Fascinating physical properties of water

When temperatures dive below zero degrees Fahrenheit, why not Mambo, or rather, why not Mpemba! The “Mpemba Effect” is a technical term for hot water freezing faster than cold water given otherwise similar conditions. On social media, the “Boiling Water Challenge” takes advantage of this and other unique physical properties of water. Hot water gives off a lot of steam, and when you toss a cupful up in the air, the steam coming off thousands of droplets (creating more surface area) can yield the most magical photos and videos. If attempting the challenge, you must be mindful of the inherent risks associated with handling scalding water. 

As fellow water nerds and photographers, we had to give the Boiling Water Challenge a shot, which got us thinking about water’s other unique physical properties. For example, a water molecule is electrically polarized. Two hydrogen atoms with a positive charge are attached to one side of a negatively charged oxygen atom. Up close it looks like a famous Disney mouse character. This polarization makes water a strong solvent. It easily dissolves many solids and gases, some of which are negatively charged and attach to one end of the water molecule. Others are positively charged and attach to the other end. This “sticky” nature of water is also why pollution is so difficult to remove from water. 

The unique polarization of the water molecule creates other important physical properties. Water molecules bond together very tightly. This strength of bonds creates surface tension. The bugs we call water striders skim across the surface of a lake not on buoyancy, but instead using this surface tension. Try floating a paper clip in a cup of water, and you are using the same principle. Another fun experiment is to see how many drops you can place on a penny, it’s more than you might think because of surface tension! 

When liquid water freezes, it expands by about 10%. Most substances decrease in volume as they get colder, and this continues when they change to their solid state. Solid metal or rock will sink when placed in its molten form. Water also “shrinks” in volume as it gets colder — that is until it reaches 4° C (about 39° F). Then it starts to expand. When water freezes, the molecules can’t huddle close together. Instead, they form a six-sided lattice that has more space between molecules than fluid water. While this phenomenon is disruptive when our pipes freeze and break, it also prevents larger bodies of water from freezing solid from the bottom up. The ice insulates the water below, keeping it habitable for aquatic life like fishes, frogs, crayfish and clams. Most scientists agree that without this unique property of water, life on Earth would have had a much harder time getting started. 

One last important property of water is its relatively high specific heat capacity, which allows water to resist changes in temperature compared to air and land. “Specific heat capacity” refers to the amount of energy required to change the temperature of a substance, such as water. This thermodynamic property is one of the reasons, in addition to volume and flow, that Lake Coeur d’Alene has not frozen over (yet) this winter and why, on summer mornings, the beach sand feels cooler than the nearby lake water. It's also why water is great for radiators and industrial cooling systems (second only to ammonia). Water across the Earth buffers us from big temperature fluctuations; most of the additional energy stored in the climate system since the Industrial Revolution is stored in the oceans. 

And, when you fling a cup full of hot water into very cold air, the droplets keep steaming as long as they are hot. Once they cool off, they don’t steam anymore. By then they have already evaporated or are on the ground, and hopefully, your friend has taken a banner profile photograph commemorating the fascinating properties of water! 

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Our Gem’s guest authors, both based in Coeur d’Alene, are Jim Ekins, Ph.D., U-Idaho’s Extension's Water Educator; and Kim Holzer, Ph.D., an aquatic invasive species biologist with U.S. Fish and Wildlife Service.

The Our Gem Coeur d’Alene Lake Collaborative is a team of committed and passionate professionals working to preserve lake health and protect water quality by promoting community awareness of local water resources through education, outreach and stewardship. Our Gem includes local experts from the University of Idaho Community Water Resource Center, Coeur d’Alene Tribe, Idaho Department of Environmental Quality, the Basin Environmental Improvement Project Commission, Kootenai Environmental Alliance, Coeur d’Alene Regional Chamber of Commerce, and Connect Kootenai.