Physical Science II
Physical Science II SCI 3120
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This 4 page Class Notes was uploaded by Amaya McDermott on Monday October 5, 2015. The Class Notes belongs to SCI 3120 at Clayton State University taught by Harold Banke in Fall. Since its upload, it has received 38 views. For similar materials see /class/219550/sci-3120-clayton-state-university in Science at Clayton State University.
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Date Created: 10/05/15
Chapter 25 Acids and Bases Acids and bases defined The term comes from the Latin term acidus meaning sour Most foods that taste sour are acidic in nature The term M comes from the property of these materials to react with acids to fOI H l chemicals called salts Thus they are the base upon which salts are built Bases also have the property of reacting with oils to form soaps a property that makes them feel slippery to the touch because they react with skin oil to form a thin layer of soap Solutions of bases are called alkaline from the Arabic term for ashes which feel slippery because of the bases they contain The chemical nature of acids and bases was first discovered at the end of the 19th century by a Swedish chemist named Svante Arrhenius Arrhenius defined acids as substances that release hydrogen ions H when dissolved in water He defined bases as substance that produces hydroxide ions OH39HO39 when dissolved in water HClg 9 Haq Claq NaOH5 9 Naaq OHaq Thus the chemical formula often discloses whether a substance is an acid or base acids often begin with H and bases end with OH The Arrhenius definition is limited however since some chemicals have the properties of acids or bases without producing H or OH A more general definition is known as the Br nstedLow1y definition an acid is defined as a substance that donates a H ion and a base is a substance that accepts a H ion A H ion is actually a proton so a BronstedLowry acid is also called a proton donor and a BronstedLowry base is a proton acceptor DIAGRAM water HCl The products are a chloride ion and a hydronium ion a water molecule with a proton stuck on it Ammonia NH3 is seen to be a base using the BL definition DIAGRAM ammonia water Water behaves as an acid in some reactions and a base in other Substances that do this are called amphoteric The BL definition emphasizes the fact that the terms acid and base refer to a particular type of behavior rather than a general class of materials since it is the behavior of accepting a proton that makes a substance a base rather than the structure or composition of the substance Questions p 429 identify acid or base behavior Salt the ionic product of an acid and a base We usually use the term glt to refer to a particular food seasoning but in chemistry it refers to a substance formed by the reaction between an acid and a base NaOH HCl 9 NaCl H20 KOH HCl 9 KCl H20 In each reaction the salt is formed by the neutralization of an acid by a base Water is usually produced as another product The positive ion comes from the base and the negative ion comes from the acid A rather exotic salt is one form of cocaine In the presence of HCl cocaine acts as a base and accepts a proton The chloride ion tags along making a polar molecule called cocaine hydrochloride salt a watersoluble compound that can be absorbed through the mucous membranes of the nose Crack cocaine is the nonsalt form Since it is nonpolar it vaporizes easily and the vapor is inhaled directly into the lungs Acid strength Acid and base solutions are classified as strong or weak This does not refer to the concentration of the solutions but rather to the number of hydronium ions or hydroxide ions formed in water solutions An acid such as HCl has a very strong tendency to break up into ions DIAGRAM HCl and water The large number of hydronium ions produced makes HCl a strong acid Acetic acid on the other hand has a very weak tendency to form H ions so very few hydronium ions are formed in water solutions Acetic acid is classified as weak DIAGRAM acetic acid and water p433 The strength of acids and bases can be tested by electrical conduction P433 The ability of the solution to conduct electricity is directly related to the number of ions either H or OH Acidic basic or neutral Pure water looks like a nonconductor thus it seems to produce neither H or OH In fact water produces small number of both DIAGRAM p 434 The molar concentration of H ions multiplied by the molar concentration of OH ions produces a very small number called KW l X 1039 DIAGRAM If acids or bases are dissolved in water the concentration of one of the ions goes up but the concentration of the other ion goes down so the KW remains constant An acid dissolved in water release many H ions which neutralize many OH ions so the concentration of H goes up while the concentration of OH goes down Questions p 435 Acidic solutions are defined as those in which the concentration of hydronium ions is greater than the concentration of hydroxide ions A m solution is the opposite A neutral solution is one in which the number of ions is equal The pH scale The pH scale uses the concentration of hydronium ions in a water solution to define the relative acidic or basic properties of a solution The power of ten in the hydronium ion concentration is the basic standard for pH The power of 10 is called the logarithm or log of the concentration of hydronium ions but pH is the negative log of the hydronium ion concentration thus a positive number when in fact the power of 10 is always negative since the concentration is such a small number EXAIVIPLE Before HCl is added to a sample of water what is the hydronium ion concentration in the water 10397 After HCl is added the H3O concentration does what What happens to the power of 10 Let s say the concentration becomes 104 what is the negative log of the concentration 4 What is the pH 4 pH scale near 0 acid to 7 neutral to near 14 base Litmus bluebase redacid Acid rain and basic oceans An example of a naturally occurring acid is normal rain As rain falls through the atmosphere it reacts with C02 to form carbonic acid H2CO3 This is a weak acid with a pH of about 56 Rain having a pH below 5 is called acid rain Acid rain forms when 802 combines with 02 to form 803 sulfur trioxide This in turn combines with rainwater to form a very strong acid H2 804 sulfuric acid an acid capable of much harm through corrosion of surfaces and poisoning of ecosystems The environmental damage of acid rain depends to a certain extent on the geological environment In the Midwestern US the ground contains deposits of the alkaline compound CaCO3 formed by sediments of sea creature s shells from geological periods when the Midwest was covered by ocean Acid rain fall in this ground is partially neutralized by the calcium carbonate In other parts of the US CaCO3 is less prevalent and the ground minerals contain mainly inert SiOg such as granite rocks Here the effects of acid rain are greater The problem of acid rain is primarily a problem of producing 802 Most of this comes from the actions of humans such as burning fossil fuels like gasoline and coal Some measures have been taken to reduce the emission of 802 but it is still a global problem which calls for global cooperation for a solution Another global problem is the overproduction of C02 by the burning of fossil fuels C02 normally dissolves in ocean water but at the rate it is being produced it is accumulating in the atmosphere faster than it can dissolve in the oceans This is leading to an increase in the concentration of C02 in the atmosphere The problem with this increase is that C02 acts to trap heat radiation in the atmosphere not allowing it to escape into space The result is a warming of our planet This effect is called the Greenhouse Effect and it is a problem of global proportions since C02 from any nation collects in the atmosphere and heat gradually spreads throughout the entire planet
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