Toxins Unit

Investigation III: Precipitating ToxinsLesson 1: Solid EvidenceLesson 2: I’ve Got My Ion YouLesson 3: Sticks and StonesLesson 4: BlockheadLesson 5: Mass AppealLesson 6: Get the Lead OutLesson 7: Grammies

Toxins Unit – Investigation III

Lesson 1:

Solid Evidence

Unit IV • Investigation III-X

ChemCatalyst

Below is a double displacement reaction that results in the formation of one type of kidney stone.

CaCl2 (aq) + Na2C2O4 (aq)

2 NaCl (aq) + CaC2O4 (s)

• What do you expect to see in the beaker if you complete this reaction?

• Kidney stones are insoluble. Which compound is the kidney stone?

The Big Question

• What is a precipitation reaction and how can you determine whether a precipitate will form?

You will be able to:

Use a solubility table to predict whether a particular chemical reaction will be a precipitation reaction.

CaCl2 (aq) + Na2C2O4 (aq)

2 NaCl (aq) + CaC2O4 (s)

(cont.)

• Precipitate: A substance of a different phase that separates out of a solution.

• A reaction in which a precipitate forms is called a precipitation reaction.

Notes (cont.)

(cont.)

Solubility Table Most alkali metals Li+, Na+,

K+, and also NH4

Most alkaline earth metals Mg2+, Ca2+,

Some 1st row transition

metals Fe3+, Co3+, Ni2+, Cu2+, Zn2+

Most “heavy metals” Ag+, Pb2+, Hg2+

NO3– (nitrate) S S S S

Cl– (chloride) S S S N

Br– (bromide) S S S N

I– (iodide) S S S N

OH- (hydroxide) S N N N

SO42– (sulfate) S S S N

S2– (sulfide) S S N N

CO32– (carbonate) S N N N

C2O42– (oxalate) S N N N

PO43– (phosphate) S N N N

S = very soluble, N = not very soluble

Activity

Purpose: In this experiment, you will predict the solubility of various ionic solids and then test your predictions.

Making Sense

• Write three solubility rules. (Example: Alkali metal salts tend to be soluble.)

If we examine the solubility table and the results of the experiment, certain patterns emerge: • Most Group I and NH4

+ salts are soluble.

• Most nitrates, NO3–, salts are soluble.

• Most chlorides, bromides, and iodides are soluble (except for Ag+, Pb2+, Hg2+)

• Most carbonates, oxalates, and phosphates are insoluble.

• Most salts of heavy metals are insoluble.

(cont.)

The pros and cons of the solubility of toxins: • (Con) Things that are soluble get into the

water-based systems of our bodies more easily. Once dissolved in the bloodstream they may interact in negative ways with our bodies.

• (Pro) Things that are soluble are easier to filter out of the body using our natural filtration systems.

Notes (cont.)

(cont.)

• (Con) Things that are insoluble may build up inside the body, causing blockages.

• (Pro) Things that are insoluble may pass right through the body without causing harm.

Notes (cont.)

Check-In

• A solution of K2SO4 is combined with a solution of Pb(NO3)2 and a solid forms. Write the chemical formula for the solid that formed.

Wrap-Up

• A precipitate is a solid produced in a chemical reaction between two solutions.

• Most alkali metal compounds and most metal nitrates are soluble. Halides tend to be soluble, except for heavy metal halides. Heavy metal compounds tend to be insoluble.

• Solubility can interact with the human body in either positive or negative ways.

Lesson 2:

I’ve Got My Ion You

ChemCatalyst

• Use your results from the experiments you did yesterday to write a balanced chemical reaction to describe what happens when you mix Na2CO3 (aq), sodium carbonate, with Mg(NO3)2 (aq), magnesium nitrate.

The Big Question

• What is the role of ions in the precipitation reaction process?

Predict the products of precipitation reactions and write balanced chemical equations that represent the precipitation reaction process.

Activity

Purpose: This activity provides practice with equations involving ionic compounds.

(cont.)

acetate C2H3O2– chromate CrO4

2– oxalate C2O42–

ammonium NH4+ cyanide CN– permanganate MnO4

arsenate AsO43– dichromate Cr2O7

2– phosphate PO43–

bicarbonate HCO3– hydroxide OH– selenate SeO4

bisulfate HSO4– manganate MnO4

2– sulfate SO42–

carbonate CO32– nitrate NO3

– thiosulfate S2O32–

(cont.)

