Ch 8 Water Everywhere: A Most Precious Resource
H+
hydrogen ion or proton Since the hydrogen ion has no electron and only one proton (hence the positive charge) the hydrogen ion is sometimes referred to as a proton.
Strong vs Weak Electrolytes
if a compound completely dissociates into ions in water it is a STRONG electrolyte. If a compound partially dissociates into ions in water it is a WEAK electrolyte If a compound dissolves in water but does not dissociate into ions it is a NONelectrolyte
5 and 6, 3-5, 8.2
Normal rain has a pH value of between _______________. Acid rain is around _______________. Sea water is around _________.
Hydrogen bonds
What type of bond helps stabilize the shape of large biological molecules like DNA and proteins?
surface water
fresh water found in lakes, rivers, and streams
groundwater
fresh water found in underground reservoirs also knows as aquifers
non polar, polar
1) A molecule that contains only non polar bonds must be ________________. For example, homonuclear diatomic elements such as O₂, molecules are ___________________. 2) A molecule that contains polar covalent bonds may or not be _________. The polarity depends on the shape of the molecule. For
Water treatment plant
1) pass the water through a screen that physically remove large impurities such as weeds, sticks, and beverage bottles. 2) Add aluminum sulfate (Al₂(SO₄)₃) and calcium hydroxide (Ca(OH)₂) which react in water to form a gel of aluminum hydroxide that collects suspended dirt particles on its surface. When the gel settles, it carries particles with it that were suspended in the water. Any remaining particles are removed as the water is filtered through charcoal or gravel and then sand 3) Chlorination disinfects the water is accomplished by adding chlorine gas (Cl₂), sodium hypochlorite(NaClO) , or calcium hypochlorite (Ca(ClO)₂) that generate the antibacterial agent hypochlorous acid which remains to protect the water against further bacterial contamination.
Water's boiling point compared to similar structured liquids
100 degrees Celsius Liquids with similar molecular structures such as hydrogen sulfide has a much lower boiling point.
Ionic Compounds
97% of the water on our planet is found in the salt water of oceans. Since water is polar the partial negative(-) charges on the oxygen atoms are attracted to the positively charged Na+ ions of the salt crystal. Likewise partial positive (+) charges on the hydrogen atoms surround the Cl ions of the salt. This results in the dissolution of the salt.
parts per million (ppm)
A concentration of one part out a million. One ppm is a unit of concentration 10,000 times smaller than 1% (one part per hundred). Used when the concentration is very low. 1 g solute/1,000,000 g water = 1 mg solute/1 L water
Polar Covalent Bonds
A covalent bond in which the electrons are not equally shared but rather are closer to the more electronegative atom.
non polar covalent bond
A covalent bond in which the electrons are shared equally. Ex: N₂ and O₂, because the atoms are identical so there is no electronegativity difference between them.
Solution
A homogenous mixture of a solvent and one or more solutes.
Electronegativity
A measure of the attraction of an atom for electrons in a chemical bonds. The greater the electronegativity the more an atom attracts the electrons in a chemical bond toward itself. F is the most electronegative element.
"Like dissolves Like"
A polar compound (eg ethanol) will dossolve in a polar solvent (eg water) A nonpolar compound (eg oil) will dissolve in a nonpolar solvent (eg gasoline) BUT a polar compound (eg water) will NOT dissolve a nonpolar solved (eg oil) and vice versa
neutral solution
A solution that is neither acidic nor basic; that is, it has equal concentrations of H+ and OH- Examples include pure water and some salt solutions, such as the one formed by dissolving solid NaCl in water
Molarity
A unit of concentration represented by the number of moles of solute present in one liter of solution M = moles of solute/liter of solution Brackets are used to indicate concentration of : [NaCl]=1.0 M. This means that there are 1.0 moles of NaCl per liter of solution. Also this solution contains 1.0 M of Na+ ions and 1.0 M of Cl- ions. [Na+]=1.0 M and [Cl-]=1.0M
1.0 M NaCl Solution
A volumetric flask is used to prepare a 1.0 M NaCl solution. Remember: to calculate desired grams, multiply desired moles by its molar mass. Note: You do not add 58.5 NaCl to 1 L of water. The 58.5 g will take up some volume resulting in slightly more than the 1 L of solution and the molarity would be lower. 1. Add 1 mol (58.5 g) NaCl to an empy 1 L flask. 2. Add water until flask is about half full. Swirl to mix water and NaCl. 3. Add water until liquid level is even with 1000 mL mark. 4. Stopper and mix well.
