{"id":22,"date":"2017-08-16T07:14:26","date_gmt":"2017-08-16T07:14:26","guid":{"rendered":"http:\/\/americanboard.org\/Subjects\/biology\/?page_id=22"},"modified":"2017-09-18T14:58:19","modified_gmt":"2017-09-18T14:58:19","slug":"basic-chemistry-part-ii","status":"publish","type":"page","link":"https:\/\/americanboard.org\/Subjects\/biology\/basic-chemistry-part-ii\/","title":{"rendered":"Basic Chemistry, Part II"},"content":{"rendered":"<div class=\"twelve columns\" style=\"margin-top: 10%;\">\n<p class=\"advance\"><a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/biology\/basic-chemistry-part-i\">\u2b05 Previous Lesson<\/a> <a class=\"button\" href=\"http:\/\/americanboard.org\/Subjects\/biology\/basic-science-core\">Workshop Index<\/a> <a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/biology\/earth-science\">Next Lesson \u27a1<\/a><\/p>\n<h1 id=\"title\">Basic Chemistry, Part II<\/h1>\n<h4>Objective<\/h4>\n<p>In this lesson, you will review chemical reactions; the concept of the mole as a unit of measurement and how to use it; the properties of chemical solutions and how they are classified; and how absorption or energy release are related to chemical reactions.<\/p>\n<h4>Previously Covered:<\/h4>\n<ul>\n<li>Atoms are composed of a nucleus (containing protons and neutrons) surrounded by electrons.<\/li>\n<li>Elements are defined by the number of protons in the atom.<\/li>\n<li>A neutral atom has equal numbers of electrons and protons, balancing the charge of the atom.<\/li>\n<\/ul>\n<section>\n<h3>Reactions<\/h3>\n<p>Matter is constantly changing. The food that you eat becomes part of your body; gasoline becomes carbon dioxide, water, heat, and the energy that runs your car; the ink in your printer cartridge binds with paper to form a document. The process by which atoms of substances rearrange to form new substances is called a <abbr title=\"process by which atoms of substances become rearranged to form new substances\">chemical reaction<\/abbr>. Some indications of a chemical reaction include a change in temperature, such as in fire, a color change that indicates the presence of a different substance, and the generation of electrical current by a battery. Chemical reactions are written using shorthand similar to a mathematical equation:<\/p>\n<p class=\"center\"><strong>reactant A + reactant B \u2192 product C + product D<\/strong><\/p>\n<p>But there are many different types of reactions. For example, burning hydrogen in oxygen can be written as:<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p2_clip_image002.gif\" alt=\"2H2 + O2 = 2H20\" \/><\/center><br \/>\nIn this reaction, two reactants (hydrogen and oxygen) combine to form one product\u2014water.<\/p>\n<p>You can see that the equation for the reaction of hydrogen and oxygen indicates more than just the reactants and products. It further shows that two molecules of hydrogen react with a single molecule of oxygen to produce two molecules of water. The total number of hydrogen atoms (four) and the total number of oxygen atoms (two) are the same on both sides (reactants and products) of the reaction. Unlike nuclear reactions, chemical reactions do not change the identity of any atom. There are always the same numbers and types of atoms before and after the reaction; they are just arranged differently. Although new combinations of molecules exist, the equation must be <em>balanced<\/em> to show all atoms are accounted for.<\/p>\n<p>Equations are balanced by changing the number of molecules in the equation. Coefficients, which indicate number of units, can be changed. Subscripts that identify the number of atoms within a molecule, however, cannot be changed.