Chem Lab C

[_deltaV]

From my experience, the three competitions this year have had very different tests and labs:

Cypress Falls invitational, Texas: The lab was reacting an unknown amount of sodium bicarbonate and collecting the gas over water, then using that and stoichiometry to determine the amount of bicarbonate. The test was moderately difficult but what I would call AP level with a few harder questions

MIT invitational, Massachusetts: The lab was very basic (sorry for bad chem puns). It consisted of reacting different amounts of food coloring with bleach and determining the rate. Surprisingly hard. The test was upper level kinetics and gas laws, covering everything including application based questions such as uranium enrichment. It covered kinetics and gas laws extensively, including two step reactions, pseudo order reactions, stuff involving solar fusion, and other stuff like that. Was expected because MIT level chemistry.

Regionals, FAU, Florida: Two labs, the iodine clock reaction with sodium thiosulfate and hydrogen peroxide to demonstrate kinetics including calculating molarity of solutions to determine the order of the reaction. I had a problem with this because the rules explicitly say we won't be asked to determine rate laws experimentally at regionals, but I was familiar with the lab and we took third in the event. The second lab was reacting magnesium ribbon with hydrochloric acid to collect hydrogen gas and determining the moles of gas produced. We were given a very nice setup with analytical balances out to the thousandth of a gram and Vernier data collection devices to measure temperature and pressure for this bit of the lab. We didn't have a test, just these two labs. The setup was really nice because it was conducted in a university laboratory.

In terms of calculators, we use the TI Nspire CX CAS calculators for this event because they can store information on them, and they are legal. We haven't had a problem with any supervisors so far

In terms of what to wear, any exposed skin is grounds for disqualification. Long pants and sleeves, closed toed shoes, EYE PROTECTION, and chemical smocks or lab coats.

If anybody is interested, I can publish detailed instructions on how to do the iodine clock lab.

[Eureka314]

Were you guys able to fill up all five sheets front and back? We were only able to fill three; should we have like definitions on there?

Also, will the lab and test be timed separately? Like will they give you a certain amount of time to do the test, and then give you a certain amount of time to do the lab?

[inwhite]

Were you guys able to fill up all five sheets front and back? We were only able to fill three; should we have like definitions on there?

Also, will the lab and test be timed separately? Like will they give you a certain amount of time to do the test, and then give you a certain amount of time to do the lab?

We weren't able to fill up all five pages, to be honest. You could put definitions on there, if you'd like. Perhaps an AP Chem Equation sheet?

As for your second question, that's up to the event supervisor. It really depends on the length of experiment you are requested to do and/or if you're told to do an experiment at all. I haven't even been asked to do an experiment yet.

[kaylie2000]

So just to clarify, are we given the exact instructions on how to do the lab?

[kaylie2000]

From my experience, the three competitions this year have had very different tests and labs:

Cypress Falls invitational, Texas: The lab was reacting an unknown amount of sodium bicarbonate and collecting the gas over water, then using that and stoichiometry to determine the amount of bicarbonate. The test was moderately difficult but what I would call AP level with a few harder questions

MIT invitational, Massachusetts: The lab was very basic (sorry for bad chem puns). It consisted of reacting different amounts of food coloring with bleach and determining the rate. Surprisingly hard. The test was upper level kinetics and gas laws, covering everything including application based questions such as uranium enrichment. It covered kinetics and gas laws extensively, including two step reactions, pseudo order reactions, stuff involving solar fusion, and other stuff like that. Was expected because MIT level chemistry.

Regionals, FAU, Florida: Two labs, the iodine clock reaction with sodium thiosulfate and hydrogen peroxide to demonstrate kinetics including calculating molarity of solutions to determine the order of the reaction. I had a problem with this because the rules explicitly say we won't be asked to determine rate laws experimentally at regionals, but I was familiar with the lab and we took third in the event. The second lab was reacting magnesium ribbon with hydrochloric acid to collect hydrogen gas and determining the moles of gas produced. We were given a very nice setup with analytical balances out to the thousandth of a gram and Vernier data collection devices to measure temperature and pressure for this bit of the lab. We didn't have a test, just these two labs. The setup was really nice because it was conducted in a university laboratory.

