Question of the Day RulesQuestion of the Day Rules

You must work aloneYou must work alone You may use your textbook You may use your textbook

todaytoday You have 10 minutes to You have 10 minutes to

complete the QODcomplete the QOD

Good luck!!Good luck!!

QODQOD

Read page 136-137 of your Read page 136-137 of your textbook and answer textbook and answer question 1 & 2 at the question 1 & 2 at the bottom of the page.bottom of the page.

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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.

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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.

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What are we doing Today?What are we doing Today?Chapter 4Chapter 4

QODQOD Acid Base Lab Nov. 17Acid Base Lab Nov. 17 Don’t forget your test, Nov 24Don’t forget your test, Nov 24 Ch. 4 Ch. 4 Balancing Equations Balancing Equations Balancing Equations Balancing Equations

WorksheetWorksheet

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If a chemical equation does not obey the law ofconservation of mass the equation is said to be what?

NOT BALANCED

So Let’s look at the steps we need to take toBALANCE chemical equations

Fe + O2 Fe2O3

Let’s work with the following equation:

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#R atom #P

1 Fe 22 O 3

For example:

Fe + O2 Fe2O3

Step 1. Create a RAP table (what’s a RAP table ??)

A table that shows us what atoms are present in thisreaction, how many there are and are they reactantsor products?

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#R atom #P

1 Fe 22 O 3

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

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#R atom #P

1 Fe 22 O 3

2Fe + O2 Fe2O3

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

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#R atom #P

2 Fe 2 2 O 3

2Fe + 3O2 2Fe2O3

3. Move to the next unbalanced atom. What is it?

How can we balance the Oxygen?

#R atom #P

2 Fe 23x2 O 3x2

Adjust the equation to reflect yourchanges

But notice that by changing Oxygen we alsoChanged Iron. We need to go back and fix this.

Multiply Reactants by 3 and Products by 2

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#R atom #P

2 Fe 4 6 O 6

4Fe + 3O2 2Fe2O3

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 reflectingThe new changes you’ve made.

Yes we do!

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PolyatomicsPolyatomicsWhen an equation has Polyatomics in it, such as in thisBalanced chemical equation

2AgNO3 + MgCl2 2AgCl + Mg(NO3)2

And the polyatomic appears on BOTH the reactant and productSide of the equation Count the polyatomic as an “ATOM”

So the above reactant atoms would be: #R atom #P

2 Ag 22 NO3 21 Mg 12 Cl 2

If the same polyatomic does notAppear on both sides break the Polyatomic down into atoms!

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#R atom #P

1 NA 11 OH 21 Ca 12 Br 1

Is this equation balanced?

NaOH + CaBr2 Ca(OH)2 + NaBr

What atoms do we have inThis 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

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#R atom #P

1 Na 11 OH 21 Ca 12 Br 1

We’ll start with balancing Hydroxide

NaOH + CaBr2 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 nextUnbalanced atom, which is? …

Next step> rewrite the modified eqn.

2NaOH + CaBr2 Ca(OH)2 + NaBr

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#R atom #P

2 Na 12 OH 21 Ca 12 Br 1

What can we do to balance the Bromine?

2NaOH + CaBr2 Ca(OH)2 + 2NaBr

Now adjust the table to reflectThe changes and then rewrite theEqn.

Sure! Multiply the #P Bromine by 2

x2

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#R atom #P

2 Na 22 OH 21 Ca 12 Br 2

Let’s update the RAP table with the new #’sBased on our updated equation.

2NaOH + CaBr2 Ca(OH)2 + 2NaBr

Are we now balanced?

Sure!

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#R atom #P

2 C 16 H 22 O 3

Ok Try Balancing this equation:

C2H6 + O2 CO2 + H2O

Step 2. Balance the #P Carbon

#R atom #P

2 C 26 H 22 O 5

C2H6 + O2 2CO2 + H2O

Step 1. Total up the atoms

& Re-write the equation

Are we done?

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#R atom #P

2 C 26 H 22 O 5

C2H6 + O2 2CO2 + 3H2O#R atom #P

2 C 26 H 62 O 7

Step 3. Carbons are balanced now but Hydrogen isn’t. So, balance Hydrogen atoms next

Carbon and Hydrogen are nowbalanced but oxygen isn’t.

Multiply #P Hydrogen by 3

Step 4. Re-write the eqn. & Retotal the number of atoms

x3

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C2H6 + 3½ O2 2CO2 + 3H2O

#R atom #P

2 C 26 H 62 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 wholeNumbers are allowed.

So what do we need to do to fix this?

3 ½ x

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C2H6 + 3½ O2 2CO2 + 3H2O

#R atom #P

4 C 412 H 1214 O 14

Step 7. Let’s clean this up by Multiply everything by 2

Step 8. Retotal #R and the #P atoms

2C2H6 + 7 O2 4CO2 + 6H2O

Are we balanced? YES!

x 2

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Try this problem

NH4OH + FeCl3 Fe(OH)3 + NH4Cl

#R atom #P

1 NH4 11 OH 31 Fe 13 Cl 1

Start here. Recognize weHave polyatomics but theyAppear on both sides of theEquation.

OK … Now finish it up

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Answer to previous problemAnswer to previous problem

3NH4OH + FeCl3 Fe(OH)3 + 3NH4Cl

Class Work Class Work

1) Assignment Chapter 4 (Law 1) Assignment Chapter 4 (Law of Conservation of Mass and of Conservation of Mass and Balancing Equations)Balancing Equations)

2) Complete the PreLab 33 2) Complete the PreLab 33 (first page) for the (first page) for the Neutralization Lab on MondayNeutralization Lab on Monday

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