<\/p>\n<p>In order to balance an equation, we start with a basic equation that shows all the reactants and the products. For example:<\/p>\n<p class=\"center\"><strong>ethane + oxygen \u2192 carbon dioxide + water<\/strong><\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p3_clip_image002.gif\" alt=\"\" \/><\/center>To balance the reaction, count the atoms on each side of the equation:<\/p>\n<p class=\"center\">reactant: C \u2013 2 ; H \u2013 6 ; O \u2013 2<\/p>\n<p class=\"center\">product: C \u2013 1 ; H \u2013 2 ; O \u2013 3<\/p>\n<p>Adjust coefficients so that carbon is balanced on both sides:<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p3_clip_image004.gif\" \/><\/center><\/p>\n<p class=\"center\">reactant: C \u2013 2 ; H \u2013 6 ; O \u2013 2<\/p>\n<p class=\"center\">product: C \u2013 2 ; H \u2013 2 ; O \u2013 5<\/p>\n<p>Next, adjust coefficients so that carbon is balanced on both sides:<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p3_clip_image006.gif\" \/><\/center><\/p>\n<p class=\"center\">reactant: C \u2013 2 ; H \u2013 6 ; O \u2013 3<\/p>\n<p class=\"center\">product: C \u2013 2 ; H \u2013 6 ; O \u2013 7<\/p>\n<p>Then adjust coefficients so that oxygen is balanced on both sides:<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p3_clip_image008.gif\" \/><\/center><\/p>\n<p class=\"center\">reactant: C \u2013 2 ; H \u2013 6 ; O \u2013 7<\/p>\n<p class=\"center\">product: C \u2013 2 ; H \u2013 6 ; O \u2013 7<\/p>\n<p>And finally, make all coefficients whole numbers:<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p3_clip_image010.gif\" \/><\/center>Many compounds include <abbr title=\"group of charged covalently bonded atoms\">polyatomic ions<\/abbr>, groups of atoms that are held together by chemical bonds and react as if they were a single atom. When balancing equations involving polyatomic ions, they are treated as a unit:<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p3_clip_image012.gif\" \/><\/center><\/p>\n<p class=\"center\">balances to:<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p3_clip_image014.gif\" \/><\/center><\/p>\n<h3>Types of Chemical Reactions<\/h3>\n<p>There are millions of different chemical reactions that occur everyday all around us. Chemists organize information about reactions by classifying them by patterns of chemical change. This classification helps predict the products and conditions of a chemical change. Most chemical reactions fall into four categories:<\/p>\n<p><abbr title=\"a reaction in which two or more reactants combine to form a single product; also called a composition reaction\">Synthesis Reaction<\/abbr> is a reaction in which two or more reactants combine to form a single product (also called a composition reaction):<\/p>\n<p class=\"center\"><strong>A + B \u2192 C<\/strong><\/p>\n<p>An example of a synthesis reaction is:<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p4_clip_CaO.gif\" alt=\"CaO + H20 = Ca(OH)2\" \/><\/center><abbr title=\"a reaction in which a single compound breaks down into two or more elements or compounds\">Decomposition Reaction<\/abbr> is a reaction in which a single compound breaks down into two or more elements or compounds:<\/p>\n<p class=\"center\"><strong>AB \u2192 A + B<\/strong><\/p>\n<p>An example of decomposition is the breakdown of hydrogen peroxide when it is exposed to light:<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p4_clip_H2O.gif\" alt=\"H2O2 = H2 + O2\" \/><\/center><abbr title=\"\">Single-displacement Reaction<\/abbr> is a reaction in which the atoms of one element replace the atoms of another element in a compound:<\/p>\n<p class=\"center\"><strong>AB + C \u2192 A + BC<\/strong><\/p>\n<p>An example of a single-displacement reaction is:<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p4_clip_image006.gif\" alt=\"2KBr + Cl2 = 2KCl + Br2\" \/><\/center><abbr title=\"a reaction in which two different ionic compounds exchange ions\">Double-displacement Reaction<\/abbr> is a reaction in which two different ionic compounds exchange ions:<\/p>\n<p class=\"center\"><strong>AB + CD \u2192 AC + BD<\/strong><\/p>\n<p>An example of a double-displacement reaction is:<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p4_clip_image008.gif\" alt=\"BaCl2 + Na4SO4 = BaSO4 + 2 NaCl\" \/><\/center><\/p>\n<section class=\"question\">\n<h4>Question<\/h4>\n<p>Which of the following is a synthesis reaction?