Question of the Day Rules You must work alone You must work alone You may use your textbook today You may use your textbook today You have 10 minutes to complete the QOD You have 10 minutes to complete the QOD Good luck!! Good luck!!

QOD Read page of your textbook and answer question 1 & 2 at the bottom of the page. Read page of your textbook and answer question 1 & 2 at the bottom of the page. 2

Why is it difficult to protect people from the radiation given off by radioactive elements? Why is this radiation harmful to human health? Answer: Some radiation, such as gamma rays, is stopped only by high-density materials, like concrete or lead, so it passes easily through the human body. Radiation can be harmful to health because of its ability to alter a cell’s DNA, which can lead to the development of cancer cells. 3

Cesium-137 has a half-life of about 30 years. Is it normal that after more than 20 years, levels of radioactivity in the ground near Chernobyl are still very high? Explain your answer. Answer: Yes, because a half-life of 30 years means that it takes 30 years for half of the amount of cesium to decay. Therefore, after 20 years, more than half of the cesium still remains in the ground. 4

What are we doing Today? Chapter 4 QOD QOD Acid Base Lab Nov. 17 Acid Base Lab Nov. 17 Don’t forget your test, Nov 24 Don’t forget your test, Nov 24 Ch. 4  Balancing Equations Ch. 4  Balancing Equations Balancing Equations Worksheet Balancing Equations Worksheet

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7 If a chemical equation does not obey the law of conservation of mass the equation is said to be what? NOT BALANCED So Let’s look at the steps we need to take to BALANCE chemical equations Fe + O 2  Fe 2 O 3 Let’s work with the following equation:

8 #R atom #P 1 Fe 2 2 O 3 For example: Fe + O 2  Fe 2 O 3 Step 1. Create a RAP table (what’s a RAP table ??) A table that shows us what atoms are present in this reaction, how many there are and are they reactants or products?

9 #R atom #P 1 Fe2 2O3 Rule 2. Go to the first atom that’s not balanced and balance it! Since Fe atoms are not balanced what do we need to do to balance it? Right! Multiply it by 2 (Only multiply) 2x

10 #R atom #P 1 Fe2 2O3 2Fe + O 2  Fe 2 O 3 In step 2 we balanced the number of Fe atoms by multiplying the reactant side by 2. This now becomes the new coefficient in the chemical equation. Modify the equation to reflect the change Are all atoms balanced? 2x

11 #R atom #P 2 Fe 2 2 O 3 2Fe + 3O 2  2Fe 2 O 3 3. Move to the next unbalanced atom. What is it? How can we balance the Oxygen? #R atom #P 2 Fe 2 3x2 O 3x2 Adjust the equation to reflect your changes But notice that by changing Oxygen we also Changed Iron. We need to go back and fix this. Multiply Reactants by 3 and Products by 2

12 #R atom #P 2 Fe 4 6 O 6 4Fe + 3O 2  2Fe 2 O 3 4. Write out the updated RAP table. How can we Balance the Iron? Sure! Multiply the # of Reactant Fe atoms by 2 ! Do we have a balanced Chemical Equation now? 2x Re-write the equation reflecting The new changes you’ve made. Yes we do!

13 Polyatomics When an equation has Polyatomics in it, such as in this Balanced chemical equation 2AgNO 3 + MgCl 2  2AgCl + Mg(NO 3 ) 2 And the polyatomic appears on BOTH the reactant and product Side of the equation Count the polyatomic as an “ATOM” So the above reactant atoms would be: #R atom #P 2 Ag 2 2 NO Mg 1 2Cl 2 If the same polyatomic does not Appear on both sides break the Polyatomic down into atoms!

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15 #R atom #P 1 NA 1 1 OH 2 1 Ca 1 2 Br 1 Is this equation balanced? NaOH + CaBr 2  Ca(OH) 2 + NaBr What atoms do we have in This equation? 1) Count atoms & Start the RAP table 2) Do the #Reactant atoms = the # of Product atoms? 3) So pick the 1st unbalanced atom & begin balancing

16 #R atom #P 1 Na 1 1 OH 2 1 Ca 1 2 Br 1 We’ll start with balancing Hydroxide NaOH + CaBr 2  Ca(OH) 2 +NaBr How can we make both Hydroxides equal? Sure we’ll multiply #R OH by 2 2x Hydroxide is now balanced so let’s move to the next Unbalanced atom, which is? … Next step> rewrite the modified eqn. 2NaOH + CaBr 2  Ca(OH) 2 + NaBr

17 #R atom #P 2 Na 1 2 OH 2 1 Ca 1 2 Br 1 What can we do to balance the Bromine? 2NaOH + CaBr 2  Ca(OH) 2 + 2NaBr Now adjust the table to reflect The changes and then rewrite the Eqn. Sure! Multiply the #P Bromine by 2 x2x2

18 #R atom #P 2Na 2 2 OH 2 1 Ca 1 2 Br 2 Let’s update the RAP table with the new #’s Based on our updated equation. 2NaOH + CaBr 2  Ca(OH) 2 + 2NaBr Are we now balanced? Sure!

19 #R atom #P 2 C 1 6 H 2 2 O 3 Ok Try Balancing this equation: C 2 H 6 + O 2  CO 2 + H 2 O Step 2. Balance the #P Carbon #R atom #P 2 C 2 6 H 2 2 O 5 C 2 H 6 + O 2  2CO 2 + H 2 O Step 1. Total up the atoms & Re-write the equation Are we done?

20 #R atom #P 2 C 2 6 H 2 2 O 5 C 2 H 6 + O 2  2CO 2 + 3H 2 O #R atom #P 2 C 2 6 H 6 2 O 7 Step 3. Carbons are balanced now but Hydrogen isn’t. So, balance Hydrogen atoms next Carbon and Hydrogen are now balanced but oxygen isn’t. Multiply #P Hydrogen by 3 Step 4. Re-write the eqn. & Retotal the number of atoms x3

21 C 2 H 6 + 3½ O 2  2CO 2 + 3H 2 O #R atom #P 2 C 2 6 H 6 2 O 7 Step 5. To balance Oxygen multiply O by 3½ Step 6. Re-write the eqn. & Retotal the number of atoms It looks like we’re balanced. But, are we? No! We can’t have 3 ½ Oxygen molecules! Only whole Numbers are allowed. So what do we need to do to fix this? 3 ½ x

22 C 2 H 6 + 3½ O 2  2CO 2 + 3H 2 O #R atom #P 4 C 4 12 H O 14 Step 7. Let’s clean this up by Multiply everything by 2 Step 8. Retotal #R and the #P atoms 2C 2 H O 2  4CO 2 + 6H 2 O Are we balanced? YES! x 2

23 Try this problem NH 4 OH + FeCl 3  Fe(OH) 3 + NH 4 Cl #R atom #P 1 NH OH 3 1 Fe 1 3 Cl 1 Start here. Recognize we Have polyatomics but they Appear on both sides of the Equation. OK … Now finish it up

24 Answer to previous problem 3NH 4 OH + FeCl 3  Fe(OH) 3 + 3NH 4 Cl

Class Work 1) Assignment Chapter 4 (Law of Conservation of Mass and Balancing Equations) 2) Complete the PreLab 33 (first page) for the Neutralization Lab on Monday 25