Measuring Sugar Content of a Liquid with a Laser Pointer.

[Alaa1991]

Oh thanks,
no I seemed to understand everything even more than before. And I can see that using the semi-circle after following the instruction that Craig posted, it so much easier, and helpful I have tried it, but still I am still going to try the different liquids,
but I just want to know how can you calculate theta 1 and 2?

[Louise]

Oh thanks,
no I seemed to understand everything even more than before. And I can see that using the semi-circle after following the instruction that Craig posted, it so much easier, and helpful I have tried it, but still I am still going to try the different liquids,
but I just want to know how can you calculate theta 1 and 2?

You don't calculate theta 1 and theta 2, you measure them. Look at the link Craig provided before. Figure 1 shows where theta 1 and theta 2 are.

http://phyastweb.la.asu.edu/phy114-tsen ... ht_rev.pdf


Louise

[deleted-71588]

You don't calculate theta 1 and theta 2, you measure them.

To further clarify, you choose the incident angle by where you place the laser and then you measure theta 1 with a protractor. This is an independent variable. The proceedure I gave you recommended that you run the experiment with each liquid at several incident angles (different theta1) and measure the refraction angle theta2 for each (a dependent variable). Theta2 is dependent on theta1 (the incident angle) and the refractive index of the liquid (a variable that you are trying to determine indirectly). It is this refractive index property that you are correlating to some concentration of a chemical (Is it still sugar? I haven't been following the evolution of your experiment too closely).

[Alaa1991]

Over the break I have built the prism, and I wonderd if you accidently put epoxy glue on the surface will that affect the exp.

I am have planned to try the prism, since we have four days off school.
And if it does not work with me, than I will defintily do the semi circle, a physic teacher, decided to help on the exp. with the semi-circle. Thank you engineer Carig for the steps, I will follow those steps carefully with the Physics teacher as we do the exp. if the prism does not work.

I have already finished building it, but still have done the exp. but my question is if I accidnetly put glue on the surface of the prism will it affect the exp.?
Thank you,
Alaa A.

[deleted-71588]

If the glue is on a surface in the path of the laser beam, it WILL affect the experiment as it would be another material interface. The experimental proceedure for the equilateral triangle column has the laser passing through only two of the three surfaces, so pick the best two sides. If the glue contamination is only near the bottom, then you can pick a height above the glue for the laser height.

When using an equilateral triangle column, it is VERY important for the beam to enter and leave at the same height.

The semicircular refraction technique does not require the beam to enter and leave at precisely the same height; however, it does require that the beam enter precisely at the focus.

[Alaa1991]

I am really really tired of building that prism, its my 5th or 6th time building it, its so so hard to keep the glue away from the surface, my hand has to touch it in order to hold the side, I do not know what to do.
I keep on using so many slides.

After all this effort, I can see why the semi circle is so easy. It took me three days building that prism, every single time I have it done and strong to hold the water, still it turns out to be that the surface has glue on it. I am using a 3 by 1 inch slides, and I am putting two over each others to fill enough water.

For the semi-circle, from the steps I understand that I am to get a lined paper, fold it into a half, draw the semi plastic on the middle of the paper, find the center of the semi cirlce, ( meaning the focus), draw a pependicular line to the semi -circle, then direct the laser at the focus of the semi circle.

DO I put a paper on the wall where I measure where the laser beam hits, when the semi circle is empty, then add water and see where it refracts?

Its so confusing, that this project is not becoming easy rather, more complex, and diifucult.
I already know the result anyway, but just have to find the index of refraction. I know that as you add more sugar, the index of refraction increased.
Thank you,

[deleted-71588]

Fabricating experimental apparatus is always a challenge.

Do you have a hot glue gun? It should be easier to control where the glue goes. Up the outside corners and around the outside bottom should be enough. A small 30-60-90 degree triangle can be used to position two slides at a 60 degree angle at the bottom and a narrow piece of tape can be used to hold the top corner together. Glue the outsides to the base then up the outside of the corner. Once this is in place, then position the third slide using a narrow piece of tape to hold the top corners. Glue the outside of the base, let it cool, then up the remaining two outside corners.

