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Navi
22-01-2006, 10:00 AM
Hey there people,


I have been playing around with salt water trying to get it to last longger when frozen Ie in esky when camping, (after reading a thread on this site #RE: keeping ice longer http://www.ausfish.com.au/cgi-ausfish/yabb2/YaBB.cgi?num=1136867824/28#28 ) Then I came across this web is where some one actully did the test #see results below.

cheers Chris #8-)

Navi
22-01-2006, 10:00 AM
TITLE: Melting Rate of Various Materials

STUDENT RESEARCHER: Jeff Carollo
SCHOOL: Mandeville Middle School
Mandeville La.
GRADE: 6
TEACHER: Ellen Marino, M.Ed.



I. STATEMENT OF PURPOSE AND HYPOTHESIS:

I wanted to do a scientific research project on the melting
rate of various materials. My hypothesis stated that frozen
sugar water would melt slower than frozen salt water and frozen
tap water.

II. METHODOLOGY:

First, I stated my purpose, reviewed the literature the
freezing of liquids, and developed my hypothesis. Next, I got
three cups of the same size and filled them each with the same
amount of water. I labeled the first cup 1, the second cup 2,
and the third cup 3. I then added yellow food coloring to cup
1 and poured the contents of the cup into four sections of a
twelve section ice cube tray. Then I added sugar to cup 2
until it no longer dissolved and mixed in some green food
coloring. I then added salt to cup three until it no longer
dissolved and mixed in some red food coloring. I then poured
sugar water from cup 2 into four sections of the ice cube tray
and salt water from cup 3 into the remaining four sections of
the tray. I put the tray into the freezer. When the cubes
were finally frozen I removed the cubes and placed them on a
cooking sheet each assorted into their own group. From there I
recorded onto my data collection sheet how long it took for
each cube to dissolve. Finally, I analyzed my data, wrote my
summary and conclusion, and applied my findings to the real
world.

III. ANALYSIS OF DATA:

The first salt cube melted in just 35 minutes, the second in 40
minutes, the third in just 32 minutes, and the fourth in just
33 minutes for an average of 35 minutes. This was the fastest
melting water. The first sugar cube melted in 44 minutes, the
second in 47 minutes, the third in 48 minutes, and the fourth
sugar cube melted 48 minutes and for an average of 47 minutes.
This liquid was second fastest melting in my experiment. The
first tap water ice cube lasted for an hour and fifteen
minutes, the second lasted for an hour and four minutes, the
third lasted an hour and two minutes, and the fourth cube
lasted an hour and fourteen minutes. The tap water cubes took
an average hour and eight minutes to melt.

IV. SUMMARY AND CONCLUSION:

The frozen salt water melted in an average 35 minutes, the
frozen sugar water in an average 47 minutes, and the frozen tap
water melted in an average time of 68 minutes. Therefore, I
reject my hypothesis which stated that frozen sugar water would
melt slower than frozen salt water and frozen tap water.

V. APPLICATION:

The next time I need to keep something in a cooler for a long
time I will know to use ice made form frozen tap water because
it melts slowest.

DICER
22-01-2006, 10:13 AM
don't forget we chuck salt on roads in the northern hemisphere to remove/melt ice or snow.

Whatever
22-01-2006, 10:21 AM
Yes, no surprise there.

Salt water has lower freezing point hence it will melt faster than tap water at same temp.

bay_firey
22-01-2006, 10:21 AM
This kid is in Grade 6 - whats that make him 11/12

I couldn't right a report like that well done

DICER
22-01-2006, 10:29 AM
Yes it's a very well written scientific report for a 6th Grader!!! :o

Dug
22-01-2006, 10:38 AM
Not quite correct though, because of the lower melting point of the salt water the relative coldness of the water will remain the same keeping objects in a cooler at the same temperature as the still frozen tap water. #


This is why a slurry of salt water is better at keeping beer or fish cold than a slurry of tap water the water. The salt liquid is actually colder than a tap water slurry of the same consistency.


Still a nice analysis and he is not the first to get the procedure correct and the conclusion wrong.


