# Why does water have a density?

• sameeralord
In summary: The intent of the pre-SI system was to have 1 liter of pure water (at 4 C) weigh exactly 1 kg (at standard gravity; representing 1 kg of mass). In fact, this was still too imprecise for a metric standard. Today, the standard is a 1 kg platinum-iridium cylinder kept at a secure location in France.

#### sameeralord

Ok density of water is 1000 g/ 1 L

I don't know isn't this 1 L composed completely of water. This is confusing me. Do find the concentration you have to find the moles and divide by 1 L. 1000/18=55 M . I thought concentration of pure water you can't find because the solution is complete water. I hope you understand what I mean. Thanks

Are you confusing density with concentration? There is 1000g of water in a volume of 1L if that 1L contains entirely water...

sameeralord said:
Ok density of water is 1000 g/ 1 L

I don't know isn't this 1 L composed completely of water. This is confusing me. Do find the concentration you have to find the moles and divide by 1 L. 1000/18=55 M . I thought concentration of pure water you can't find because the solution is complete water. I hope you understand what I mean. Thanks

your math and equations are right. the density is just 1 kg/L as you have shown. The concentration of moles / liter is actually moles of solute / liter of solvent. so technically the solute mole would be 0, the 55 mole is actually the solvent mole. So again technically it's 0 mole /1 L so it's 0 still. The 55 is useless, and unnecessary. Just a definition thing, don't fuss over it too much. You got the big stuff right

water is a universal liquid or solution or whatever you can call it.

Accept its density as a universal fact !

:tongue2:

your theory is right though but everything which we come across today has already been proved, hasnt it ? !

sameeralord said:
Ok density of water is 1000 g/ 1 L

I don't know isn't this 1 L composed completely of water. This is confusing me. Do find the concentration you have to find the moles and divide by 1 L. 1000/18=55 M . I thought concentration of pure water you can't find because the solution is complete water. I hope you understand what I mean. Thanks

The intent of the pre-SI system was to have 1 liter of pure water (at 4 C) weigh exactly 1 kg (at standard gravity; representing 1 kg of mass). In fact, this was still too imprecise for a metric standard. Today, the standard is a 1 kg platinum-iridium cylinder kept at a secure location in France.

http://www.essex1.com/people/speer/mass.html [Broken]

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## 1. Why does water have a density?

Water has a density because of its unique molecular structure. Each water molecule is made up of two hydrogen atoms and one oxygen atom, arranged in a bent shape. This arrangement allows for the formation of hydrogen bonds between neighboring water molecules, creating a tighter, more compact structure compared to other molecules. This density is also affected by temperature and pressure.

## 2. What is the density of water?

The density of water is approximately 1 gram per cubic centimeter (g/cm3) at room temperature (25°C). This means that one cubic centimeter of water weighs 1 gram. However, the density of water can vary slightly depending on temperature and salinity.

## 3. How does water's density affect its behavior?

Water's density plays a crucial role in its behavior and functions. For example, because ice is less dense than liquid water, it floats on the surface of bodies of water, insulating the water below and allowing aquatic life to survive during cold weather. Additionally, water's density also affects ocean currents, as colder and denser water sinks and warmer and less dense water rises.

## 4. Can water's density change?

Yes, water's density can change depending on its temperature and salinity. As water gets colder, it becomes more dense, until it reaches its maximum density at 4°C. Any further decrease in temperature causes the water to expand and become less dense, which is why ice floats on top of liquid water. Salinity also affects water's density, as saltwater is denser than freshwater.

## 5. How is water's density measured?

Water's density is typically measured using a hydrometer, which is a device that floats in a liquid and measures its density based on how high it floats. The density of water can also be calculated by dividing its mass by its volume, which is known as its specific gravity. This is often done in laboratory settings where precise measurements are needed.