Refractive Index of Water

[perrrelet]

I'm studying physics at a-level and we have began the years practical part of the course. The only problem is i can't measure my variable accurately enough to produce any results.

My experiment title is "the affects that dissovled substances have on the refractive index of water"

I chose to slowly add salt to a sample of water, systematically measuring the refractive index of the water at each step. I used the "apparent depth" method, where a traveling microsope is used to focus firstly on the base of a beaker, secondly on the surface of water when it is added to the beaker and thirdly on the new apparent position of the base of the beaker (through the water). By noting the scale of the microscope at each focus you can find the value of n.

I successfully managed to find the value of n for water, the only problem is that when i add salt the change in n is too small to measure. (my error is greater than my variable).

Does anyone have any suggestions?
Are their any substances that will alter the refractive index of water enough to measure it?

Any help will be greatly appreciated as I am drastically running out of time.

Many Thanks,
Jamie

[brachiopod]

Not sure what your guideline / remit is, but what about two miscible liquids? eg ethanol and water. Miscible in all proportions, so you can go from 100% H2) to 100% ethanol* (well, as high a percentage as the materials available).

Oh, and one small, possibly pedantic point - you are looking for the effects of a dissolved substance.
(A may well affect B, but you attempt to measure the effect)
It won't look good if you make that mistake in the title - the first thing your marker / examiner will see.

[jake-the-peg]

Hand held refractometers are used to measure the concentration of anti-freeze in car coolant - you could try that.

Would you believe there's even a refractometer shop

http://www.refractometershop.com/

Where you can buy things like calibration fluids

Remember though that as the magnification of a microscope increases it's depth of field reduces so you want to use the highest magnification ou can get to get the smallest depth of field and the most accurate focus point.

[Hamish]

Ethanol water would be good. You can see the effects when you add a drop of water to whisky! I would expect salt to only have a small affect on the RI at low concs. I know that sodium hydroxide has a larger effect at high concs, you can dissolve about 2g in 1g of water. MAKE SURE YOU DO A SAFTY ASSESSMENT IF YOU TRY THIS NaOH IS VERY CORROSIVE AND WILL ETCH LEATHER AND GLASS AT HIGH CONCS. I would have gone for the methanol, ethanol, acetone, (can suggest more if you are well equipt; THF, DMSO (V toxic), Phenol (toxic).)

[penny1996]

With the FJD atc refractometer, you can measure the sugar content, salinity, baume degree, moisture content, and dissolved solids in coffees (TDS).
maple syrup refractometer
hand held refractometer
atc refractometer
‌brix meter
https://www.fjdretail.com/

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