Chemistry ch 10
molar mass
If you substitute grams for amu, you can find the ....
Mass = 2.5 mol X (89.8 g/mol) = 225 g Fe(OH)2 The molar mass of Fe(OH)2 is 89.8 g/mol Fe = 55.8 g/mol O2 = 16.0 X 2 = 32.0 g/mol H2 = 1.0 X 2 = 2.0 g/mol
Calculate the mass, in grams, of 2.50 mol of iron(II) hydroxide. Mass (g) = number of moles X (mass (g) / 1 mol)
Converting Moles to Number of Particles
Representative particles = moles X (6.02 x 1023 representative particles / 1 mol)
Volume of O2 = 0.375 mol X 22.4 L / 1.00 mol = 8.40 L
Suppose you have 0.375 mol of oxygen. What volume will the gas occupy STP?
1 mol or 6.02 x 10^23 atoms
The molar mass of an element contains ... or ...
temperature and pressure
The volume of a gas varies with ... and ... but is usually measured at standard temperature and pressure (STP).
atomic mass
The weighted average mass of all the naturally occurring isotopes of a single element
atomic masses
You can calculate the mass of a mole compound by adding the .... of the atoms that make up the molecule. (Round to the nearest tenth)
percent composition as a conversion factor
You can use percent composition to calculate the number of grams of any element in a specific mass of a compound EX: Propane (81.8% carbon and 18% hydrogen) mass C = 82.0g (81.8%) = 67.1g C mass H = 82.0g (18%) = 15g H (MUST use % button on calculator for this method )
representative particle
atoms, molecule, ion, etc
empirical formula
gives the lowest whole number ratio (the basic ratio) of atoms of the elements in a compound - may or may not be the same as a molecular formula
percent composition
if you divide the molar mass of each element by the molar mass of the compound and multiply by 100 you can calculate the ... % mass = (mass of an element in 1 mol compound / molar mass of compound ) X 100
mass
if you know the chemical formula of a compound, the subscripts are used to calculate the .... of each element in a mole of a compound (percent composition from the chemical formula)
% mass = ( mass g element / mass g compound ) X 100
the percent by mass of an element in a compound is the number of grams of the element divided by the mass in grams of the compound, multiplied by 100
percent composition
the relative amounts of the elements in a compound
Multiply the empirical formula by the multiplier to find the molecular formula
the second step to finding the molecular formula of a compound:
Molar volume
used to convert a known number of moles of gas to the volume of the gas at STP.
Calculating Molar Mass from Density
molar mass = density at STP X molar volume at STP g / mol = g / L X 22.4 L / 1.00 mol
converting number of particles to moles
mole = representative particles X (1 mole / 6.02 X 10^23 representative particles)
Volume of gas
moles of gas X (22.4 L / 1.00 mol)
molecular formula
simple whole number multiple of its empirical formula - can be the same as the empirical formula
Mole
the amount of a substance that contains as many entities as there are atoms in exactly 12.0g of carbon -12
steps in determining the empirical formula of a compound
step 1: change % to g step 2: convert g to mol step 3: divide each mol value by the smaller number of mol found to get the number of atoms
Find the multiplier by dividing the molar mass by a compounds formula mass (empirical formula mass)
the first step to finding the molecular formula of a compound:
Avogadro's number
6.02 x 10^23
substance, moles
Use the molar mass of an element or compound to convert between the mass of a .... and the ... of a substance. - Mass (g) = number of moles X (mass (g) / 1 mole)' (pg 12 of refrence table)
molecular
can be reduced
molar mass
you can calculate the molecular formula of a compound from the empirical formula if you know the compounds....
Percent Composition From Mass Data
% by mass of element = mass of element / mass of compound times 100%
P = 31.0 g/mol Cl = 35.5 g/mol x 3 = 106.5 g/mol The molar mass of PCl3 is 137.5 g/mol
Find the molar mass of phosphorus trichloride.
Atoms = 1.14 mol SO3 X (6.02x1023 molecules SO3/ 1 mol SO3) X 4 atoms / 1 molecule SO3 = 2.75 X 1024 atoms.
How many atoms are in 1.14 mol SO3?
Moles = 2.80 X 1024 atom Si x (1 mol Si / 6.02 X 1023 atoms Si) = 4.65 mol Si
How many moles is 2.80 X 1024 atoms of silicon? - round to the number of sig figs
22.4 L
Molar volume of a gas = ...
atomic mass
The ... of an element expressed in grams is the mass of a mole of that element
molar mass
The mass of a mole of an element is called its ... Ex: The .... of Carbon is 12.0 g / mol and the ... of Oxygen is 16.0 g/ mol
number of grams
To calculate the molar mass of a compound, find the ... of each element in 1 mole of the compound. Then add the masses of the elements in the compound.
Density = molar mass X molar volume = (83.8 g/mol) / (22.4 L / 1.00 mol) = 3.74 g / L Kr
What is the density of krypton at STP?
32.1 + (16.0 X 3) = 80.1 amu
What is the molecular mass (this is in amu) of sulfur trioxide?
empirical
can't be reduced anymore
STP
means temperatures at 0oC or 273oK and a pressure of 101.3 kPa or 1 atmosphere (atm) 1 mol or 6.02X10^23 representative particles of any gas occupies a volume of 22.4 L.
% value
each different element in a compound consists of a ... that total to 100%
CO2, HO
empirical formula EX: The molecular formula for carbon dioxide is CO2. what is the empirical formula? The molecular formula for hydrogen peroxide is H2O2. what is the empirical formula?
Avogadro's hypothesis
equal volumes of gases at the same temperature and pressure contain an equal number of particles.
counting, mass, and volume
how do we measure matter
6.02 x 10^23
in one mole there are ... representative particles in an (atom, molecule, ion, etc) - a mole of any substance contains ... representative particles
Mass (g) = number of moles X (mass (g) / 1 mole) First we need to calculate the molar mass of NaCl, 58.5 g/mol Now all we need to do to calculate the molecular mass is multiply by 3. Mass = 3.00 mol X (58.5 g / mol) = 176 g NaCl
what are the steps needed to solve this problem: What is the mass of 3.00 moles of NaCl? (remember sig. figs.)
