how to solve any problem involving conversion of units

How to solve any problem involving conversion of units

Final Exam Review

1. First write down what you know.

2. Then write down what you are looking for.

3. In between them, write “x------- =”

4. On the bottom, write the units of what you know (not the number!).

5. On the top, write the units of what you are looking for.

6. Find the ratio.

7. Multiply.

A silly example

A florist receives a shipment of 200 long stem roses. How many bundles of a dozen can she make?

A florist receives a shipment of 200 long stem roses. How many bundles of a dozen can she make?

First write down what you know.

A florist receives a shipment of 200 long stem roses. How many bundles of a dozen can she make?

First write down what you know.

200 roses

A florist receives a shipment of 200 long stem roses. How many bundles of a dozen can she make?

Then write down what you are looking for.

200 roses

A florist receives a shipment of 200 long stem roses. How many bundles of a dozen can she make?

Then write down what you are looking for.

200 roses dozens

A florist receives a shipment of 200 long stem roses. How many bundles of a dozen can she make?

Between them, write “x--------- =”

200 roses dozens

A florist receives a shipment of 200 long stem roses. How many bundles of a dozen can she make?

Between them, write “x--------- =”

200 roses x = dozens

A florist receives a shipment of 200 long stem roses. How many bundles of a dozen can she make?

On the bottom, write the units of what you know (not the number!)

200 roses x = dozens

A florist receives a shipment of 200 long stem roses. How many bundles of a dozen can she make?

On the bottom, write the units of what you know (not the number!)

200 roses x = dozens roses

A florist receives a shipment of 200 long stem roses. How many bundles of a dozen can she make?

On the top, write the units of what you are looking for. 200 roses x = dozens roses

A florist receives a shipment of 200 long stem roses. How many bundles of a dozen can she make?

On the top, write the units of what you are looking for. dozen200 roses x = dozens roses

A florist receives a shipment of 200 long stem roses. How many bundles of a dozen can she make?

Find the ratio.

dozen200 roses x = dozens roses

A florist receives a shipment of 200 long stem roses. How many bundles of a dozen can she make?

Find the ratio.

1 dozen200 roses x = dozens 12 roses

A florist receives a shipment of 200 long stem roses. How many bundles of a dozen can she make?

Multiply.

1 dozen200 roses x = dozens 12 roses

A florist receives a shipment of 200 long stem roses. How many bundles of a dozen can she make?

Multiply.

1 dozen200 roses x = 16.67 dozens 12 roses

A serious example

A slab of titanium has a mass of 431 g. How many moles of titanium atoms are in the slab?

A slab of titanium has a mass of 431 g. How many moles of titanium atoms are in the slab?

First write down what you know.

A slab of titanium has a mass of 431 g. How many moles of titanium atoms are in the slab?

First write down what you know.

431 g

A slab of titanium has a mass of 431 g. How many moles of titanium atoms are in the slab?

Then write down what you are looking for.

431 g

A slab of titanium has a mass of 431 g. How many moles of titanium atoms are in the slab?

Then write down what you are looking for.

431 g moles

A slab of titanium has a mass of 431 g. How many moles of titanium atoms are in the slab?

Between them, write “x--------- =”

431 g moles

A slab of titanium has a mass of 431 g. How many moles of titanium atoms are in the slab?

Between them, write “x--------- =”

431 g x = moles

A slab of titanium has a mass of 431 g. How many moles of titanium atoms are in the slab?

On the bottom, write the units of what you know (not the number!)

431 g x = moles

A slab of titanium has a mass of 431 g. How many moles of titanium atoms are in the slab?

On the bottom, write the units of what you know (not the number!)

431 g x = moles g

A slab of titanium has a mass of 431 g. How many moles of titanium atoms are in the slab?

On the top, write the units of what you are looking for. 431 g x = moles g

A slab of titanium has a mass of 431 g. How many moles of titanium atoms are in the slab?

On the top, write the units of what you are looking for. mole431 g x = moles g

A slab of titanium has a mass of 431 g. How many moles of titanium atoms are in the slab?

Find the ratio.

mole431 g x = moles g

A slab of titanium has a mass of 431 g. How many moles of titanium atoms are in the slab?

Find the ratio.

1 mole431 g x = moles 47.9 g

A slab of titanium has a mass of 431 g. How many moles of titanium atoms are in the slab?

