LIVING BY
CHEMISTRY
Unit 4: TOXINS
Stoichiometry, Solution Chemistry, and Acids and Bases
In this unit you will learn:
•
•
•
how toxins are defined
how chemists determine toxicity
the mechanisms by which toxic substances act
in our bodies and what this has to do with
chemical reactions
Section V: Toxic Cleanup
• Lesson 23 Solid Evidence
• Lesson 24 Mole to Mole
• Lesson 25 Mole Tunnel
• Lesson 26 Get the Lead Out
• Lesson 27 Call Poison Control
Lesson 23: Solid Evidence
• Precipitation Reactions
ChemCatalyst
• Kidney stones are solid blockages that
sometimes occur in the kidney. Below is the
chemical equation for a double exchange
reaction between calcium chloride and sodium
oxalate that results in the formation of one type of
kidney stone.
• CaCl2(aq) + Na2C2O4(aq) 2NaCl(aq) +
CaC2O4(s)
a. What do you expect to see in the beaker if you
complete this reaction?
b. Which compound is the kidney stone? What is
your reasoning?
Key Question
• Which substances precipitate from aqueous solutions?
You will be able to:
• explain what a precipitation reaction is
• write net ionic equations for precipitation reactions
Prepare for the Lab
• Work in pairs.
• Precipitate: A solid produced in a chemical reaction
between two solutions.
Discussion Notes
• CaCl2(aq) + Na2C2O4(aq)  2NaCl(aq) +
CaC2O4(s)
• The mixing of two ionic solutions sometimes
results in the formation of a solid precipitate.
• Precipitation is not limited to solids.
• The degree to which a compound dissolves in
water is called its solubility.
Discussion Notes (cont.)
• Solubility varies from compound to compound.
Solubility Trends
Anions
NO3–
CL–
OH–
SO42–
CO32–
C2O42–
PO43–
Most alkali metals, such
as Li+, Na+, K+, NH4+
S
S
S
S
S
S
S
Most alkaline earth
metals, such as Mg2+,
Ca2+, Sr2+
S
S
N
S
N
N
N
Period 4 transition
metals, such as Fe3+,
Co3+, Ni2+, Cu2+, Zn2+
S
S
N
S
N
N
N
Other transition metals,
such as Ag+, Pb2+, Hg2+
S
N
N
N
N
N
N
Discussion Notes (cont.)
• There are positive and negative aspects to the
solubility of toxic substances.
• Once a substance is absorbed, it may be difficult
for the body to get rid of it through its natural
filtration systems, the kidneys and the liver.
Wrap Up
• Which substances precipitate from aqueous
solutions?
• Precipitation depends on solubility; compounds
that are not very soluble tend to form
precipitates.
• Mixing two aqueous salt solutions often results in
the formation of a precipitate.
• Soluble substances can interact with the human
body in either positive or negative ways.
Check-in
• A solution of K2SO4 is mixed with a solution of
Pb(NO3)2, and a precipitate forms.
a. Write the chemical equation for this
reaction.
b. What is the precipitate that forms? How do
you know?
Lesson 24: Mole to Mole
• Mole Ratios
ChemCatalyst
• One way to remove potentially toxic substances from a water
source is to precipitate out the harmful ions. Consider the
removal of copper ions by precipitation.
• 2NaOH(aq) + Cu(NO3)2(aq) 2NaNO3(aq) + Cu(OH)2(s)
• Suppose you add 100 mL of 0.10 M NaOH(aq) to 100 mL of
0.10 M Cu(NO3)2(aq).
a. Have you added equal numbers of moles of the two
substances? Explain your thinking.
b. Have you added equal numbers of grams of the two
substances? Explain your thinking.
c. Have you added enough NaOH(aq) to remove all the
copper from the solution? Explain your thinking.
Key Question
• How can you convert all the reactants to products?
You will be able to:
• define a mole ratio
• explain how to combine reactants in order to make the
most product from a reaction
• identify a limiting reactant
Prepare for the Lab
• Work in groups of four.
• Wear safety goggles at all times.
• Sodium hydroxide, NaOH, is corrosive. Do not
get any on skin or near eyes.
• In case of spills, rinse with large amounts of
water.
Discussion Notes
• The coefficients in chemical equations indicate how many
counting units (such as moles) of each reactant combine
and how many counting units of each product formed in a
single reaction.
• Coefficients in chemical equations always refer to the
number of units (molecules, ions, moles) that are
combining.
Discussion Notes (cont.)
• The mole ratios are the proportions in which two
substances (reactants, products, or both) combine or
form.
• Mole ratio: The ratio represented by the coefficients in a
chemical equation showing how many units of each
substance must combine to make the maximum amount
of product.
• When reactants are not combined in their exact mole
ratios, one of the reactants runs out and the other is left
over.
