What is the simple way to determine salinity of the seawater in lab?

Question

What kind of procedure can be used to simply determie the salinity of the seawater in lab?dehydration, crystalization,etc.,

Answer 1

Pure water is not a good conductor of electricity. Salt water is an excellent conductor, one of the best in fact. So a test of the current that passes through a tank of sample water will be a good indicator of how much salt it has in it (apply a voltage and check the "speed" amperage and resistance of the water sample). Most of seawater is not made up of simple NaCl (Sodium Chloride) it is made up of many salts. As rocks and minerals weather they are eroded away, end up in the fresh water system, and finally into the ocean. These minerals frequently combine with Sodium Chloride to form various salts. That's because chloride and sodium are very active elements and they want to bond with whatever they can.

Crystallization can only be determined by letting the water evaporate, boiling it will shorten this process. Then what remains in the sample container is mostly the various salts. To find out which salts will require a battery of chemistry tests, but most of the stuff in the container will be salts of one form or another.

The best way to measure dehydration is to take the sample container, that has had all its water evaporated, and slowly add distilled water. How much water is required to put the salts into solution will be your amount of dehydration.

PH strips determine the level of acids and bases in the solution. They don't break it down to the various components only the total value of the solution. Once you re-hydrate your salt solution, to find the point of dehydration, then you can test the PH value of that solution to determine the PH value of all the salts in it.

Answer 2

If you mean, in a very formal way how much sodium chloride can be obtained from seawater, you will need to test both the sodium level and the chloride level. Go with the lower of the two values.

A very easy way to estimate the total dissolved solids is with an analytical balance and a burette or pipette. I have done this several times after beach trips. I think the value I keep hitting is in a range around 1.025 g/mL for density, where the normal density of water should be 1.000 g/mL. So you have 25 mg of dissolved solids per mL. Better to think of it as 20-30 mg. Wikipedia gives different values, but I remember being pleased to see my numbers closely coinciding with an old chemical engineering text from the '40s.

Answer 3

The standard way to determing total dissolved solids (TDS) is to dehydrate a known weight sample at 180C, and weighing the residue. Units are typically mg/L

Salinity is actually a relative measure based on an ideal KCl solution, and its values are typically given in ppt (parts per thousand).

Electrical probes simply are estimating tools, and are inherently inaccurate with un-ideal samples.

Answer 4

the easyest is crystallization.

But you can create a list of values for resistance

put 2 electrodes with some separation (fixed non changeable) and measure resistance with a multimeter, the lower the value for resistance, the higher the salinity, the higher resistance lower salinity.

Answer 5

the simplest way to do that is by using multi functions pH meter this device has 2 or 3 probes which can determine pH, conductivity,,potential,, salinity and TDS, etc

Answer 6

any pet store sells strips that give you acid/alkiline numbers. thats where i would start my quest.