Category Archives: College

Chemistry Games!

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There are only a few weeks left in the semester, which means it’s time to create chemistry games for my students to play at our last meeting.

This trivia game is meant to be played in small groups. I will ask the class whether they want to play with cell phones and Google, or without. If they want to play with, then we’ll arrange the groups so that each one has someone with a phone with internet. There are fifteen questions, so they will only get about 5-6 minutes to complete as many of them as they can. When the timer goes off, scores get tallied, and the winning group gets a prize. The answers, the trivia handout linked above, and other chemistry games and resources can be found on the “Chemistry Games and Resources” tab above.

There will also be a chemical equation balancing relay race. Each team will line up behind a line. One person from each team will run to the front of the room, take the top page from face down in their team’s stack, flip it over, balance the equation, and run back to tag in the next team member. I will stand behind the desk to check answers. If the first person got it wrong, the second person must solve the first equation correctly, and must tag in a third person to solve the next equation in the stack. The first team to get through their whole stack wins a prize.

The class has also decided to hold a potluck that last week, so there may not be time for more games. Eating and studying will finish out the hour. I’m so proud of my students. They’ve all worked really hard, and it’s paid off.

Balancing Chemical Equations: Simple Example

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I have a lot of people asking for help with balancing chemical equations. Below is my personal method, with a simple example. Click here for a PDF of a redox example.

Feel free to use this material in any way you find valuable. It would be great if you cite bluntrose.com in any handouts, and if you use the printer-friendly 2-page PDF version, it’s already on the page for you.

Directions:

  1. Make a table that shows how many of each element there are on each side of the equation.
  2. Identify an atom that is both out of balance and located in only one molecule on the left, and only one molecule on the right. (If no such atom exists, try to find one that is only in one molecule on one side, even if it is in more than one on the other side.) Start by adding coefficients that balance this atom on both sides. Cross off and update the numbers in your table to reflect the new totals for each atom.
  3. If that was not enough to balance the equation, proceed to the next atom that is in the fewest number of molecules, and repeat Step 2. Continue to do this until all atoms are balanced.
  4. Double-check by re-adding the totals for each atom to ensure that your answer is correct.

Example:

___KI(aq) + ___Pb(NO3)2(aq) → ___ PbI2(ppt) + ___ KNO3(aq)

Step 1:

1

K

1

1

I

2

1

Pb

1

2

NO3*

1

*NO3 (nitrate) can be listed as one unit here because it does not separate. If nitrogen or oxygen appeared separated in the product, or if nitrate was present in the product in addition to oxygen or nitrogen appearing in some other part of this product, then this would not work. NO3 is the same on both sides, so we are able to treat it like a single unit for the sake of balancing this equation.

Step 2:

Iodine and nitrate are the only things out of balance here. Iodine is only in one molecule on the left and only in one molecule on the right. The same is true of nitrate. This means it doesn’t matter which one we start with. Let’s try starting with iodine, chosen arbitrarily:

_2_KI(aq) + ___Pb(NO3)2(aq) → ___ PbI2(ppt) + ___ KNO3(aq)

2    1

K

1

2    1

I

2

1

Pb

1

2

NO3*

1

At first glance, this might seem wrong because the potassium (K) is no longer balanced. Take a look at what else is not balanced: nitrate. Nitrate and potassium happen to be in the same molecule on the right, so the next step is to choose a coefficient for that molecule that balances both potassium and nitrate if possible. Luckily, it is!

Step 3:

_2_KI(aq) + ___Pb(NO3)2(aq) → ___ PbI2(ppt) + _2_ KNO3(aq)

2    1

K

1    2

2    1

I

2

1

Pb

1

2

NO3*

1    2

This looks balanced now, according to our accounting table. The last step is to double-check to make sure it is right.

Step 4: To check your work, translate the formula into an equation for each element or molecule.

