The Mole The Mole Chapter 7 Chemical

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					   The Mole
    Chapter 7
Chemical Quantities
What’s a mole anyway?
Well do you remember how to find
the molecular mass of a substance?
  Get out a periodic table. Find the
 atomic mass of carbon. What is it?

12
       What unit goes at the end?

 Amu (u) or atomic mass units.
 Well it so happens that if you take that same
  number and put grams instead of u, you have
  one mole of that substance.
 In other words, trade u for g and you now
  have a mole of carbon.
 So one mole of carbon is 12 grams of carbon.
Scientists use moles because
 atoms and molecules are too tiny
 to count. Instead electronic
 balances are used to measure
 atoms and molecules in grams.
How many grams of carbon in 4
     moles of carbon?



        48 g
How many moles of carbon
 are there in 500 g of carbon?
500 g (1 mol)
        ( 12 g)
How many moles of carbon
 are there in 500 g of carbon?
41.6 mole
How many moles of oxygen
 are there in 500 g of oxygen?
500 g (1 mol)
        ( 16 g)
How many moles of oxygen are
 there in 500 g of oxygen?
500 g (1 mol)= 31.25 mol
       ( 16 g)
 How many grams of calcium must be
  weighed out in order to obtain a
  sample containing 3 moles of atoms?
 a) 40 g
 b) 3 x 6 x 1023 g
 c) 120 g
 120 g
What is the difference
 between molecular
mass and molar mass?
 Molecular mass is
 in atomic mass
 units; molar mass
 is in grams.
Find the number of moles in
         24 g of CO

  24 g     (1 mole)
            ( 28 g )
  = 0.86 moles of CO
Convert 872 g of
ammonium oxide
  into moles.
First find the correct
formula for ammonium
oxide.
(NH4)2O
Find the molar mass
of ammonium oxide
 (NH4)2O
 N – 2 x 14 = 28
 H–8x1= 8
 O – 1 x 16 = 16
Find the molar mass
of ammonium oxide
 (NH4)2O = 52 grams
 Set up a conversion
 factor to change from
 872 g to moles.
Conversion factor

872 g ( 1 mol)
       52 g
= 16.8
   What is
 Avogadro’s
  number?
6.02 x10 23

units of a
substance
44. Which of the following equals
 9.2 x 1024 divided by
6.3 x 104?
A. 1.46 X 1024
B. 1.46 X 10 20

C. 1.46 X 10 6

D. 1.46 X 1028
    Avogadros's number,
6.02 x 10 23 , is also called a
 mole, in the same way that
500 sheets of paper is called
a ream, or 144 is referred to
         as a gross.
http://www.wiredchemist.com/chemis
try/instructional/chem_modules_mole
              _lecture.html
 How many ping-pong balls are there in a mole of
  ping-pong balls? What would their molar mass
  be if one ping-pong ball weighs 1.0 g?
 6.02 x 1023 ping-pong balls in a mole of ping-
  pong balls.
 If each ball weighs 1.0 grams, the molar mass
  will be 6.02 x 1023 g.
 We would normally express this as 6.02 x 1023
  g/mole.
 Are you saying that we can have a mole of
  anything? Sure, can't you have a dozen
  pencils, a dozen ducks, a dozen bricks?
  However, we normally use the term mole in
  dealing with atomic particles--atoms, ions,
  molecules.
 How many atoms are present in 31 g of
  phosphorus?
 a) 1 mole        b) 6.022 x 1023
 c) Avogardro's number d) a, b, and c
 All three are correct
 Your Zork particle counter has just
  informed you that there are 3 x 1020
  atoms of radon in your basement.
  How many moles of radon is this?
 3 x 1020 particles/ 6 x 1023 particles
  per mole) = 5 x 10-4 mole.
 Your lab partner is staring out the window as usual
  when he suddenly exclaims, "Gadzooks! There are
  1 x 10-23 moles of dogs running down the street!"
  Could he be right for a change?
 Yes, 1 x 10-23 moles is:
  1 x 10-23 moles x 6 x 1023 dogs per mole = 6 dogs.
  If you like to solve problems with dimensional
  analysis you would probably set this up as:
  1 x 10-23 moles x 6 x 1023 dogs / 1 mole = 6 dogs.
  What about
   volume?
The mole road map
shows a conversion
for volume.
     volume
1 mole of any gas at
STP = 22.4 L
 What’s STP?
STP means
standard
temperature and
pressure.
 What’s STP?
Standard
temperature is 0° C
Standard pressure is
1 atm or 101.3 KPa
Find the volume that 24 g of
   CO occupies at STP.

  24 g     (1 mole)
            ( 28 g )
  = 0.86 moles of CO
Find the volume that 24 g of
   CO occupies at STP.

  0.86 moles (22.4 L)
            ( 1 mol )
  = 19.264 Liters
Find the number of atoms
      in 24 g of CO

0.86 mol (6.02 x   1023)

              (1 mol)
5.2 x  1023

molecules of CO
Find the density of one mole
     of CO gas at STP.

