Atoms & Moles; Molar Mass & % Composition; … 6 Atoms & Moles; Molar Mass & % Composition; Formulas...
Transcript of Atoms & Moles; Molar Mass & % Composition; … 6 Atoms & Moles; Molar Mass & % Composition; Formulas...
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
1. To understand the concept of average mass 2. To learn how counting can be done by weighing 3. To understand atomic mass and learn how it is
determined 4. To understand the mole concept and Avogadro’s
number 5. To learn to convert among moles, mass, and number of
atoms
Objectives
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
Some Questions……… • How many atoms are there in a bucket of water? How
could we determine that without having to count them all individually?
• I know that one atom of carbon reacts with one molecule of oxygen to make one molecule of carbon dioxide. If I have a sample of carbon how can I predict how much oxygen to react with it? Can I do it by counting out atoms? C + O2 reacts to give CO2
• What do the atomic masses in the Periodic Table stand for? periodic table
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
A. Counting by Weighing
• We can count objects by knowing how much each one weighs and weighing the sample
• Objects do not need to have identical masses to be counted by weighing. – All we need to know is the average mass of the
objects. • To count the atoms in a sample of a given element by
weighing we must know the mass of the sample and the average mass for that element.
=
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
A. Counting by Weighing
Averaging the Mass of Similar Objects
Example: How can we count out 1000 jelly beans?
3. Now we can find the average mass of a bean.
4. Finally we can multiply to find the mass of 1000 beans. We can then weigh out 1000 beans.
1. Not all jelly beans have the same mass. 2. Suppose we weigh 10 jelly beans and find:
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
B. Atomic Masses: How Much Do Atoms Weigh?
• Atoms have very tiny masses so scientists made a unit to avoid using very small numbers.
• 1 atomic mass unit (amu) is 1/12 of the mass of a 12C atom
• 1 amu = 1.66 ×10-24 g
How many amu’s does a 12C atom weigh? How many grams does a 12C atom weigh?
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
B. Atomic Masses: Counting Atoms by Weighing
• The average atomic mass for an element is the weighted average of the masses of all the isotopes of an element.
• The Periodic Table shows the atomic mass of each element in amu’s. This is different to the mass number
periodic table What is the average atomic mass in amu’s of an atom of:
Barium
Fluorine
Xenon
Nickel (P210 Q5,6)
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
Isotope Atomic Mass amu
Natural Abundance %
Abundance x Atomic Mass
54Fe 53.9396127 5.845 3.153
56Fe 55.9349393 91.754 51.323
57Fe 56.9353958 2.119 1.206
58Fe 57.9332773 0.282 0.163
Calculate the Average Atomic Mass of Naturally Occurring Iron:
Sum of the final column = 55.845 amu
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
Calculate the atomic masses of one of the following elements. Use the isotope masses and % abundance from the Dynamic Periodic Table – Cu, C, K
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
The MOLE!!?!?! - A spicy sauce flavored with chocolate, usually served with turkey or chicken - Any of various small insectivorous mammals, esp. of the family Talpidae, living chiefly underground, and having velvety fur, very small eyes, and strong forefeet. - A spy who becomes part of and works from within the ranks of an enemy governmental staff or intelligence agency. - A large, powerful machine for boring through earth or rock, used in the construction of tunnels - A small, congenital spot or blemish on the human skin, usually of a dark color, slightly elevated - A very large number: 6.022 x 1023 - The atomic or molecular weight of a substance expressed in grams
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
C. The Mole
Multiple Units • One dozen eggs is twelve eggs • One class is twenty students • One kilometer is 1000 meters
• One alphabet is …………? • One Liter is ………..? • One gross is………...?
Can you think of some multiple units?
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
C. The Mole
• One mole of anything contains 6.022 x 1023 units of that substance. – Avogadro’s number is 6.022 x 1023.
• A sample of an element with a mass equal to that element’s average atomic mass (expressed in g) contains one mole of atoms.
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
C. The Mole
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
One marble has a diameter of 1cm and covers approx. one sq cm Area of USA is 10 million sq km = 107 sq km = 1017 sq cm Depth of marbles in a mole is 6 x 1023 / 1017 = 6 x 106 cm = 60 km
One Mole of marbles would cover the USA to a depth of approximately 60 km!!!
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
If you had a ball of string that was 1 mole of millimeters long would it reach around the Earth? (The circumference of the Earth is 40,076 km)
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
How many grams do the following weigh?
