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Name: ___Teacher key____ Class Period: _______ Due Date: ______ Unit 2 – What are we made of? Unit 2.2 Test Review TEKS covered: 8.5D recognize that chemical formulas are used to identify substances and determine the number of atoms of each element in chemical formulas containing substances 8.5F recognize whether a chemical equation containing coefficients is balanced or not and how that relates to the law of conservation of mass 8.5E investigate how evidence of chemical reactions indicate that new substances with different properties are formed 7.6A identify that organic compounds contain carbon, hydrogen, oxygen, phosphorus, nitrogen or sulfur 7.6B distinguish between physical and chemical changes in matter Answer the following questions: 1. Above is the chemical equation for photosynthesis. a. Circle the coefficients. b. Put a square around the subscripts. c. How many elements are involved in the equation for photosynthesis? 3 d. What are the elements involved in the equation for photosynthesis? Carbon, Hydrogen, Oxygen e. What are the compounds involved in the equation for photosynthesis? C6H12O6, CO2, H2O f. How many atoms of O are there in 6H2O? 6 g. What are the reactants in the equation for photosynthesis? CO2, H2O h. What are the products in the equation for photosynthesis? C6H12O6, O2 2. What does the Law of Conservation of Mass state? Mass is neither created nor destroyed during a chemical reaction 3. How does the Law of Conservation of Mass impact the balancing of chemical equations? The Law of Conservation of Mass means that there are the same number and type of atoms on the reactant side as there are on the product side, creating a balanced equation. 4. Explain what is happening with the mass and matter in a chemical equation. Matter is conserved or destroyed) Mass is conserved or destroyed) type of atoms does not change (Nothing is created amount of atoms cannot change (Nothing is created 5. Write if each equation demonstrates or does not demonstrate the Conservation of Mass. Then explain why is does or does not demonstrate it. Reaction 1 SnO2 + H2 → Sn + 2H2O 2 NH3 + HCl 3 2Rb + P 4 2C + 2SO2 NH4Cl Rb3P CS2 + Demonstrates or Does not Demonstrate Does not demonstrate Demonstrates Does not demonstrate Does not Why? There are more hydrogen atoms in the product than the reactant, so mass is unbalanced All types and amounts of atoms are the same in the reactants and products (mass and matter are balanced) There are more Rb atoms in the products than the reactants, so mass is unbalanced There is a new element(or type of 2HO2 demonstrate atom) on the product side, so matter is unbalanced 6. In this chemical formula, 7H2OSP3 a. Which element has the greatest number of atoms? ____P___ b. What is the number of elements it has? __4_ 7. List each element, and how many of each in the substance 7H2OSP3 ____ hydrogen – 14; O – oxygen – 7; S – Sulfur – 7, P - Phosphorus_21__ H- 8. Complete the chart below. In the “Evidence: How do you know” column, explain how you know that the equation is a balanced or not balanced one. Equation 2NaOH + H2CO3 H2O Na2CO3 + N2 + H2 → NH3 4FeS2 + 11O2 Balanced or Not Balanced Not Balanced Not Balanced 2Fe2O3 + 8SO2 3Fe + 4H2O → Fe3O4 + 4H2 Balanced Balanced Evidence: How do you know? There are 4 H atoms in the reactant and only 2 in the product and there are more O atoms in the reactant than in the product There are more N atoms in the reactant than the product and there are more hydrogen atoms in the product than the reactant All types and amounts of atoms are the same in the reactants and products All types and amounts of atoms are the same in the reactants and products O H Pa O O O H H Write the chemical formula for the substance above. ____ H3PO4 9. Draw a model of H2O2 and 2OH in the table below. Model H H O O Atom Count H=2 O= 2 H=2 H O H O O= 2 Are they, H2O2 and 2OH, the same substance? __No___ Explain your answer: No they are not the same substance even though they have the same amount and type of atoms. H2O2 is one molecule of Hydrogen Peroxide that has all of its atoms bonded together. Whereas, 2OH is two molecules of OH bonded together. 10. Label the diagram with the names of each part or step: Yields Reactants Na Products NaO Coefficient Subscripts 11. What do subscripts in chemical formulas tell you? The number of atoms of each element that are in the formula 12. What do coefficients in chemical formulas tell you? The number of molecules of a compound 13. What are the main six indicators/evidence that a chemical reaction has occurred? Precipitate forms Gas is formed Light is produced Temperature change Odor change Color change (sometimes 14. Explain why a color change when two or more substances are mixed together, does not always indicate a chemical change. Color change can also be a physical change - for example, mixing kool-aid in water. It is an expected color change. It is a chemical change only when it is unexpected- for example mixing two clear liquids and having the substance turn blue. 15. In a chemical reaction, what happens to the elements? Elements that are combined chemically go through a reaction and are rearranged into new substances 16. 