Quick Answer
Water has a density of approximately 1.0 g/cm3 at 4°C. This means 1 cubic centimeter or 1 milliliter of water has a mass of 1 gram at this temperature. The density of water varies slightly with temperature, being lower at higher temperatures and higher at lower temperatures, but is very close to 1.0 g/cm3 at room temperature.
What is Density?
Density is a physical property of matter that describes how tightly matter is packed together. It is defined as the mass contained in a given unit volume. Density is calculated by dividing the mass of an object by its volume.
| Formula | Density = Mass / Volume |
|---|---|
| Units | g/cm3 (grams per cubic centimeter) |
| Examples |
– Water: 1.0 g/cm3 at 4°C – Gold: 19.3 g/cm3 – Air: 0.00129 g/cm3 at 0°C |
The density of a substance gives an indication of how tightly the atoms, ions or molecules are packed together. Substances with higher densities have more mass concentrated in a given volume. For example, gold has a density of 19.3 g/cm3, much higher than water’s 1 g/cm3, indicating gold packs together more tightly.
Density is an intensive property, meaning it does not depend on the quantity of material present. One cubic centimeter of water will have the same density as a swimming pool full of water. Density is highly dependent on temperature and pressure. As temperature increases, density decreases for most substances as the molecules move faster and spread apart. Under higher pressure, density increases as molecules are forced closer together.
Why Does Water Have a Density of 1 g/cm3?
Water has a density of approximately 1.0 g/cm3 (0.998 g/cm3 at 4°C to be exact). This means 1 milliliter or 1 cubic centimeter of water at this temperature has a mass of 1 gram.
But why does water have this unusual density? The answer lies in water’s molecular structure. A water molecule (H2O) contains one oxygen atom bonded to two hydrogen atoms. Water molecules are polar, with the oxygen carrying a slight negative charge and the hydrogen atoms carrying a slight positive charge. This allows water molecules to strongly attract each other through hydrogen bonds.
| PROPERTY | DESCRIPTION |
|---|---|
| Molecular polarity | Allows for hydrogen bonding between water molecules |
| Hydrogen bonding | Attractive force between polar water molecules |
| Liquid at room temperature | Water molecules can move past each other while still hydrogen bonded |
The hydrogen bonding makes water cohesive – the molecules like to stick together. This allows water to resist compression and retain its volume when placed under pressure. In contrast, weaker intermolecular forces in other liquids like gasoline make them far more compressible.
Water’s hydrogen bonding makes it dense enough to remain a liquid at room temperature unlike similar small molecules like hydrogen sulfide (H2S) which are gases. The water molecules can still move past each other while remaining hydrogen bonded, allowing water to flow as a liquid but still retain density through cohesion.
How Does Temperature Affect Water Density?
The density of water varies with temperature. At lower temperatures, density increases reaching a maximum of 0.999972 g/cm3 at 3.98°C. Above this temperature, density decreases with increasing temperature. This is why ice floats on liquid water – solid ice is less dense than liquid water, an unusual property shared by very few other substances.
| Temperature (°C) | Density of Water (g/cm3) |
|---|---|
| 0 | 0.99987 |
| 10 | 0.99970 |
| 20 | 0.99820 |
| 30 | 0.99565 |
| 100 | 0.95840 |
As temperature increases, the water molecules move faster breaking hydrogen bonds between molecules. The molecules take up more space moving further apart decreasing density.
Water reaches its maximum density at 4°C just above its freezing point. As it cools below this temperature, the hydrogen bonded network of water molecules forms an open tetrahedral structure that takes up more space than the liquid, causing density to decrease.
The unusual density properties of water with temperature have major impacts on life on Earth. Water’s maximum density at 4°C allows ice to float at the surface of lakes and oceans. If water was most dense as a solid, ice would sink disrupting aquatic ecosystems. The temperature variation in density also drives lake turnover and ocean currents, distributing nutrients and oxygen.