<\/p>\n<ol>\n<li><img decoding=\"async\" style=\"vertical-align: middle; display: inline;\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p4_clip_image010.gif\" alt=\"2H2 + O2 = 2H20\" \/><\/li>\n<li><img decoding=\"async\" style=\"vertical-align: middle; display: inline;\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p4_clip_image012.gif\" alt=\"2NaOH + CuCl2 = 2NaCl + Cu(OH)2\" \/><\/li>\n<li><img decoding=\"async\" style=\"vertical-align: middle; display: inline;\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p4_clip_image014.gif\" alt=\"Bi + H2O = Bi2O3 + H2\" \/><\/li>\n<li><img decoding=\"async\" style=\"vertical-align: middle; display: inline;\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p4_clip_image016.gif\" alt=\"2H2) = 2H2 + O2\" \/><\/li>\n<\/ol>\n<p><a class=\"q-answer button button-primary\">Reveal Answer<\/a><\/p>\n<p class=\"q-reveal\">The correct choice is A. B is a double-displacement reaction; C is a single-displacement reaction; D is a decomposition reaction.<\/p>\n<\/section>\n<h3>The Mole and How We Use It<\/h3>\n<p>Chemical equations express chemical changes in terms of a specific ratio of atoms, molecules, or ions. Remember that all of these particles are extremely small, so we never observe the reaction between one atom of A and one atom of B. In fact, scientists rarely work in units of hundreds, or even billions of atoms. In the SI system, the base unit for measuring an amount of material is the <abbr title=\"a convenient measure that identifies the number of particles, 6.02 x 10&lt;sup&gt;23&lt;\/sup&gt;, and is equal to the number of grams of a substance from the atomic mass on the periodic table\">mole<\/abbr> (abbreviated mol). A mole is the number of carbon atoms in exactly 12 grams of pure carbon-12. The mole has been determined experimentally (although no one has actually counted a mole of anything) as <strong>6.0221367 \u00d7 10<sup>23<\/sup><\/strong>, also known as <abbr title=\"number of particles in a mole: 6.02 x 10&lt;sup&gt;23&lt;\/sup&gt;\">Avogadro&#8217;s number<\/abbr>. It is generally rounded to three or four significant figures \u2014 <strong>6.022 \u00d7 10<sup>23<\/sup><\/strong>. Because it is a unit of quantity, a mole can apply to anything\u2014one mole of atoms, one mole of ions, even one mole of moles (the animal). In reality, the number is so big that it finds little use outside of chemistry and related fields. (One mole of moles would cover the whole planet with a layer of animals tens of kilometers deep.)<\/p>\n<p>Avogadro&#8217;s number is very useful in chemistry. One mole of any substance weighs as many grams as its atomic mass. Therefore, the mass of one mole of a pure substance, called its <abbr title=\"mass of one mole of a pure substance\">molar mass,<\/abbr> is equal to its atomic mass with units of grams\/mole. The atomic mass of oxygen, for example, is 16.0 and its molar mass is 16.0 g\/mol. The molar mass of water is 18.0 g\/mol, so if you measure out exactly 18 grams of water (or ice), you will have 6.02 \u00d7 10<sup>23<\/sup> molecules in a beaker.<\/p>\n<p>Avogadro&#8217;s number can also be used to determine the volume of a gas. Avogadro was the first to propose the principle that equal volumes of all gases at the same temperature and pressure contain the same number of particles. The molar volume for a gas is the volume that one mole of gas occupies at 0.00\u00b0C and 1.00 atm pressure, conditions known as standard temperature and pressure (STP). This volume is 22.4 liters for every gas. That means that 22.4 liters of hydrogen at STP will have a mass of 2.00 grams (remember that hydrogen has diatomic molecules), while the same volume of helium has a mass of 4.00 grams. The conversion factor, 22.4 L\/mol, allows you to calculate the number of particles in a given volume of gas at STP or, combined with the molar mass of a substance, this conversion factor can be used to determine the mass of a given volume of gas.