Chemistry molecular Geometry and other significant studies plus electronic configuration

7/29/2019 Chemistry molecular Geometry and other significant studies plus electronic configuration

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We measure ordinary objects either

by counting or weighing them,

depending on which method is more convenient

Silberberg, M. 2010. Principles of General Chemistry. 2

nd

ed. New York: McGraw-Hill.http://weyume.com/wp-content/uploads/2011/04/rice.jpg

http://farm1.static.flickr.com/21/90994367_5613e69fd9.jpg



Dozen = 12

Pair = 2

Certain nouns can be used to define

a collection of objects



The mole



The mole (n or mol) is the amount of matter that

contains as many entities (atoms, molecules,

ions, or other particles) as there are atoms inexactly 12 g of the carbon-12 isotope (12C)

• The actual number of atoms in 12 g of

carbon-12 was determined experimentally

• Avogadro’s number (N A)

N A

= 6.02 x 1023

Brown, , E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

Chan R. 2002. Chemistr 7th ed. Sin a ore: McGraw-Hill.



Just as 1 dozen of oranges contains 12 oranges,

1 mole of matter contains 6.02 x 1023 entities

Brown, , E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

Chan R. 2002. Chemistr 7th ed. Sin a ore: McGraw-Hill.

1 mole 12C atoms = 6.02 x 1023 12C atoms

1 mole H2O molecules = 6.02 x 1023 H2O molecules

1 mole NO3

-

ions = 6.02 x 10

23

NO3

-

ions



Each of these contains one mole of the

substance

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

copper iron

carbon sulfur

mercury



One mole (or an Avogadro’s number)

is an extremely big number

• One mole of softdrink cans would cover

the surface of the earth to a depth of over

300 kilometers

• If we were able to count the number of

atoms at a rate of 10 million per second, it

would take about 2 billion years to count a

mole of atoms



Molar mass



The molar mass (M ) of a substance is the mass

of one mole of its entities (atoms, molecules,

ions, or other particles) in units of g/mol

M H2O = 18.0 g/mol

(one mole of H2O molecule weighs 18.0 g)

M NO3- = 62.0 g/mol

(one mole of NO3- ion weighs 62.0 g)

M C = 12.01 g/mol

(one mole of C atom weighs 12.01 g)

Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.



The periodic table is indispensable for

calculating the molar mass of a substance

• Elements

–M is the numerical value from the

periodic table


M H = 1.008 g/mol

M O = 16.00 g/mol





• Compounds

–M is the sum of the molar masses of the

atoms of the elements in the formula


M SO2 = M S + (2 x M O)

= 32.07 g/mol + (2 x 16.00 g/mol)

= 64.07 g/mol





• Compounds

–M is the sum of the molar masses of the

atoms of the elements in the formula


M K2S = (2 x M K) + M S

= (2 x 39.10 g/mol) + 32.07 g/mol

= 110.27 g/mol



Interconverting moles, mass,

and chemical entities

(atoms, molecules, ions, or other particles)



The factor-label method is used to convert

from one unit to another

1 peso = 4 25-centavos

1 peso

4 25-centavos = 1

1 peso

4 25-centavos = 1

unit factor




Alexa bought 18 fresh chicken’s eggs. How

many dozens of egg did she buy?

dozens of egg = x18 eggs 1 dozen egg

12 eggs

= 1.5 dozens of egg

unit factor



In order to convert between moles, mass, and

chemical entities, the factor label method is used




Methane (CH4) is the principal component of

natural gas. How many moles of methane

are present in 6.07 g of CH4?M CH4 = M C + (4 x M H)

= 12.01 g/mol + (4 x 1.01 g/mol)

= 16.05 g/mol

Report final answer with the correct number of significantfi ures!

nCH4 = x

6.07 g CH4 1 mol CH4

16.05 g CH4

= 0.378 mol CH4



How many molecules of methane are

present 6.07 g of CH4?

molecules CH4 = x

6.07 g CH4 1 mol CH4

16.05 g CH4

= 2.28 x 1023 molecules CH4

x6.02 x 1023 molecules CH4

mol CH4



Glucose (C6H12O6), also known as blood sugar,

is used by the body as energy source.

How many moles of glucose are present in1.75 x 1022 molecules of glucose?

nC6H12O6 = x1.75 x 1022 molecules C6H12O6 1 mol C6H12O6

6.02 x 1023

moleculesC6H12O6

= 0.0291 mol C6H12O6



How many grams of glucose are present in

1.75 x 1022 molecules of glucose?

M C6H12O6 = (6 x M C) + (12 x M H) + (6 x M O)

= (6 x 12.01 g/mol) + (12 x 1.01 g/mol)

+ (6 x 16.00 g/mol)

= 180.18 g/mol



How many grams of glucose are present in

1.75 x 1022 molecules of glucose?

nC6H12O6 = x1.75 x 1022 molecules C6H12O6 1 mol C6H12O6

6.02 x 1023

molecules

C6H12O6

180.18 g C6H12O6

x 1 mol C6H12O6

= 5.24 g C6H12O6



1. Urea [(NH2)2CO] is used in animalfeeds, as fertilizer and in the

manufacture of polymers.a. Draw the Lewis structure of area. C is

surrounded by O and the N’s. (Where are the

H’s connected?) b. Calculate its molar mass.

c. Consider 25.6 g of urea. How many moles of

urea present?

d. How many moles of N are present?

e. How many moles of C are present?

f. How many molecules of urea are present?

g. How many atoms of N are present?



