Water and Water Hardness PDF

CHEM115 CHEMISTRY WATER & WATER HARDNESS ÖĞR GÖR SEDEF ÖZCAN PHYSICAL & CHEMICAL PROPERTIES OF WATER  Water is polar molecule with Hydrogen Bonding which provide unusual properties: Universal solvent Cohesion behavior (high surface tension) High heat of vaporization...

CHEM115 CHEMISTRY WATER & WATER HARDNESS ÖĞR GÖR SEDEF ÖZCAN PHYSICAL & CHEMICAL PROPERTIES OF WATER  Water is polar molecule with Hydrogen Bonding which provide unusual properties: Universal solvent Cohesion behavior (high surface tension) High heat of vaporization High density @ 4 oC (expand upon freezing) Resistance in T changes  Has neutral pH  Has high specific heat (c (J/g.oC) PHYSICAL & CHEMICAL PROPERTIES OF WATER  Water can dissolve many compounds due to its polarity ability. Many biochemical reactions can take place in water by dissolving.  Pure Water has a neutral pH (7-7.5). So, it is neither acidic nor basic. Why is it important??  Most biological functions take place in a neutral pH  Water changes its pH depending on the relative concentration of hydrogen ions which comes from dissolved substance. Rain has a naturally acidic pH of about 5.6 because it contains naturally derived carbon dioxide and sulfur dioxide. PHYSICAL & CHEMICAL PROPERTIES OF WATER  Water has a high specific heat  absorb high amount of heat of energy before getting hot Specific heat (c) is the amount of energy that must be absorbed or lost for 1 g of substance to change its temperature by 1 oC.  Water conducts heat more easily than any liquid except mercury. This fact causes lakes and oceans to have essentially a uniform temperature profile. PHYSICAL & CHEMICAL PROPERTIES OF WATER  Pure water has a low electrical conductivity, but this increases significantly with the dissolution of a small amount of ionic material such as sodium chloride.  Water molecules exist in liquid form over an important range of temperature from 0 – 100 °C. This range allows water molecules to exist as a liquid in most places on our planet.  Water is the only substance on Earth that naturally exist in all three physical states of matter: solid, liquid, and gas. PHYSICAL & CHEMICAL PROPERTIES OF WATER Density, d (g/mL) of water is max (1 g/mL) at 4 oC. Contracts until 4 oC Expands from 4 oC to 0 oC.  d of ice < d of water Why important??  Prevent lakes from total freezing so aquatic organisms can live.  Ice forms on the surface first the freezing of the water releases heat to the water below creating insulation. Under the layer of ice freezing process is slow so surviving of livings at 4 oC.  SEA WATER  Sea water is one of the most fascinating and plentiful substance on the planet.  The key roles of the oceans are: o Absorption and reflection of sun light o Storage of the heat and then its transportation o Major changes in the climate system o The main source of atmospheric water vapor o Exchange of gases (e.g. CO2) with the atmosphere.  PHYSICAL PROPERTIES of SEA WATER o The average density of seawater at the ocean surface is 1.027 g/ml. d of fresh and pure water < d of sea water o In the world's oceans, salinity of about 3.5% (35 g/L). o The freezing point of seawater is about −2 °C at typical salinity. It decreases as salt concentration increases. o Has highest surface tension in all liquids. o Blue color is the most dominant reflected since it has the shorthest wavelength. So, blue is the color of ocean. COMPARISION OF SEA WATER AND PURE WATER PROPERTIES PROPERTY SEA WATER PURE WATER Density (g/ml) 1,027 1,0029 Specific Conductivity 0,0532 - (ohm-1 ) pH 7.5-8.4 7-7.5 Viscosity (milipoise) 9,02 8,90 Temperature of max. -3,25 3,98 Density (°C) Freezing Point (°C) -1,91 0,00  SEA WATER COMPOSITION  Contains more dissolved ions than all other types of water. 