<\/p>\n<h3>The Solution is Obvious<\/h3>\n<p>We are surrounded by solutions\u2014and we are composed of solutions. A solution is a homogeneous mixture containing two or more substances. It is impossible to distinguish one substance from the other in a solution, which can be a gas, liquid, or solid. The air you breathe is a solution that contains oxygen, carbon dioxide, water vapor, and several other gases dissolved in nitrogen. Most of the matter inside of your body is filled with solutions of numerous substances in water. The major component of a solution \u2014 nitrogen or water in these examples \u2014 is the <abbr title=\"substance that dissolves the solute in a solution\">solvent<\/abbr>. The substance that forms a solution in the solvent is the <abbr title=\"substance added to a solvent to produce a solution\">solute<\/abbr>.<\/p>\n<p>Water is the most common solvent of liquid solutions and is referred to as the universal solvent. Almost all substances dissolve in water. The process of forming a solution depends on interactions between the particles \u2014 atom, ions, or molecules \u2014 of the solvent and the solute. Because of the shape of water molecules and the tendency of electrons to spend more time around the oxygen atom than around the hydrogen atoms, one side of the molecule is slightly electrically positive and the other is electrically negative. Water molecules are <abbr title=\"molecular structure having one or more poles that attract opposites to each other, as in phospholids, where the polar heads arrange themselves opposite each other to create an oily membrane interior\">polar<\/abbr>. Other substances that are also polar tend to dissolve more easily in water than substances that are <abbr title=\"substance that has an equal distribution of electrons between atoms or symmetrical shape so that no part of the molecule is more positive or negative\">nonpolar<\/abbr>. As shown below, many ionic compounds dissociate in an aqueous (water) solution. The negative ions are attracted to the positive, or hydrogen, end of the water molecule and positive ions are attracted to the negative end. Nonpolar molecules, which have no separation of charge, such as the components of olive oil, dissolve well in nonpolar solvents, but not in water.<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/solutions-table.jpg\" alt=\"Solutions Table\" \/><\/center>Table salt dissolves easily in water, but if you put too much salt in the water, some of it will settle to the bottom of the container. The <abbr title=\"maximum amount of a substance that will dissolve in a particular solvent at a given temperature and pressure\">solubility<\/abbr> of a substance is the maximum amount that will dissolve in a particular solvent at a given temperature and pressure. These conditions must be specified because solubility is different under different conditions. For example, at 20\u00b0C and one atmosphere of pressure, 36.4 grams of aluminum sulfate will dissolve in 100 grams of water. At 60\u00b0C, the solubility increases to 59.2 grams per 100 grams of water. When the amount of solute is equal to the solubility under given conditions, the solution is <abbr title=\"a solution that has all the solute dissolved that can be physically dissolved in that solution; for electrons, saturation occurs when one electron is shared per atom as apposed to two electrons shared with two atoms (a double bond) therefore there are only single bonds present in the hydrocarbons\">saturated solution<\/abbr> and no more of the substance can dissolve. Below this solubility limit, the solution is an <abbr title=\"solution containing less solute than the solubility under given conditions\">unsaturated solution<\/abbr>.<\/p>\n<p>Sometimes a solution can contain more solute than a normal saturated solvent at a particular temperature. This <abbr title=\"unstable solution which under the right trigger will precipitate a solid\">supersaturated solution<\/abbr> normally occurs when a saturated solution is formed and then cooled. As the solubility decreases, the solute can stay in solution at a concentration higher than its normal solubility limit. If the supersaturated solution is disturbed, the excess solute comes out of solution as a solid, a process called <abbr title=\"&lt;em&gt;Earth science:&lt;\/em&gt; water falling to Earth in the form of rain, snow, sleet, or hail; &lt;em&gt;Chemistry:&lt;\/em&gt; separating a substance from a solution as a solid\">precipitation<\/abbr>. Supersaturated solutions can also be formed when some of the solvent evaporates.