2 Cl and 1 Zn atoms. Zn H H H Cl Zn H Cl Cl Cl S C I E N C E Making silver Aim To observe the formation of pure silver by a chemical reaction. 15 cm of copper wire (Cu, sanded or scraped to remove outer layer 5 ml of silver nitrate solution (AgNO 3 pencil test-tube Safety Contact with silver nitrate can stain skin and clothing. Wear laboratory coats and eye protection during this experiment and report any spills to your teacher immediately. Complete an RAS before you start this activity. Alternatively, this experiment could be a teacher demonstration. Method 1. Pour 5 ml of silver nitrate solution into a test-tube. 2. Make a coil of copper wire by winding it around a pencil. 3. Place the copper coil into the silver nitrate solution. 4. Observe the reaction. 1. Describe the crystals formed. What could they consist of? 2. What happens to the solution? What causes this change? 3. Write a word equation for this reaction. Evaluation Are you satisfied that you know what the products of this chemical reaction are? Did you encounter any problems in completing your experiment? How could you overcome these problems? Extension EXPERIMENT 1.4 copper wire test-tube silver nitrate solution Figure 1.15 The experimental set-up to make pure silver. Redesign this experiment so that the masses of the reactants and the products can be compared. Always use the minimum amount of reactants. Do you think the mass of the test-tube and its contents will vary over the course of the reaction? Discuss your ideas with your teacher. Complete an RAS before you carry out your experiment.! 14 Heinemann Science Links 4

2 Balancing chemical equations Did you out that when copper and silver nitrate reacted in the last experiment, crystals of silver and a solution of copper nitrate were created? This reaction can be expressed as a word equation: copper + silver nitrate silver + copper nitrate You can replace each part of the word equation by a chemical formula: Cu + AgNO 3 Ag + Cu(NO 3 2 Looking at both sides of this equation, you can see that it is not balanced. Although the silver and copper are balanced, the nitrate ion (NO 3 is not. To balance this equation, you need to add numbers in front of some of the chemical formulae. You could start by putting a 2 in front of the AgNO 3 to balance the NO 3 ions, but that would cause the Ag + ions to be unbalanced. Another 2 is therefore needed in front of the Ag. After this trial and error, you have now balanced the equation: Cu + 2AgNO 3 2Ag + Cu(NO 3 2 Checking the number of atoms shows that there is one Cu, two Ag, two N and six O atoms on both sides of the equation. An equation cannot be balanced by changing any of the chemical formulae. It can only be balanced by putting numbers in front of a formula. Moreover, the balanced equation includes the symbols that show the state of matter for each reactant and product. Cu(s + 2AgNO 3 (aq 2Ag(s + Cu(NO 3 2 (aq Cu AgNO3 AgNO3 Ag Cu(NO32 Ag scifile Synchrotron sources can be used to look deep within the crystalline structure of solids to a level we have never before seen. By observing patterns that the intense beam of high energy synchrotron X-rays make as they scatter from a source, we are given information about the inner structure of the source being tested. One pharmaceutical company put synchrotron science to good use recently. The company successfully argued that their own patented top-selling drug had been copied by a generic manufacturer. Analysis using synchrotron light revealed that the crystalline structure of the patented drug and the generic version were so identical that the manufacturer producing the generic version was ruled to have been selling their drug illegally. chapter chemical interactions 01 Figure 1.16 A balanced equation. 15

