Good morning and welcome to chemistry!

Molar mass is used on a daily basis in many chemistry labs, pharmacies and industries dealing with chemical substances. Periodic Tables vary in their reporting precision of each element’s mass.

Your goal today: Find an online periodic table that has the most precision for each element possible. We normally round oxygen to 16? Our textbook has it listed at 15.999 g/mol. I found another one listing it at 15.9994 g/mol. You can do better.

Include your source and then find the molar masses to the maximum decimal places of the following compounds:

1. Aluminum Sulfate
2. Barium chloride
3. Sodium Oxide

Show all your work and take a clear pic and send it to Mr. Brown on Remind.

Thank you!

Stay healthy and Stay Breezy,

T. Brown

Good morning and welcome to chemistry. I hope you all had a good weekend, under the circumstances. I woke up this morning to an Internet outage and had to scramble to get it going. I think the high winds may have played a part.

So, today’s assignment you will turn in to Remind, again. Show all your work in a pic that you take. Show units and substances.

1. How many grams is 14.4 moles of oxygen gas?
2. How many molecules of oxygen gas is 23.3 moles?
3. What is the mass of 1 molecule of oxygen?

Remember HOFBrINCl.

Thank you,

T. Brown

Happy Friday, everybody! Today’s chemistry is still deep, DEEEEP in mole territory.

Ethanol ( C₂H₅OH) a domestically produced fuel source, is often blended with gasoline. A sample of ethanol has a mass of 45.6 grams.

a. How many carbon atoms does the sample contain?

b. How many hydrogen atoms are present?

c. How many oxygen atoms are present?

These are three “three-step” problems.

1. Find molar mass of the compound (using the Periodic Table) and then change grams of ethanol to moles of ethanol.
2. Change moles of EtOH (Ethanol’s abbreviation) into molecules of EtOH using Avogadro’s number.
3. Finally, multiply your number of molecules by each element’s subscript to find the atom’s of each.

Be especially careful of hydrogen. It’s a bit tricky. We write ethanol as C₂H₅OH because the “-OH” shows that it has an alcohol portion to the molecule, so it gives a chemist additional information just by writing the formula this way.

I will try to send yesterday’s answers in Remind even as you are taking a picture of today’s work and sending it to me in Remind. Show all your work.

Stay healthy and stay breezy!

T. Brown

Today is less math intensive as we are simply balancing chemical equations and indicating the reaction type.

The five types of chemical reactions that we have talked about in class cover about 90% of all chemical reactions. The remaining 10% are more complex.

The five types:

A. Combustion: HC + 2O₂ —> CO₂ + 2H₂O

B. Synthesis: A + B –> AB

C. Decomposition: AB —> A + B

D. Single Replacement: AX + B —> BX + A

E: Double Replacement: AX + BY —> AY + BX

Chemical reactions are balanced when we have equal numbers of each type of element on both sides of the arrow. So if there are 7 hydrogen atoms on the left, there needs to be 7 on the right. Use only whole number coefficients. Do not change subscripts.

Do the attached seven problems and send the results only to Mr. Brown on Remind.

https://drive.google.com/file/d/12caxoDvu6db2GYC7lAq7wGI4DUWy1-mn/view?usp=sharing

Final note: the place where most newer chemistry students make mistakes in these kinds of problems is if the same element is in two compounds on one side of the equation. You must add them to get the total. Combustion reactions have this twist.

So, if A has the coefficients 1,2,3,4 and is a single replacement you’d send:

A: 1,2,3,4 SR

Thank you,

Stay healthy and Stay Breezy

T. Brown

Good Morning and welcome to Chemistry.

We’ve been talking about the mole the last few days. Today, we are continuing with the mole theme and asking you to calculate the %composition of a substance. You’ll need a calculator and a periodic table.

For example: Water’s molar mass is 18 grams.

O = 16 g (The periodic table says 15.999 g, so we can do a little rounding)

H = 1 g x 2 = 2 g

Add 16+2 and the molar mass of water is 18 grams.

The percent by mass is {(mass of one element in the compound)/(molar mass of total compound)} x 100

(16/18) * 100 = 88.9% Oxygen

(2/18) * 100 = 11.1% Hydrogen.

They percentages should add up close to 100%.

I’d like you to find the percent by mass of each element in the following substances:

A. Aluminum Sulfate (see yesterday’s work for the formula)

B. Phosphoric Acid (H₃PO₄)

C. Calcium Chloride, CaCl₂

D. Ethane C₂H₆

E. The mineral Ilmenite, FeTiO₃ (Note: it contains Titanium)

Please show all work on paper and send a picture of your work to me in Remind.

Thanks,

Stay healthy and Stay Breezy.

T. Brown

Good morning and welcome to chemistry!

We continue today with a two-part math problem.

You’ll need to find the molar mass.

Then set up your double cross of science.

Put the given in the top left section.