_2_KI(aq) + ___Pb(NO3)2(aq) → ___ PbI2(ppt) + _2_ KNO3(aq)

Potassium:

(2 X 1) + 0 → 0 + (2 X 1)
2 → 2
Therefore, potassium is correct.

Iodine:

(2 X 1) + 0 → (1 X 2) + 0
2 → 2
Therefore, potassium is correct.

Lead:

0 + (1 X 1) → (1 X 1) + 0
1 → 1
Therefore, potassium is correct.

Nitrate:

0 + (1 X 2) → 0 + (2 X 1)
2 → 2
Therefore, potassium is correct.

FINAL ANSWER: 2KI(aq) + Pb(NO3)2(aq) → PbI2(ppt) + 2KNO3(aq)

Feel free to use the printer-friendly 2-page PDF of this material in any capacity you find valuable.

Stoichiometry Game

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One of my very favorite parts of my life right now is the small study group I lead for an hour every Tuesday afternoon. I get 1.5 units of college credit for keeping 15 introductory chemistry students on task. I assign groups, encourage group work skills, and help them figure out how to use basic study tools to figure out answers when they get stuck. Every now and then I throw in something fancy to shake things up a little, and this was one of those weeks!

“Stoichiometry” is a fancy word for “the study of the amounts of substances in a reaction.” How much hydrogen and oxygen do you need to make water? Well, the formula is H2O so you need two hydrogen atoms for each oxygen atom. That’s stoichiometry. Simple stuff, fancy word. It’s simple in principle, but just like math, it can layer on top of itself and become more complicated. Then again, in my opinion, stoichiometry is just a fancy word for ratio maths applied to chemical notation.

Typically, my students know to go to the front of the room, sign in, and then find their assigned seat. This week we did something completely different. I put the sign-in sheet by the door and asked them as they came in to sign in, put their things down, and come back out. As they did, I let them each select an index card. Each one was green, yellow, or red, and had “6.022 X 1023 = 1 mole” written on one side. Chemists use moles of atoms in stoichiometry calculations in order to allow easy use of macroscopic measurements in calculations. For more information, check out Khan Academy’s video “Avogadro’s Number and Moles.” It’s 9:43 in length.

“Okay, everyone,” I said when they had gathered. “I am an artist. I make miniature sculptures out of index cards. They are small, so I sell them in bulk. In fact, I sell them by the mole! Each one of you represents my inventory. That card in your hand represents an entire MOLE of index cards! My first client wants a type of sculpture that needs one red index card, two green index cards, and one yellow index card per sculpture. Get in groups of one red, two green, and one yellow so we can see how many moles of sculptures I can make!”

The students moved around until they had made as many complete groups as they could.

“How many complete groups do we have?” I asked.

“Two,” several voices chimed in.

“How many sculptures does that mean I can make with my current inventory?”

“Two moles of sculptures!” someone said.

“YES! Exactly! And what do we have left over?”

“Green and red,” came the forlorn voices of the leftover students.

“What does that mean in terms of what limited how many batches of sculptures I could sell from my inventory?”

Blank stares all around.

“Which thing did I run out of first, and therefore meant I could not make more sculptures?”

“Yellow!” They all asserted together.

“Yes! That means yellow, if this was a chemical reaction, would be my limiting reagent.”

Noises of sudden understanding permeated about two-thirds of the group.

We ran the same drill five or six more times with different mole ratios, and each time more of the students visibly or vocally had that lovely “Ah-ha!” moment I was hoping for. Later on in the classroom, the game served as a reference point for helping students understand the concepts in their assigned work. A three-minute game reinforced all the concepts they will be directly working with for the next month, and directly or indirectly working with for as long as they study chemistry. This was one of the best ideas I have had in a classroom capacity. I find that this success, while relatively tiny in the grand scheme of things, serves to fuel my desire to become a chemistry professor.

Here is a PDF I made with instructions for running this game. Feel free to use it in any capacity you find valuable!