Use the first two sides positioned accurately at 60 degress for the incident (entry) and exit surfaces as these sides will be the most accurate.

As to the semicircular method, you can just put a piece of paper on the semicircle to see where the laser exits. Note: If you allign the laser so that it exits the flat side into the air at the focus on the inside surface, it will enter and exit the semicircular surfaces at the same angle it entered.

This is because of the special geometry of the semi-circular dish. Any line (or ray) that passes through the focus of the inside semi-circle will be normal (perpendicular) to the tangent at the point it passes through the semi-circle. Any ray of light normal to an interface surface will exit that surface at the same angle. Same holds for the outer semi-circular surface.

NOTE: As you change the incident angle (theta 1) in figure 1 that I referenced, you have to adjust the point where it hits the outer flat surface so that the refraction offset in the flat wall is accounted for. The magic focus point is on the inner side of the flat wall.

[Louise]

Fabricating experimental apparatus is always a challenge.

Do you have a hot glue gun? It should be easier to control where the glue goes. Up the outside corners and around the outside bottom should be enough. A small 30-60-90 degree triangle can be used to position two slides at a 60 degree angle at the bottom and a narrow piece of tape can be used to hold the top corner together. Glue the outsides to the base then up the outside of the corner. Once this is in place, then position the third slide using a narrow piece of tape to hold the top corners. Glue the outside of the base, let it cool, then up the remaining two outside corners.
[snip]

Hot glue doesn't work well with glass, I think.

The instructions have you taping the triangle together first and then gluing it. They also have you applying the glue with a toothpick, so I'm not sure how your hand it touching it.

If you get a little epoxy on the side, it is okay. You just have to get the beam through. Your beam spot is very small compared to the 1 inch x 1 inch surface.

It may be that you can clean the epoxy off when it is still wet using a solvent. Read the label, and maybe you can use a q-tip to clean excess expoxy with a chemical like acetone. READ THE LABEL FIRST! Don't use a chemical unless the epoxy container says you can.

Making the device is the hardest part (well, maybe understanding the experiment is the hardest part )- the experiment should not take too long compared to this.

Louise

[Alaa1991]

What are some of the error that could occur in the experiment?

I thought maybe some of the errors that could occur, are accidently adding more sugar
- moving the laser during the experimentation
- not directing the laser on the right focus of the semi circle

These are some that I came I believe could occur.

[/quote]

[Louise]

What are some of the error that could occur in the experiment?

I thought maybe some of the errors that could occur, are accidently adding more sugar
- moving the laser during the experimentation
- not directing the laser on the right focus of the semi circle

These are some that I came I believe could occur.

[/quote]

I would add:
not measuring/ setting theta1 or theta2 correctly

I would say instead of adding more sugar- that you have error in both the volume of the water and the mass of the sugar- but the result is the same- a mistake in concentration.

I think those (your list plus my one thing) are the major source of errors experimentally.

If you measured each standard several times, the reproducibility of that number will tell you about the experimental error. If you look at all the standards (at each concentration) then they should be on a line- if you fit it to a line, the quality of that fit (such as "r^2" value) tells you about the error too. An r^2 of .99 is very good, but r^2 of something like 0.3 means that you don't really have a line!

There could also be error in your analysis- doing the math wrong, for example. Also, if your calibration is for certain concentration ranges and your unknown is outside that range, then you do not know how much error there might be. (when you look at your measured refractive indices from the standards and take the largest and the smallest, your unknown's refractive index must be in between those two values)

If anything above is unclear- ask!

So, I guess you got something to work! The semicircle I guess... I will write the people who wrote the experiment, and tell them of your difficulty with making the prism.


Louise

[Alaa1991]

When I get my result, in the Discussion I am supposed to compare it to the theortical value.

What is the theortical value?

What about if there was no theortical value, do I just write there was no theortical value, or what?

Thank you

[Alaa1991]

As a result I found that as the sugar concentration increases, the index of refraction also increases.

I will be doing a graph for the different concentration and their index of refraction

Do I have to do a graph of the curve
mx=b

[Louise]

As a result I found that as the sugar concentration increases, the index of refraction also increases.

