Which ion causes the color?
You are here because I didn’t like your answer to one of your lab questions. Don’t worry, this isn’t a punishment. It is just a bunch of hints.
Why didn’t I write them on your paper? Pick whichever answer you like best: (1) I type faster than I write. (2) Ouch, my aching hand!
If you still need further clarification there is a nifty comments feature. No, you don’t have to sign up for an account to use it. And if I’m not around to help, perhaps another of your classmates who have found their way here will be able to help you.
Without further ado –
Flame Test Data Table
These are much prettier, cleaner colors than we were able to get in the lab. Why? Because whoever took this picture re-did the experiment until they finally got the color they wanted. If we had infinite time, we could have gotten these colors, too
Hydrogen Emission Tube Data
Wavelength. Did you remember to put the x10-7 m on the number that you read off of the spectroscope? If you used the spectrum from my website, did you tack on the x 10-9 m?
Frequency. Did you use the formula c = λν? Are you using 3.0 x 108 for c? Did you use the wavelengths from the previous column as your value for λ?
Energy. Did you use the formula E = hν? Are you using 6.626 x 10-34 for h? Did you use the frequency from the previous column as your value for ν?
Transition. Now that you are armed with an energy (from the previous column), did you look at your interpreting graphics worksheet? Did you find an energy that was close to the one you calculated in the Energy column? Did you look one column to the left to find the transition that they had listed there? Did you copy down exactly what that datum said (should be a number → number)?
1. Why is it important to test the flame test colors of the cotton swab and the water?
What two things can we count on being in every flame that we created in the lab?
Are those two things what we are actually testing?
Wouldn’t it be helpful to eliminate any coloration due to those two things?
How might we design a procedure to do this elimination?
Did we actually conduct that procedure?
Ye gads, I think you are now on the right track!
2. Which ion is responsible for the colors created by the unknown? Explain.
What color did you see when you burned the unknown?
Which ion were we changing between the stations: cation or anion?
Which of the known cations produced a color that was similar to the one that you saw from the unknown? If you wrote “orange” for all of the colors, this is your wake-up call that you need to be more descriptive in your data. Perhaps a flame test color refresher might help.
Your answer is not complete until you actually name the cation that you think is responsible.
3. Which of the ionic compounds in this experiment would be good for making purple fireworks? Red fireworks?
Which cation produces a purple flame color?
Which cation produces a red flame color?
4. How would you tell the following three white artificial sweetener powders apart using flame tests?
Cations and anions are present in which type of bonding: ionic or covalent?
If it isn’t ionic, then does it have cations?
What are the cations for the sweeteners?
What colors are associated with those cations?
5. What is similar about all of the transitions from the hydrogen emission tube?
What do you notice about the starting number?
What do you notice about the ending number?
Any of them the same?
6. Knowing what you know about wavelengths, explain the overall color of the hydrogen emission tube.
If you add all of the wavelengths, do you get a wavelength that corresponds to the overall color?
If you subtract all of the wavelengths, do you get a wavelength that corresponds to the overall color?
If you multiply all of the wavelengths, do you get a wavelength that corresponds to the overall color?
If you divide all of the wavelengths, do you get a wavelength that corresponds to the overall color?
If you average all of the wavelengths, do you get a wavelength that corresponds to the overall color?
If nothing has worked so far, what other mathematical operations can you come up with that might work?
7. How much total energy does it take to power the hydrogen emission tube.
Did you calculate energies for each of the wavelengths?
Doesn’t there need to be enough energy to get each of the wavelengths?
What does the word “total” mean in math-speak? Add? Subtract? Multiply? Divide?
Do that to the energies of each of the wavelengths.
