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Science Buddies: "Ask an Expert" • Trouble measuring sugar content, please help!
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Trouble measuring sugar content, please help!

Posted: Fri Nov 23, 2012 5:46 pm
by gus1996
Hi, I am conducting this experiement of measuring sugar content with a a laser pointer. I have done all the steps that the website says and am using sciencebuddies.org equipment as well. I have measured all index of refraction for all liquids with %10, %20, and %30 sugar concentration as shown in the table. However, I am stuck in the step that asks me to use the index of refraction to measure the sugar content. I don't know how to get from the index of refraction to the percentage of sugar concentration of an unknown liquid. Please help me as I have been trying to figure this out for a very long time and my project is due in less than a week.
Thank you, I really appreciate your help
Gustavo

Re: Trouble measuring sugar content, please help!

Posted: Mon Nov 26, 2012 7:13 pm
by gus1996
The project is due in two days, any suggestions can help. Thanks

Re: Trouble measuring sugar content, please help!

Posted: Tue Nov 27, 2012 11:05 am
by wendellwiggins
Hello gus1996,

I just reviewed the project at https://www.sciencebuddies.org/science- ... ml#summary.

I think you are expected to "interpolate" the sugar content from the results of your experiments on known-concentration solutions. You can do this using a very common technique called "linear interpolation." What that means is that you assume the index of refraction varies linearly (along a straight line) between your measured values.

Here's an example. Suppose you measure n(10%) = 1.3479 and n(20%) = 1.3639. Then you measure the index of refraction of an unknown solution and get n(unknown) = 1.3575.

1.3575 is at 60% of the distance between 1.3479 and 1.3639. The concentration of the unknown solution is then 60% of the distance between 10% sugar and 20% sugar, or 16% sugar.

Hope this helps, WW

Re: Trouble measuring sugar content, please help!

Posted: Tue Nov 27, 2012 10:18 pm
by gus1996
Thank you so much, I found a formula on excel that interpolated the values for me. You really helped!
Thanks

Re: Trouble measuring sugar content, please help!

Posted: Sun Dec 02, 2012 5:20 pm
by AstroPie
i have already done this whole project, the trick is not to measure the length of diverted beam and use sin, but to measure length x and L and use tan.
when measuring the content of sugar you have to go 0g 5g 10g etc of sugar and then 100g 95g 90g with water. I used an electronic gram scale and just pored everything into a small container on the gram scale and normally you would subtract the weight of the container but mine had a feature that did it on it's own.

and yes when measuring unknown sources you would go by what info you already have, but a quicker way is:

since you already have the measurements on the wall across from the laser you can say, "ok, I know 5% is here and 10% is here, my beam is aproxiamatly inbetween the 2 and so I will make it 7.5%