I will be doing a graph for the different concentration and their index of refraction

Do I have to do a graph of the curve
mx=b

For your known samples, I believe you should have a line. There is probably an intercept (since even at 0 concentration you still refract light), so it should be of the form:
y= mx + B

However, you should verify this is a good model (by using a parameter such as R^2 which I mentioned in another post). This R^2 parameter should be quite high (say between 0.9-1) if the data is a line.

Louise

[Alaa1991]

Um... I wonder when I did the exp. I am still not done with the exp. yet but finally started. I wonder does the angle of incidence is the same for all.
I mean, angle of incidence is the angle of the laser beam that enters, I am to keep the laser at a fixed position, does that mean that the angle of incidence is the same for all trials and concentration, and of course the angle of refraction changes?
This what I kind of get now, am I thinking right?

for concentration of 5% it is kind of close to the index of refraction of water, I got 1.33 as an averge.

Thank you

[Louise]

Um... I wonder when I did the exp. I am still not done with the exp. yet but finally started. I wonder does the angle of incidence is the same for all.
I mean, angle of incidence is the angle of the laser beam that enters, I am to keep the laser at a fixed position, does that mean that the angle of incidence is the same for all trials and concentration, and of course the angle of refraction changes?
This what I kind of get now, am I thinking right?

for concentration of 5% it is kind of close to the index of refraction of water, I got 1.33 as an averge.

Thank you

Assuming everything stayed fixed (you did not move the refraction box or the laser between the samples) then the angle should not change.

Also, it is good that the lowest concentration is most similar to water-you should point that out in the discussion. If you extrapolate to 0 concentration do you get the value for water? [This would be the intercept of your line]

Louise

[Alaa1991]

Finally I finished my experiment yesterday, and finished all the calculation and measurements. I got the following results: Distilled water: 1.334, 5% was 1.342, 10% was 1.345, 15% was 1.351, 20% was 1.358, 25% was 1.366, and 30% was 1.381. I also tested Diet coke which had the index of refraction of 1.334, I tested also coke, which had the index of refraction of 1.364 which showed that it might have about 20% sugar concentration.

For each solution, I used 100 mL . I kept it constant as you told me.

[b]I want to know how can I make a graph for this, I tried doing it, but didn't turn out to be the way it is supposed to be. [/b]

After all this result , I believe that I should add the following to the discussion.


- The index of refraction for Diet coke, was 1.334, as in a distilled water. This shows that index of refraction is not affected by the color of a solution, rather by the sugar concentration.
- As the sugar concentration increased the index of refraction increased.

[b]Is there anything important that I should also add to the Discussion[/b]

How many graphs should I make?
I thought that I should have two graphs, one that shows that as the sugar concentration increases the index of refraction also increases, and another that has to do with what you told me last time I believe its ^R thing. Could you clarify that for me a little.

I just got to finish my conc. and discussion part, since my last day is on the 28th.


Thank you
Alaa A.

[Louise]

Finally I finished my experiment yesterday, and finished all the calculation and measurements. I got the following results: Distilled water: 1.334, 5% was 1.342, 10% was 1.345, 15% was 1.351, 20% was 1.358, 25% was 1.366, and 30% was 1.381. I also tested Diet coke which had the index of refraction of 1.334, I tested also coke, which had the index of refraction of 1.364 which showed that it might have about 20% sugar concentration.

For each solution, I used 100 mL . I kept it constant as you told me.

I want to know how can I make a graph for this, I tried doing it, but didn't turn out to be the way it is supposed to be.

After all this result , I believe that I should add the following to the discussion.


- The index of refraction for Diet coke, was 1.334, as in a distilled water. This shows that index of refraction is not affected by the color of a solution, rather by the sugar concentration.
- As the sugar concentration increased the index of refraction increased.

Is there anything important that I should also add to the Discussion

How many graphs should I make?
I thought that I should have two graphs, one that shows that as the sugar concentration increases the index of refraction also increases, and another that has to do with what you told me last time I believe its ^R thing. Could you clarify that for me a little.