3 hydrogen oxygen Rules for writing balanced chemical equations water electrodes power supply Figure 1.17 This apparatus can be used to decompose water into hydrogen and oxygen gas. scifile + Atoms and molecules are so small that they can t easily be handled singly or in small numbers. When bundling atoms or molecules, scientists use an amount called a mole. A mole is a very large number of atoms. For example, 1 mole of water has a mass of 18.0 g and consists of ( molecules. It s handy that you don t order soft drink by the mole! 1 Write a word equation for the chemical reaction. 2 Write a formula for each of the reactants and products. (Refer to Table 1.1 if necessary. 3 Use numbers in front of the formulae to balance the numbers of atoms on each side of the equation. (It helps to try to balance the more complex compounds first. 4 Check each type of atom to make sure that the equation is balanced. 5 Include the symbols for the states of matter for the substances involved. You might find it useful to use a table to write and balance chemical equations. For example, we could consider the reaction that occurs when electricity is passed through water, as shown in Figure The electric current makes the water decompose into the products hydrogen and oxygen gas. Table 1.5 shows how we can balance the chemical equation for this reaction. Before you read it, have a go yourself! Table 1.5 Balancing a chemical equation Reactants Products Word equation water hydrogen + oxygen Chemical formulae H 2 O H 2 + O 2 Use numbers in front of formulae to balance atoms 2H 2 O 2H 2 + O 2 Checking 4 H, 2 O 4 H, 2 O Balanced equation 2H 2 O(l 2H 2 (g + O 2 (g S C I E N C E Activity 1.5 The X factor 1. Working with a partner, examine the following three chemical equations. In each case, see if you can choose the correct value for x (from the options in brackets to balance each equation. (a H 2 (g + Cl 2 (g xhcl(g (x = 2, 3 or 4 (b AgNO 3 (aq + NaCl(aq xagcl(s + NaNO 3 (aq (x = 1, 2 or 3 (c xnaoh(aq + H 2 SO 4 (aq Na 2 SO 4 (aq + xh 2 O(l (x = 1, 2 or 4 2. In answering part (a above, explain why you could certainly not rewrite the final product to be H 2 Cl 2. Draw a diagram to assist your explanation of why answering in this way could cause your science teacher to pull their hair out! 3. Complete a PMI chart for this activity. 16 Heinemann Science Links 4

4 S C I E N C E Swapping ions Aim To observe a chemical reaction and to write a balanced chemical equation. barium nitrate solution (Ba(NO 3 2 copper sulfate solution (CuSO 4 test-tubes Safety Barium nitrate and copper sulfate are poisonous and can be harmful if inhaled. Handle them with care, and wash your hands thoroughly after using them. Complete an RAS before you start this activity. Method 1. Pour about 1 cm depth of barium nitrate solution into one test-tube and about 1 cm depth of copper sulfate solution into the other. 2. Pour the contents of the test-tubes into a third test-tube. 3. Allow the mixture to settle. 4. Record your observations. In this reaction, the ions from one substance combine with the ions of the other to form a solid. 1. List which ions are present in the reactants used in this experiment. 2. Now write a word equation for this reaction, showing how the ions swap from one substance to the other. 3. What product remains dissolved in the clear solution? How could you obtain a solid product from this solution? 4. Write a balanced chemical equation for this reaction. Evaluation barium nitrate test-tube barium sulfate EXPERIMENT 1.6 test-tube Can you be certain that your experiment was a success? Suggest a way that you could verify your result as correct and not the product of unclean glassware or contaminated chemical reactants.! copper sulfate precipitate Figure 1.18 A precipitate of barium sulfate is formed in this reaction. chapter chemical interactions 01 questions What is the law of conservation of mass? Write this law in a simple form aimed at a Year 7 student. 2. Lauren conducts an experiment where she weighs four icy-pole sticks, burns them in a metal tin and carefully weighs the ashes that result. How will the mass of the ashes compare with that of the original ice-cream sticks? Explain the difference in the two masses. 3. Write a word equation and a formula equation for each of the following. (a Silver nitrate and sodium chloride solutions were added together and solid silver chloride formed, as well as a solution of sodium nitrate. (b If solid copper(ii carbonate is heated, carbon dioxide gas is given off and copper(ii oxide remains. 17

