Download Chapter 3 Test Review

Chapter 3 Test Review
-Two short answer and one word
problem for each concept
- Test will take while. Start Monday
and finish by Wednesday.
- Homework for all of chapter one is
due before break of else all days will
be minimal.
Test Monday 11/24/-11/26
Topic 1: Atomic Masses and Mass
Spectrometry

Atomic masses
 Atoms don’t always retain the same weight
 Mass of an atom is determined as Protons + Neutrons
 With a specific element, protons do not change but
neutrons can change
 This is called an isotope
*Topic 1 Question
There are three isotopes for neon. How many protons,
electrons, and neutrons a
20Ne, 21Ne, and 22Nere there for each isotope?

Topic 1: Atomic Masses and Mass
Spectrometry
*Topic 1 Question:
Element E occurs in two isotopes. 15% of all atoms of E
have a relative atomic mass of 51.05 and the rest a relative
atomic mass of 52.05. What is the average relative atomic
mass for the element E? What element might E be?
Draw a mass spec for element E
Topic 2: Molar Mass
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
One mole of anything is 6.02X1023
A mole is defined as the amount of atoms in 12 grams of
Carbon
*Topic 2 Question:
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1) How many grams are in 1 mole of aluminum?
II) Based on this, what do you think is the most common
isotope of aluminum?
III) What is the molar mass of ammonium phosphite?
Topic 2: Molar Mass
*Topic 2 Question:
How many atoms are in 6.4 micrograms of Au?
Topic 3) Percent Composition

Percent composition is calculated by finding the percent
of each atom in a compound.
*Topic 3 Question
1) What is the percent composition of each atom in
ammonium dihydrogen phosphate?
II) On an AP test 2 years ago, the test asked for “decimal
notation.” Answer the above question in decimal notation.
Don’t let the wording trick you.
Topic 4: Empirical and Molecular Formulas

Empirical formula is a formula in lowest terms. While
molecular formula is “real” formula.
*Topic IV Questions
 I) What is the empirical and molecular formula of water?
 II) What is the empirical and molecular formula of
hydrogen peroxide?
 III) What is the empirical and molecular formula of
glucose?
Topic 4: Determine Empirical and Molecular
Formulas for a Compound

This is how you determine empirical and molecular formulas.
You will be given the percent composition to determine the
empirical formula and the atomic mass IF they want you to
determine the molecular formula



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Step 1) Turn mass percent into grams. Hence you now have a 100
gram sample
Step II) Calculate the amount of moles of each type of element in
the 100 gram sample
Step III) Divide of the total amount of moles by the lowest
number of moles determined
Step IV) Make sure each number is a whole number (you may
have to multiple by 2. This is now the EMPIRICAL FORMULA for
the compound.
Step V) To find molecular formula, divide the GIVEN molar mass
of the molecular formula but the molar mass of the empirical
formula (you must calculate)
Step VI) Multiple the empirical formula by the number found in
the step above. Remember this must be a whole number.
Topic 4: Determine Empirical and Molecular
Formulas for a Compound
*Topic 4 Question
Caffeine has an elemental analysis of 49.48% carbon, 5.190%
hydrogen, 16.47% oxygen, and 28.85% nitrogen. It has a
molar mass of 194.19 g/mol. What is the molecular formula
of caffeine?
Topic 5: Chemical Equations



Write the chemical equations from the words. Include
whether each substance is a solid (s), liquid (l), gas (g) or a
dissolved salt in water which means aqueous (aq)
Reactants  Products
After you write out the equation, make sure each side is
balanced
Topic 5: Chemical Equations
*Topic 5 Question
Calcium hydroxide aqueous solution reacts with phosphoric
acid to yield calcium phosphate precipitate and water.
Determine the balanced equation.
Topic 6: Reaction Stoichiometry


Balance both sides of the equation
Know how to do mole ratios between products and
reactants
*Topic 6 Question
What is the mole ratio of hydrogen gas to oxygen gas?
What is the mole ratio of hydrogen gas to water?
What is the mole ratio of oxygen gas to water?
Topic 6: Reaction Stoichiometry

CaCO3+2HCl->CaCl2+H2O+CO2
*Topic 6 Questions
1) 5.00 grams of calcium carbonate in excess hydrochloric
acid produces how much carbon dioxide?
II) How many moles of hydrochloric acid is needed to
produce 3.45X1012 molecules of calcium chloride?
III) How many moles of calcium carbonate was asses if 12
grams of water was formed?
Topic 7: Limiting Reactants and Percent
Yields
*Topic 7 question
How many grams of NH3 can be produced (theoretically)
from the reaction of 5.0 g of nitrogen gas and 5.0g of
hydrogen gas?
Note: you must first determine the limiting reagent?
Topic 7: Limiting Reactants and Percent
Yields
*Topic 7 question
If 8.52 g are actually formed, what is the percent yield of
NH3?