Water and the Fitness of the Environment PDF

Water and the Fitness of the Environment https://www.thestatesman.com northeast-india-sees-heavy-ex Lecture Outcomes Appreciate the role of covalent polar bonds in water molecules and formation of hydrogen bonds as the basis o...

Water and the Fitness of the Environment https://www.thestatesman.com northeast-india-sees-heavy-ex Lecture Outcomes Appreciate the role of covalent polar bonds in water molecules and formation of hydrogen bonds as the basis of water’s properties Understand how four properties of water contribute to Earth’s suitability for life How acidic and basic pH conditions affect living organisms Calories One unit we use to measure heat is the calorie (cal). 1 calorie = is the amount of heat it takes to raise the temperature of 1 g of water by 1°C. Conversely, a calorie is also the amount of heat that 1 g of water releases when it cools by 1°C. The ability of water to stabilize temperature stems from its relatively high specific heat Specific Heat The ability of water to stabilize temperature stems from its relatively high specific heat value Specific heat = the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1°C Specific Heat of Water We already know water’s specific heat because we have defined a calorie as the amount of heat that causes 1 g of water to change its temperature by 1°C Therefore, the specific heat of water is 1 calorie per gram and per degree Celsius, abbreviated as 1 cal/g.°C Compared with most other substances, water has an unusually high specific heat Because of the high specific heat of water relative to other materials, water will change its temperature less when it absorbs or loses a given amount of heat Why is this important for life on Earth? https://www.georgetown.edu/ne ws/the-un-agreed-to-a-historic- treaty-to-protect-marine-life-  A large body of water can absorb and store a huge amount of heat from the sun in the daytime and during summer while warming up only a few degrees At night and during winter, the gradually cooling water can warm the air. This is the reason coastal areas generally have milder climates than inland regions The high specific heat of water also tends to stabilize ocean temperatures, creating a favorable environment for marine life Thus, because of its high specific heat, the water that covers most of Earth keeps temperature fluctuations on land and in water within limits that permit life Also, because organisms are made primarily of water, they are better able to resist changes in their own temperature than if they were made of a liquid with a lower specific heat 3. Floating of Ice on Water Water is one of the few substances that are less dense as a solid than as a liquid. In other words, ice floats on liquid water While other materials contract and become denser when they solidify, water expands This means that when water in a lake freezes, it floats to the top, and doesn’t harm the creatures living in the lake 4: Water dissolves a lot of molecules Sugar placed in a glass of water will dissolve The glass will then contain a uniform mixture of sugar and water The concentration of dissolved sugar will be the same everywhere in the mixture https://www.uen.org/lessonplan/view/ 868  A liquid that is a completely homogeneous mixture of two or more substances is called a solution. The dissolving agent of a solution is the solvent, and the substance that is dissolved is the solute. In this case, water is the solvent and sugar is the solute An aqueous solution is one in which water is the solvent.  ▪ compounds dissolve when water molecules surround each of the solute molecules, forming hydrogen bonds with them. ▪ A compound does not need to be ionic to dissolve in water; many compounds made up of nonionic polar molecules, such as sugars, are also water-soluble.  Water is a very versatile solvent, meaning that it can dissolve a lot of compounds, including ionic and covalent compounds This is due to the polarity of the water molecule The sphere of water molecules around each dissolved ion is called a hydration shell Hydrophilic and hydrophobic substances Hydrophilic = water-loving Hydrophobic = water-hating These are molecules that can form These are substances that are non- hydrogen bonds with water. This ionic and non-polar (cannot form allows them to dissolve in water hydrogen bonds) But sometimes, substances can be E.g. Oils do not dissolve in water hydrophilic without actually dissolving because they do not have polar covalent bonds Instead, they remain suspended in water Such a mixture is called a colloid, a stable suspension of fine particles in a liquid Acids and Bases Sometimes, a hydrogen atom from one water (H2O) molecule is pulled away to another water (H2O) molecule. Without hydrogen, the first H2O molecule becomes OH- and the second molecule becomes H3O+  This reaction is reversible, meaning that H3O+ can give back the hydrogen to OH- so that they can return to H2O To make things simple, H3O+ is usually referred to as H+  Water is not the only molecule that can release hydrogen (H+) Compounds that can release H+ are called acids Compounds that take H+ are called bases The concentration of H+ in a solution is important because H+ is reactive E.g. it can change the shape of proteins E.g. it can interfere with chemical reactions in cells  Since H+ concentration can affect the shape of proteins and interfere with chemical reactions in living cells it is important to measure its concentration We measure H+ concentration using a pH scale Important pH values pH value of 7 is considered neutral, meaning not acidic or basic pH values lower than 7 are acidic. The lower the value the stronger the acid (= more H+ released) pH values higher than 7 are basic. The higher the value the more basic (=more H+ removed) Pure water exists at pH level of 7 Our blood maintains pH value of 7.4  Many proteins in our body work at pH 7.4 A change in pH can interfere with the protein function This could have harmful effects, and could also be deadly for the cells Many of our food contains acids e.g. lemon and oranges How are we able to eat acidic foods without changing our pH? https://edition.cnn.com ealth/citrus-winter-reci wellness/index.html Buffers Our blood and cells contain buffers Buffers help maintain pH by absorbing extra H+ if an acid is introduced, and release extra H+ if a base is introduced