I just got to finish my conc. and discussion part, since my last day is on the 28th.


Thank you
Alaa A.

Are you using a program to graph your data and fit it? You should be able to get the R^2 value from a program like Excel.

When I graph your data, it looks like not a line.

I am not sure if graphing the percent sugar is correct. Maybe it should be mass or molar instead. Did you find any information on this?

Louise

[Louise]

Finally I finished my experiment yesterday, and finished all the calculation and measurements. I got the following results: Distilled water: 1.334, 5% was 1.342, 10% was 1.345, 15% was 1.351, 20% was 1.358, 25% was 1.366, and 30% was 1.381. I also tested Diet coke which had the index of refraction of 1.334, I tested also coke, which had the index of refraction of 1.364 which showed that it might have about 20% sugar concentration.

For each solution, I used 100 mL . I kept it constant as you told me.

I want to know how can I make a graph for this, I tried doing it, but didn't turn out to be the way it is supposed to be.

After all this result , I believe that I should add the following to the discussion.


- The index of refraction for Diet coke, was 1.334, as in a distilled water. This shows that index of refraction is not affected by the color of a solution, rather by the sugar concentration.
- As the sugar concentration increased the index of refraction increased.

Is there anything important that I should also add to the Discussion

How many graphs should I make?
I thought that I should have two graphs, one that shows that as the sugar concentration increases the index of refraction also increases, and another that has to do with what you told me last time I believe its ^R thing. Could you clarify that for me a little.

I just got to finish my conc. and discussion part, since my last day is on the 28th.


Thank you
Alaa A.

Are you using a program to graph your data and fit it? You should be able to get the R^2 value from a program like Excel.

When I graph your data, it looks like not a line.

I am not sure if graphing the percent sugar is correct. Maybe it should be mass or molar instead. Did you find any information on this?

Louise

I see that the sciencebuddies procedure has you decrease the water as you increase the sugar (this actually gives you the value in Brix)... I told you to hold the water constant. (Actually, I said to do it volumetrically if possible), but this is not important. I corrected your data to be in brix, and it still isn't a line.

You can compare you data to reported values.
http://www.topac.com/Salinity_brix.html

So, to make your data in to brix, use the fact that 1 mL of water weighs 1 gram. So, the solution that is 25 g sugar and 100 mL of water is 25/(100+25)=0.2 or 20 Brix. This has should have a refractive index of ~1.36 on that chart, which is pretty close to what you got.

So your values in brix are:
(%) (Brix)
5 4.761904762
10 9.090909091
15 13.04347826
20 16.66666667
25 20
30 23.07692308

Don't use all those digits! I just cut and pasted from excel!


Louise

[Alaa1991]

That so cool.

So I use this website that you gave me to compare my result to.
For example I will be like 5% sugar concentration index of refraction is 1.342 which is according to the theortical value.

is the ^R called the brix, I am little confused. How can I add Diet coke and coke in the graph? is it supposed to be added in the graph?

I also tried what you gave me, but it didnot turn out to be a graph that make sense.

What is R squared or R^2, I don't know what that is.

[Louise]

That so cool.

So I use this website that you gave me to compare my result to.
For example I will be like 5% sugar concentration index of refraction is 1.342 which is according to the theortical value.

is the ^R called the brix, I am little confused. How can I add Diet coke and coke in the graph? is it supposed to be added in the graph?

I also tried what you gave me, but it didnot turn out to be a graph that make sense.

What is R squared or R^2, I don't know what that is.

No, on the site you tested, you have to use Brix instead of %. This is why I calculated all your % values to Brix values.


R^2 is not anything about brix. R^2 is a measure of how well your data fits to a model. For example, I said that your data should be a line if you plot x (%) vs. y (refractive index). The line will have the equation y= mx+b (where B should be the value of pure water). If this is true- that the data forms a line, the R^2 will be 1. If it is not true, it will be much less than 1 (like 0.45). So, you can use this to say how good your model is. For your data, when you plot it, you see it curves upwards at high concentrations. It is clearly not a line. The r^2 value for fitting your data to a line is 0.94. This is not a great value. So, your data probably should not be on a line. The reason you want to fit your data to a line (or some other equation) is because it makes it very easy to calculate your unknown sugar ammount. You just put the refractive index in for coke at y, and then solve for x. The answer is the exact percentage. If you don't have an equation, then you have to estimate- like you did, to get about 20%. This is fine. But, if you can find what type of equation to use, then your analysis is better.

