chemistry problem!?

Question

we have been taught that:
relative density of substance=density of substance/density of water at 4 degree C.
my question is why we only take "4 degree C"..??why only 4 ???

sincere answers will be appreciated with best answer..otherwise abuse will be reported.

Answer 1

Relative density of any substance is defined as the comparative density of the substance compared to the density of water. Further the density of any substance is defined as mass of unit volume of that substance.

Now volume of a substance is variable since it increases and decreases with change in temperature. The volume change may not be noticeable easily.

Hence the density of water has been defined at 4 degrees which is the least temperature where it fully remians in liquid state (at normal atmospheric pressure) Below 4 degrees C the crystalisation (freezing into ice) process starts which completes at 0 degrees C. Interestingly water is a substance which expands on solidification also (due to typical crystal structure of ice) Thus water has the least volume at 4 degrees C.

Answer 2

Noun
relative density

(sciences) A measure of the density of a material. The ratio of the density of a substance to the density of water at the same temperature. It is dimensionless and therefor has no units.
Typical relative densities (approximate)
ethanol: 0.79
water: 1.00
iron: 7.8
gold: 19.3

Synonyms
specific gravity
Retrieved from "http://en.wiktionary.org/wiki/relative_density"

I don't see anything in there about water at 4 degrees C, but I guess to be accurate the water would have to have some standard temperature, why not 4 C?

Answer 3

Actually, what my teacher taught me was
r.d=density of the substance/density of water.

I'll try checking more on the internet and I'll get back to u on dat.Peace.

Answer 4

Because at 4 deg.C water has a density of 1.

Answer 5

Water is at the densest at 4C. Cool water below 4C and it expands until if forms ice (which floats because it is less dense than liquid water). Heat water above 4C and it also expands (warm water flows up, cooler water sinks; hence variation of density).

Since 4C is the temperature of densest water you can have, it makes for a natural reference.

Answer 6

As stated. water is densest at 4 degrees C.
It is the only liquid which is densest at a temperature higher than its freezing point (& what makes life on Earth possible).

Answer 7

I have no clue what you ae talking about

does you sink have cold water?

good.

does your freezer have ice?

good.

any questions?