5 4. Giovanni takes a piece of magnesium ribbon, weighs it and heats it in a crucible over a Bunsen burner, as shown in Figure The product is a white powder, which has a mass greater than the original magnesium metal. Where has the extra mass come from? Write a word equation for this reaction. 8. What does Figure 1.20 tell us about the total mass of reactants and products at any time during a chemical reaction? reactants crucible and lid magnesium ribbon gauze mat Mass tripod Figure 1.19 Giovanni s experimental set-up. Bunsen burner 5. Which of the following reactions are not balanced? Explain why. (a H 2 (g + O 2 (g H 2 O(l (b N 2 (g + 3H 2 (g NH 3 (g (c Mg(s + 2HCl(aq MgCl 2 (aq + H 2 (g (d Mg(s + O 2 (g MgO(s 6. You are a tiny atom of barium. Happy with your friends, the hydroxides, you undergo a saga of heart-wrenching separation, but eventually find soul mates once more. Write a story or role-play about your ordeal. CuCl 2 (aq + Ba(OH 2 (aq BaCl 2 (aq + Cu(OH 2 (s 7. Using the rules that you have learnt, balance the following equations. (a Fe(s + HCl(aq FeCl 2 (s + H 2 (g (b Na(s + Cl 2 (g NaCl(s (c CH 4 (g + O 2 (g CO 2 (g + H 2 O(g (d CO(g + O 2 (g CO 2 (g products Time Figure 1.20 This graph indicates how the masses of the reactants and products change during a chemical reaction. 9. Write balanced equations for each of the following reactions. (a If a mixture of carbon and copper oxide is heated, solid copper is produced as well as carbon dioxide. (b Sulfur trioxide can be produced by burning sulfur dioxide in oxygen. (c Water, ammonia (NH 3 and carbon dioxide are produced when solid ammonium carbonate decomposes. (d Cane sugar (C 12 H 22 O 11 can be decomposed to give water and carbon. 10. Balance these equations and write sentence descriptions for each reaction. (a NaOH(aq + H 2 SO 4 (aq Na 2 SO 4 (aq + H 2 O(l (b CuCO 3 (s + HCl(aq CuCl 2 (aq + H 2 O(l + CO 2 (g 11. Using a format of your choice, design a presentation of rules for writing balanced chemical equations, along with an example. Deliver your presentation to your class with illustrations. It could be presented orally, as a written document or by electronic media. 18 Heinemann Science Links 4

6 1.3 Types of chemical reactions There are various ways that chemical reactions can be grouped together. Some reactions use up energy and some give off energy. Some reactions have a larger number of reactants than products while others have more products than reactants. Other reactions have the same number of reactants as products but ions are swapped around. Your understanding of chemical equations will help you to be able to identify some different types of reactions. S C I E N C E Pulling compounds apart Safety To avoid bromothymol blue being sucked back into the first test-tube, ensure that once a colour change has been observed, the bromothymol blue test-tube is removed before the heating flame is turned off. Complete an RAS before you start this activity. Aim To observe a chemical reaction in which carbon dioxide gas is produced. copper carbonate powder (CuCO 3 2 test-tubes delivery tube clamp Method bromothymol blue one-holed stopper retort stand Bunsen burner 1. Set up the apparatus shown in Figure 1.21, with 1 2 cm depth of copper carbonate in one test-tube and 4 5 cm depth of bromothymol blue in the other. 2. Carefully heat the copper carbonate and note any changes you observe. 3. Allow any gas given off to bubble through the bromothymol blue. 4. Once a colour change is observed in the bromothymol blue, remove this test-tube from the delivery tube. 5. Turn off the Bunsen burner and record your observations. copper carbonate Bunsen burner EXPERIMENT 1.7 retort stand Figure 1.21 The experimental set-up.! bromothymol blue chapter chemical interactions Given that bromothymol blue turns yellow in the presence of carbon dioxide gas, was the gas given off carbon dioxide? 2. What changes in the copper carbonate could be observed? 3. What elements could the remaining solid consist of? 4. Why was the test-tube of bromothymol blue removed before the heating flame was turned off? Explain what could have happened, and why. 19

7 Conclusion 1. Write a statement that summarises the chemical reaction that has occurred. 2. Explain how you can use your knowledge of chemical reactions to predict the make-up of the solid that is left over. If there was no such thing as the law of conservation of mass, do you think this would be possible? Evaluation Did you have any problems with observing or recording changes? If so, suggest improvements in the method to overcome these problems. Extension In a fume cupboard and using protective clothing, your teacher may take some of the remaining solid and add concentrated sulfuric acid. Try to explain the changes that are observed. scif ile A sparkler is made up of a mixture of chemicals that is coated on a wire. The sparkler is designed to burn relatively slowly, compared with a firecracker that explodes rapidly. Some metals, such as aluminium, iron, zinc or magnesium, can be used to produce bright sparks. A fuel is required, like sulfur or charcoal, and an oxidiser is used to produce oxygen to keep the sparkler burning. Such an oxidiser undergoes a decomposition reaction to produce oxygen. One oxidiser that may be used is potassium nitrate. This decomposes as follows: Decomposition reactions During a decomposition reaction, a single substance is broken down into simpler compounds or elements. There is one reacting substance and two or more product substances. In 1.7 you conducted a decomposition reaction in which copper carbonate decomposed to release carbon dioxide and left the solid copper oxide: copper carbonate CuCO3(s heat heat copper oxide + carbon dioxide CuO(s + CO2(g 2KNO3 2KNO + O2 The oxygen produced here keeps that sparkler sparkling! Figure Sparklers consist of a chemical mixture that is coated to a stick that is ignited. Part of this mixture consists of an oxidiser that decomposes to produce oxygen. 20 C1_SI.indd 20 Heinemann Science Link s 4 19/9/06 4:14:04 PM