The second question is: how good is this method?
You have several known amounts of sugar and water. Do you get the correct refractive index values for each one? This is what I meant for you to check with the table. If you got close to the correct values for all your known samples, then you might be certain that this method gave you the correct answer for coke and diet coke.

The tables of the correct values are in a unit called brix. A brix is defined as: {(number of grams of sugar)/(number of grams sugar + number of grams of water)} * 100. Brix are a unit of measure only used for sugar- and is widely used by people who make drinks with sugar.

100 mL of water has a mass of 100 g. So, I just calculated what all your percentages were in brix so you could use the table.

Louise

[Louise]

That so cool.

So I use this website that you gave me to compare my result to.
For example I will be like 5% sugar concentration index of refraction is 1.342 which is according to the theortical value.

is the ^R called the brix, I am little confused. How can I add Diet coke and coke in the graph? is it supposed to be added in the graph?

I also tried what you gave me, but it didnot turn out to be a graph that make sense.

What is R squared or R^2, I don't know what that is.

No, on the site you tested, you have to use Brix instead of %. This is why I calculated all your % values to Brix values.


R^2 is not anything about brix. R^2 is a measure of how well your data fits to a model. For example, I said that your data should be a line if you plot x (%) vs. y (refractive index). The line will have the equation y= mx+b (where B should be the value of pure water). If this is true- that the data forms a line, the R^2 will be 1. If it is not true, it will be much less than 1 (like 0.45). So, you can use this to say how good your model is. For your data, when you plot it, you see it curves upwards at high concentrations. It is clearly not a line. The r^2 value for fitting your data to a line is 0.94. This is not a great value. So, your data probably should not be on a line. The reason you want to fit your data to a line (or some other equation) is because it makes it very easy to calculate your unknown sugar ammount. You just put the refractive index in for coke at y, and then solve for x. The answer is the exact percentage. If you don't have an equation, then you have to estimate- like you did, to get about 20%. This is fine. But, if you can find what type of equation to use, then your analysis is better.

The second question is: how good is this method?
You have several known amounts of sugar and water. Do you get the correct refractive index values for each one? This is what I meant for you to check with the table. If you got close to the correct values for all your known samples, then you might be certain that this method gave you the correct answer for coke and diet coke.

The tables of the correct values are in a unit called brix. A brix is defined as: {(number of grams of sugar)/(number of grams sugar + number of grams of water)} * 100. Brix are a unit of measure only used for sugar- and is widely used by people who make drinks with sugar.

100 mL of water has a mass of 100 g. So, I just calculated what all your percentages were in brix so you could use the table.

Louise

One other thing, you can put the coke and diet coke on your graph if you want... but make those data points in different colors from the known solutions. That way, people can easily see the approximate sugar content of the coke and diet coke.

Louise

[Alaa1991]

Oh Now I understand why you got those brix value,

So I make a graph using the brix value instead of the %. Is that right?

And I have to change my tables instead of 5% it would be the brix value instead. Or do I just keep the tables that way they are, but just do it for the graph.

Do I need to explain that I used the brix value in my discussion?

THANK YOU SO MUCH.

[Alaa1991]

Here is my abstract:

[i]The problem that I am studying is whether it is possible to determine the sugar concentration of a liquid with a laser pointer. The semi circle method was used to test the index of refraction of six different concentrations. The laser pointer was directed at the focus point of the semi circle. To find the focus of the semi circle dish, the dish was traced after aligning the flat side to about the middle of a ruler paper & then folding the paper to make sure the dish corresponds to a vertical perpendicular line. The laser beam was placed at an angle, and was kept at a fixed position. 100 mL of water were poured in the dish with the correct amount of sugar concentration. Where the laser beam enters & exit were measured. I used Snell’s law to calculate the index of refraction for each solution, which were averaged out. The index of refraction for distilled water was 1.334, 5% was 1.342, 10% was 1.345, 15% was 1.351, 20% was1.358, 25% was 1.366, and 30% was 1.381. [/i]


Here instead of the percentage do I need to change it to brix value?