Making Sense

• How can you predict whether you will see a solid when you dissolve a salt in water?

• What patterns do you notice between charges and solubility, in question 5?

To create a correct chemical equation:

1. The compounds must be accurately written, with atoms in the right proportions. (Check your subscripts and make sure the charges are balanced. The periodic table can help you with this step.)

2. The entire equation must be balanced, with the same number of each kind of atom on either side of the equation. (Count and balance.)

(cont.)

3. The correct phase of the reactants and products must be indicated. (Check solubility rules or tables.)

Notes (cont.)

(cont.)

• Polyatomic ion: An ion consisting of several non-metal atoms covalently bonded to one another.

Notes (cont.)

(cont.)

NaCl (aq) + AgNO3 (aq)

AgCl (s) + NaNO3 (aq)

Notes (cont.)

(cont.)

Na+(aq) + Cl–(aq) + Ag+(aq) + NO3–(aq)

AgCl(s) + Na+(aq) + NO3–(aq)

Notes (cont.)

(cont.)

Na+(aq) + Cl–(aq) + Ag+(aq) + NO3–(aq)

AgCl(s) + Na+(aq) + NO3–(aq)

Notes (cont.)

(cont.)

Ag+(aq) + Cl–(aq) AgCl(s)

Notes (cont.)

(cont.)

• Overall ionic equation: Chemical equation written with the dissolved salts as aqueous ions.

• Net ionic equation: Equation written with only those species that participate in the reaction.

• Spectator ions: Ions that do not participate in the reaction.

Notes (cont.)

Check-In

• Write a balanced chemical equation describing what happens when you mix sodium chromate and calcium nitrate. (The chromate ion is CrO4

• Predict whether each compound should be labeled as (aq) or (s).

Wrap-Up

• The specific charges on ions can be deduced from the periodic table.

• Some non-metal atoms remain covalently bonded as polyatomic ions.

• If the charges of the cation and anion are low (e.g., +1 and –1), the compound tends to be soluble. If the charges are higher (e.g., +2 and –2 or –3), the compounds tend to be insoluble.

Lesson 3:

Sticks and Stones

ChemCatalyst

Oxalate compounds are a common part of our daily diet. Some examples of foods that are high in oxalate are chocolate, eggplant, graham crackers, and strawberries. Too much oxalate in the body can cause kidney stones.

(cont.)

Kidney stones are formed by the following precipitation reaction:

CaI2 (aq) + Na2C2O4 (aq)

calcium iodide sodium oxalate

CaC2O4 (s) + 2 NaI (aq)

calcium oxalate sodium iodide

• Do you think 1.0 g of CaI2 (aq) and 1.0 g of Na2C2O4 (aq) will produce 1.0 g of kidney stones, CaC2O4 (s)? Explain your thinking.

Notes (cont.)

The Big Question

• What do the coefficients in a balanced chemical reaction mean, and how do they relate to real-world observations?

Experimentally find the highest-yielding ratios of reactants in a precipitation reaction and relate your results to the balanced chemical equation for the reaction.

Activity

Purpose: You will determine what ratio of reactants gives the maximum amount of products.

(cont.)

Test tube # 1 2 3 4 5

Drops of 0.1 M CaCl2 2 4 6 8 10

Drops of 0.1 M Na2C2O4

10 8 6 4 2

CaCl2 : Na2C2O41:5

Calcium oxalate – kidney stones

(cont.)

Calcium phosphate – bones

Test tube # 6 7 8 9

Drops of 0.1 M CaCl2 2 4 6 8

Drops of 0.1 M Na3PO4

8 6 4 2

CaCl2 : Na3PO41:4

(cont.)

Making Sense

• Explain how you can use the coefficients in the balanced chemical equation to determine the ratio of reactants that will produce the maximum amount of product.

• A formula unit is the chemical formula that describes a substance that is not molecular. It is the simplest ratio of atoms found in the substance. For example, CaCl2 represents one formula unit of calcium chloride.

Check-In

The reaction to form silver phosphate, Ag3PO4 (s) is given below:

AgNO3 (aq) + Na3PO4 (aq)

Ag3PO4 (s) + NaNO3 (aq)

(cont.)