9 out of 10

Dug
22-01-2006, 10:58 AM
For camping trips if you need ice for a long period try Dr Karl Kruszelnicki's suggestion of 2 eskys.

one with food and water ice, one with dry ice and water ice only.

Open the dry ice esky only when you need to replace ice in the other esky.

It seems to work.

We usually camp in the desert in winter our solution is to leave the esky open before we go to bed and close it in the morning before dawn. Make sure it is away from thing that would eat your food our is in the back of the ute in a cage.

The subzero night temperatures cool everything down and keep it cool for the hot days.


No suitable for beach fishing in Queensland summer though :)

Navi
22-01-2006, 12:55 PM
Right I have been getting my head around this and found this on the web, (I just can't stop trying to work it out )


The introduction of salt to the water creates a solution whose freezing point is lower than 0C. Pure water ice in that solution is no longer thermodynamically stable and so it melts. However, it takes energy to do that. The energy comes from the heat supply of the salt solution, and anything in contact with the salt solution (like a can of cold, refreshing, malt beverage), lowering the temperature. Water takes a lot of energy to change phases. If you can force a phase change by adding salt, then the increased melting rate of the ice means an increased heat-loss rate from anything in contact with the ice, as energy is consumed in the melting process.
If the background environment were held stable at the freezing temperature of the target salt-solution, then the salt and ice could coexist comfortably together with no melting, because there would be no energetic advantage to melting and refreezing. Salt solution melts ice only if there is a heat reservoir at a temperature above the freezing point of the salt solution.


Cheers Chris #8-)

PinHead
22-01-2006, 01:58 PM
Right I have been getting my head around this and found this on the web, (I just can't stop trying to work it out )


The introduction of salt to the water creates a solution whose freezing point is lower than 0C. Pure water ice in that solution is no longer thermodynamically stable and so it melts. However, it takes energy to do that. The energy comes from the heat supply of the salt solution, and anything in contact with the salt solution (like a can of cold, refreshing, malt beverage), lowering the temperature. Water takes a lot of energy to change phases. If you can force a phase change by adding salt, then the increased melting rate of the ice means an increased heat-loss rate from anything in contact with the ice, as energy is consumed in the melting process.
If the background environment were held stable at the freezing temperature of the target salt-solution, then the salt and ice could coexist comfortably together with no melting, because there would be no energetic advantage to melting and refreezing. Salt solution melts ice only if there is a heat reservoir at a temperature above the freezing point of the salt solution.


Cheers Chris #8-)

Change of state ..it is called latent heat

Fishinmishin
22-01-2006, 02:03 PM
The problem is that he probably only froze the ice blocks till they were just frozen. To become TRUE hard ice the salt water takes a lot longer to freeze fully. This factor could have played into the results :-?.
Cheers, Jay

Grand_Marlin
22-01-2006, 06:07 PM
It would have been helpful if he had taken temperatures of the ice at the point of melting.

Grand_Marlin has read all above correspondence, scratched his head, scratched his nuts and decided it is easier to buy an extra bag of ice for 2 bucks than become a rocket scientist....

bay_firey
22-01-2006, 07:31 PM
I am with you there Marlin :o

onerabbit
22-01-2006, 08:07 PM
Nice to see someone actually tried to find out in a practical manner, often we procrastinate over this or that, with learned knowledge, admittedly, but this young man has tried the theory in a very practical way, & offered his results. Sure many different factors come into this topic, but has anyone else conducted a similar experiment???
WELL DONE CHRIS ;)
Muzz

Jeremy87
22-01-2006, 08:46 PM
You've more or less got it now Navi.