8 S C I E N C E Cooking with gas! In this experiment you will explore a common decomposition reaction that has great importance without it, our cakes would not rise! In the kitchen, ingredients are used instead of reactants, a recipe instead of a method, and the products are hopefully referred to as a culinary delight! Warning If possible, carry out this experiment in a home economics kitchen. If prepared in the laboratory, these scones should not be eaten as equipment could be contaminated from previous experiments. Safety Complete an RAS before you start this activity. Heating apparatus should be used carefully to avoid burns. Aim To observe the results of chemical changes that take place when cooking baked foods, like scones and cakes. 150 ml plain flour 30 ml milk bicarbonate of soda (sodium hydrogen carbonate or sodium bicarbonate three 100 ml beakers stirring rod metal lid or aluminium pie tray electric hotplate or Bunsen burner with tripod and gauze mat Method EXPERIMENT In each of the three beakers, carefully measure equal quantities of plain flour to the 50 ml mark on the beaker. 2. To the first beaker add, while stirring, a small quantity of tap-water at a time until the flour just holds together. The mixture should be able to be pressed together into a small scone. 3. To the second beaker, add approximately half a teaspoon of bicarbonate of soda and enough water to produce a scone similar to the first. 4. To the third beaker, add approximately half a teaspoon of bicarbonate of soda and enough milk to make a small scone. 5. Ensure that each scone contains a similar amount of liquid. Press the scone down until it is no more than 1 cm thick. Make each scone a similar size and shape. 6. Place the scones on the metal lid on top of an electric hotplate or over a Bunsen burner, and heat the scone very gently for about 15 minutes. (Alternatively use an oven if one is available. 7. Remove the scones from the heat and allow them to cool. 8. Record your observations of the appearance of the scones after cooking. Once cooled, carefully break each one open and note the appearance inside the scones.! chapter chemical interactions Which scone is the smallest? What do you note about its texture inside that has caused it to be the smallest? 2. Which scone is the largest? What do you note about its texture inside that has caused it to be the largest? 3. Which scone appears most edible? Why? 4. Given that the chemical formula of bicarbonate of soda is NaHCO 3 and that this decomposes to carbon dioxide, water and sodium carbonate (Na 2 CO 3, write a balanced chemical equation for this decomposition reaction. 21

9 Conclusion Comment on how the decomposition of bicarbonate of soda assists in making lighter scones. Evaluation Did you feel like a culinary success? List any problems that you needed to overcome in your cooking experience. If you were to repeat this activity, would you make any changes to your method? Explain. S C I E N C E On the rise Using 1.8 as a starting point, design an experimental investigation into ways of making baked goods rise. Cooks use other acids besides milk to react with sodium hydrogen carbonate and produce carbon dioxide. These include cream of tartar (tartaric acid and citric acid. You could start with some library research into the chemical structure of these acids, where they come from and how they are used. Then design an experimental investigation using various amounts of acids and sodium hydrogen carbonate to find the best conditions for making baked items and get cooking! Include an RAS in your design. Write a scientific report on your or create a presentation to reveal your findings to your class. i n v e st i g at i o n 1.9 Figure Too much of one reactant can have unexpected results! Synthesis reactions Synthesis reactions are sometimes also known as combination reactions because they involve several substances combining to give a new substance. There are more reacting substances than product substances. Most metals, if exposed to air, will react with oxygen: zinc + oxygen zinc oxide 2Zn(s + O2(g 2ZnO(s This is a synthesis reaction. Two substances (zinc and oxygen combine to give one new substance (zinc oxide. Coal (carbon also reacts with oxygen during combustion (burning. Not only is carbon dioxide produced, but energy is also released carbon + oxygen carbon dioxide C(s + O2(g CO2(g Figure Living things make use of synthesis reactions. Plants take simple substances, such as water, nitrogen, carbon dioxide and oxygen, and produce large complex molecules, such as sugars, other carbohydrates and proteins which then can be used as food by animals. 22 C1_SI.indd 22 Heinemann Science Link s 4 19/9/06 4:14:14 PM