Ozone as a disinfectant
Advantages: Lower concentration of ozone relative to chlorine is required to kill bacteria More effective than chlorine against waterborne viruses Disadvantages: - Only becomes economical for large water treatment plants - Decomposes quickly and hence does not protect water from possible contamination as it is piped through the municipal distribution system so a low dose of chlorine must be added
How pH levels affect habitats
As carbon dioxide dissolves in ocean water, it forms carbonic acid. This in turn dissociates to produce "extra" acidity in the form of H+. The H+ ions react with carbonate ions, thereby depleting it and producing more bicarbonate ions. Calcium carbonate then dissolves to replace the carbonate that was depleted. In the next 40 years, the carbonate ion concentration will reach a low enough level that the shells of sea creatures near the ocean surface will begin to dissolve.
UVC as a disinfectant
Can break down DNA and micro organisms, including bacteria Advantages: Is fast, leaves no residual byproducts, and it's economical for small installations, including rural homes and unsafe well water Disadvantages: Does not protect the water after it leaves the treatment site so a low-dose of chlorine must be added
Why is rainwater naturally acidic
Carbon dioxide in the atmosphere dissolves to a slight extent in water and reacts with it to produce a slightly acidic solution of carbonic acid. The carbonic acid dissociates slightly leading to rain with a ph of around 5.3
Acids
Consider hydrogen Chloride gas dissolved in water. The HCl molecules dissolve, and become surrounded by polar water molecules. Once dissolved, these molecules break apart or dissociates into two ions: H+ and Cl-. Because it dissociates completely into ions, it is a STRONG acid.
Macroscopic Properties of Solids
Does not take shape of container Does not completely fill container Has definite volume and definite shape
Macroscopic Properties of Liquids
Does take shape of container Does not completely fill container Has definite volume No definite shape
Macroscopic properties of a gas
Does take the shape of container Does completely fill container Does not have definite volume Does not have definite shape
The Hydronium Ion
H+ ions are much too reactive to exist alone so they attach to something else such as to water molecules. When dissolved in water each HCl donates a proton (H+) to an H2O molecule, forming H3O or the ____________________. The Cl- ion remains unchanged.
fish and other aquatic life are affected because only a few species can survive below pH 5.0. (acidification)
Healthy lakes have a Ph of 6.5 or slightly above and if the pH is lowered below 6.0...
When CO₂ dissolves in water, it produces carbonic acid: H₂CO₃ The carbonic acid dissolves to produce tiny amounts of H+ and the hydrogen carbonate ion HCO₃- because carbon dioxide is only slightly soluble in water.
How can CO₂ be an acid if it doesn't have hydrogen atoms?
Washing = spent detergent and whatever soiled the clothes. Toilet flushing = liquid and solid wastes Dirty streets = add solutes to rainwater run-off Agricultural practices = add fertilizers and other soluble compounds
How do humans contribute to substances in dissolved water?
aqueducts
How does the U.S. move water from one region to another?
If the bond dipoles are not positioned
If the bond dipoles are not positioned at 180° from one another and do not cancel, the molecule is polar. If the bond dipoles cancel one another, it is non polar.