  Density = Mass
  divided by volume
  D = 28 g      =
       22.4 L
Find the density of one mole
     of CO gas at STP.

  Density = Mass
  divided by volume
  D = 28 g      =   1. 25 g/L
       22.4 L
Determine the percent composition
           of Fe(OH)2

       Fe – 1 x 55.8 = 55.8
         O – 2 x 16 = 32
         H–2x1= 2
       Molar mass = 89.8
Divide element mass by molar
 mass, then multiply by 100.

       Fe – 55.8 x 100
            89.8
        O – 32 x 100
            89.8
Divide element mass by molar
 mass, then multiply by 100.

         H –2 x 100
            89.8
Percent compositions

% composition Fe = 62.1%
 % composition 0 = 35.6%
 % composition H = 2.2%
Add them up. Do they total
          100?
Empirical formulas

Which of the following are
  empirical formulas?
         HCl
        K2C2O4
        Pb2O4
Empirical formulas

Only one is an empirical
       formula.
         HCl
The subscripts cannot
     be reduced.
  What is the difference
 between a 6 M solution of
H2SO4 and a 1 M solution of
         H2SO4 ?
  The 6 M (molar) sulfuric
  acid is much stronger. It
  has 6 moles of the acid
  dissolved in 1 liter of
  solution. The 1 M has 1
  mole dissolved in 1 liter.
 So how many grams of
H2SO4 would you need to
  make a 1 M solution?
A 1 M solution has 1 mole
dissolved in 1 liter so find
the molar mass of H2SO4
H 2x1=2
S 1 x 32 = 32
O 4 x 16 = 64
    That totals 98 g.

A 1 M solution has 1 mole
dissolved in 1 liter so add
98 grams of H2SO4 to
almost one liter of water
and then add enough
water to make exactly 1 L.
 So how many grams of HCl
would you need to make a 2 M
          solution?
A 2 M solution has 2 moles
dissolved in 1 liter so find
the molar mass of HCl.
H 1
Cl 35.5
 Total = 36.5 g
 So how many grams of HCl
would you need to make a 2 M
          solution?
A 2 M solution has 2 moles
dissolved in 1 liter so add
73 grams of HCl to almost
one liter of water then add
enough water to make exactly
one liter of solution.
This aqueous solution of HCl is
 named hydrochloric acid!!!

 A 2 M solution of HCl can
 do some serious damage to
 clothes and skin so beware.
 Rinse immediately and put
 baking soda on spills
 ASAP.
 History of the Mole
  The number of objects in one mole, that is,
  6.02 x 1023, is commonly referred to as
  Avogadro's number. Amadeo Avogadro was
  an Italian physics professor who proposed in
  1811 that equal volumes of different gases at
  the same temperature contain equal numbers
  of molecules.
 History of the Mole
  About fifty years later, an Italian scientist named
  Stanislao Cannizzaro used Avogadro's hypothesis
  to develop a set of atomic weights for the known
  elements by comparing the masses of equal
  volumes of gas. Building on this work, an Austrian
  high school teacher named Josef Loschmidt
  calculated the size of a molecule of air in 1865, and
  thus developed an estimate for the number of
  molecules in a given volume of air. While these
  early estimates have since been refined, they led to
  the concept of the mole - that is, the theory that in a
  defined mass of an element (its atomic weight)
  there is a precise number of atoms: Avogadro's
  number.
 Molar Mass
  A sample of any element with a mass equal to that
  element's atomic weight (in grams) will contain
  precisely one mole of atoms (6.02 x 1023
  atoms). For example, helium has an atomic weight
  of 4.00. Therefore, 4.00 grams of helium will
  contain one mole of helium atoms. You can also
  work with fractions (or multiples) of moles:
        Mole challenge activity

 Do you know why the mole is an important
  unit?
 Here’s your chance to show your knowledge
  and solve a problem.
 The challenge: Using iron and sulfur, mass
  out a number of grams of each that should
  combine perfectly with no waste. Record
  both masses.
          Mole challenge activity

 Put chemicals together in a test tube.
 Use a magnet on the outside of the test tube to
  move around the iron in the inside (just to show that
  iron is magnetic).
 With a wooden splint or glass stirring rod, mix well.
 Using test tube holder and bunsen burner, heat the
  chemicals until there is a chemical reaction.
          Mole challenge activity

Using test tube holder and bunsen burner, heat the
  chemicals until there is a chemical reaction.
Allow substance to cool.
Bring test tube to teacher who will evaluate the
  product (FeS). If successful, there won’t be
  anything magnetic (iron) or any sulfur leftover.
  Only FeS should exist and that compound is NOT
  magnetic. Test with a magnet. It may be necessary
  to break the test tube to extract the substance. Your
  teacher will do that for you. DON’T you break it.
How many moles of HCl
would you need to make
2 L of a 3M solution?
http://www.chem1.com/acad/webt
        ext/intro/MOL.html

				
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posted:2/3/2012
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