Transcript Homework - PHA Science

20 Sept. 2011
Objective: You will be able to:
 Review making calculations and
manipulating measurements
 Determine the formula for copper (II)
sulfate hydrate
 Homework Quiz: Week of Sept. 19
 How will you know when to stop heating
your copper (II) sulfate sample? Why?

Agenda
Turn in Problem Set 2
II. Problem Set 1: Commonly missed
questions
III. Finish lab procedure
IV. Clean up
Homework:
Quiz on chapters 1-2: tomorrow
Lab notebook due Thurs.
I.
Clean Up
CuSO4 in trash
 All equipment washed and hung up to dry
 Ring stands, Bunsen burners and strikers,
etc. back in cabinets
 Wipe down counters
 Start planning out your calculations

Homework

Quiz on ch. 1-2 tomorrow!
Safety
Wear goggles until all your equipment has
been cleaned and returned.
 A hot crucible looks just like a cold
crucible! Always use crucible tongs.
 Work efficiently but carefully.

Technical notes
Heat the crucible uncovered or with the
cover tilted to allow water vapor to escape.
 Cool the crucible with the cover on.
 Cool the crucible in the desiccator for very
best results.
 Never mass a hot or warm crucible.
 Oil from your fingers will stick to the
crucible and effect your data.

Work Ethic
Work quickly. If you have “down time,”
think: “What can I do now to save time
later?”
 Set up data tables and calculations while
you wait.

This period
Carry out your procedure and collect data.
 Begin calculations as soon as you can!
 Percent of water in the hydrate by mass.
 Mole ratio of anhydrous CuSO4 to H2O
in your sample.
 Work to show how you got your number
of molecules of water of hydration.

Homework
Ch. 2 problem set: tomorrow
 Quiz on chapters 1-2: tomorrow
 Lab notebook due Thurs.

21 September 2011
Objective: You will be able to:
 show what you know about chapters 1
and 2: calculations and compounds
 Do now: Questions?

Quiz
Flip it over when you’re done.
 Zero tolerance policy for disruptions.
 When you finish: Work on lab calculations
silently.

Homework
Check chapter 3 summer assignment
answers online: Tomorrow
 Lab notebook: calculations: tomorrow

22 September 2011



Take Out: Lab Notebook
Objective: You will be able to:
 review Avogadro’s number, moles, molar
mass, conversions, empirical and
molecular formulas
Homework Quiz:
1. How many atoms of silver are equal to
3.50 moles of silver?
2. Calculate the molar mass of silver nitrate.
(Nitrate is NO3-)
Agenda
Homework Quiz
II. Review of Avogadro’s number, moles,
molar mass, conversions, empirical and
molecular formulas
III. Challenge problem!
Homework: p. 110 #18, 22, 26, 30, 44, 54:
Mon.
I.
The Mole

Atoms are so tiny; how do we quantify
their masses?
The mole
Mole: The unit for amount of substance
23 atoms or molecules
 =6.02x10
23
 Avogadro’s Number = 6.02x10
 This is equal to the number of atoms of
carbon in 12 grams of Carbon-12.

Example
a)
b)
How many moles of helium atoms are in
6.46 g of He?
How many atoms is this?
Problems
a)
b)
c)
How many moles of magnesium are
there in 87.3 g of Mg?
How many atoms is this?
Zinc is a silvery metal that is used in
making brass (with copper). How many
grams of Zn are in 0.356 mole of Zn?
Sulfur is a nonmetallic element present in
coal. When coal is burned, sulfur is
converted to sulfur dioxide and eventually
to sulfuric acid that gives rise to the acid
rain phenomenon. How many atoms are
in 16.4 g of S?
 Calculate the number of atoms in 0.551 g
of potassium.

Molar Mass
The mass of a molecule.
 Calculate the molar mass of:
 sulfur dioxide (SO2)
 caffeine (C8H10N4O2)
 methanol (CH4O)

SWBAT convert between grams, moles and number of particles of
elements and compounds.
Using Molar Mass
Methane (CH4) is the principal component
of natural gas. How many moles of
methane are present in 6.07 g of CH4?
 Calculate the number of moles of
chloroform (CHCl3) in 198 g of
chloroform.

