Chapter 5 Flashcards
What is the atomic mass of the elements in the periodic table based on?
carbon 12
What is the atomic mass of carbon 12?
12 amu
How do you calculate the atomic mass of an element?
atomic mass = (fractional abundance times the mass of the isotope 1 (percent written in decimal form) + (fractional abundance times the mass of the isotope 2 (percent written in decimal form))
Sample Problem: Neon gas naturally exists as a mixture of 3 isotopes (20Ne, 21Ne, and 22Ne) and has an atomic mass of 20.1797 amu. What is the percent abundance of 22Ne (21.9914 amu)?
•91.84% 20Ne (19.9924 amu)
•0.47% 21Ne (20.9940 amu)
7.69 %
What is a mole?
a mole is a number equal to the number of carbon atoms in exactly 12 grams of carbon 12
amount of any substance (like how dozen = 12, pair = 2)
What does 1 mol equal?
6.022 x 10^23 molecules/atoms
Sample problem: A copper wire is found to have a mass of 325g. Copper comes as an avg mass of 65.546 g
a) Calculate the number of moles of copper in the wire.
b) Calculate the number of copper atoms in the wire.
a) 1 mol Cu = 4.96
b) 2.98 x 10^24
What do moles allow us to do?
moles allow us to express a chemical’s atomic mass in grams
If an element has a mass of a certain amount, how many moles does that equal?
1 mol of that certain element
Molar mass = ____ mass
molar mass = atomic mass x number of element type present (g/mol)
What is the molar mass of oxygen gas?
15.999 x 2 = g/mol of O2
If we are calculating the molar mass of a covalently bound molecule, we use what type of formula?
the molecular formula (C6H12O6)
If we are calculating the molar mass of an ionic compound, we use what type of formula?
the formula unit (ex: CaCl2)
How many water molecules are in a 500 mL amount of water?
1.67 x 10 ^25 water molecules
Chalk is comprised of calcium carbonate. How many formula units of calcium carbonate are present in 20.0g of chalk?
1.20 x 10^23 formula units
If you have the amount of a substance in moles, what do you use to figure out the number of particles?
Avogadro’s number
If you have the amount of a substance in moles and you want to find the mass, what do you use?
the molar mass
What can composition be described by?
1) the number of atoms of each element
2) the percentage (mass) of each element
What do you do when you want to calculate the mass percent of a certain element in a compound?
mass percent = (mass of a particular element in a compound / total mass of a compound) x 100
Sample Problem: Acetetopmenophene is C8H9NO2
a) calculate the molar mass
b) calculate each of the percentages
a) 151.165 g/mol
b) % C is 63.565, & H is 6.001%, % N is 9.266%, %O is 21. 168
Sample Problem: C12H18Ox molecules have 75.69285% C, what’s the chemical formula?
C3H18O2
What are empirical formulas?
simplest whole-number ratios of atoms in a compound (H2O, CO2, NaCl)
What are molecular formulas?
formulas containing all atoms in a molecule (ex: C6H12O6)
What type of formula do ionic compounds have?
always empirical formula
When calculating empirical formulas from mass percentage, how many grams do you assume there are of the substance?
100g (so that something like 38.67 % C gets converted to 38.67 g of C)
What are chemical reactions?
involve the rearrangement of atoms in one or more substances
What are chemical equations used for?
used to represent and describe chemical reactions
What info can you get from chemical equations?
natures of reactants and products and the ratio in which they react
What level do chemical reactions happen?
the molecular level
What is the sign for solid, liquid, gas?
s, l , g
What is the sign for states in which the compound is dissolved in water?
aq
How do you balance equations?
balance one element at a time
start by balancing the largest compound
if element exists by itself, balance it last
change only the coefficient, not the elements
What is stoichiometry?
relates the measure of substance in a chemical reaction
What is mass of oxygen is required to react completely with 20.0 g of methane?
79.8 g
What is the mass of water produced given 20.0 g of methane?
44.9 g of H2O
What are limiting reactants?
the substance that limits the amount of product that is made, it runs out first
What is the first step in determining the limiting reactant?
making a balanced equation
What is the second step in determining the limiting reactant?
convert reactants to moles
What is the third step in determining the limiting reactant?
calculate the amount of product that each reactant can make
What is the theoretical yield?
amount of product formed when limiting reactant is completely consumed
What is the percent yield?
percentage of theoretical yield
What is the equation for percent yield?
actual experimental yield/theoretical yield x 100