2.5 % salts, and smaller amounts of other substances: dissolved inorganic and organic materials, suspended solids  Contains dissolved gasses (nitrogen, oxygen, carbon dioxide)  Is the nutrient for animals and plants living in marine environment  SEA WATER COMPOSITION SALINITY Is the saltiness or dissolved salt content in water. It is a general term used to describe the levels of different salts such as sodium and magnesium chloride, magnesium and calcium sulfates, and bicarbonates. Influences ocean circulation, climate, marine life, and the water cycle. Although the vast majority of seawater has a salinity of between 3.1% and 3.8%, seawater is not uniformly saline throughout the world due to environmental factors.  SEA WATER COMPOSITION Variations occur in ocean salinity due to several factors. Evaporation: Removes water and increases the relative concentration of salts, raising salinity. Precipitation (rain): Adds freshwater like rain, diluting salts and lowering salinity. Evaporation > Precipitation salinity increases (since salt is not evaporated into the atmosphere). Evaporation < Precipitation salinity decreases  SEA WATER COMPOSITION ALKALINITY Alkalinity measures the ability of a solution to neutralize acids to the equivalence of carbonate or bicarbonate. The alkalinity is equal to the stoichiometric sum of the bases in solution. Alkalinity=[HCO3−]+2[CO32−]+[OH−]  SEA WATER COMPOSITION pH is a measure of the acidity or alkalinity of a substance and is one of the stable measurements in seawater. Ocean water has an excellent buffering system with the interaction of carbon dioxide and water so that it is generally at a pH of 7.5 to 8.5. Anything either highly acid or alkaline would kill marine life but the oceans are very stable with regard to pH.  SEA WATER COMPOSITION pH Carbon dioxide is of major importance in controlling acidity in the sea water. CO2(g) + H2O(l) → [HCO3]– + [H]+ 2[H]+ + CO3 → H2CO3 lower pH  Major sources of carbon dioxide are respiration and decomposition.  SEA WATER COMPOSITION DENSITY  The density of fresh water is 1.00 g/mL but the density of sea water is 1.027 g/mL. So, addition of salts increase d. The saltier the water, the higher its density.  When water warms, it expands and becomes less dense. The colder the water, the denser it becomes.  SEA WATER COMPOSITION DISSOLVED GASSES In order of decreasing abundance, the major gases in the sea are; nitrogen (N2), oxygen (O2), carbon dioxide (CO2) and the noble gases, argon (Ar), neon (Ne) and helium (He). Gas Molecule % in % in surface mg/kg (ppm) atmosphere sea water in sea water Nitrogen 78% 47.5% 12.5 Oxygen 21% 36% 7 Carbon dioxide 0,03% 15.1% 90 Argon 1% 1.4% 0.4  SEA WATER COMPOSITION DISSOLVED GASSES Gas composition at the ocean surface is in equilibrium with atmosphere. The solubility and saturation value for gases in sea water;  increases as temperature decrease  increases as pressure increases  decreases as salinity increases Plants reduce the conc of CO2 in the presence of sunlight, whereas animals do the opposite.  HARDNESS of WATER Measure of the concentration of dissolved minerals, primarily calcium (Ca²⁺) and magnesium (Mg²⁺), in water. (mg/L) Hard water has high mineral content. Source is mostly limestone (CaCO3) and gypsum (CaSO4.2H2O). The higher dissolved amount of calcium (Ca²⁺) and magnesium (Mg²⁺), the greater the hardness. o Hard water is generally not harmful to one's health but can cause serious problems in industrial settings.  HARDNESS of WATER The ions which result in, or produce, hardness include Mg+2, Ca+2, Sr+2, Fe+2, and Mn+2, and to a lesser extent, Ba+2 and Zn+2 and other divalent ions. There are different forms of hardness: 1. Total hardness: Ca and Mg expressed as CaCO3 2. Calcium hardness: Ca expressed as CaCO3 3. Magnesium hardness: Mg expressed as CaCO3 4.Temporary hardness: Caused by bicarbonates of calcium and magnesium. 5. Permanent hardness: Is due to the sulphates and chlorides of calcium and magnesium.  TYPES OF HARDNESS Temporary hardness (Carbonate Hardness) Temporary hardness is a type of water hardness caused by the presence of dissolved bicarbonate minerals. When dissolved, these minerals yield calcium and magnesium cations (Ca2+, Mg2+) and bicarbonate anions (HCO3-). The presence of the metal cations makes the water hard..  