• What ratio of reactants give 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 moles AgNO3 to 1.0 moles Na3PO4

D. 3.0 moles AgNO3 to 1.0 moles Na3PO4

Notes (cont.)

Wrap-Up

• The coefficients found in chemical equations stand for counting units such as number of molecules, number of moles, etc.

• Coefficients in chemical equations represent the ratio in which reactants combine and products form.

• Mass and volume amounts cannot be substituted for coefficients.

Lesson 4:

Blockhead

ChemCatalyst

You have white, gray, and black blocks. You rearrange the pieces on the left side to give the new combinations on the right side.

4 g 3 g 5 g

(cont.)

• How much does the gray block weigh?

• If you have 40 g of black blocks and 30 g of white-gray pieces, how many white-black blocks can you make?

Notes (cont.)

The Big Question

• How does the mole concept help you predict the amount of each product in a particular reaction?

Calculate the quantity of a product formed in a reaction from a given quantity of starting reactants.

Activity

Purpose: You will relate grams of reactants and grams of products using moles as an intermediary.

(cont.)

Starting Materials End Products

grams needed to make 36 g white-blue pieces

# pieces needed to make 36 g white-blue pieces

(cont.)

Reactants End Products

CaI2 (aq) Na2C2O4 (aq)grams needed to make 128 g calcium oxalate

294 g 134 g

moles needed to make 128 g calcium oxalate

1.0 moles 1.0 moles

grams needed to make 12.8 g calcium oxalatemoles needed to make 12.8 g calcium oxalate

(cont.)

Making Sense

• Explain how you determined the number of grams of white-purple pieces you needed to make approximately 36 grams of white-blue pieces. Explain how you determined the number of grams of Na2C2O4 you need to make 12.8 g of CaC2O4.

Check-In

Mercury was extracted from mercury sulfide for use in gold mining by the reaction given below:

HgS (s) Hg (l) + S (s)

• What would you observe?

• If you have 0.5 moles of HgS, how many moles of Hg can you make?

• How many grams of HgS do you need to produce 2 moles of Hg?

Wrap-Up

• In order to make a specified mass of product, chemists must determine how many moles of that product they are trying to create.

• In completing calculations for chemical reactions, chemists convert back and forth between grams and moles.

Lesson 5:

Mass Appeal

ChemCatalyst

The reaction given below produces the main substance found in human bones (calcium phosphate)

3 CaCl2 (aq) + 2 Na3PO4 (aq)

calcium chloride sodium phosphate

Ca3(PO4)2 (s) + 6 NaCl (aq)

calcium phosphate sodium chloride(cont.)

• If you react 6 moles of calcium chloride, CaCl2, how many moles of calcium phosphate can you make?

• If you react 111 grams of CaCl2, how many moles of calcium phosphate can you make?

(cont.)

The Big Question

• How can the mole concept be used to calculate the actual mass of products produced, or the mass of reactants needed, in a chemical reaction?

Use the mole concept and balanced chemical equations to convert back and forth between masses of reactants.

• Stoichiometry: Problems involving conversions between masses and moles of reactants and products.

• Mole ratio: The proportions in which two substances combine or form.

N2 + 3 H2 2 NH3

Activity

Purpose: In this activity you will perform stoichiometric calculations.

(cont.)

calcium iodide sodium

oxalate

calcium

oxalate

sodium iodide

(cont.)

Expt. Quantity CaI2 (aq) Na2C2O4 (aq) CaC2O4 (s) 2 NaI (aq)

1 moles 1.0 moles 1.0 moles 1.0 moles 2.0 moles

grams 294 g 134 g 128 g 300 g

2 moles 0.50 moles

grams 147 g 64.0 g 150 g

3 moles 0.10 moles 0.10 moles

4 moles

grams 10 g

(cont.)

calcium

chloride

sodium

phosphate

calcium

phosphate

sodium

chloride

(cont.)

Expt. Quantity 3 CaCl2 (aq)

2 Na3PO4 (aq)

Ca3(PO4)2 (s)

6 NaCl (aq)

1 moles 3.0 moles 2.0 moles 1.0 moles 6.0 moles

grams 333 g 328 g 310 g 351 g

2 moles 2.0 moles

grams 666 g 620 g 702 g

3 moles

grams 10 g

(cont.)

Making Sense

• Outline the steps you took to calculate the number of grams of calcium chloride needed to make 50 grams of calcium phosphate.

(cont.)