<\/p>\n<p>The concentration of a solution is a measure of how much solute is dissolved. Concentration can be expressed quantitatively as a ratio of the amount of solute to the amount of solvent, or the total amount of solution. Chemists frequently use the ratio of mass of solute or the number of moles of solute per volume of solution. The molarity of a solution, indicated by the symbol M, refers to the moles of solute\/liter of solution.<\/p>\n<h4>Calculating the molarity of a solution from a known mass of solute:<\/h4>\n<p>Example: 50.0 g NaCl in 500 milliliters of solution<\/p>\n<ul>\n<li>Use the molar mass to calculate the number of moles: <img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p8_clip_image002.gif\" alt=\"\" \/><\/li>\n<li>Convert the volume to liters of solution:\u00a0<img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p8_clip_image004.gif\" alt=\"\" \/><\/li>\n<li>Calculate molarity:\u00a0<img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p8_clip_image006.gif\" alt=\"\" \/><\/li>\n<\/ul>\n<h4>Calculating the mass of solute in a solution:<\/h4>\n<p>Example: 450 ml of a 2.50M solution of LiBr<\/p>\n<ol>\n<li>Use the molarity and volume to determine number of moles:<br \/>\n2.50M \u00d7 450 mL = 2.50 mol\/ L \u00d7 0.450 L = 1.125 mol LiBr<\/li>\n<li>Convert the moles of solute to grams of solvent: <img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p8_clip_image008.gif\" alt=\"\" \/><\/li>\n<\/ol>\n<p>The chemical properties of a solution depend on how the solvent and solute interact with other substances. However, there are some properties of solutions that are affected by the number of particles in solution, regardless of identity of the solute. These <abbr title=\"characteristics of a solution that are a function of concentration\">colligative properties<\/abbr> are a function of concentration. When a covalent compound, such as sucrose (sugar), is dissolved in water, the effect of the colligative properties is determined by the molarity of the solution. Ionic compounds, however, dissociate into ions, so the number of particles is a multiple of the molarity of the compound in solution. This means that a 1 M solution of sodium chloride has the same effect as a 2 M solution of sucrose because there are twice as many particles in solution. Colligative properties include:<\/p>\n<ul>\n<li><strong>Boiling Point Elevation<\/strong> The boiling point of a solution is higher than the boiling point of the pure solvent. The amount of increase depends on the solvent and the concentration of the solution. For water, the boiling point increases by 0.512\u00b0C\/mol. Therefore a 1.00 M solution of NaCl in water boils at 101.2\u00b0C under standard conditions (remember that there are two ions per mole of NaCl in solution).<\/li>\n<li><strong>Freezing Point Depression<\/strong> The freezing point of a solution is lower than the freezing point of pure solvent, in direct proportion to concentration of solute. One mole of solute molecules or ions decreases the freezing point of water by 1.86\u00b0C\/mol. Therefore a 2 M solution of CaCl 2 in water decreases the freezing point to -11.2\u00b0C (six moles of ions \u00d7 -1.86\u00b0C). Calcium chloride is used to prevent water from freezing on roads in cold weather.<\/li>\n<\/ul>\n<h3>Understanding Acids and Bases<\/h3>\n<p>All aqueous solutions contain hydrogen ions (H<sup>+<\/sup>) and hydroxide ions (OH<sup>&#8211;<\/sup>). The relative amount of these two ions determines whether a solution is neutral, acidic, or basic. In a neutral solution, the concentration of the two ions is identical. In addition to pure water, solutions of salts such as NaCl, are neutral. An <abbr title=\"a solution that contains more hydrogen ions than hydroxide ions\">acidic solution<\/abbr> contains more hydrogen ions than hydroxide ions; a <abbr title=\"a solution that contains more hydroxide ions than hydrogen ions\">basic solution<\/abbr> contains more hydroxide ions than hydrogen ions. This ratio depends on the composition of the dissolved substance and how it interacts with water.