1.00 mol Se
2.00 mol Fe
72.5 mol Pb
0.102 mol Mg
0.521 mol Ni
1.23 x 10-3 mol Pt
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
26.2 g Gold
41.5 g Calcium
335 mg Barium
12.01 g Carbon
1.42 x 10-3 g Palladium
How many moles in the following samples?
(P211 Q16)
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
Relationships Between Moles, Mass and Atoms
Avogadro’s Number
6.022x1023
Atomic Mass from Periodic
Table
Moles Atoms Mass
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
Summary • One amu is one-twelfth of the mass of a 12C atom • One amu is close to the mass of one proton or
one neutron.
• One amu is a very small mass – 1.66 x 10-24 g
• One mole is 6.022 x 1023 units of anything • One mole (of atoms) of an element will have a
mass in grams equal to the mass in amu of one atom of that element
• “One Mole” refers to 6.022 x 1023 atoms or to the atomic mass expressed in grams of an element
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
Some Questions……… • How many atoms are there in a bucket of water? How
could we determine that without having to count them all individually?
• I know that one atom of carbon reacts with one molecule of oxygen to make one molecule of carbon dioxide. How many grams of oxygen react with 12 grams of carbon to make carbon dioxide? C + O2 reacts to give CO2
• How are the atomic masses in the Periodic Table different to mass numbers?
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
1. To understand the definition of molar mass 2. To learn to convert between moles and mass 3. To learn to calculate the mass percent of an element in
a compound
Objectives
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
A. Molar Mass
• A compound is a collection of atoms bound together.
• The molar mass of (“one mole of”) a compound is obtained by summing the masses of the appropriate number of moles of component atoms.
1 mole of methane 1 mole of
carbon and 4 moles of hydrogen
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
A. Molar Mass
• For compounds containing ions the molar mass is obtained by summing the masses of the component ions. This is sometimes called the formula weight.
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
What is the Molar Mass of the following Compounds?
Na3N
CS2
NH4Br
C2H5OH
H2SO3
H2SO4
MgSO4
Ni3(PO4)2
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
A. Molar Mass
• Moles of a compound (g) =
Calculations Using Molar Mass
mass of the sample (g)gmolar mass of the compound ( )
mol
• Mass of a sample (g) = moles of sample (mol) x molar
mass of compound (g/mol)
• Number of atoms in moles of a sample = number of moles x number of atoms in formula x Avogadro’s number
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
Relationships Between Moles, Mass and Atoms
Avogadro’s Number
6.022x1023
Atomic Mass from Periodic
Table
Moles Atoms Mass
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
Relationships Between Moles, Mass, Molecules and Atoms
Avogadro’s Number
6.022x1023
Molar Mass using Periodic
Table
Molecules Moles Mass
Atoms
Molecular Formula
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
B. Percent Composition of Compounds
• Percent composition consists of the mass percent of each element in a compound:
mass of a given element in 1 mol of compound 100%mass of 1 mol of compound
× Mass percent =
What are the mass percentages of C, H and O in Ethanol?
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
Calculate the Mass Percent of These Compounds
LiBr
CuOH
SrSO4
C6H12O6
C2H4O
C4H8O2
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
1. To understand the meaning of empirical formula 2. To learn to calculate empirical formulas 3. To learn to calculate the molecular formula of a
compound
Objectives
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
What is the Formula? Mass Spectrometry
• If I analyze a compound by mass as 7.7% Hydrogen and 92.3 % Carbon what is its formula?
• If I have 100g of the compound how many grams do I have of each element?
• How many moles of each element do I have? • What is the simple number ratio between the two
numbers of moles?
• What is the formula?
• Is this the only possible formula?
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
A. Empirical Formulas
• The empirical formula of a compound is the simplest whole number ratio of the atoms present in the compound.
What is the empirical formula of the following compounds?
• Sodium Peroxide Na2O2
• Terephthalic acid C8H6O4
• Phenobarbital C12H12N2O3
• 1,4-dichloro-2-butene C4H6Cl2
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
B. Calculation of Empirical Formulas
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
What is the Empirical Formula of a Compound Containing…..
0.0806g Carbon, 0.01353 g Hydrogen, 0.1074 g Oxygen?
P212 Q36-39
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
C. Calculation of Molecular Formulas
• The molecular formula is the exact formula of the molecules present in a substance.
• The molecular formula is always an integer multiple of the empirical formula. Molecular formula = (empirical formula)n
where n is a whole number
Empirical Formula: CH
Molar Mass = 78
Molecular Formula?
Chapter 6 Atoms & Moles; Molar Mass & % Composition; Formulas of Compounds
Formula Summary For the sugar glucose