Toxins Unit – Investigation 5

Lesson 4:

Mass Appeal

© 2004 Key Curriculum Press.

Unit IV • Investigation III-X

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

3 CaCl2 + 2 Na3PO4 Ca3(PO4)2 + 6 NaCl

• If you react 6 moles of CaCl2, how many moles of Ca3(PO)4 can you make?

• If you react 10 moles of CaCl2, how many moles of NaCl will you make?

© 2004 Key Curriculum Press.

Big Question

• What is stoichiometry and how can we use it?

© 2004 Key Curriculum Press.

Objectives

Students will be able to:• Define stoichiometry• Convert between moles of substances in balanced chemical equations.• Convert between the masses of substances in balanced chemical equations.

Unit IV • Investigation III-X

© 2004 Key Curriculum Press.

Agenda

• Admit Slip• Notes and Example Problems• Worksheet• Exit Slip

© 2004 Key Curriculum Press.

Unit IV • Investigation III-X

Stoichiometry: Problems involving

conversions between masses and moles of

reactants and products.

Notes Stoichiometry 3 / 15 / 10

© 2004 Key Curriculum Press.

Warm Up Question

Before we jump back into mass, moles, and chemical equation, let’s think about a similar situation, with food.

How about s’mores?

© 2004 Key Curriculum Press.

S’mores Chemical Equation

2 Marshmallows + 3 Chocolate P. + 2 G. Crackers 1 S’more

2 M + 3C + 2G M2C3G2

© 2004 Key Curriculum Press.

S’mores Example Continued

2 M + 3 C + 2 G M2C3G2

The mass of 1 piece of each ingredient (molar mass)

is :

1 Marshmallow : 6 g

1 Chocolate Piece: 4 g

1 Graham Cracker: 7 g

© 2004 Key Curriculum Press.

S’mores Example Continued

2 M + 3 C + 2 G M2C3G2

1) How much does a s’more, M2C3G2 weigh?

2(6) + 3(4) + 2(7) = 38 g

© 2004 Key Curriculum Press.

S’mores Example Continued

2 M + 3 C + 2 G M2C3G2

2) If you have 15 pieces of chocolate, how many s’mores could you make?

15 C * 1 s’more / 3 C = 5 s’mores

© 2004 Key Curriculum Press.

S’mores Example Continued

2 M + 3 C + 2 G M2C3G2

3) If you have 24 g of marshmallows, how many s’mores could you make?

24 g M / 6 g = 4 M

4 M * 1 s’more / 2 M = 2 s’mores

© 2004 Key Curriculum Press.

S’mores Example Continued

2 M + 3 C + 2 G M2C3G2

4) If you have 35 g of graham crackers, how many s’mores could you make?

35 g G / 7g = 5 G

5 G * 1 s’more / 2 G = 2.5 s’mores

© 2004 Key Curriculum Press.

S’mores Example Continued

2 M + 3 C + 2 G M2C3G2

5) If you have 76 g of s’mores, how many grams of chocolate would you need?

76 g s’mores / 38 g = 2 s’mores

2 s’mores * 3 C / 1 s’more = 6 C

6 C * 4g = 24 g chocolate

© 2004 Key Curriculum Press.

Unit IV • Investigation III-X

(When we were converting between different ingredients, we were using a version of the mole ratio.)

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

N2 + 3 H2 2 NH3

ex: mole ratio of H2 to NH3 is

Notes

3

2

2

3

molesNH

molesH

© 2004 Key Curriculum Press.

Unit IV • Investigation III-X

Notes• You must use the mole ratio to convert from one substance to another in a chemical equation.

N2

+

3

H2

2

NH3

• For a mole ratio, what you want to know goes on top of the fraction, and what you already know goes on the bottom.

what you want what you know

2

3

3

2

molesH

molesNH

© 2004 Key Curriculum Press.

Unit IV • Investigation III-X

Notes

(cont.)

© 2004 Key Curriculum Press.

Unit IV • Investigation III-X

Example:How many grams of Ca(OH)2 can you make from 20 grams of NaOH through this reaction?

CaCl2 + 2 NaOH Ca(OH)2 + 2 NaCl (aq)

The molar mass of NaOH is 23 + 16 + 1 = 40 g / mol

20 g NaOH / 40/mol = 0.5 mol NaOH

0.5 mol NaOH * = 0.25 mol Ca(OH)2molNaOH

OHmolCa

2

)(1 2

© 2004 Key Curriculum Press.

Unit IV • Investigation III-X

Example continued:How many grams of Ca(OH)2 can you make from 20 grams of NaOH through this reaction? CaCl2 + 2 NaOH Ca(OH)2 + 2 NaCl (aq) ?

0.25 mol Ca(OH)2

The molar mass of Ca(OH)2 is 40 + 32 + 2 = 74 g / mol

0.25 mol Ca(OH)2 * 74 g/mol = 18.5 g Ca(OH)2

© 2004 Key Curriculum Press.

Unit IV • Investigation III-X

Exit slip

Consider the following reaction:

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

How many grams of magnesium, Mg, do you

need to produce 190 g, of magnesium chloride, MgCl2?

© 2004 Key Curriculum Press.

Unit IV • Investigation III-X

How do you convert between grams and moles to determine the amount 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 back again to mass.

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