Ammonia NH₃ in water
It is a weak base, even though it has no OH- group. Equilibrium reaction: - When an ammonia molecule reacts with a water molecule, the water molecule transfers H+ to the NH₃ molecule, An ammonium ion NH₄+, and a hydroxide ion, OH- are formed. Conjugate acid base pairs: NH₄+ (Conjugate acid) NH3 (base) OH- (Conjugate base) H2O (Acid)
Aquatic Life and Ph
Lakes are dead - 4 Most aquatic life disappears - 5 Many fish disappear - 5.6 Normal aquatic life 6.5-9.5
Residual chlorine
Name given to chlorine containing chemicals that remain in the water after the chlorination step. These include hypochlorous acid, the hypochlorite ion, and dissolved elemental chlorine.
pH Scale Approxomations
Stomach acid 1.5 Lemon Juice 2.5 Cola 2.7 Tomato Juice 4 Milk 6.5 Pure water 7 Blood 7.5 Sea water 8 Milk of magnesia 10.5 Household ammonia 11.5 Oven cleaner (lye) 14 Acid rain 3-5 Normal rain 5.3
Limestone rock, oxygen and carbon dioxide
Substances that can only dissolve in water in tiny amounts include...?
Salt, sugar, ethanol and the air pollutant SO₂
Substances very soluble in water include...?
Hydrogen bond
The H in the -OH group of an ethanol can ___________________ with water?
How chemical species affects seawater
The H+ produced by the dissociation of carbonic acid reacts with carbonate ion in seawater to form the bicarbonate ion. The net effect is to reduce the concentration of carbonate ions in seawater, The calcium carbonate in the shells of sea creatures then begins to dissolve in response to the decreased concentration of carbonate ions in seawater
bond dipole
The difference in electronegativity between two atoms in a polar covalent bond, which gives rise to partial positive/negative charges on the atoms. A convention to indicate the bond dipole uses an arrow to point in the direction of the more negatively charged end of the covalent bond.
Connection between electronegativity and polarity
The greater the difference in the electronegativity between two bonded atoms, the more polar it is.
carbonate ion, bicarbonate ion, carbonic acid
Three chemical species that arise from dissolved carbon dioxide in water and play a role in maintaining the ocean pH at approx. 8.2.
Water compared to other compounds
Water is a liquid at standard temperature and pressure (STP 25 degree Celsius and 1 atm) All other compounds with similar molar masses ( for instance nitrogen oxygen and carbon dioxide) are gases under these conditions.
SO₂ and NO𝙭
Water is never 100% pure. When water on our planet comes in contact with air, it dissolves tiny amounts of gas in the air, most notably oxygen and carbon dioxide. When it rains, the water actually cleans some of the pollutants out of the air such as _________ and __________ resulting in acid rain.
low boiling point
Weak intermolecular forces =
The sucrose molecules disperse uniformly among the H2O molecules. Unlike ionic compounds, the sucrose molecules remain intact and do not separate into ions. Although sugar molecules act as non-electrolytes, they still interact with water molecules, since they're both polar and are attracted to one another. They also hydrogen bonds with water.
What happens to sucrose molecules when it dissolves in water?
The sodium ions and sulfate ions separate
What happens when solid sodium sulfate and other ionic compounds dissolve in water?
Concentration Calculations
What is the concentration (in molarity and mass percentage) of the resulting solution when you add 5 grams of NaOH to 95 mL of water? Assum the density of water is 1 g/mL therefore 95 mL of H2O = 95 grams of H2O. = 5.3% NaOH
The compounds completely dissociates into positively charged ions (cations) and negatively charged ions. If an electrical potential (voltage) is applied to such a solution, the cations and anions are drawn to a positively charged electrodes, giving rise to electrical conductivity
When a strong electrolyte such as NaCl or another ionic compounds is placed into a polar solvent such as water, what happens?
The molecules in the liquid state are more closely packed than in the solid state. A volume of 1 cm³ of liquid water contains more molecules than 1 cm³ of ice.
When ice melts, the hexagonal pattern is lost and individual H₂O molecules can enter the open channels. As a result...
Electrical Conductivity of Electrolyte Solutions
When ions (charged particles) are in aqueous solutions, the solutions are able to conduct electricity. The images below show a) pure distilled water (non conducting) b) sugar dissolved in water (non conducting): a nonelectrolyte c) NaCl dissolved in water (conducting) : a strong electrolyte
100 ppm
Whereas the EPA guideline for lead in drinking water is 15 ppm, several water samples taken from homes in the Flint area contained Pb levels higher than ...?