Particles, Moles and Mass
1.
2.
3.
4.
Calculate the mass of 1.2x1024 molecules
of carbon dioxide.
How many molecules of glucose are in
2.50x10-3 grams of glucose?
Calculate the mass of 1 molecule of water.
How many molecules of carbon dioxide
are there in 0.0003 grams of carbon
dioxide?
SWBAT convert between grams, moles and number of particles of
elements and compounds.
Percent Composition by Mass

the percent by mass of each element in a
compound.
 Can be used to determine the purity of a
substance by comparing empirical data
to known composition.
Practice Problems
Calculate the percent by mass of each
element in hydrogen peroxide.
 Phosphoric acid (H3PO4) is a colorless,
syrupy liquid used in detergents,
fertilizers, toothpastes and in carbonated
beverages for a “tangy” flavor. Calculate
the percent composition by mass of H, P
and O in this compound.

Empirical Formulas
Given the percent composition, you can
determine the empirical formula of a
compound (reverse of calculating percent
composition)
 This data is often found by experiment.

Practice Problems


Ascorbic acid (vitamin C) cures scurvy. It is
composed of 40.92% carbon, 4.58%
hydrogen and 54.50% oxygen by mass.
Determine its empirical formula.
A sample of a compound contains 1.52 grams
of nitrogen and 3.47 grams of oxygen. The
molar mass of this compound is between 90
and 95 g. Determine its molecular formula
and accurate molar mass.
More practice problems
1.
2.
Determine the empirical formula of a
compound having the following percent
composition by mass: K: 24.75%, Mn:
34.77%, O: 40.51%
A sample of a compound containing boron
and hydrogen contains 6.444g of boron and
1.803 g of hydrogen. The molar mass of the
compound is about 30 g. What is its
molecular formula and exact molar mass?
One more…

Chalcopyrite (CuFeS2) is a principal
mineral of copper. Calculate the number
of kilograms of copper in 3.71x103 kg of
chalcopyrite.
Challenge!
A 0.1005 g sample of menthol (composed
of C, H and O) is combusted, producing
0.2829 g of CO2 and 0.1159 g of H2O.
What is the empirical formula? (Hint: Be
aware that some oxygen in the product
comes from the air, and some from the
menthol!)
 the compound has a molar mass of 156
g/mol what is the molecular formula?

Homework
p. 110 #18, 22, 26, 30, 44, 54: Mon.
 Finish challenge problem

26 September 2011


1.
2.
Objective: You will be able to:
 write and balance chemical equations and
calculate mole to mole and mass to mass
stoichiometry.
Homework Quiz
Calculate the mass of 1 atom of palladium.
Calculate the empirical formula of a
compound composed of H, O and S, which
has 2.1 percent H and 65.3 percent O.
Agenda
Homework Quiz
II. Go over homework
III. Review writing and balancing equations,
mole and mass stoichiometry
IV. Practice Problems
Homework: 112 #60c, e, g, h, k and l, 64,
66, 71, 74: tomorrow
Correct Quiz for a small quiz grade: Weds.
I.
Decoding Chemical Equations

2H2(g) + O2(g) → 2H2O(l)
Balancing Chemical Equations
Ex 1. KClO3  KCl + O2
Ex 2. C2H6 + O2  CO2 + H2O
Write and balance:
1.
2.
3.
4.
Ammonia gas reacts with oxygen gas to
produce nitrogen monoxide gas and liquid
water.
Solid lithium reacts with nitrogen gas to
produce solid lithium nitride.
Nitroglycerin (C3H5N3O9) decomposes
explosively to produce nitrogen gas, carbon
dioxide gas, water vapor and oxygen gas.
Carbon dioxide gas reacts with potassium
hydroxide to produce potassium carbonate
and water vapor.
Mole Ratios
Coefficients indicate the number of moles
(or molecules) of each compound
 Ex 1. N2(g) + 3H2(g)  2NH3(g)
1. How many moles of hydrogen gas react
with 1 mole of nitrogen gas?
2. How many moles of ammonia gas are
produced by the reaction of 3 moles of
hydrogen gas in excess nitrogen gas?