Find the ratio.

1 mole431 g x = moles 47.9 g

Atomic mass of titanium

A slab of titanium has a mass of 431 g. How many moles of titanium atoms are in the slab?

Multiply.

1 mole431 g x = moles 47.9 g

A slab of titanium has a mass of 431 g. How many moles of titanium atoms are in the slab?

Multiply.

1 mole431 g x = 9 moles 47.9 g

A more complicated example

A bottle contains 5 moles of AlCl3. What is the mass of chloride ion in this sample?

A bottle contains 5 moles of AlCl3. What is the mass of chloride ion in this sample?

5 m.AlCl3

A bottle contains 5 moles of AlCl3. What is the mass of chloride ion in this sample?

5 m.AlCl3

g Cl

x =

A bottle contains 5 moles of AlCl3. What is the mass of chloride ion in this sample?

5 m.AlCl3

g Cl

x =

A bottle contains 5 moles of AlCl3. What is the mass of chloride ion in this sample?

5 m.AlCl3

g Clg Cl

m.AlCl3

x =

A bottle contains 5 moles of AlCl3. What is the mass of chloride ion in this sample?

5 m.AlCl3

g Clg Cl

m.AlCl3

Atomic mass of chlorine is 35.45

x =

A bottle contains 5 moles of AlCl3. What is the mass of chloride ion in this sample?

5 m.AlCl3

g Clg Cl

m.AlCl3

Atomic mass of chlorine is 35.45There are 3 Cl’s in each AlCl3

x =

A bottle contains 5 moles of AlCl3. What is the mass of chloride ion in this sample?

5 m.AlCl3

g Clg Cl

m.AlCl3

Atomic mass of chlorine is 35.453 x 35.45 = 106.35 There are 3 Cl’s in each AlCl3

x =

A bottle contains 5 moles of AlCl3. What is the mass of chloride ion in this sample?

5 m.AlCl3

g Clg Cl

m.AlCl3

Atomic mass of chlorine is 35.453 x 35.45 = 106.35 There are 3 Cl’s in each AlCl3

106.35 1

x =

A bottle contains 5 moles of AlCl3. What is the mass of chloride ion in this sample?

5 m.AlCl3

g Clg Cl

m.AlCl3

Atomic mass of chlorine is 35.453 x 35.45 = 106.35 There are 3 Cl’s in each AlCl3

106.35 1

531.75

The same steps work for any kind of conversion problem.

How many atoms of oxygen are in 4 moles of Al2(SO4)3?

How many atoms of oxygen are in 4 moles of Al2(SO4)3?

4m Al2(SO4)3

How many atoms of oxygen are in 4 moles of Al2(SO4)3?

4m Al2(SO4)3 O

atoms

How many atoms of oxygen are in 4 moles of Al2(SO4)3?

O

atomsx x =4m Al2(SO4)3

How many atoms of oxygen are in 4 moles of Al2(SO4)3?

x x =4m Al2(SO4)3 O

atoms

mol O

mol Al2(SO4)3

How many atoms of oxygen are in 4 moles of Al2(SO4)3?

atomsx x =4m Al2(SO4)3 O

atoms mol O

mol O

mol Al2(SO4)3

How many atoms of oxygen are in 4 moles of Al2(SO4)3?

x x =4m Al2(SO4)3 mol O

mol O

mol Al2(SO4)3

121

atomsO

atoms

How many atoms of oxygen are in 4 moles of Al2(SO4)3?

x x =4m Al2(SO4)3 mol O

mol O

mol Al2(SO4)3

121

6.02x1023

1O

atoms

How many atoms of oxygen are in 4 moles of Al2(SO4)3?

x x =4m Al2(SO4)3

= 2.89 x 1025 O atoms

mol O

mol O

mol Al2(SO4)3

121

6.02x1023

1

1. First write down what you know.

2. Then write down what you are looking for.

3. In between them, write “x------- =”

4. On the bottom, write the units of what you know (not the number!).

5. On the top, write the units of what you are looking for.

6. Find the ratio.

7. Multiply.

Homework:

Pg 311-312, # 1-4

Pg 321, # 20

Pg 322, # 25

Pg 323, # 27

Pg 324, # 30a

Pg 326, # 31