In terms of calculators, we use the TI Nspire CX CAS calculators for this event because they can store information on them, and they are legal. We haven't had a problem with any supervisors so far

In terms of what to wear, any exposed skin is grounds for disqualification. Long pants and sleeves, closed toed shoes, EYE PROTECTION, and chemical smocks or lab coats.

If anybody is interested, I can publish detailed instructions on how to do the iodine clock lab.

Can you please publish the instructions for the iodine lab or any other labs you think would be useful to know?

[chem2000]

So just to clarify, are we given the exact instructions on how to do the lab?

Depends on where you take the test. Instructions will probably not be given though. The main things you should definitely know:
- using a manometer (height difference)
- collecting a gas over water (subtract vapor pressure of water, equalizing water level)
- calculating rate (change in quantity / time gives you average rate)


When you come across an unfamiliar lab, step back for a few minutes -- Think about (1) the data you need and then (2) how to get that data.

If a gas is evolved in a reaction, remember that you can find the amount of gas evolved by measuring the change in mass of the reaction vessel.

You are probably not going to see the iodine clock reaction. However, this Wikipedia article is good: https://en.wikipedia.org/wiki/Iodine_clock_reaction

[_deltaV]

Iodine clock lab:
Materials needed:
- 2 150ml. erlenmeyer flasks
- 1 200 ml. graduated cylinder
- 1 10 ml. graduated cylinder
-GLOVES. Acid is involved
- 2 test tubes
- test tube rack

We prepare our own solutions, but sometimes stock solutions are available. They all work, but will alter your reaction times.
Solutions needed:
Acetone
0.5 M sodium thiosulfate
0.5 M potassium iodide
3% hydrogen peroxide
1 M sulfuric acid
Deionized water if available. If not, use distilled water.
Most importantly, starch solution. The concentration doesn't matter, the solution should look cloudy. Make sure the starch is WATER SOLUBLE. The chemical container should be labelled starch, soluble, or something along the lines of that. The reaction won't happen if it isn't this kind of starch. Cornstarch WILL NOT WORK. Test your starch solution with iodine to make sure it
reacts and turns black.

Procedure:
Label the two flasks: Flask 1 and Flask 2
To the graduated cylinder, add 46.5 ml. deionized water, 3.5 ml KI solution, 10ml. sulfuric acid, 5ml. starch solution, and 10 ml. sodium thiosulfate solution
Add this to flask 1
Rinse the graduated cylinder with DI water, then add 48.25 ml deionized water, 1.75 ml KI solution, 10 ml. sulfuric acid, 5ml. starch solution, and 10 ml. sodium thiosulfate solution.
Add this to flask 2

Add 5ml. hydrogen peroxide to each test tube and place them in the rack.
To start the reaction, add the hydrogen peroxide in each tube to each flask and stir them vigorously. Start timing as soon as you add the peroxide. You must stir the flasks by swishing them for the entire time. It sucks and your arm gets tired but the reaction goes a lot slower otherwise.

If after ~5ish minutes your solutions turn a pale gold color instead of black, you used the wrong kind of starch.

[_deltaV]

Another more common lab is the precipitation of solid sulfur by reacting sodium thiosulfate with hydrochlorid acid. Much easier to set up.
Materials:
5 200ml erlenmeyer flasks
100 ml graduated cylinder
1M hydrochloric acid
0.5M sodium thiosulfate
Deionized or distilled water
sharpie marker
paper

Draw an x in sharpie on the bottom of each flask

To flask 1: add 50ml of the thiosulfate solution and 50ml. water
flask 2: add 40ml. thiosulfate and 60 ml water
flask 3: 30ml. thiosulfate and 70ml water
flask 4: 20ml. thiosulfate and 80ml water
flask 5: 10ml. thiosulfate and 90ml water
Measure out 5ml. of HCl, and pour this into the first flask. Start timing it as soon as you add the acid. Make sure the flask is on top of the paper. Looking into the flask, stop the time when the x can no longer be seen. Repeat this with each flask.

[Eureka314]

Do the note sheets need to be in a binder or folder or anything like that?

[kenniky]

Do the note sheets need to be in a binder or folder or anything like that?

They shouldn't need to be, just bring them and make sure you have all five and no more.

Binders are really only for events where you can have any number of cheat sheets