Chapter 10 Chemical Quantities

Measuring Matter measure the amt of something by by count, by mass, and by volume. 2

Measuring Matter (1) Atoms, molecules and formula units are extremely small. so many of them in even the smallest sample that it’s impossible to actually count. Counting unit: mole.

Measuring Matter (2) mole (mol) SI base unit used to measure the amt (# of representative particles) of a sub. 1 mole of C = # C atoms in exactly 12 g pure C-12 = 6.02 x 1023 atoms of C

Representative particles Substance atoms Elements, cpds Molecules Covalent (molecular cpds) Formula units Ionic cpds Ions, e-

atoms, molecules, formula units, e-, ions. Measuring Matter (3) 1 mole of anything contains 6.02 x 1023 rep particles. Avogadro’s # atoms, molecules, formula units, e-, ions.

What is a Mole? (1) Atomic nitrogen atoms N 6.02 x 1023 atoms substance Representative particles Chemical formula # of representative particles in 1 mole Atomic nitrogen atoms N 6.02 x 1023 atoms Nitrogen gas molecules N2 6.02 x 1023 molecules Water H2O Calcium ions ions Ca2+ 6.02 x 1023 ions Calcium Fluoride formula units CaF2 6.02 x 1023 Sucrose C12H22O12

6.02 x 1023 -----Avogadro’s number (A) Measuring Matter (4) 6.02 x 1023 -----Avogadro’s number (A) 602,000,000,000,000,000,000,000

Question 1 Calculate the # of molecules in 15.7 mol CO2. 9

Answer 9.45 x 1024 molecular CO2 10

Convert moles to # of atoms Propane is a gas used for cooking and heating. How many atoms are in 2.12 mole of propane (C3H8).

Measuring Matter (6) The rep particle in H2O is water molecule.

Measuring Matter The rep particle in Cu is Cu atom.

Measuring Matter The rep particle in NaCl is NaCl formula unit.

Converting Moles to Particles Find how many particles of sucrose are in 3.50 moles of sucrose. 1 mole contains 6.02 x 1023 rep particles. write a conversion factor that relates rep particles to moles of a sub.

Converting Moles to Particles There are 2.11 x 1024 molecules of sucrose in 3.50 moles.

Question 2 Calculate the # of moles in 9.22 x 1023 atom Fe. 17

Answer 1.53 mol Fe 18

Converting Particles to Moles Zn is used as a corrosion-resistant coating on iron and steel. It is also an essential trace element in your diet. Calculate the # mol that contain 4.50 x 1024 atoms Zn.

Converting Particles to Moles Multiply the # Zn atoms by the conversion factor that is the inverse of Avogadro’s #.

The Mass of a Mole molar mass mass in g of 1 mole of any pure sub (an element or a cpd) molar mass of any element = its atomic mass has the units g/mol. molar mass of a cpd = sum of the # of g of each element in one mole of the cpd has the units g/mol

Converting Mass to Moles A roll of Cu wire has a mass of 848 g. How many moles Cu are in the roll? Use the atomic mass Cu given on the PT to apply a conversion factor to the mass given.

Converting Moles to Mass Calculate the mass of 0.625 moles of Ca. Use the molar mass Ca to apply a conversion factor to the # moles given. According to the PT, the atomic mass Ca is 40.078 amu. So the molar mass Ca is 40.078 g.

Converting Moles to Mass

Question 3 Calculate the mass of 6.89 mol Sb. 25

Answer 839g Sb 26

Question 4 A chemist needs 0.0700 mol Se for a rxn. What mass Se should the chemist use? 27

Answer 5.53g Se 28

Converting Mass to # of Particles Calculate the # atoms in 4.77 g Pb. To find the # of atoms in the sample, you must first determine how many moles are in 4.77 g Pb.

Converting Mass to # of Particles According to data from the PT, the molar mass of Pb is 207.2 g/mol. Apply a conversion factor to convert mass to moles.

Converting Mass to # of Particles Now use a 2nd conversion factor to convert moles to # particles.

Converting Mass to # of Particles Convert from # particles to mass # moles = # particles divided by Avogadro’s # Mass = # moles multiplied by molar mass

Moles of Cpds 1 mole is Avogadro’s # (6.02 x 1023) of particles of a sub. If the sub is a molecular cpd (e.g. ammonia (NH3), a mole is 6.02 x 1023 molecules of NH3. If the sub is an ionic cpd (e.g. baking soda-- NaHCO3), a mole is 6.02 x 1023 formula units of NaHCO3

Moles of Cpds 1 mole of a cpd contains as many moles of each element as are indicated by the subscripts in the formula for the cpd. e.g. 1 mole NH3 consists of 1 mole N atoms and 3 moles H atoms.