Uses of 1 g/cm3 as a Reference Density
The density of water at 1 g/cm3 provides a useful reference point for comparing other substances. With this reference density:
- Substances denser than water sink in water
- Substances less dense than water float on water
- A substance with density 5 g/cm3 is 5 times denser than water
- A substance with density 0.5 g/cm3 is half as dense as water
Some common examples using water’s density as a reference:
| Substance | Density (g/cm3) | Comparison to Water |
|---|---|---|
| Aluminum | 2.7 | 2.7 times denser than water |
| Ice | 0.92 | Less dense than water |
| Gasoline | 0.68 | Floats on water |
| Cork | 0.24 | Much less dense than water |
Water’s density at 1 g/cm3 provides a convenient reference for materials scientists and engineers when considering density in designing applications. Substances can easily be categorized as denser or less dense than water. Deviations from 1 g/cm3 also give information about the strength of intermolecular bonding in other liquids.
How is the Density of Water Experimentally Determined?
The density of water must be determined through careful experimentation and measurements. Here is a typical experimental procedure to measure water density:
- Prepare a graduated cylinder, analytical balance, thermometer and water sample.
- Measure the mass of the empty graduated cylinder.
- Add a water sample to the graduated cylinder and measure its initial volume in mL or cm3.
- Measure the temperature of the water sample.
- Weigh the graduated cylinder with the water sample and record the mass.
- Subtract the mass of the empty graduated cylinder to find the mass of just the water sample.
- Divide the water sample mass by its volume to determine density.
- Repeat steps 2-7, measuring with different volumes of water to improve accuracy.
- Consult a table of water density vs. temperature values to verify results.
Proper technique is required to achieve accurate density measurements. The graduated cylinder must have volume markings precise to 0.1 mL. The scale should measure mass to 0.01 g. Reading the meniscus at eye level reduces volume errors. Multiple measurements improve precision.
Automated density meters are also commonly used to measure water density, eliminating human errors in volume and mass measurements. However they must be calibrated against known standards.
Regardless of technique, the density of water measured will be close but not exactly 1.0 g/cm3 due to variations with temperature, pressure and purity. Published data accounts for these to give the accepted standard value.
Water Density in Various Applications
The density of water at 1 g/cm3 makes it useful for many scientific and industrial applications:
Unit of Density
Water’s density provides a useful unit for density – grams per milliliter. The density of any liquid can easily be compared by how many times more or less dense it is than water.
Standard for Hydrometers
Hydrometers use the principle of buoyancy to measure density. The calibration scale is graded relative to the assumed density of water. A properly calibrated hydrometer will read 1.000 in pure water at 4°C.
Calculating Buoyant Force
The buoyant force on an object in water can be calculated from its volume using water density. FB = ρVg where ρ is 1.0 g/cm3 for water. This allows designing vessels and objects that will float.
Checking Purity of Liquids
The density of a liquid can indicate if it is contaminated. Food oils, alcohols, and fuels will deviate from published densities if their composition is not pure. Water density provides a reference point.
Oceanography
Measuring seawater density helps determine ocean stratification, currents and sea levels. These densities are compared to the standard 1 g/cm3 density of pure water.
Medical Applications
Many body fluids like blood and urine have published density ranges which can indicate disease. These ranges use water density as a comparison point.
Substances Other Than Water with Densities Near 1 g/cm3
While water has a density very close to 1.0 g/cm3 under standard conditions, there are a few other substances with densities near this same value:
Ethanol
Ethanol or ethyl alcohol has a density of 0.789 g/cm3, fairly close to water’s 1 g/cm3 density. Ethanol is polar and capable of hydrogen bonding like water. However, ethanol’s nonpolar ethyl group disrupts intermolecular bonding compared to water, accounting for ethanol’s lower density.