Water
Which substance has one of the highest specific heats of any substance at 4.18 J/g ∙ ℃., making it an exceptional coolant?
Because PCB's and pesticide DDT's are non polar compounds and they dissolve in other non polar substances such as body fat.
Why are harmful PCB and pesticide DDT's ingested in the body fat of fish rather than their blood?
Strong base
a base that dissociates completely in water NaOH, a water-soluble ionic compounds, dissolves in water to produce sodium ions and hydroxide ions.
weak base
a base that dissociates only to a small extent in aqueous solution
Neutralization Reactions
a chemical reaction in which the hydrogen ions from an acid combined with the hydroxide ions from a base to form water molecules The other product is a salt (ionic compound)
Acid
a compound that releases hydrogen ions, H+, in aqueous solution. Can react with materials that contain the carbonate ion CO²₃ -, either as calcium carbonate or magnesium carbonate. It reacts with a carbonate to produce carbon dioxide.
Bases
a compound that releases hydroxide ions (OH-) in aqueous solutions. Characterisstic properties of bases - bitter taste - slippery, soapy feel Common examples include household ammonia and lye
intermolecular forces
a force that occurs between molecules
biological oxygen demand
a measure of the amount of dissolved O₂ that microorganisms use up as they decompose organic wastes found in water. A low BOD is one indicator of good water quality Nitrates and phosphates contribute because these ions are important nutrients for aquatic life. An overabundance of either can disrupt the normal flow of nutrients and lead to algal blooms that clog waterways and deplete oxygen from the water which lead to massive fish kills.
surfactants
a molecule that has both polar and nonpolar regions that allows it to help solubilize different classes of molecules The polar groups allow the surfactant to dissolve in water, while the non-polar ones are able to dissolve the grease
Reverse osmosis
a process that uses pressure to force the movement of water through a semipermeable membrane from a solution that is more concentrated to a solution that is less concentrated pressure is applied to the saltwater side, forcing water through a membrane to leave the salt and other impurities behind technology can be used to produce some bottled water, as well as ultra-pure water used in the microelectronic and Pharma industries
equilibrium reaction
a reaction that proceeds in both directions in which reactants form products, and products may re-form reactants
Distillation
a separation process in which a liquid solution is heated to its boiling point and the vapors are condensed and collected Energy is needed rather it be a Bunsen burner or the Sun Large scale distillation energy requirement is still high and is usually provided by burning fossil fuels
electrolytes
a solute that conducts electricity in an aqueous solution
Aqueous solutions
a solution in which the solvent is water
solvent
a substance, often a liquid, capable of dissolving one or more pure substances
standard temperature and pressure (STP)
a temperature of 25 ℃ and a pressure of 1 atm Water is a liquid at..
volumetric flask
a type of glassware that contains a precise amount of solution when filled to the mark on its neck
weak acid
an acid that dissociates only to a small extent in aqueous solution such as carbonic acid
water footprints China and India
an estimate of the volume of fresh water used to produce a particular good or to provide a service The U.S. has an average water footprint of 760 L. Which countries have higher water footprints?
aquifers
an underground permeable rock formation for which groundwater may be extracted using a well
Desalination
any process that removes sodium chloride and other minerals from salty water, thus producing potable water.
Water contaminant
anything physical, chemical, biological, or radioactive that is harmful to human health or degrades the taste or color of the water. The EPA regulates more than 90 substances known to contaminate drinking water
trihalomethane
compounds such as CHCl₃ (chloroform), CHBr₃ (bromoform), CHBrCl₂ (bromodichloromethane), and CHBr₂Cl (dibromochloromethane) that form from the reaction of chlorine or bromine with organic matter in drinking water byproducts in drinking water at concentrations that may be toxic
non-potable water
contains contaminants that include particulates from dirt, toxic metals such as arsenic, or bacteria that cause cholera. ∙ Water from rivers or lakes may be hauled trucks and used to wash sidewalks, to reduce roadway dust or to irrigate ∙ If treated at a water plant, recycled water is distributed to communities through purple pipes to irrigate athletic fields, flush toilets or fight fires.
