Chapter 10 Chemical Quantities
Measuring Matter • Matter can be measured by 3 methods • By count • the number of CDs you have • The number of atoms or molecules you have • By mass or weight • You buy vegetables by the pound • The mass(g) of a compound or element you have • By volume • You buy soda in two liter bottles • The number of milliliters of a substance you have
Measuring Matter • Every measurement has a MAGNITUDE and DIMENSION • Magnitude is the numerical value • Dimension is the unit of measurement (gram, pound, etc)
Conversion factors • Relationships between two numbers • 1 Dozen = 12 things • 1 Pair = 2 things • 1 Minute = 60 seconds • 1000 Meter= 1 kilometer
Conversion Factors continued • Can also be written as fractions… • 1 dozen 12 things
Dimensional Analysis • Using conversion factors (T boxes ) to solve problems is called dimensional analysis
Finding Mass from a Count • What is the mass of 90 average-sized apples if a dozen apples has a mass of 2.0kg? Hint: use “T” box 1 dozen 2.0kg 90 apples 12 apples 1 dozen apples = 15 kg or 15,000g
Practice Problems • If 0.20 bushel is 1 dozen apples and a dozen apples has a mass of 3.0 kg, what is the mass of 0.50 bushel of apples? 7.5 kg or 7500g
Assume 3.0 kg of apples is 1 dozen and that each apple has 8 seeds. How many apple seeds are in 14kg of apples? 448 seeds
When determining quantities in chemistry the method is the same….. You just use different units !!!!!!!!
Comparing mass of molecules -mass is measured in a.m.u. (atomic mass units) -Formula mass: the mass of the atoms in the compound in amu - round to the nearest hundredth. Formula Mass= H H Ex. Water 1.01 1.01 1.01 O 1.01 +16.00 16.00 18.02 a.m.u.
Finding formula mass: 1. Multiply # of atoms of each element by its mass (amu) 2. Add them together Ex. Fe2O3 Fe = 55.85 x 2 = 111.70 O = 16.00 x 3 = +48.00 = 159.70 amu
Calculate the formula mass for each of the following: AgNO3 = KC2H3O2 =
Formula Mass of Hydrates * Remember f.m. of hydrate includes the mass of the water • Calculate the f.m. of compound 2. Calculate the f.m. of H2O x # of molecules 3. Add together
Ex. BaCl2 2H2O Step 1: Ba= 1 x 137.33 = 137.33 Cl = 2 x 35.45 = + 70.90 208.23 Step 2: H= 2 x 1.01 = 2.02 O= 1 x 16.00 = +16.00 18.02 x 2 =36.04 Step 3: 208.23 + 36.04 = 244.27a.m.u.
But we have a problem….. We can’t measure amu’s in lab so scientists had to come up with a measurement we could use.
The Mole • Mole = 6.02 x 1023 particles of a substance –could be atoms, molecules, or formula units • Ex: A mole of hydrogen atoms is 6.02 x 1023 hydrogen atoms, a mole of paper is 6.02 x 1023 piece of paper • 6.02 x 1023 is known as Avogadro’s number-Avogadro was an Italian scientist in the 1800’s helped clarify the difference between atoms and molecules
A mole of any substance contains 6.02 x 1023 representative particles
mole is a unit • TedEd
Mass of a Mole • The atomic mass of an element expressed in grams is the mass of one mole of that element. • Example- 1 mole of carbon is 12.0 grams. • The molar mass of any two elements contain the same number of atoms • Ex: a dozen apples – 12 apples • a dozen oranges – 12 oranges
Molar mass (MOM) 1 mole of carbon atoms (6.02 x 1023atoms) Formula Mass 1 atom carbon 12.01 amu 12.01 grams
Would a mole of ping pong balls have the same mass as a mole of bowling balls?
Would a mole of carbon atoms have the same mass as a mole of sodium atoms? What would a mole of carbon atoms weigh in grams? What about a mole of sodium atoms?
Mass of a Mole of a Compound • Find the number of grams of each element in the compound, then add the masses together. • Ex: Find the molar mass of water. • Step 1- write down the formula H2O • Step 2- determine masses of each element 2 H atoms x 1.0 g = 2.0 g H 1 O atom x 16.0 g = 16.0 g O Step 3- add masses together 16.0 g O + 2.0 g H = 18.0 g H2O The molar mass of water is 18.0 g/mol
Cl Cl H H O C Cl Cl Which would have a higher mass…. a mole of water or a mole of carbon tetrachloride?
We can use the molar mass of a compound to convert between moles and masses of compounds
Avogadro’s Number (6.02 x 1023) -is the # of atoms in the molar mass of an element. 12.01g Carbon = 6.02 x 1023 atoms
OR - is the # of molecules in the molar mass of a compound. 18.02g H2O = 6.02 x 1023 molecules
Finding the Mass of a Mole of a compound • The decomposition of hydrogen peroxide (H2O2) provides sufficient energy to launch a rocket. What is the molar mass of hydrogen peroxide? 34.02g
Practice problems • Find the molar mass (MOM) of PCl3. 137.32g/mol • What is the molar mass(MOM) of 1.00 mol sodium hydrogen carbonate? (NaHCO3) 84.01g
Mole to Mass Conversion • Use the molar mass of an element or compound to convert between the mass of a substance and the moles of a substance • Conversion factor 12 inches = 1 foot 3 feet = 1 yard molar mass = 1 mole ex: 18.0 g H2O = 1 mol H2O
Mole – Mass Relationship • Use the molar mass of an element or compound to convert between the mass and moles of a substance. • ****Remember: molar mass = 1mol
Let’s try them with “T” boxes/conversion factors… • What is the mass of 3.4 moles of Mg? • What is the mass of 23.9 moles of Sn? • How many grams are in 18.1 moles of F? • How many grams are in 98.5 moles of Zn? • How many grams are in 2.7 x102mol Pb?
Find the mass in grams of 4.52x10-3mol of C20H42. 1.27g C20H42 • Calculate the mass in grams of 2.50 mol of Iron(II)hydroxide. 225g Fe(OH)2
What is the mass of 3.0 mol of NaCl? 176g • Whatis the mass of 9.45 mol of Aluminum oxide? 964g Al2O3
Find the number of moles in 3.70 x10-1g of boron. 3.43 x 10-2 mol B Calculate the number of moles in 75.0 g dinitrogen trioxide. 0.987 mol N2O3
Which would have more atoms a mole of carbon or a mole of sulfur? … both would have 6.02 x 1023 atoms
Converting # of atoms to Moles How many moles of magnesium is 1.25 x 10 23 atoms of magnesium? (hint: use “T” box) 2.08 x 10-1mol Mg or 0.208 mol Mg
Practice Problems How many moles is 2.80 x 1024 atoms of silicon? 4.65mol Si How many moles is 2.17 x 1023 representative particles of bromine? 0.360 mol Br2
Use “T” Boxes to calculate these….. • How many moles is 15.38 x 1023 atoms of Ni? • How many moles is 2 x 1032 atoms of Ti? • How many moles is 17.93 x 1018 atoms of Be? • How many moles is 8.7 x 10 23 atoms of Ag?
Cl Cl H H O C Cl Cl Which would have more atoms…. a mole of water or a mole of carbon tetrachloride? …so a mole of different compounds can have different numbers of atoms
Converting Moles of Compound to Number Of Atoms • Is C an element or compound? • Element- 1 mole is 6.02 x 1023 atoms • Is CO2 an element or compound? • Compound – 1 mole is 6.02 x 1023 molecules (or formula units) • Remember a mole is 6.02 x 1023 things !!!