17. A chemical change produces a new ____substance______ whose properties are ____different____compared to the properties of the reactants. Some students conducted an investigation in which they added four different solid substances to separate beakers of water. They stirred the mixtures for one minute and then recorded their answers in this data table: Which substance most likely caused a new substance to be formed when mixed with water? Explain why you chose your substance. Substance 2, bubbles were formed. This is evidence of a probable chemical reaction 18. How many atoms are represented in this formula? Write your answer on the blank. P4S3 = ___ There are 4 P, 3 S, so 7 atoms in all 19. What is an endothermic reaction? A chemical reaction that absorbs or uses energy, usually in the form of heat (temperature drops) 20. What is an exothermic reaction? A chemical reaction that gives off or expels energy, usually in the form of heat (temperature increases) 21. Look at the graphs. Explain what each graph is representing and how the lines show energy changes. Endothermic: Left graph – shows that the energy is being absorbed – when you look at the data line, the products have more energy than the initial reactants Exothermic: Right graph – shows that the energy is being released – when you look at the data line, the products have less energy than the initial reactants 22. A student mixes two unknown substances together and observes what happens. What evidence is shown that a chemical reaction may have occurred? Two liquids were combined and in the second picture solid particles are seen. The is a precipitate that has formed from the mixing of two liquids 23. How do you know that when iron is exposed to air, the result is a chemical reaction? When iron is exposed to air (or water for that matter) it reacts with the oxygen molecules. This reaction has a new substance as the product, known as rust. Chemists call it iron oxide or ferric oxide. (Fe2O3) 24. Which equation shows that the total mass during a chemical reaction stays the same? Circle the correct one. 2Na + 2H20 NaOH + H2 H2 + O2 H2O Mg + Cl2 MgCl2 25. In a chemical reaction, the elements and numbers of each atom remain the same. If this true, what must also be true about the mass (grams)? The mass must also be the same on both sides of the chemical reaction 26. What elements are in an organic compound? ____carbon and hydrogen______ 27. What are physical properties? Physical properties can be observed or measured without changing the composition of matter. 28. List at least 5 physical properties Physical properties can include: appearance, texture, color, odor, melting point, density, solubility, polarity, etc. 29. Explain why a “state of matter” change is NOT evidence of a chemical reaction. When a state of matter change occurs, it is usually because there is an increase or decrease of heat. Think about a chocolate bunny. If you leave it out in the sun, it melts. But if you had it on a plate, you could, in theory, put the plate of melted chocolate in the fridge and it would form back into a solid. The shape would have changed, but it is still chocolate!! More to the point, no new substance was made, no other evidences of a chemical reaction is shown. Use what you know to logically work each of these problems!! Examples of state of matter changes (These are NOT chemical reactions!) Water – liquid to solid to water vapor (steam) Aluminum – we can shape it into a soda can, melt it, freeze it, but it is still aluminum! Lava – molten rock, solid rock Study Tips and Reminders 1. Complete this test review and then study! 2. Text book pages that relate to this material: Unit 3 – p. 109 – 135 and 139 – 168 (the second half of the unit focuses on the second half of Unit 3 in the textbook) 3. Notes are always posted on the website – look in Unit 2.2 4. Remember, the “Unit Enrichment and Review” section at the bottom of every unit has even more videos and links. 5. The labs and their concepts turn into questions on the test! Take a look at the chemical reactions lab and notice evidences that a chemical reaction has occurred. 6. Main concepts: Know how read a chemical formula – what do the subscripts and coefficients mean? How can you tell which elements are present. Know the Law of Conservation of Mass and how it is applied to chemical reactions Know what makes a compound organic or not Know the difference between physical and chemical properties and changes Exothermic and endothermic reactions Know how to recognize what a balanced equation looks like