5 replies to this topic

[enchanted]

I am a first year Undergraduate Chem Eng student. For one of our labs, we conducted an experiment about Viscosity on the Falling Ball Technique. One of our calculations required the calculation of density of the substance that the ball was falling through (A sucrose solution). The technique was repeated using different concentrations of the solution (water was added progressively to dilute it)
A hydrometer was used to measure the Brix and Specific Gravity of the solution after the time taken for the ball to be dropped was measured.
One of our questions required calculating the density of the solution for each of its concentrations. I was wondering though, if there is a connection between Specific Gravity and Density that i could calculate the density from my SG values...

Thanks very much in advance for any assistance and in advance, and for reading my post..

[gvdlans]

First of all I would like to make you a compliment about your post. It is clear, complete and gives us sufficient background information about you and your question. I wished all postings were like this.

On the other hand, you could have easily found the answer yourself by doing a Google or Wikipedia search on "specific gravity". I expect someone to first do such a search before posting it on this forum.

My answer is: see http://en.wikipedia....pecific_gravity

Assuming your reference is water with a density of 1000 kg/m3, a specific gravity of say 1.1 means the solution has a density of 1.1 x 1000 = 1100 kg/m3

[Art Montemayor]

I want to join Guido in complementing you on your very clear, concise, and explained query. I, too, wish other students would heed and follow your good example.

I only want to introduce the following recommendation: when employing or referring to Specific Gravity, always bear in mind that this measurement is a reference to the density of water at a pre-determined and referenced temperature & atmospheric pressure. In the USA, it is conventionally referred to 60 ^oF. In other words, the Specific Gravity of a fluid is compared to 62.371 lb_m /ft³.

HOWEVER, bear in mind that this is not a universal and 100% accepted "truth" by all who use it! It is unfortunate (& I consider it sloppy & flawed engineering) that many engineers don't make mention of their reference when they employ the term Specific Gravity (or even Relative Density). I've known some engineers who think that the reference is another temperature reference - since they are not told the specific reference temperature. In my experience, I've found that college profs - especially in Chemistry - are the most guilty of being mentally lazy and failing to cite their reference temperatures and points. I don't say this is true of all profs - just those I've associated with or studied under. My firm advice is to ALWAYS cite your reference temperature when employing relative density or Specific Gravity. The same logic applies to so-called "Standard Conditions".

[P.K.Rao]

Mr Art Montemayor and Mr GVDLans have already complimented you for your clarity and sincerity. I add myself to that and attach a sheet showing density of water at various temperatures. What you do is multiply the specific gravity by the density of water at the the temperature of reference in your case to get density at the temperature (again in your case).

P.K.Rao

Attached Files

•  Density_of_water_at_different_temperatures.pdf   201.89KB   183 downloads

[enchanted]

Thank you all for your help and kind words. It has been much appreciated.

In reply to the first response, prior to posting here I had consulted that exact Wiki page, but there was a disclaimer at the top regarding the accuracy of that information, and I was hesistant to risk it, since this report will consist for about 35% of my final. Another thing that led me to this post was that for several of the pages that I read, there was a mention of specific temperatures such as 4 degrees and 15 degrees that confused me.

In reply to the second response, the day after I posted this, I consulted with my lab group to find out that were using the density of water as 1000 kg/m3. But thank you for your suggestions, I will mention it specifically in my report.

Thank you P.K. Rao for that file, I will be sure to consult it when writing up my report

Thank you again to everyone who replied, gvdlans, P.K. Rao and Art Montemayor
Your help was greatly appreciated.


I have another question about this lab, one regarding plotting a graph using Brix measurement in this same lab, can I post it in this same thread to avoid cluttering your forum or do I have to create a new topic for organisation of ideas in your forum? I am unsure..

[gvdlans]

Please create a new post for your new question... That way you can be sure it gets the right attention (and it's for free...)