2. Vitamin C, ascorbic acid, is oftensold as sodium ascorbate.

a. Calculate its molar mass.b. Consider a 500.-mg tablet. How many moles

of sodium ascorbate are present?

c. How many moles of C are present?

d. How many moles of Na are present?

e. How many formula units of sodium

ascorbate are present?

f. How many atoms of Na are present?

O

O

OH

-O

HO

OH

Na+



Chemical reactions and

chemical equations



A chemical reaction shows the process in

which a substance (or substances) is

changed into one or more new substances




A chemical equation uses chemical symbols to

show what happens during a chemical reaction

reactants product

(g) (g) (l)

“Two molecules of hydrogen react with one molecule of

oxygen to yield two moles of water”




The Law of Conservation of Mass states that

matter is neither created nor destroyed




To conform with the Law of Conservation of Mass, there

must be the same number of each type of atom on both

sides of the arrow. Hence, we balance the equation by

adding coefficients before each chemical symbol




Calculating the amounts of

reactant and product



Stoichiometry a double

cheeseburger

2 bun slices + 2 cheese slices+ 2 burger patties =

I b l d ti th b f l f



In a balanced equation, the number of moles of

one substance is equivalent to the number of

moles of any of the other substances

2CO(g) + O2(g) 2CO2(g)

2 mol CO = 1 mol O2

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

2 mol CO

1 mol O2

= 11 mol O2

2 mol CO

= 1







2CO(g) + O2(g) 2CO2(g)

2 mol CO = 2 mol CO2


2 mol CO

2 mol CO2

= 12 mol CO2

2 mol CO

= 1







2CO(g) + O2(g) 2CO2(g)

1 mol O2 = 2 mol CO2


1 mol O2

2 mol CO2

= 12 mol CO2

1 mol O2

= 1



The amount of one substance in a reaction

is related to that of any other




All alkali metals react with water to produce

hydrogen gas and the corresponding

alkali metal hydroxide

2Li(s) + 2H2O(l) 2LiOH(aq) + H2(g)



How many moles of H2 will be formed by the

complete reaction of 6.23 moles of Li with water?

nH2 = x6.23 mol Li 1 mol H2

2 mol Li

= 3.12 mol H2




How many grams of H2 will be formed by the

complete reaction of 80.57 g of Li with water?


mH2 = x x80.57 g Li 1 mol Li 1 mol H

2

6.941 g Li 2 mol Li

2.016 g H2 x1 mol H2

= 11.70 g H2



In a lifetime, the average American uses about

794 kg of copper in coins, plumbing, and wiring.

Copper is obtained from sulfide ores (such asCu2S) by a multistep process. After an initial

grinding, the first step is to “roast” the ore (heat it

strongly with O2) to form Cu2O and SO2

2Cu2S(s) + 3O2(g) 2Cu2O(s) + 2SO2(g)



How many moles of oxygen are required

to roast 10.0 mol of Cu2S?

2Cu2S(s) + 3O2(g) 2Cu2O(s) + 2SO2(g)

nO2 = x10.0 mol Cu2S 3 mol O2

2 mol Cu2S

= 15.0 mol O2



How many grams of SO2 are formed when

10.0 mol of Cu2S is roasted?

2Cu2S(s) + 3O2(g) 2Cu2O(s) + 2SO2(g)

mSO2 = x x10.0 mol Cu2S 2 mol SO2 64.07 g SO2

2 mol Cu2S 1 mol SO2

= 641 g SO2



Ch 2 F

• No meeting this Friday

• Lab discussion moved to March 2

• 1:30-3:30 pm• SOM 201



How many grams of O2 are required to form

2.86 kg of Cu2O?

2Cu2S(s) + 3O2(g) 2Cu2O(s) + 2SO2(g)

mO2 = x x2.86 kg Cu

2

O 1000 g Cu2

O 1 mol Cu2

O

1 kg Cu2O 143.10 g Cu2O

3 mol O2 32.00 g O2 x x2 mol Cu2O 1 mol O2

= 960 g O2



Limiting Reactants

The reactant used up first in a chemical

reaction is called the limiting reactant. Excess

reactants are present in quantities greater than

necessary to react with the quantity of thelimiting reactant.

A + B --- C + D

Given the amounts of A and B, which is the

limiting reactant?



Urea is prepared by reacting ammonia with

carbon dioxide:

2NH3(g) + CO2(g) -- (NH2)2CO(aq) + H2O(l)

In one process, 637.2 g of NH3 are allowed toreact with 1142 g of CO2.

(a) Which is the limiting reactant?

(b) How much urea (in grams) is produced?

(c) How much of the excess reactant (in grams)

is left at the end of the reaction?



Strategy

• Convert mass of each reactant to moles

• Calculate the amount of product formed

from the each of the reactants.

• The reactant the produces the less

amount is the limiting reactant.

1. The reaction between aluminum and iron (III) oxide can generate



( ) gtemperatures around 3000⁰C and is used in welding metals:

2Al + Fe2O3 -- Al2O3 + 2Fe

In one process, 124 g of Al are reacted with 601 g of ferric oxide.

(a)Which is the limiting reactant?

(b)How much Al2O3 (in grams) is produced?

(c)How much of the excess reactant (in grams) is left at the end of

the reaction?

2. Titanium is a strong & light metal used in rockets & aircrafts. It is

prepared by the reaction between titanium (IV) chloride with moltenmagnesium at around 1000⁰C: TiCl4 + 2Mg -- Ti + 2MgCl2

In a certain industrial operation, 3.54 x 107g of TiCl4 are reacted with

1.13 x 107 g of magnesium.(a)Which is the limiting reactant?

(b)How much Ti (in grams) is produced?

(c)How much of the excess reactant (in grams) is left at the end of

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Chemistry molecular Geometry and other significant studies plus electronic configuration