Chemistry Unit 8 Lesson 1: The Mole and Intro to Stoich

Chemistry Unit 8

Chemistry

​Lesson 1: The Mole and Intro to Stoich

In this Unit we will be taking all of the conceptual knowledge we have learned this year and finally looking at how it is applied to real life.

This is called stoichiometry. This is the "recipe" for how chemists or scientists put together reactants in certain amounts and know how much product to expect in return.

​Stoichiometry

Stoichiometry

In other words stoichiometry is calculating how much product should be made based on how much reactant you have.

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But atoms are too small to be seen or measured. Stoichiometry is also a way to convert information from balanced equations to measurable information. ​

Defined as the relationship between the relative quantities of substances taking part in a reaction or forming a compound.

​Stoichiometry

Stoichiometry

The best description I have ever heard for the concept of stoichiometry is this. Imagine having to count out $1,000,000,000 in pennies.

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This seems impossible right? It would simply take forever.

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This is what it would be like counting the molecules in a small sample of a reactant.

Stoichiometry

But with not changing the value of the money only the unit this process can get easier.

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Now imagine counting out $1,000,000,000 but doing so in $100 bills. Seems much more manageable. But would still take us a long period of time.

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What if we counted it out in $1,000,000 bills? That is as simple as counting to 1000.

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Stoichiometry

This is how unit conversions in stoichiometry work.

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Your simply changing a unit to make the process of measuring a substance manageable.

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The hard part to always keep in mind is that even though the number might be changing because of the unit conversion the actual amount or total value is not. Meaning 8 quarters, 2 dollar bills, and 20 dimes; are all the same total value with just different units.

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Stoichiometry

Multiple Choice

Using our understanding of the units of time, which of the following of these numbers does NOT have the same total value. (Notice the 3 that are the same total value don't have the same number because the unit is different)

• 144 hours

• 6 days

• 1 week

• 8640 minutes

When it comes to stoichiometry the unit we must utilize the most and will be the hardest to first wrap our head around is the mole.

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The mole is a massive number of atoms of any element designed to give us a large enough sample to be visible and measurable.

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Like having a dozen eggs or a dozen donuts the mole is an unchanging number no matter the element you are talking about.

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1 mole of any substance is equal to 6.02 x 10²³ atoms of that substance​.

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Stoichiometry

Multiple Choice

How many atoms would be found in 1 mole of Sodium (Na)?

• 6.02 x 10²³ atoms

• 3.01 x 10²³ atoms

• 1.20 x 10²⁴ atoms

• 1 atom

Multiple Choice

How many atoms would be found in 1 mole of Strontium (Sr)

• 6.02 x 10²³ atoms

• 3.01 x 10²³ atoms

• 1.20 x 10²⁴ atoms

• 1 atom

Multiple Choice

How many atoms would be found in 2 moles of Carbon (C)

• 6.02 x 10²³ atoms

• 3.01 x 10²³ atoms

• 1.20 x 10²⁴ atoms

• 1 atom

Because we have 2 moles of carbon we simply multiply 6.02 x 10²³ by 2. Just like if we have 2 dozen donuts we would find this was 24 total donuts by taking 12 x 2.

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Stoichiometry

Multiple Choice

How many Hydrogen atoms would be found in 1 mole of Water (H₂O)

• 6.02 x 10²³ atoms

• 3.01 x 10²³ atoms

• 1.20 x 10²⁴ atoms

• 1 atom

In a single water molecule we have 2 hydrogen atoms. So if we have 1 mole of water molecules, we have 1 x 2 x 6.02 x 10²³ atoms of hydrogen.

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Stoichiometry

Multiple Choice

How many Oxygen atoms would be found in 3 moles of Carbon dioxide (CO₂)

• 6.02 x 10²³ atoms

• 1.81 x 10²⁴ atoms

• 1.20 x 10²⁴ atoms

• 3.61 x 10²⁴ atoms

In a single carbon dioxide molecule we have 2 oxygen atoms. So if we have 3 moles of carbon dioxide molecules, we have 3 x 2 x 6.02 x 10²³ atoms of oxygen.

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Stoichiometry

Poll

How would you rate your understanding so far of using moles?

• I could teach others

• I feel comfortable but still have questions

• I am really lost and need to reach out for extra help

• I think I have it down but don't think I could explain it to others

Another skill that is required when performing stoichiometry is being able to calculate molar mass.

​This is a skill we learned several unit ago but let's refresh our understanding. ​

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Stoichiometry

Find the molar mass of

SO₂

C₃H₈O

Ca​(NO₃)₂

​​Answers explained in video​ on next slide

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Stoichiometry

Find the molar mass of

SO₂ - 64 g/mol

C₃H₈O - 60 g/mol

Ca​(NO₃)₂ - 164 g/mol

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Stoichiometry

Multiple Choice

What is the molar mass of H₂O?

• 16.0 g/mol

• 17.01 g/mol

• 18.01 g/mol

• 10.0 g/mol

So the stoichiometry skills we will learn today is how to convert between

atoms <--> moles and moles<-->grams.

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Moles are like the universal go between.

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Stoichiometry

Stoichiometry

So the stoichiometry skills we will learn today is how to convert between

atoms <--> moles and moles<-->grams.

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Moles are like the universal go between.

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Stoichiometry

Let's start with moles to atoms/molecules or atoms/molecules t0 moles.

How many ​molecules are in 0.63 moles?

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​Answer explained in video.

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Stoichiometry

Let's start with moles to atoms/molecules or atoms/molecules t0 moles.

How many ​molecules are in 0.63 moles?

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3.8 x 10²³ molecules​

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Stoichiometry

Let's start with moles to atoms/molecules or atoms/molecules t0 moles.

How many ​moles are in 3.9 x 10²⁰ atoms?

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​Answer explained in video.

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Stoichiometry

Let's start with moles to atoms/molecules or atoms/molecules t0 moles.

How many ​moles are in 3.9 x 10²⁰ atoms?

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0.65 moles

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Stoichiometry

How does this change if we are converting moles to mass or back again?

What is the mass in grams​ of 4.3 moles of Aluminum ?

Answer explained in video.

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Stoichiometry

How does this change if we are converting moles to mass or back again?

What is the mass in grams​ of 4.3 moles of Aluminum ?

116.1 grams of Al

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Stoichiometry

How does this change if we are converting moles to mass or back again?

How many moles are in 127.5 grams of NaCl?

​Answer explained in video.

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Stoichiometry

How does this change if we are converting moles to mass or back again?

How many moles are in 127.5 grams of NaCl?

​2.2 moles of NaCl

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Stoichiometry

Multiple Choice

How many moles are in 200 grams of Iron (Fe)?

• 7.69 moles

• 3.58 moles

• 1.12 x 10⁴ moles

• 55.85 moles

Multiple Choice

How many grams are in 3.2 moles of BeCl₂? HINT MUST FIND MOLAR MASS FIRST

• 79.92 g

• 255.74 g

• 24.98 g

• 121.6 g

Multiple Choice

How many atoms are in 15 grams of sulfur powder? HINT YOU MUST FIND MOLES THAN FIND ATOMS.

• 2.89 x 10^-23 atoms

• 2.82 x 10²³ atoms

• 2.82 x 10^-23 atoms

• 2.89 x 10²³ atoms

Stoichiometry

​Always refer back to your road map