Sorry I know I am asking so many questions, I just want to make sure that I understand, and doing the right thing. I apolozied for taking so much of your time.
Thank you

[deleted-71576]

As Louise pointed out, since you were decreasing the mass of water as you increased the mass of sugar, you were using the Brix method.

Therefore you should use it in your discussion and graphs.

Also, in your last sentence, you should say what the brix is of -- In other words:

The index of refraction for distilled water was 1.334, for 4.7 brix of sugar is 1.342, for 9.1 brix was 1.345, .....

No need to apologize for asking questions. That is what all of the experts here volunteer to answer. It's our pleasure.

Also, as Louise was asking, have you looked into different shaped curves that your data might better fit to? (Something with a higher r^2 value)

[Alaa1991]

So that means I need to change my tables, since we are using the brix method. See I did my tables in this way:

Trial / Amount of sugar (g) /Amount of water /incidence angle/ angle refraction/ index of refraction

Amount of sugar was based on the concentration, Amount of water was kept constant to 100 mL, angle of incidence was same for all, angle of refraction depends on bending, index of refraction was gotten by using snell's law.
For example one of them would look like


5% Concentration

Trial Amount of Sugar (g) Amount of Water (mL) Angle of incidence Refraction angle Index of refraction
1 5 100 41.0 29.3 1.340
2 5 100 41.0 29.2 1.344
3 5 100 41.0 29.2 1.344


Average: 1.342

( its kind of messed up) but is this how it is supposed to be, or does it need to be changed. Since we are using the brix value. Does the amount of water needs to be changed?



A bar graph will be used. Showing the index of refraction increased as sugar concentration increased

I tried the graph the bar graphed worked perfect. It shows what I want to show.
The line graph as you said WAS a curve when I tried it. ( This of course I did index of refraction vs. Brix valule) and I also tried doing it index of refraction vs. sugar concentrtaion it worked but that is if you add Diet coke and coke. ( if you try it you will see what I mean) So maybe that will work out.

Any advice?
( The brix worked, but do I have to change my tables? )

[deleted-71576]

Now you've got me confused. If you kept the amount of water constant at 100ml, you really aren't using the Brix method (which involves decreasing the water as you increase the sugar, as is done on the project on the web site), you are doing it volumetrically (keeping the water at 100ml), so % sugar concentration is what's needed. All the values need to be reported that way.

You can't mix and match. If you are just now doing the experimental runs now, you could use the Brix method and vary the amount of water. Otherwise, if you have already done it with a volumetric approach, stick with that.

You are still mixing % concentration and Brix. If I understand the equation correctly, you should be using % concentration due to the way you performed the experiment.

If you could use a program that could determine what the equation would be relating the refraction to the % concentration value, so much the better. (You've just found out it's a curve, not a straight line.) Those programs exist, I just can't think of the name of one right now (someone else might chime in here and help.) It certainly isn't essential at your level by any means, just a nice plus if you can do it.


It sounds like your graph shows good results.

[Louise]

So that means I need to change my tables, since we are using the brix method. See I did my tables in this way:

Trial / Amount of sugar (g) /Amount of water /incidence angle/ angle refraction/ index of refraction

Amount of sugar was based on the concentration, Amount of water was kept constant to 100 mL, angle of incidence was same for all, angle of refraction depends on bending, index of refraction was gotten by using snell's law.
For example one of them would look like


5% Concentration

Trial Amount of Sugar (g) Amount of Water (mL) Angle of incidence Refraction angle Index of refraction
1 5 100 41.0 29.3 1.340
2 5 100 41.0 29.2 1.344
3 5 100 41.0 29.2 1.344


Average: 1.342

( its kind of messed up) but is this how it is supposed to be, or does it need to be changed. Since we are using the brix value. Does the amount of water needs to be changed?



