Water Quality B/C

[ptkid]

I noticed that I was making a mistake calibrating my salinometer, and I'm thinking this might be a common mistake. When mixing saline solutions I would mess up my total. For example, if I wanted 4% salinity, I would mix 400 g of distilled water with 16 g of salt, because 16 is 4% of 400. However, my total solute to solution ratio would be 16 g of salt over 416 total grams of saltwater solution, and 16 is not 4% of 416. Basically, my results were thrown off because I didn't take into account the total amount of solution. What I should have done to get 400 g of 4% salt water was to mix 16 grams of salt with 384 grams of water. Has anyone else made this mistake?

wait, back in the first year of WQ there was a rules clarification on how to make the saline solution for salinometer testing.

It said "Note: At Nationals, the saltwater solution (most likely NaCl) will be made by adding salt to a volume of water until a predetermined total volume is reached (e.g., a 6.5% solution can be made by dissolving 65g of NaCl in water until a total volume of 1L is reached. Teams will record concentrations in percent (1-10 and estimate the tenth). At Nationals (maybe State) any percent ± 0.5 (maybe ± 1 at Invitationals/Regional) will be given full credit (partial credit may be awarded for other percents). The points for this testing should be approximately 5% of the total score (e.g., if a team recorded between 6.0-7.0%, they could receive 5 points out of 100). There is no restriction on the salinometer type as long as the team builds it."

So if I understand this correctly you would (to make a 6.5% solution):
1. get a graduated cylinder for 1L and dump 65g of NaCl into it.
2. fill the graduated cylinder with water until the meniscus of the water reaches 1L.
3. Then mix.

This would have a greater mass than the way you described above about by creating the solution by mass right? These 2 ways are definitely not the same.
So which way is correct?

EDIT: If by mass, I have calibrated my salinometer wrong for every competition.

[rtunnel97]

i have never done it by mass. just filled to the 100mL mark on the graduated cylinder.

[Smithy0013]

Anyone else find it a little ridiculous that they can throw literally any salt they want at us? like not just NaCl. There are so many salts its insane. Can you imagine going into a competion and hearing "alright tell us what percent potassium dichromate is in the water" I know I'd be drooling. So anyway... Does anyone actually compensate for this? If so... how? Chem was kinda my weak science so I'm lost aside from testing every salt in my chem teachers back room.

[caseyotis]

It says most likely NaCl, and to be honest, I don't know why they'd do any other type of salt...

[rtunnel97]

every competition ive been to, they have used NaCl, i have always calibrated my device with NaCl

[Cjkowalcz]

Electronic salinometers are allowed right? Just to clarify-- don't wanna get DQ'd or anything

[Skink]

Electronic salinometers are allowed right? Just to clarify-- don't wanna get DQ'd or anything

Go to section 3.c. of the rules and read the third sentence after the bolded one. Looking back to section 2 says the same thing. As long as you've built it, anything goes, and there have been teams in the past (particularly in the C division) who have used electronic meters. As a result, the only consideration for you is the cost-benefit analysis of whether to spend the time learning to build an electronic one or not when you can save both time and money to get a serviceable one, say, using Science Olympiad's instructions. If you have one, awesome. If not, note that it's only 5% of your score. A team who has mastered the material and does not bring a salinometer can easily win. I'm not saying don't, but you get the idea.

[Cjkowalcz]

Electronic salinometers are allowed right? Just to clarify-- don't wanna get DQ'd or anything

Go to section 3.c. of the rules and read the third sentence after the bolded one. Looking back to section 2 says the same thing. As long as you've built it, anything goes, and there have been teams in the past (particularly in the C division) who have used electronic meters. As a result, the only consideration for you is the cost-benefit analysis of whether to spend the time learning to build an electronic one or not when you can save both time and money to get a serviceable one, say, using Science Olympiad's instructions. If you have one, awesome. If not, note that it's only 5% of your score. A team who has mastered the material and does not bring a salinometer can easily win. I'm not saying don't, but you get the idea.

Yeah I know; we have won medals in water quality and we usually get the salinometer question wrong ..... but this year my friend made an electronic one, and i just wasn't sure if it counted as "built" because we bought parts Thanks

[alkire14]

Good Afternoon,

I'm in need of a Water Quality test. I'm new to the event and would like to have one to look at for future reference. Yes, I'm aware that there are example tests posted on the Wiki, but I'm looking for a test that you have created to run with your students, possibly a test that was used at an invitational, or a test that will be used at your regional for this year (if you or someone you know is running the regional event).

I have been a regional test supervisor for the following events:
- Crime Busters
- Can't Judge A Powder
- Meteorology
- Solar System

I would be willing to exchange a test in any of these events for a 2014 - Water Quality Division B Test.

I have tests created for all of these events listed above based on the 2014 rules. They are ready to go in exchange for 2014 - Water Quality Division B Test. Let me know if you are interested!

Thanks!!!

[silentsage]

alkire14,
I can not help but feel that you want to use a test as some sort of information currency. This isn't what scioly is about, or to me at least. We should be freely sharing what we know, and not safeguarding it until someone offers equally valuable information of their own. I am a fairly experienced test writer, and could write you one to practice on, but would post on the test exchange for anyone to use. I haven't written for a competition, but I have written tests that are a far sight better than some invitationals I have attended, and even at the regional level as well. As are many of those on the exchange. I hope not to seem condemning.