10 Single replacement reactions A single replacement reaction involves removing one element or group of elements and replacing them with another element or group of elements. In 1.4 you observed the silver crystals formed during a single replacement reaction: copper + silver nitrate silver + copper nitrate Cu(s + 2AgNO3(aq 2Ag(s + Cu(NO32(aq The silver in silver nitrate is replaced by copper. Copper nitrate is formed as well as crystals of pure silver. Sometimes when two compounds react, they totally swap ions. Two new compounds are formed. Instead of one element or group of elements being replaced, two lots are replaced. This is called a double replacement reaction. You observed this type of reaction in 1.6. This is called swapping ions because it is a double replacement reaction: copper sulfate + barium nitrate copper nitrate + barium sulfate Figure Magnesium metal burns in oxygen with an intense white flame. This is an example of a synthesis reaction. Can you out an equation for this reaction? Ba(NO32 (aq + CuSO4(aq BaSO4(s + Cu(NO32(aq In this experiment, an insoluble compound (BaSO4 was formed and appeared as a solid that settled out of solution. The insoluble barium sulfate is known as a precipitate. Reactions that have precipitates as their products are known as precipitation reactions. chemical interactions Double replacement reactions chapter 01 Figure Now that you know what a single replacement reaction is, can you guess what a double replacement reaction is? The reaction between potassium iodide solution and lead nitrate solution is a spectacular example of a double replacement reaction. S C I E N C E Identifying reactions Aim To observe and identify some different types of chemical reactions. EX P E R I M E N T 1.1 0! Part A: Making chalk two 250 ml beakers distilled water retort stand and ring filter funnel filter paper stirring rod 2.5 g sodium carbonate powder (Na2CO3 20 ml of 1.0 M calcium chloride solution (CaCl2 23 C1_SI.indd 23 19/9/06 4:14:31 PM

11 Method 1. Place the sodium carbonate into a beaker and dissolve it in about 20 ml of distilled water. 2. To this solution add 20 ml of calcium chloride solution. Mix the solutions by swirling the beaker. 3. Filter the mixture using the apparatus in Figure Pour two lots of 10 ml of distilled water over the product to wash it. 5. Place the filter paper in a beaker to dry. retort stand filter paper filter funnel ring beaker 1. Describe the chalk produced during this experiment. 2. If chalk is calcium carbonate, what other product is formed? 3. Write a word equation and balanced equation for this reaction. 4. What type of reaction is this? Part B: A more complex reaction Sometimes a reaction may occur with a couple of stages, incorporating a combination of the reaction types that we have studied. This is such a reaction. Safety Copper carbonate is a poison. Treat it with care and wash your hands thoroughly after using it. two test-tubes test-tube rack rubber stopper and delivery tube copper carbonate powder (CuCO 3 2 M sulfuric acid (H 2 SO 4 limewater (Ca(OH 2 Method 1. Pour 4 5 cm depth of limewater into a test-tube. 2. In the second test-tube, place 1 2 cm depth of copper carbonate and add 5 ml of sulfuric acid. 3. Quickly insert the rubber stopper and delivery tube into this second test-tube, and direct the delivery tube into the limewater that you poured into the first test-tube. 4. Record any changes to the limewater. 1. This reaction occurs in two stages. Write the reactant down for the chemicals that were added together in the second test-tube. Looking at these reactants, write down the products you would expect to find if a double replacement reaction occurred. Can you balance this equation? 2. One of the products of this reaction is hydrogen carbonate. Remembering back to your in making scones in 1.8, what type of reaction would you expect to occur now? 3. Given that limewater turns cloudy in the presence of carbon dioxide gas, did you detect the presence of carbon dioxide gas in the limewater? 4. What other products would you expect to form in this reaction? 5. Write a balanced chemical equation for this chemical reaction. Evaluation Figure 1.27 The experimental set-up for making chalk. Were you satisfied with the way you and your partner completed this experiment? List any stages that could have been dangerous without full concentration. Make a list of possible hazards and ways to avoid each one. 24 Heinemann Science Links 4