Yeh not a bad report but unfortunatley fundamentally flawed. Mind you not many 11 year olds have a solid grasp of thermodynamics and endothermic reactions. Should anyone wish to test this properly you would firstly need to control the concentrations of solute (say 1 mole/l of salt/sugar) another control (which is probably fairer)would be to allow the solvent to become completely saturated at its melting point, alow the 2 mixtures and the pure water to freeze and reach the same temperature (ie equalibrium with the freezer). From here you would need to devise a way of measuring which substance has (a)the lowest entropy and (b) the highest specific heat capacity. Measureing the latent energy however would be more difficult but could be achieved after the specific heat is attained. This could be achieved by intruducing a known amount of enthalpy into an isolated system. Say introduce a lead shot of mass x with a temperature of y and record the equalibrium temperature to attain the specific heat capacity of the 3 substances, and then slowly intruduce more lead shots until complete liquid form is attained at equalibrium. The best refrigerant has the highest specific heat capacity (ie requires the most energy per change in termperature). The original procedure is flawed in 2 ways. Firstly the level of solvent is not controlled. Secondly the wrong scalar quantity is being measured in the test (melting point instead of specific heat capacity). This is probably the thought process level and knowledge required in late high-school early university level chemistry so as before not a bad job for an 11 year old.

Grand_Marlin
22-01-2006, 10:52 PM
Actually, after reading Jeremy's report, I think I will keep all my fish at room temperature, Ice is just too complicated these days.... :o

DICER
23-01-2006, 08:37 AM
For the 6th grader - he only failed in application! Hypothesis testing was fine.

drevil
23-01-2006, 08:42 AM
Zzzzzzzzzzzzzzzzzzzz...

frankj
23-01-2006, 11:25 AM
Jeremy87

I was going to say that.

szopen
23-01-2006, 04:02 PM
I can see the ice subject being discussed in a few places around the board.

Must be hot summer.

Well it is cold in here.

Anyway.

The results of his test: tap water ice cubes lasting longest, sugar water ice cubes second and salt water ice cubes melting fastest are correct for the materials used.

Why?

He has used tap water, saturated sugar solution and saturated salt (in the last two he mixed the stuff until it no longer dissolved).

Than he frozen all three types of ice cubes (let’s assume that they were properly frozen and at the same temperature).

For melting test he exposed all three types of ice cubes to the same ambient conditions.

A quick explanation of what is involved in melting the ice cube.
1 stage.
Heat from outside the cube is absorbed by the ice first raising the temperature of surface to the melting point and than ice starts melting.
2 stage.
Heat from outside is absorbed by the liquid on the ice surface and than transferred to solid ice underneath. Liquid on the surface stays at the melting point temperature and solid ice melts (changes state).

Under this conditions (same for all three types of ice cubes) the melting speed of the cubes will depend on two factors:

1. “Speed of heat transfer” meaning how fast the heat is being absorbed by object.
Formula Q=K*(t1-t2) where K is a coefficient depending on heat absorption situation and materials used (same melting process as described above so it will be practically the same for all three ice cube types).
In this situation the speed of heat transfer would depend only on the temperature difference between ice cubes and ambient air (the bigger the difference between the ice cube temperature the faster heat absorption).

2. “Heat absorption capacity” meaning how much heat can the object absorb.
From the practical point of view almost all the heat absorbed is used to melt ice into water (heat required to raise the temperature of salt or sugar is not relevant). As both solutions contain dissolved solids (salt and sugar) ice cubes made with them will be able to absorb less heat than one made with pure water.

So salt water ice cube will be have a lowest melting point and as such will be coldest so it will be absorbing heat faster, it also will have less heat absorption capacity than pure water ice cube because it contains “less” water.

Clear???

One more thing to remember is that salt water ice will have a melting point lower than 0C only at certain salt concentrations with melting point dropping down up to ~23% salt and than raising again reaching back 0C at 26.3%.

Louis
23-01-2006, 04:25 PM
This is all to complicated for me.

Who would have thought it was all so complicated.


Louis

szopen
23-01-2006, 04:58 PM
That was a very very simple version of explaining the issue.

In reality it is way more complicated.

Leaving theory behind.

From practical point of view two solutions are good.

1. Using ice made with salt water say about 10% solution.
2. Dropping a good handful of salt on normal ice.

shaman
23-01-2006, 06:46 PM
"STUDENTS OF THE ENQUIRING MIND".
Apparently hot water freezes faster than cold water, how does that work?? :-?

Dug
23-01-2006, 07:03 PM
Does anyone have the recipe for just ordinary ice please

I have lost my copy. ;)

Huggy_B
23-01-2006, 08:27 PM
clearly didnt use tap water from South Australia.......