3.
4.
5.
N2(g) + 3H2(g)  2NH3(g)
How many moles of hydrogen gas are
required to react with 15 moles of nitrogen
gas?
How many moles of hydrogen gas are
required to produce 25.0 moles of ammonia
gas?
If 10 moles of nitrogen gas was reacted with
10 moles of hydrogen gas, which would be
completely reacted? Which would be
excess?
Mass to mass stoichiometric
relationships: Ex 1.
The food we eat is degraded in our bodies to
provide energy for growth and function. A
general equation for this very complex
process is:
C6H12O6 + 6O2  6CO2 + 6H2O
If 856 g of C6H12O6 is consumed by a person
over a certain period, what is the mass of
CO2 produced?
Example 2
All alkali metals react with water to
produce hydrogen gas and the
corresponding alkali metal hydroxide. A
typical reaction is that between lithium
and water:
2Li(s) + 2H2O(l)  2LiOH(aq) + H2(g)
How many grams of Li are needed to
produce 9.89 grams of H2?

Example 3
Methanol (CH3OH) burns in air according
to the equation
2 CH3OH + 3O2  2CO2 + 4H2O
If 209 g of methanol are used up in the
combustion process, what is the mass of
H2O produced?

Homework

112 #60c, e, g, h, k and l, 64, 66, 71, 74
27 September 2011
Objective: You will be able to:
 determine which reactant is the limiting
reagent and calculate percent yield.
 Homework Quiz
1.
Balance: P4O10 + H2O → H3PO4
2. If 10.0 grams of tetraphosphorus decaoxide
is reacted with excess water, calculate the
number of grams of phosphoric acid
produced.
Bonus: What mass of water reacts with 10.0
grams of P4O10?

Agenda
Homework Quiz
II. Go over homework
III. Review limiting reagent and percent
yield
IV. Practice Problems
Homework: p. 114 #84, 85, 89, 93, 107,
131
Correct Quiz for a small quiz grade: Weds.
Ch. 1-3 test Thursday.
I.
Example 4
The reaction between nitric oxide and
oxygen to form nitrogen dioxide is a key
step in photochemical smog formation:
2NO(g) + O2(g)  2NO2(g)
How many grams of O2 are needed to
produce 2.21 g of NO2?

Limiting Reagents Ex 1.
Urea is prepared by reacting ammonia with
carbon dioxide:
2NH3(g) + CO2(g) (NH2)2CO(aq) + H2O(l)
In one process, 637.2 g of NH3 are treated with
1142 g of CO2.
a) Which of the two reactants is the limiting
reactant?
b) Calculate the mass of (NH2)2CO formed.
c) How much excess reagent (in grams) is left at
the end of the reaction?

Example 2
The reaction between aluminum and iron(III)
oxide can generate temperatures approaching
3000oC and is used in welding metals:
2Al + Fe2O3  Al2O3 + 2Fe
In one process, 124 g of Al are reacted with 601 g
of Fe2O3.
a) Calculate the mass (in grams) of Al2O3 formed.
b) How much of the excess reagent is left at the
end of the reaction?

30 Sept. 2010
Objective: SWBAT determine limiting
reagent, and calculate percent yield.
 Do now:
TiCl4(g) + 2Mg(l)  Ti(s) + 2MgCl2(l)
If 3.54x107 g of TiCl4 are reacted with
1.13x107 g of Mg, calculate the limiting
reagent and the theoretical yield of Ti.

Reaction Yield
theoretical yield: the amount of product that
would result if all of the limiting reagent
reacted.
actual yield: amount of product actually
obtained from a reaction
% yield 
actualyiel d
theoretica lyield
 100 %
28 September 2011


Objective: You will be able to:
 practice all chapter 3 skills
Homework Quiz
P4O10 + 6H2O → 4H3PO4
1. In the lab, 10.00 grams of tetraphosphorus
decaoxide were reacted with 5.00 grams of
water. Determine the number of grams of
phosphoric acid produced.
2. If 12.5 grams of H3PO4 were produced when
this reaction was performed in the lab,
calculate the percent yield.
Agenda
Homework Quiz
II. Hand in Quiz Corrections
III. Go over homework
IV. Chapter 3 Problem Set
Homework: Ch. 1-3 test Tuesday (new
unit starts tomorrow!)
Chapter 3 Problem Set: Tuesday
I.
Percent Yield Ex 1
Titanium is a strong, lightweight, corrosionresistant metal that is used in rockets, aircraft,
jet engines and bicycle frames. It is prepared by
the reaction of titanium (IV) chloride with
molten magnesium between 950oC and 1150oC:
 TiCl4(g) + 2Mg(l)  Ti(s) + 2MgCl2(l)
3.54x107 g of TiCl4 are reacted with 1.13x107 g of
Mg. a) Calculate the theoretical yield of Ti in
grams. g) Calculate the percent yield if 7.91x106
g of Ti are actually obtained.