Molar Mass of a Cpd The molar mass of a cpd is the mass of 1 mole of the rep particles of the cpd. Because each rep particle is composed of 2 or more atoms, the molar mass of the cpd is found by adding the molar masses of all of the atoms in the rep particle.

Molar Mass of a Cpd molar mass NH3 = mass 1 mole N atoms + the mass 3 moles H atoms.

Molar Mass of a Cpd Molar mass NH3 = molar mass N + 3 (molar mass H) Molar mass NH3 = 14 g + 3(1g) = 17 g/mol You can use the molar mass of a cpd to convert between mass and moles

Converting Mass of a Cpd to Moles molar mass H2O = 2(molar mass H) + molar mass O The molar mass H2O as a conversion factor to determine moles H2O. Notice that 1.000 kg is converted to 1.000 x 103 g for the calculn.

Converting Mass of a Cpd to Moles

Molar Volume (1) Molar volume Volume of a mole of gas STP std temp (0°C or 273 K) and pressure (1 atm pressure or 101.3kPa)

Molar Volume (2) At STP, 1 mol of any gas occupies a vol of 22.4 L At STP, volume of any gas is 22.4L At STP, density of a gas = molar mass divided by molar volume = molar mass (g) divided by 22.4 L

Molar Volume (2) What is the vol of 3.20 x 10-3 mol CO2 at STP?

Molar Volume (3) What is the vol of 3.70 mol N2 at STP?

Molar Volume (4) At STP, what volume do 1.25 mol He occupy?

Molar Volume (5) At STP, what vol. do 0.335 mol C2H6 occupy?

Question 5 Calculate the # of moles in 17.2 g of benzene (C6H6).

Answer 0.220 mol C6H6

CST example 1 A 3.00 moles B 6.00 moles C 12.0 moles D 16.0 moles How many moles of CH4 are contained in 96.0 g of CH4?

CST example 2 A 0.5 moles B 2.0 moles C 3.01 x 1023 moles D 6.02 x 1023 moles How many moles of C-12 are contained in exactly 6 g of C-12?

CST example 3 A 5.16 x 1030 B 3.01 x 1023 C 1.20 x 1024 D 1.10 x 1028 How many atoms are contained in 97.6 g of platinum (Pt)?

CST example 4 A 1.5 x 1023 B 3.3 x 1023 C 1.9 x 1026 D 2.4 x 1024 How many atoms are in a chromium sample with a mass of 13 g?

CST example 5 When methane (CH4) gas is burned in the presence of oxygen, the following chemical rxn occurs. CH4 + 2O2 → CO2 + 2H2O If 1 mole of methane reacts with 2 moles of oxygen, then A 6.02x1023 molecules of CO2 and 6.02x1023 molecules of H2O are produced. B 1.2x1024 molecules of CO2 and 1.2x 1024 molecules C 6.02x1023 molecules of CO2 and 1.2x1024 molecules of H2O are produced. D 1.2x1024 molecules of CO2 and 6.02x1023 molecules of

CST problem 6 How many moles of chlorine gas are contained in 9.02 x 1023 molecules? A 1.5 moles B 2.0 moles C 6.02 moles D 9.03 moles

The Mass of a Mole of an Element The atomic mass of an element expressed in g is the mass of a mole of the element. The mass of a mole of an element is its molar mass.

The Mass of a Mole of an Element One molar mass of C, S, Hg, and Fe are shown.

The Mass of a Mole of an Element

The Mass of a Mole of a Cpd How is the mass of a mole of a cpd calculated?

The Mass of a Mole of a Cpd To calculate the molar mass of a cpd, find the # of g of each element in 1 mole of the cpd. Then add the masses of the elements in the cpd.

The Mass of a Mole of a Cpd Substitute the unit g for a.m.u. Thus 1 mol of SO3 has a mass of 80.1 g.

Quiz 2. A mole of hydrogen gas, H2(g), contains 6.02 x 1023 molecules. atoms. amu. grams.

Quiz 3. The atomic mass of fluorine is 19.0 amu, so the molar mass is 19.0 g. 6.02 x 1023 amu. 6.02 x 1023 g.

Quiz 4. Calculate the molar mass of ammonium nitrate. 45.02 g 80.05 g

Converting Moles to Particles Find the # of rep particles in a # of moles just as you found the # of roses in 3.5 dz. the rep particle is a molecule, so the # of molecules of sucrose is obtained by multiplying 3.50 moles of sucrose by the conv. factor, Avogadro’s #. 63

Converting Particles to Moles Find out how many moles are represented by a certain # of rep particles Use the inverse of Avogadro’s # as a conversion. factor. 64

Mass of a Mole atomic masses can be found on the PT, but the values shown are not integers. e.g. 12.011 amu for C, 1.008 amu for H, and 4.003 amu for He. These differences occur because the recorded values are weighted averages of the masses of all the naturally occurring isotopes of each element. 65