andykee Posted May 29, 2005 Share Posted May 29, 2005 having a small discussion (argument) about this topic... does the temperature of water have any effect on the salinity of the water? i'm not talking about the measurements taken by various devices, but the TRUE salinity of the water? by definition, salinity is the total weight of solids dissolved per unit weight of water Link to comment
inkto Posted May 29, 2005 Share Posted May 29, 2005 I don't believe so. I can understand the confusion however in some respects given that the measure of salinity is done utilizing other characteristics of the water that are affected by temperature... such as density (ie.using a hydrometer) Link to comment
supernip Posted May 29, 2005 Share Posted May 29, 2005 I think less solute would dissolve, but I don't think that's a factor for us. Besides, a rise in temperature would probably cause evaporation and thus affect your water's salinity. Link to comment
Caesar777 Posted May 30, 2005 Share Posted May 30, 2005 Yes. Water has a higher density at a lower temperature....As a liquid, it expands when warmed (even one degree). Barometric pressure also plays a part, though not enough to matter as far as measuring salinity of an aquarium... So one CC (cubic centimeter) in "standard" conditions would weigh one gram, but it can very by tenths of a degree. Long story short, cold water mixed with a specific amount of salt may read higher than if it was warmed. But really, not a big deal, it's pretty simple: most "hobbyist" hydrometers are calibrated for about 75 degrees F, so measure the salinity of warmer water for accuracy. Link to comment
Caesar777 Posted May 30, 2005 Share Posted May 30, 2005 And that's all I can remember from Chem 204... Link to comment
bgoode Posted May 31, 2005 Share Posted May 31, 2005 Water temp does NOT affect salinity. Salinity is a measure of solids dissolved per unit liquid. Temp does affect density, which is what a hydrometer measures. Hydrometers are usually calibrated to 75 degrees F, so water at a temp other than that 75 degrees F will read incorrectly. Link to comment
andykee Posted May 31, 2005 Author Share Posted May 31, 2005 caesar: since water volume has nothing to do with the "true" (not instrument measured) salinity, and 1 gram of hot water obviously weighs the same as 1 gram of cold water (although there are more water molecules present in the gram of cold water), and since the temperature of the water has nothing to do with the weight of the solids dissolved in it (unless you are approaching the holding capacity of the water and differentiating between dissolved and pure solids, but that is a whole new discussion) then wouldn't it follow that the salinity is the same in the hot and cold water, allbeit the volumes are different? btw, i think i won the argument! Link to comment
FAC_WNY Posted May 31, 2005 Share Posted May 31, 2005 Salinity remains the same....specific gravity varies (because the density of the water varies). Cheers, Fred Link to comment
cadesun Posted May 31, 2005 Share Posted May 31, 2005 fred is correct... it is only our ability to measure correctly that varies with temperature due to changes in s.g., not the actual salinity of the water. Link to comment
Caesar777 Posted June 1, 2005 Share Posted June 1, 2005 Well, I emailed my brother, who majored in chemistry (and currently works in a lab) and has a minor in math, and he says that I'm correct. As I said, it's minimal, but it DOES make a very slight difference. Link to comment
bgoode Posted June 1, 2005 Share Posted June 1, 2005 Salinity is a concentration measured in parts per thousand (ppt) which is grams of salt per liter of water. 1 liter of water is the same independent of the temperature. Densities and weights may vary with temp, but volume doesn't. Link to comment
Caesar777 Posted June 1, 2005 Share Posted June 1, 2005 Yes, weight and volume vary by temperature. Hon, I think the chemistry major knows what he's talking about. Link to comment
Pili4444 Posted June 1, 2005 Share Posted June 1, 2005 I can email my cousin who has his PhD in quantum chemistry if that would help. Link to comment
cadesun Posted June 1, 2005 Share Posted June 1, 2005 if by weight you mean mass, mass does not change with temperature. mass is constant throughout the universe under any condition. if you put 5g of salt in water, there will always be 5g of salt in that water at any temperature, period. however, if you did in fact mean weight, weight is the effect of gravity on a mass, and this does change quite a bit. hence the changes in s.g. with temperature. Link to comment
andykee Posted June 1, 2005 Author Share Posted June 1, 2005 temperature has ZERO effect on weight of a quantity of water. try for yourself... drop a gallon of 10 deg C distilled water on a scale... 8.33 lbs. now drop a gallon of 50 deg C distilled water on the same scale... i bet $1000 it still weighs 8.33 lbs Link to comment
Pili4444 Posted June 1, 2005 Share Posted June 1, 2005 So temp affects the density of water, agreed. So when the density increases within the same mass, the volume has to decrease to maintain the mass. When the volume decreases and the same amount of salt is still dissolved, then the concentration should increase, right? So the salinity increases. Link to comment
steelhealr Posted June 1, 2005 Share Posted June 1, 2005 Hi...specific gravity is affected by temperature: SG = = ñ / ñH2O where SG = specific gravity ñ = density of fluid/mass ñH2O = density of water The density of water IS affected by temperature. Water gets more dense with decreasing temp until ice is formed which is LESS dense (floats). Salinity is the amount of solids (g's) dissolved in 1 kg of water. Since the weight is fixed, salinity should not vary with temperature. SH Link to comment
bradarmi Posted June 2, 2005 Share Posted June 2, 2005 This might help for the pictorally-minded. http://www.classzone.com/books/earth_scien...s2202page03.cfm Link to comment
andykee Posted June 2, 2005 Author Share Posted June 2, 2005 i think that everyone agrees that the density of water is a function of the water temperature, and under special circumstances (i.e. an open system: 1 gal of water in a 1 gal jug where the water will overflow over the edge of the jug as the volume increases due to a temperature change) the salinity will be a function of temperature, BUT in a closed system where the only variable is the water temperature, salinity will not fluctuate as a function of temperature alone. Link to comment
FAC_WNY Posted June 2, 2005 Share Posted June 2, 2005 Oy vey...some people's children.... Salinity isn't going to vary in a closed system...if you take 5 grams of salt and put it in 1L of water, no matter what happens you have your salinity is 5g/L as salinity is a measure of mass over volume. And whoever said that weight doesn't change, you're crazy. Take a given mass of water and put it on the surface of the earth, then take the same mass and put it on the moon and they'll weigh very different amounts. As was stated previously..mass never changes, weight does. Cheers, Fred Link to comment
andykee Posted June 2, 2005 Author Share Posted June 2, 2005 i suppose i should have mentioned that i am only interested in earth-based salinity readings so the difference between mass and weight can be negated Link to comment
Caesar777 Posted June 2, 2005 Share Posted June 2, 2005 i suppose i should have mentioned that i am only interested in earth-based salinity readings so the difference between mass and weight can be negated Link to comment
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