Methanol
With a density of 0.791 g/cm3, methanol has a similar density to ethanol. Methanol has shorter methyl nonpolar groups compared to ethanol so exhibits slightly stronger intermolecular hydrogen bonding and higher density. Methanol is completely miscible with water.
Formic Acid
This organic acid has the chemical formula CH2O2. Its density is 1.22 g/cm3, slightly higher than water. The polar carboxyl group allows strong hydrogen bonding to account for this high density in the liquid state.
Sodium Chloride Brine
A fully saturated solution of sodium chloride in water measures around 1.2 g/cm3, slightly denser than pure water. The dissolved salt ions hinder hydrogen bonding and spacing between water molecules.
Blood Plasma
Blood plasma, the liquid component of blood, has a density around 1.025 g/cm3. Blood contains various dissolved proteins, salts and other components which increase its density slightly over pure water.
Glycerol
This small polar molecule has a density of 1.26 g/cm3 in liquid form. The multiple hydroxyl groups allow extensive hydrogen bonding interactions, resulting in its high density relative to water. Glycerol is very viscous.
Can Objects Have Densities Higher Than Water?
Yes, many materials have densities substantially higher than water’s 1 g/cm3 density:
– Metals like iron, copper and lead have densities around 8 g/cm3, several times greater than water. The metals contain heavy atoms densely packed into solid metal lattices.
– Precious metals like gold have very high densities, such as 19.3 g/cm3 for gold and 21.4 g/cm3 for platinum. Their atoms pack tightly together.
– Osmium has the highest known density at 22.6 g/cm3, more than 20 times greater than water. This rare ultra-dense metal feels extremely heavy for its volume.
– Iridium and tungsten are also very dense refractory metals, with densities of 22.6 g/cm3 and 19.3 g/cm3 respectively. Their metals are very hard to compress.
– Dense rocks like iron ore or granite can have densities up to almost 5 g/cm3 from their mineral content.
– Lead has a density of 11.3 g/cm3, explaining why lead weights feel much heavier than similar sized objects.
– Depleted uranium has a density of 19 g/cm3, useful for armor-piercing military projectiles.
So in summary, many metals and rocks found in nature can have densities far exceeding the 1 g/cm3 density of water or other common liquids. Density gives an indication of how heavy atoms are packed into a solid substance.
What is the Densest Known Substance?
The densest known substance is the artificial material called Osmium tetroxide. With an extremely high density of 22.59 g/cm3, it is over 20 times denser than water.
Osmium tetroxide is an inorganic compound with the chemical formula OsO4. It is a toxic oxidizing agent and has a distinct strong unpleasant smell.
Some key facts about osmium tetroxide:
– Contains the dense element osmium, which on its own has a density of 22.59 g/cm3
– Crystallizes as a dense tetrahedral structure with short strong metal-oxide bonds
– Used as a heavy weight additive and staining agent in microscopy
– Toxic and dangerous if inhaled or exposed to skin
– Expensive to produce as osmium is one of the rarest metals
Other chemical compounds of heavy elements can approach the density of osmium tetroxide:
– Rhenium heptoxide: 21 g/cm3
– Iridium powder: 22 g/cm3
– Hassium oxide: 40 g/cm3 (unconfirmed theoretical prediction)
Among naturally occurring substances, the element iridium is the densest known at 22.56 g/cm3 – slightly lower than osmium tetroxide.
So if searching for the world’s densest materials, look towards the heavy atoms at the bottom of the periodic table! Their strong atomic forces result in extremely dense metallic or intermetallic compounds.
Conclusion
In summary, water has a density very close to 1.0 g/cm3 at 4°C due to its molecular structure and hydrogen bonding. This gives it unusual properties and makes it useful as a reference substance when measuring densities. While many liquids and solids have densities higher than water, none have densities as close to 1 g/cm3 under normal conditions. Water’s density changes with temperature due to effects on its intermolecular bonding. When carefully measured, the density of pure water provides an important scientific standard.