TYPES OF HARDNESS This "temporary" hardness can be reduced either by Boiling which causes the formation of carbonate from the bicarbonate and precipitates calcium carbonate out of solution. Promotes the reaction by driving off the carbon dioxide gas. Ca(HCO3)2 →CaCO3(s) + CO2(g) + H2O The addition of lime (Ca(OH)2) through the process of lime softening. Ca(OH)2 (aq) + Ca(HCO3)2 → 2 CaCO3(s) + 2 H2O  TYPES OF HARDNESS Permanent hardness (Noncarbonate Hardness) Permanent hardness is usually caused by the presence of calcium and magnesium sulphates and/or chlorides in the water. Permanent hardness cannot be removed by boiling. Permanent hardness of the water can be easily removed using a water softener, or ion exchange column.  SOURCESS OF HARDNESS Multivalent cations have a charge greater than 1+, mainly have the charge of 2+. These cations include Ca2+ and Mg2+. Cations Anions HCO3- Ca2+ CO32- Temporary Hardness Mg2+ OH- Na+ SO42- K+ Cl- Permanent Hardness NO3-  EFFECTS OF HARD WATER Hard water forms deposits called "scale“ and are composed mainly of calcium carbonate (CaCO3), magnesium hydroxide (Mg(OH)2), and calcium sulfate (CaSO4). Hard water causes poor detergent/soap performance, forming residues (soap scum) on skin, surfaces.  EFFECTS OF HARD WATER In boilers (vessel’s), the deposits impair the flow of heat into water, reducing the heating efficiency and allowing the metal boiler components to overheat. This is the vessel's third boiler, Hot water boiler built in 1953 by Kincaid in Scotland for ships  EFFECTS OF HARD WATER Hard water can also cause corrosion of ship boilers. Formation of scale (insoluble layer) trap of watercorrosion ions (like Cl-) concentrated  promote local corrosions overheating might affect corrosion When CO2 is dissolved in water, H2CO3 is formed making the water slightly acidic which accelerate corrosion on metal surface. EFFECTS OF HARD WATER IN DIESEL ENGINES In diesel engines, hard water causes;  Formation of scab and this can cause to crack the head of the piston  When the permanent hardness causes corrosion, the hardness of cooling water must be controlled and distillated water should be preferred to use.  If the hardness of water provided from harbors is more than 150 ppm, it should not be used as cooling water in the engines.  MEASUREMENT OF WATER HARDNESS  Hardness can be quantified by instrumental analysis. The total water hardness, including both Ca2+ and Mg2+ ions, is reported in ppm or mass/volume (mg/L) of calcium carbonate (CaCO3) in the water. Soft: 0–75 mg/L Moderately hard: 75-150 mg/L Hard: 150-300 mg/L Very hard: >300 mg/L Sea water contains approximately 400 mg/L Ca and 1300 mg/L Mg thus, is very very hard!!  WATER SOFTENING  Water softening is the reduction of the concentration of calcium, magnesium, and certain other metal cations in hard water. Water softening methods are;  Soda-lime method  Aluminum sulfate and alum method  Trisodium phosphate method  Zeolite method  Ion exchange resins  The principle of these methods are all same; removing Ca and Mg salts or changing Ca and Mg ions with Na ions  WATER SOFTENING METHODS Soda-Lime Method (Precipitation Process) It utilizes the addition of lime (Ca(OH)2) and soda (Na2CO3) to remove hardness (Ca and Mg) ions by precipitation. Lime is used to remove the temporary hardness while soda is used for permanent hardness.  WATER SOFTENING METHODS Ion exchange resin devices Most conventional water-softening devices depend on a process known as ion-exchange in which "hardness" ions trade places with sodium and chloride ions that are loosely bound to an ion-exchange resin or a zeolite.  Cation exchangers  Anion exchangers  WATER SOFTENING METHODS Ion exchange resin devices The water softening process works by passing hard water through resin beads. Magnesium and calcium ions in the water exchange places with sodium ions on the beads, softening the water.  WATER SOFTENING METHODS Negatively-charged zeolite to which [positive] sodium ions are attached. Calcium or magnesium ions in the water displace sodium ions, which are released into the water.