Ex 2.
Industrially, vanadium metal, which is
used in steel alloys, can be obtained by
reacting vanadium(V) oxide with calcium
at high temperatures:
5Ca + V2O5  5CaO + 2V
1.54x103 g of V2O5 is reacted with 1.96x103 g
of Ca. a) Calculate the theoretical yield of
V. b) Calculate the percent yield if 803 g
of V are obtained.

On the test














Classification and states of matter
Physical and chemical properties
Measurement, handling numbers
Dimensional analysis
Atomic theory and structure
Atomic number, mass number, isotopes
Molecules and Ions
Chemical formulas and names (incl. acids)
Avogadro’s number, moles, molar mass
% composition by mass
Empirical and molecular formulas
Chemical reactions and equations
Mole to Mole and Mass to Mass Stoichiometry
Limiting reagents, reaction yield
Review Game!
With your partner, solve the problem and
show all your work.
 Raise your hand when you are done.
 First group with the correct answer gets
the point and a chance at the bonus point.


An unfortunate tree is carrying on
photosynthesis in the forest. One morning,
it wakes up with dew on its leaves. The
sunshine immediately begins to evaporate
the dew. Suddenly, a storm rolls in and a
giant wind knocks the tree to the ground. A
limb is struck by lighting and partially
burns. Over the next year, the remaining
parts of the tree rot away. List all the
physical changes in one column and the
chemical changes in another.

One gallon of gasoline in an automobile’s
engine produces on the average 9.5 kg of
carbon dioxide. Calculate the annual
production of CO2 in kilograms if there are
40 million cars in the US and each car
covers a distance of 5000 mi. at a
consumption rate of 20 miles per gallon.
A transition metal with 26 protons and 24
electrons forms a bond with a polyatomic
ion consisting of phosphorus and four
atoms of oxygen with a charge of 3-.
 a) What type of bond holds this compound
together?
 b) Write the name and formula for this
compound.

Imagine this compound contains
hydrogen instead of iron.
 a) What type of compound is it?
 b) Write the name and formula for this
compound.


Imagine that acid lost one oxygen. Name
and write the formula for the newly
formed acid.

Calculate the molar mass of this acid, and
the percent by mass of each element.
A compound is formed by one carbon
atom and four chlorine atoms.
 a) What type of bond holds these atoms
together?
 b) Write the name and formula of this
compound.


Carbohydrates contain C, H and O, in
which the hydrogen to oxygen ratio is 2:1.
A certain carbohydrate contains 40.0%
carbon by mass. Calculate the empirical
and molecular formulas if the molar mass
is about 178 g.
Lysine, an essential amino acid in the
human body contains C, H, O and N. In
one experiment, the complete combustion
of 2.175 g of lysine gave 3.94 g CO2 and
1.89 g H2O. In a separate experiment,
1.873 g of lysine gave 0.436 g NH3. a)
Calculate the empirical formula.
 b) If the molar mass is about 150 g,
calculate the molecular formula.

Hydrogen gas can be prepared by reacting
propane gas (C3H8) with steam at about
400oC. The products are carbon
monoxide and hydrogen gas. a) Write a
balanced equation.
 b) How many kilograms of hydrogen gas
can be obtained from 2.84x103 kg of
propane?


Solid elemental sulfur reacts with a
solution of nitric acid to produce a
solution of sulfuric acid, nitrogen dioxide
gas and water. Write and balance a
chemical equation.
When potassium cyanide reacts with
acids, a deadly poisonous gas, hydrogen
cyanide, is given off.
 KCN(aq) + HCl(aq)  KCl(aq) + HCN(g)
 If a sample of 0.140 g of KCN is treated
with an excess of HCl, calculate the
amount of HCN formed, in grams.

Nitric oxide (NO) reacts with oxygen gas
to form nitrogen dioxide, a dark brown
gas.
 In one experiment, 0.866 mol of nitric
oxide is mixed with 0.503 mol of oxygen
gas. Calculate which is the limiting
reagent. How many moles of nitrogen
dioxide are produced?

When heated, lithium reacts with nitrogen
to form lithium nitride.
 What is the theoretical yield of lithium
nitride in grams with 12.3 grams of
lithium are heated with 33.6 grams of
nitrogen?
 If the actual yield of lithium nitride is 5.89
grams, what is the percent yield?
