Warmup (5 minutes)

1. A “dozen” is what we call a “counting unit.” What are some other counting units?

2. Write the formula for aluminum sulfate

3. Do atoms ever disappear from our universe?

Equationsand the Mole

You will have another Memorization Quiz next class: ions again, and

solubility rules too!

In science, a mole is how we count the number of a substance (like a dozen).

How much is a mole?

The number of things in 1mole has been determined to be: 6.02 x 1023

This is Avogadro’s Number (after the scientist who figured it out).

602000000000000000000000 is the number of atoms in 12 grams of carbon.

Is one mole always the same quantity?

1 mole silicon atoms

1 mole iodine atoms

Mass = 28.09 grams Mass = 126.90 grams

6.02x1023

atoms in each box

Yes: for # molecules or atoms

No: for mass

2Na(s)  +  2H2O(l)  →  2NaOH(aq)  +  H2(g)

solid liquid aqueous gas

2 moles 1 mole (no #)

Reactants Productsarrow = “yield”, “make”, “produce”, “form”

Translate the equation into a sentence!2 moles of solid sodium react with 2 moles of liquid water to yield2 moles of aqueous sodium hydroxide and 1 mole of hydrogen gas (Why H2?)

Diatomic Elements are:gaseous elements which are unstable if found as a

single atom;

H2 O2 F2 Br2 I2 N2 Cl2

Write an equation:

2 moles of solid sodium react with 1 mole of chlorine gas to yield 2 moles of aqueous sodium chloride

2Na(s) + Cl2(g) 2NaCl(aq)

Write the equation: solid calcium reacts with aqueous hydrogen chloride to yield aqueous calcium chloride and hydrogen gas

Ca(s)  +   HCl(aq)  →   CaCl2(aq)  +   H2(g)

Is this equation balanced?

Law of conservation of matter: in a chemical reaction, matter is neither

created nor destroyed

1 12 1

A balanced equation obeys this law; it has equal numbers of each type element on both sides of the equation.

“what goes in, comes out!”

_____H2 + _____ O2 _____ H2O

1 22

Balancing Tips1) Use a pencil, you might have to erase!

2) It helps to balance metal atoms first, H’s and O’s last!

3) Place whole-number coefficients in front of the formulas; NEVER change subscripts in the chemical formula. “1” is not completely necessary.

4) Multiply new coefficient times the subscript to count the total # atoms for that element on each side. (Example: 2H2= 4 hydrogen atoms total)

It takes practice…you will not learn by watching!

__Al (s) + __Fe2O3(aq) → __Al2O3(aq)+ __Fe(s)

Balancing Example: #1

2 2 1 1

Al OFeFe O O Al Al OOO Fe

FeAl

__C2H4 + __O2 → __CO2 + __H2O

2 minutes!

2 231

____ N2 + ____ H2 ____ NH3

231

Be Careful With Parentheses: How many atoms are in:

Mg(OH)23Mg(OH)

2

# of Mg atoms:

# of O atoms:

# of H atoms:

1 3

2 6

2 6

3Mg(OH2

)23

6

12

A hamburger is made of certain materials:BunLettuceMeatBun

What would an equation for the synthesis of one hamburger look like?

____Bun + ____Lettuce + ____Meat ____hamburger2 1 1 1

Mole Ratio Problems

If I wanted to make 20.5 hamburgers, how many buns would I need?

____Bun + ____Lettuce + ____Meat ____hamburger2 1 1 1

20.5 hamburger

(1 hamburger)

(2 buns)= 41.0 buns

How many hamburgers can I make if I had 17 meats (assuming I have enough of everything else)?

17 meats

(1 meat)

(1 hamburger)= 17 hamburgers

1N2 + 3H2 2NH3

Translate the equation above into a sentence:

If 1 mole N2 reacts with 3 moles H2, 2 moles NH3 are produced.

Write all the molar ratios possible given this equation

The molar ratio compares the number of moles of each compound in an equation. I will sometimes say ‘molecules’ to simplify, although this is technically inaccurate.

1 mole N2 3 moles H2 1 mole N2

3 moles H2 1 mole N2 2 moles NH3

2 moles NH3 3 moles H2 2 mole NH3

1 mole N2 2 moles NH3 3 moles H2

If 2 moles of N2 are used, how many moles of NH3 will be produced in the reaction?

1N2 + 3H2 2NH3

2 moles N2 (2 moles NH3) = 4 moles NH3

(1 mole N2)

If you want 7.70 moles of NH3, how much H2 is needed?

7.70 moles of NH3 (3 moles H2 ) = (2 moles NH3)

11.6 moles H2

Warning: Sometimes you will have to balance the equation first!