<\/p>\n<p>There are many different compounds that form acidic or basic solutions. Common acids include foods, such as orange juice and vinegar, as well acids that are dangerous to handle, such as the solution in automobile batteries. Common bases include antacid tablets that settle your stomach and drain cleaner that can dissolve clogs in sewer pipes.<\/p>\n<p>General properties of acids include:<\/p>\n<ul>\n<li>sharp or sour taste<\/li>\n<li>electrical conductivity<\/li>\n<li>reactions with many metals<\/li>\n<li>turning litmus paper red<\/li>\n<li>reacting with bases to form a salt and water<\/li>\n<\/ul>\n<p>General properties of bases include:<\/p>\n<ul>\n<li>bitter taste<\/li>\n<li>electrical conductivity<\/li>\n<li>dissolving many organic materials, such as grease<\/li>\n<li>tending not to react with metals<\/li>\n<li>feeling slippery on skin<\/li>\n<li>turning litmus paper blue<\/li>\n<li>reacting with acids to form a salt and water<\/li>\n<\/ul>\n<p>Notice that the final property listed for acids and bases is that they react with one another to form a salt and water. This process is known as <abbr title=\"a reaction between a base and an acid that produces a neutral (ph = 7) solution\">neutralization<\/abbr>. The general form of a neutralization reaction is a double-displacement between an acid (HX) and a base (YOH), which can be written as:<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p9_clip_image003.gif\" alt=\"\" \/><\/center>In solution this can be represented as:<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/s4_p9_clip_image005.gif\" alt=\"\" \/><\/center>Acids and bases vary in strength. Very strong acids, such as concentrated sulfuric acid in batteries, and very strong bases, such as the sodium hydroxide in drain cleaner, are dangerous substances. They react violently with body tissues and can cause severe &#8220;burns&#8221; and even death. On the other hand, weak acids, such as carbonic, and weak bases, such as blood, are essential for life.<\/p>\n<p><center><img decoding=\"async\" class=\"u-pull-right\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/phtable.jpg\" alt=\"pH Scale\" \/><\/center>In pure water the concentration H<sup>+<\/sup> of OH<sup>&#8211;<\/sup> and ions is equal, each ion having a concentration of 1.0 \u00d7 10<sup>-7<\/sup> M. The product of the two concentrations is 1.0 \u00d7 10<sup>-14<\/sup>. As acidic or basic materials are dissolved in the water, they add hydrogen or hydroxide ions to the solution. The product of the two concentrations, however, remains at 1.0 \u00d7 10<sup>-14<\/sup>. Therefore, in battery acid, which has a hydrogen ion concentration of 1 &amp;times 10<sup>-1<\/sup> M, the concentration of hydroxide ions is 1 \u00d7 10<sup>-13<\/sup> M. These concentrations are reversed in a very strong base, such as a concentrated sodium hydroxide solution.<\/p>\n<p>The relative strength of acids and bases is measured on a scale known as the <abbr title=\"a quantitative measure of alkalinity or acidity of a liquid solution The measure is reflected using a scale where the number 7 represents neutral and higher numbers increasing values of alkalinity Numbers lower than 7 reflect increasing acidity\">pH scale<\/abbr>. The pH is the negative logarithm of the hydrogen ion concentration. That means the pH of an acidic solution, with a hydrogen ion concentration of 1 \u00d7 10<sup>-1<\/sup> M is equal to 1. The pH of a basic solution with a hydrogen ion concentration of 1 \u00d7 10<sup>-13<\/sup> M is equal to 13. Solutions with very low pH values, such as 1 or 2 are considered strong acids, while solutions with a pH value of 5 or 6 are weak acids. Strong bases have high pH values, such as 13 or 14, while weak bases are solutions whose pH is in the 8 to 9 range. The strength of an acid or base solution depends on the concentration of the solute and to what extent it dissociates to form hydrogen or hydroxide ions in solution.