Example:

How many grams of calcium phosphate can be made with 25 grams of calcium chloride?

(cont.)

Check-In

Consider the following reaction:

Mg (s) + 2 HCl (aq) MgCl2 (aq) +H2( g)

• What would you observe?

• How many grams of magnesium, Mg, do you need to produce 190 g, or 2 moles, of magnesium chloride, MgCl2?

Wrap-Up

• Stoichiometric calculations are those involving masses of reactants and products in chemical reactions.

• 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 back again to mass.

• Mole ratios assist in converting back and forth between moles of reactant and product.

Lesson 6:

Get the Lead Out

ChemCatalyst

Heavy metals such as thallium dissolved in the water supply can be very toxic. Thallium can be removed from water by precipitation as thallium chloride.

TlNO3 (aq) + NaCl (aq)

TlCl (s) + NaNO3 (aq)

(cont.)

• Which will produce more moles of TlCl?

A.10 g TlNO3 and 10 g NaCl

B.12 g TlNO3 and 8 g NaCl

C.8 g TlNO3 and 12 g NaCl

(cont.)

The Big Question

• What happens in a chemical reaction when one of the reactants runs out before the other?

Explain the concept of a limiting reactant and how it affects the amount of a product produced in a chemical reaction.

• In a stoichiometric mixture the reactants are mixed in the mole ratios specified by the balanced equation.

• A limiting reactant is a reactant that gets used up because the mixture is not stoichiometric.

Activity

Purpose: In this activity, you will consider how to determine if one reactant is in excess.

Making Sense

• If you have 662 g Pb(NO3)2 dissolved in a water supply and you add 230 g NaCl, how can you determine if you have enough NaCl to remove the lead as solid PbCl2?

3AB + 2CD AD + 6 CB

Notes (cont.)

Sample problem:

We take vitamins and mineral supplements so that they do not become limiting reactants in our body. If you have 13.3 g CaCl2 and 9.84 g Na3PO4 available, how many grams of Ca3(PO4)2 (bone) can you make? Should you take a calcium supplement? Explain your thinking.

(cont.)

Check-In

Consider the following reaction:

N2 (g) + 3 H2 (g) 2 NH3 (g)

• If you have 28.0 g N2 and 12.0 g H2, which reactant is the limiting reactant? Show your work.

Wrap-Up

• The limiting reactant is the substance that gets used up in a chemical reaction.

• To determine the limiting reactant, calculate how many moles of product you will make for each mole of reactant. The one that gives fewer moles is the limiting reactant.

Lesson 7:

Grammies

ChemCatalyst

These two cards represent two soluble salts that you are combining. Assume you have only one mole of each substance in solution.

Na+23.0

Br–79.9

NO3–

Pb(NO3)2

(cont.)

• Write a balanced equation for this precipitation reaction.

• What precipitate will form?

• What is the maximum number of moles of precipitate that will form when you mix 1 mole of the reactants?

• How many grams of precipitate will form?

(cont.)

The Big Question

• How can the limiting reactant concept be used to predict quantity of product from a specific chemical reaction?

Use the limiting reactant concept and a balanced chemical equation to calculate the quantity of a product that can be produced by a particular chemical reaction.

Activity

Purpose: This card game will allow you to practice all you’ve learned about precipitation reactions and solubility trends.

(cont.)

Solubility Table Most alkali metals Li+, Na+,

K+, and also NH4

Most alkaline earth metals Mg2+, Ca2+,

Some 1st row transition

metals Fe3+, Co3+, Ni2+, Cu2+, Zn2+

Most “heavy metals” Ag+, Pb2+, Hg2+

NO3– (nitrate) S S S S

Cl– (chloride) S S S N

Br– (bromide) S S S N

I– (iodide) S S S N

OH- (hydroxide) S N N N

SO42– (sulfate) S S S N

S2– (sulfide) S S N N

CO32– (carbonate) S N N N

C2O42– (oxalate) S N N N

PO43– (phosphate) S N N N

S = very soluble, N = not very soluble

Compound Formula

Compound Name

1/2 Mole or 1 Mole? Grams of Precipitate

Balanced chemical equation:

Compound Formula

Compound Name

Compound Formula

Compound Name

Compound Formula

Compound Name

Making Sense

• No Making Sense question

Check-In

• No Check-In exercise.

Wrap-Up

• No wrap-up points.

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