Change to moles.

Then, convert moles to molecules.

Show all your work, otherwise it is all for naught.

Aluminum sulfate, sometimes called Alum, is useful in cleaning up water for drinking:

Ever wonder how we manage to have safe drinking water flowing out of our faucets? You can thank aluminum sulfate. Municipal water suppliers, such as your local water utility company, make use of alum to treat water for human consumption. In addition, process water (non-drinking water) may also be treated with this chemical for purification when bacteria / sediment would cause an adverse effect.

When added to water, aluminum sulfate causes microscopic impurities to clump together into larger and larger particles. These clumps then settle to the bottom of the container and can be filtered out. This makes the water safer to drink. On the same principle, alum is also sometimes used in swimming pools to decrease water cloudiness

Source: https://www.affinitychemical.com/aluminum-sulfate-composition-and-uses/

1. How many grams of aluminum sulfate is 8.19 x 10²⁷ molecules of aluminum sulfate? The formula is Al₂(SO₄)₃ .

Send your picture in Remind to answer today’s question.

Thank you!

Stay Healthy and Stay Breezy.

T. Brown

Good morning and welcome to Chemistry. Today, we will talk a bit more about the mole. I sent you chapter 10 notes a couple of weeks ago. See if you can still find them.

A mole is Avogadro’s number of things, usually particles like atoms or molecules. These two particles are so small, you have to have a LOT of them to measure their masses on a balance. Avogadro’s Number, NA, is 6.02 x 10²³
So 2 moles of iron atoms is 2 x NA or 1.204 x 10²⁴

We can also use the Periodic Table with the mole. Let’s look at iron, Fe, again.

Iron is element number 26 on the periodic table. It has a number, usually underneath the symbol, Fe, that is a decimal. The mass of one atom of iron is 55.847 amu (atomic mass units). This isn’t very useful, since it is so small, so we have converted these masses to grams for each mole of the substance. So now, one mole of iron is 55.847 grams. If you have 2 moles it is 55.847 x 2 = 112 grams (using 3 sig figs usually).

You can convert from grams to atoms or atoms to grams by converting to moles first.

Today’s questions will require a calculator (your phone is fine for homework, but not a test or quiz) and a periodic table.

1. Find tin on the periodic table. How many atoms of tin are in 17.3 moles of tin?
2. How many grams of Sn are in 34.5 moles of Sn?
3. How many grams of Sn are in 3.05 x 10²⁹ atoms of tin?

Please do your work on paper, showing ALL of your work. Take a photo with your phone and send it to me via Remind. Do this today, please.

Thank you,

Stay healthy and stay Breezy!

T. Brown

Continuing with chemical reaction types from yesterday (ayer in Spanish) I have a couple of Double Replacement Reactions for you. I’d like you to predict the products of

A. Potassium Cyanide (KCN) being added to Hydrogen Bromide (HBr) –>

B. Aluminum Nitrate ( Al(NO₃)₃) added to sulfuric acid (H₂SO₄) –>

Note: The cyanide polyatomic ion CN^– has a single negative charge.

Note 2: The nitrate ion NO₃^– also has a single negative charge.

Note 3: The sulfate ion SO₄^2- has a 2- charge. What is the charge for Aluminum from Group 13?

Please write both chemical equations with neutral compounds and then balance the equation with coefficients. Take a picture or two of your final answers and attach it (them) to your Remind post. Remember: there can be no charges in the final compounds (they cancel out) and no superscripts. The first one is easy, the second is challenging. Good luck.

Stay healthy and Stay Breezy.

T. Brown

Happy Thursday, everybody. I hope today finds you happy and healthy. Not an easy task.

Today’s chemistry question goes all the way back to 9.2 in our chemistry textbook. Remind me to resend Ch. 9 notes in Remind.

There are five types of chemical reactions. Name the type of reaction for the following:

1. 2Na + Cl₂–> 2NaCl (I copy and pasted from a Google doc to get the subscript.)
2. CH₄ + 2O₂ —> CO₂ + 2H₂O
3. NH₄NO₃ —>  N₂O + 2H₂O

How can you tell which type of reaction they are?

Thank you,

Stay healthy and Stay Breezy

T. Brown

Dear Students of Chemistry:

Thank you (most of you) for your timely responses to my e-mail. Future contact from me will be via this Blog or Remind. So, stay tuned.

The last question: When you combine oxygen and sodium they form an ionic compound. What is the formula and name of this compound?

The answer: Na2O is called sodium oxide. The “2” should be subscripted, but I cannot do that on this blog…yet.

Our new question: Sodium oxide is an ionic compound because it transfers electrons to make two oppositely charged ions that that are pulled together electrostatically. However, some elements combine by sharing electrons. We call these covalent compounds “molecules”.

New question to answer via Remind: What is the name and formula of the compound that contains one carbon and four chlorine atoms?