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# molar mass, and other simple math! - PowerPoint PPT Presentation

molar mass, and other simple math!. 1 st of all, what is a molar mass? it is the sum of the masses of the atoms. We did this when we did molar mass, but not much. for instance - what is the molar mass of CO 2 ? you take the mass of the carbon- 12.011 and add the mass of 2 oxygens- 15.99 x 2

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1st of all, what is a molar mass? it is the sum of the masses of the atoms.

We did this when we did molar mass, but not much.

for instance - what is the molar mass of CO2 ?

you take the mass of the carbon- 12.011 and add the mass of 2 oxygens- 15.99 x 2

then add them up! 12.011 + 31.98=43.99 grams!

not too bad! try finding the molar mass of water!

great!

now, what if you had 5 moles of water, how much would that weigh?

take the moles (5) x the mass of water ( 18.0158g/mole) and get a total mass of 90.079 grams

O

C

O

C

O

O

O

C

O

How much do these compounds weigh?

HU?

if these atoms have these weights...

76.011

= 15.999 g/ mole

75.971

=12.011 g/ mol

=14.077 g/mol

44.009

that each element is in a compound.

All percents are just part over total. so there you go, find the part, find the total.

for instance, if I had a compound that had 33 grams of nitrogen and 45 grams of oxygen what is the percent composition of each?

1st find the total grams. 33 + 45= 78 grams.

now divide each

there is another way to do this, and that is from the formula itself

say you knew you had some diphosphours decaoxide, and you wanted

to know how much oxygen you had.

1st- P2O10 has a total mass of ...

( yes molar mass of this) , P=30.974 x 2= 61.948

and oxygen is 15.99 x 10 = 159.9 g

total is 221.848 grams

and oxygen % is 159.9/221.848=.72 so 72% oxygen by mass

O MASS

O

O

O

more math?

if these atoms have these weights...

=14.077 g/mol

= 15.999 g/ mole

what is the % nitrogen in this compound

O MASS

= 75.971

O

O

O

1st find the parts and the whole

= 15.999 g/ mole

=14.077 g/mol

=28.001

O MASS

75.971

O

O

O

so the part that is Nitrogen is

= 15.999 g/ mole

=28.001

=14.077 g/mol

.3685, or 36.9 %

this means "out of"

it also means divided by

now lets try emperical formula- also called simplest formula it is the smallest ratio of the elements.

if you are given a formula, it may or may not be the simplest

CO2

S4O8 SO2

H2O

HNO3

C6H12O6 CH2O

How to do it:

1st you are given grams amounts, or %s. either way, turn them into moles ( divide by molar mass)

2nd, looking at the answer from 1, divide all by smallest, this gives you whole numbers!

Br it is the smallest ratio of the elements.

Br

Ca

Br

Br

Ca

Chemical Reactions

·Product-a substance that is produced by a chemical reaction.

·Reactants- Substance that enters a chemical reaction.

Br it is the smallest ratio of the elements.

Br

Ca

Ca

Br

Br

Chemical Reactions

·Reactants- Substance that enters a chemical reaction.

·Product-a substance that is produced by a chemical reaction.

Chemical Equation it is the smallest ratio of the elements.

·

Word Eqn. Have words in them

Formula Eqn. Have symbols of the element

<http://en.wikipedia.org/wiki/Chemical_reaction

·Formula Equation - Ca +O2 → CaO

·Word Equation - Calcium + Oxygen = Calcium Oxide

3 things that must be true of chemical reactions include- it is the smallest ratio of the elements.

1. they must represent known facts

( you can’t make them up, the reaction actually has to happen)

how do you know?

2. Formula’s must be correct

( balance ionic compounds, write covalent compound correctly)

3. Law of conservation of mass

Balance reaction! Use coefficients to make sure reactant

amounts and product amounts are equal

H2 + O2 H2O

Nitrogen gas and Sulfer create Dinitrogen tetrasulfide it is the smallest ratio of the elements.

Na2O + H2O = NaOH

Ca(OH)2 + Na = NaOH + Ca

Fe + H2O = Fe2O3 + H2

Na + O it is the smallest ratio of the elements. 2 = Na2O

MgO + K = K2O + Mg

Fe + O2 = Fe2O3

H it is the smallest ratio of the elements.

H

Cl

Cl

Cl

O

O

H

H

H

H

Mg

O

O

Mg

Fe

Br

Ca

Types of reactions

all reactions can be grouped into 5 general types

1. synthesis - 2 or more reactants turn into ONE product

+

+

O it is the smallest ratio of the elements.

O

O

C

O

C

O

O

O

O

O

N

N

N

H

H

H

H

N

N

N

H

H

2. Decomposition- the reverse of synthesis, this

takes ONE REACTANT and makes 2 or more products

CO3 ⇒ C + O2

NO2⇒ N2 + O2

Br it is the smallest ratio of the elements.

Cl

Fe

C

H

Ca

O

O

O

O

C

N

Mg

H

Cl

single replacement reactions

H it is the smallest ratio of the elements.

O

H

Cl

O

Fe

O

H

O

H

Cl

N

O

Mg

O

O

N

O

O

Na

N

O

H it is the smallest ratio of the elements.

O

O

O

O

O

H

H

H

H

C

H

C

C

H

H

H

H

H

O

H

O

O

C

H

H

H

O

O

O

O

H

C