A bar graph will be used. Showing the index of refraction increased as sugar concentration increased

I tried the graph the bar graphed worked perfect. It shows what I want to show.
The line graph as you said WAS a curve when I tried it. ( This of course I did index of refraction vs. Brix valule) and I also tried doing it index of refraction vs. sugar concentrtaion it worked but that is if you add Diet coke and coke. ( if you try it you will see what I mean) So maybe that will work out.

Any advice?
( The brix worked, but do I have to change my tables? )

It does not matter how you present your data. This is like the difference between measuring the distance in centimeters or in inches.

You measured grams of sugar/ 100 mL per water. You can report this as a percent, as long as you are clear somewhere that percent is defines as (grams sugar/100 mL water )*100. This is % mass per volume, which isn't a standard unit. For your table, you should use the actual values you used- which is 5 grams per 100 mL, 10 g per 100 mL. You could also add a column with the conversion to the brix units.

I converted to brix for you because the tables of refractive indices for sugar solutions are in brix. Plus, brix is actually mass sugar/ total mass, which is actually mass percent. This unit (mass percent) is actually fairly common, and only for sugar is given the special name of "brix".

You can use both measurements, but you should know the difference between the two.

You cannot use coke and diet coke to make the line, because you don't know the value of the refractive index and the concentration. You estimate them from the known data.

It is fine that it is a curve. It is clear that there is a predictable relationship between the amount of sugar and the refractive index, which is what you need to calculate the amount of sugar in coke.

Louise

[Louise]

I would say instead of "100 mL of water were poured in the dish with the correct amount of sugar concentration"
say this "100 mL of water were poured in the dish with a known mass of sugar (5 g, 010 g, 20 g, etc)"

The, instead of using the percent, I would say: "The index of refraction for distilled water was 1.334, 5 g sugar/ 100 mL water was 1.342, 10 g sugar/ 100 mL water was 1.345, 515g sugar/ 100 mL water was 1.351..."
This is longer, but more clear as to what you did.


zzzzdoc is right- don't apologize for asking questions. I would rather answer 500 questions and know you understand the project, than answer 3 and have you be confused. If I ever seemed cross about answering questions, it was only because I was unhappy that I could not answer your questions well enough that you understood!

Louise

[Louise]

Sorry for 3 posts in a row! I found some stuff about concentrations that you might find useful:

The first is on mass-volume percentages. This is what you calculated as 5%, 10 %, etc. This should be noted as % m/v or % w/v for mass or weight. Like 5% (%w/v). It should technically be calculate on a per liter basis, since that is the SI volume.
http://www.chembuddy.com/?left=concentr ... percentage

This is about how concentrations can be confusing or unclear:
http://www.chembuddy.com/?left=concentr ... ercentages

This is about mass percentages (which are brix for sugar):
http://www.chembuddy.com/?left=concentr ... percentage

As a chemist, I don't use any of these! We (chemists) have our own special measure of concentration called molar concentration (which is closest to %m/v) but we have special glass containers called volumetric flasks, which let us avoid some of the problems involved in the mass per volume mixtures.

You can convert between any of these, as long as you are very certain what measurement is being used. 5% is not useful, since it could be a volume/volume, mass/volume or mass/mass. You have to also say which one it is!

Louise

[Alaa1991]

I searched for a program to relate index of refraction to sugar concentration and I found a program called RI-DS

http://www.corn.org/web/RIDS.pdf

I don't know if that could be used, I haven't read it all.
What kind of program could I use to relate index of refraction to sugar concentration.

In my Abstract and Discussion and conclusion I would write 5g/100mL per water, 10 g/100 mL per water. Right?
Instead of 5g was 1.342 and etc.

And I should add another column where I could put brix. And explain what the difference is, in my Discussion or Intro?

For coke and Diet coke, they should be on a sperate graph in different color compared to the 6 different concentrations. and another graph relating index of refraction to sugar concentration.
Or brix to index of refraction. I guess I will do three graphs.

So Can I put a graph that is a curve as long as it shows index of refraction relationship to sugar concentration.
Thank you for those websites