Wrap Up
• How can you convert all the reactants to
products?
• Coefficients in chemical equations represent
the proportions in which reactants combine and
products form. This proportion is also called the
mole ratio.
• If reactants are not combined in their mole
ratio, one will run out and the other will be
excess. The one that runs out is called the
limiting reactant.
Check-in
• The reaction to form silver phosphate, Ag3PO4(s), is given
by this chemical equation:
• AgNO3(aq) + Na3PO4(aq) Ag3PO4(s) + NaNO3(aq)
• 1. Balance the equation.
• 2. Which combination of reactants results in the maximum
amount of product?
a. 1.0 g AgNO3 to 1.0 g Na3PO4
b. 3.0 g AgNO3 to 1.0 g Na3PO4
c. 1.0 mole AgNO3 to 1.0 mole Na3PO4
• d. 3.0 moles AgNO3 to 1.0 mole Na3PO4
Lesson 25: Mole Tunnel
• Stoichiometry
ChemCatalyst
• This reaction produces the main substance found in
human bones (calcium phosphate):

3CaCl2(aq) +
Ca3(PO4)2(s) +
2Na3PO4(aq) Calcium
6NaCl(aq)
Calciumcan you
Sodium
a. How Sodium
many moles of calcium phosphate
make
chloride
phosphate
phosphate
chloride
using 6 moles
of calcium chloride,
CaCl2?
b. How many moles of calcium phosphate can you make
using 111 g of CaCl2?
Key Question
• How do you convert between grams and moles
to determine the mass of product?
You will be able to:
• complete stoichiometric calculations for a variety of
chemical reactions.
Prepare for the Classwork
• Work in pairs.
• Stoichiometry: the quantitative relationship between
reactants and products in a chemical reaction.
Discussion Notes
When working stoichiometric problems, grams
must be converted to moles and then moles
must be converted back to grams.
Wrap Up
• How do you convert between grams and moles to
determine the mass of product?
• In order to calculate the mass of reactant needed
to make a certain mass of product, it is
necessary to convert mass to moles and then
convert moles back to mass.
• Mole ratios assist in converting back and forth
between moles of reactant and moles of product.
Check-in
• Consider this reaction:
• Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)
• How many grams of magnesium, Mg, do you
need to produce 190 g of magnesium chloride,
MgCl2?
Lesson 26: Get the Lead Out
• Limiting Reactant and Percent
Yield
ChemCatalyst
• Sodium bicarbonate, NaHCO3, and acetic acid, CH3COOH, react to
generate CO2 gas:
• CH3COOH(aq) + NaHCO3(s)  CH3COOHNa(aq) + H2O(l) +
CO2(g)
• You set up the reactions as shown. The gas generated by the
reaction will inflate the balloon when the sodium bicarbonate is
poured into the acetic acid.
• Predict the relative order of the balloon sizes. Justify your choice.
• a. 1 = 2 = 3
b. 1 < 2 < 3
c. 1 < 2 = 3
d. 1 = 2 < 3
Key Question
• Which reactant determines how much product is made?
You will be able to:
•
•
complete stoichiometric calculations involving limiting
reactant
calculate percent yield when the actual yield is known
Prepare for the Activity
• Work in pairs.
Discussion Notes
• In the real world, substances are rarely mixed in
the exact mole ratios specified by a chemical
equation.
• In order to identify the limiting reactant, the
number of moles of the reactants on hand must
be compared with the mole ratio of the reactants.
Wrap Up
• Which reactant determines how much product is
made?
• The limiting reactant is the substance that gets
used up in a chemical reaction.
• To determine the limiting reactant, calculate how
many moles of each reactant you have. Consult
the mole ratio to see which reactant will get
used up.
Check-in
•
Consider this reaction:
•
N2(g) + 3H2(g)  2NH3(g)
a. If you mix 28.0 g of nitrogen gas, N2, and
12.0 g of hydrogen gas, H2, which reactant is
the limiting reactant? Show your work.
b. How much ammonia can be made from these
amounts of reactants?
Lesson 27: Call Poison Control
• Unit Review
ChemCatalyst
• Imagine that your little brother has spilled a
toxic substance on his skin. You decide to call
Poison Control right away.
a. What are some things you want to know
about the substance?
b. What kinds of questions do you think Poison
Control will ask you? What might you be told
to do? Explain your thinking.
Key Question
• What is the best way to deal with a toxic substance?
You will be able to:
•
create a comprehensive list of topics to use as a study
aid for a unit exam
Prepare for the Classwork
• Work individually or in pairs.
Check-in
• Balance this equation and fill in the phases for the
products:
• Ba(NO3)2(aq) + Na2SO4(aq)  BaSO4 + NaNO3
1. What solid is formed?
2. How many grams of barium nitrate must be in
the solution to make 3 moles of barium sulfate?