1.00 g/cm³ at 4℃
density of liquid water
nonpolar solvents
dissolve nonpolar molecules Widely used in the production of drugs, plastics, paints, cosmetics, and cleaning agents.
parts per billion
one part out of one billion 1 g solute/1 billion water = 1 μg solute/L water Mercury is a contaminant found in this range.
acidic, basic, neutral
pH less than 7 are __________, and those with a pH greater than 7 are ________. Solutions that are pH 7 are_____________.
percent
parts per hundred. For example, an aqueous solution containing 0.9 g of a sodium chloride in 100 g of solution is a 0.9% solution by mass, which is referred to as "normal saline" in medical settings.
Hydrochloric acid
solution from HCl being dissolved in water
liquid carbon dioxide
solvent that is friendly to the environment; it is nontoxic, nonflammable, chemically benighted, non-ozone depleting and does not contribute to the formation of smog. Joe DeSimone developed surfactant to use with this, to make it better at dissolving oils, waxes, and greases found in soiled fabrics
acid neutralizing capacity
the capacity of a lake or other body of water to resist a decrease in pH
Biomagnification
the increase in concentration of certain persistent chemicals (such as harmful non polar compounds) in successively higher levels of a food chain
Ocean Acidification
the lowering of ocean pH due to increased atmospheric carbon dioxide Over the past 200 years the amount of carbon dioxide in the atmosphere has increased so more carbon dioxide is dissolving in the oceans and forming carbonic acid.
density
the mass per unit volume
pH
the pH of a solution is a measure of the concentration of the H+ ions present in that solution. The mathmatical expression for pH is a log based scale. Since pH is a log scale based on 10 a pH change of 1 unit represents a power of 10 change. That is a solution with a pH of 2 has a [H+] ten times that of a solution with a pH of 3.
Osmosis
the passage of water through a semipermeable membrane from a solution that is less concentrated to a solution that is more concentrated The water diffuses through the membrane and the solute does not.
Ion Product Constant of Water
the product of the concentrations of hydrogen ions and hydroxide ions in water
specific heat
the quantity of heat energy that must be absorbed to increase the temperature of one gram of a substance by 1 ℃
concentration
the ration of the amount of solute to the amount of solution 3 teaspoons of sugar in 3 cups of tea is 1:1 like half a teaspoon in half a cup of tea
tragedy of the commons
the situation in which a resource is common to all and used by many, but has no one in particular who is responsible for it. As a result, the resource may be destroyed by overuse to the detriment of all that use it. Like the water from the aquifers and surface water is the resource used in common, yet no one is particular is responsible for its use.
solute
the solid, liquid, or gas that dissolves in a solvent
LifeStraw
type of pope filter created for developing countries to remove bacteria, viruses, and protozoan parasites from water to use for drinking not a long term solution to the lack of potable water and doesn't remove metals such as arsenic of mercury, or the viral microbes responsible for diarrhea
potable water
water safe for drinking and cooking
Hydrogen Bonding
• An electrostatic attraction between a H atom bonded to a highly electronegative atom and a neighboring oxygen, nitrogen or fluorine atom, either in another molecule or in a different part of the same molecule. • Are intermolecular bonds that are 1/10 as strong as and farther apart than covalent bonds. •Covalent bonds are intramolecular bonds.
Fresh water: a rare and precious resource
∙ Only 3% of water is freshwater. ∙ 67% of this fresh water is locked up in glaciers ice caps and snowfields. ∙About 30% is found underground and must be pumped to the surface for use. ∙Lakes rivers and wetlands are only 0.3% of fresh water.
86% fresh water and 14% saltwater. 45%, 32%, 12% 30%
∙ Out of the 355 billion gallons of water that is withdrawn daily in the US - what percentage is fresh water and what percentage is saltwater? ∙What percentage is used as coolant in electric power plants, crop irrigation and for homes, schools and businesses? ∙ Agriculture worldwide?