<\/p>\n<section class=\"question\">\n<h4>Question<\/h4>\n<p>An aqueous solution has a hydrogen ion concentration of 1.0 \u00d7 10<sup>-6<\/sup> M. This solution is classified as a<\/p>\n<ol>\n<li>strong acid.<\/li>\n<li>weak acid.<\/li>\n<li>strong base.<\/li>\n<li>weak base.<\/li>\n<\/ol>\n<p><a class=\"q-answer button button-primary\">Reveal Answer<\/a><\/p>\n<p class=\"q-reveal\">The correct answer is B. pH = -log[hydrogen ion concentration] = -log ( 1.0 \u00d7 10<sup>-6<\/sup> ) = 6. A pH value of 6 indicates a weak acid.<\/p>\n<\/section>\n<h3>Chemical Energy<\/h3>\n<p>Energy is the ability to do work or produce heat. Every chemical substance has <abbr title=\"the energy due to an object's motion; the energy being actively used by a plant or animal\">kinetic energy<\/abbr>, based on the motion of its atoms and molecules, as well as stored energy known as chemical <abbr title=\"energy stored and available for use by a plant or animal\">potential energy<\/abbr>. The potential energy is energy that was added to the substance as bonds formed and it interacted with other atoms and molecules. Chemical changes can release this stored energy as heat, the process of <abbr title=\"the release of stored energy through chemical changes\">energy flow<\/abbr>. Every chemical change either releases or absorbs energy. A process that absorbs energy is called <abbr title=\"reaction or process that requires energy and usually feels cold to the touch\">endothermic<\/abbr>; a process that releases energy is called <abbr title=\"process or reaction that releases energy and usually produces heat\">exothermic<\/abbr>.<\/p>\n<p>The change in potential energy during a chemical reaction can be illustrated in an exothermic energy diagram that shows the change in potential energy. In an exothermic reaction, the energy of the reactants is higher than that of the products. The change, released as heat, is indicated as Delta E in the diagram. Notice that initially some energy must be added to start the reaction. This energy, labeled E sub a is called the <abbr title=\"energy that must be added to start a chemical reaction; the smallest amount of energy needed to convert a stable, normal molecule into a reactive molecule\">activation energy<\/abbr> of the reaction. Once the reaction starts, activation energy is provided by the reaction itself. An example of activation energy in an exothermic reaction is the striking of a match. The match does not start to burn until a small amount of energy is added by the friction of the match against rough side of the box.<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/exothermic_reaction_progress.jpg\" alt=\"A graph of the exothermic reaction progress.\" \/><\/center>In an endothermic reaction, the energy of the products is higher than that of the reactants. Endothermic reactions also have activation energy. In order to keep the reaction going, however, energy must continually be added. In a <abbr title=\"a reaction in which products become reactants, and the reaction is endothermic\">reversible reaction<\/abbr>, the products become the reactants for the reverse reaction. If the forward reaction is exothermic, then the reverse reaction must be endothermic.<\/p>\n<p><center><img decoding=\"async\" class=\"u-pull-right\" src=\"http:\/\/americanboard.org\/Subjects\/biology\/wp-content\/uploads\/sites\/2\/2017\/08\/reactiongraph.jpg\" alt=\"Concentration vs time graph\" \/><\/center><abbr title=\"substance that lowers the activation energy of a reaction and therefore speeds up the resulting rate\">Catalysts<\/abbr> reduce the activation energy of a chemical reaction. This allows the reaction to start with a smaller initial energy input and it also means that the reaction can occur at a lower temperature. This is very important in biological systems, such as your body, in which the range of possible temperatures is limited. Enzymes are biological catalysts that allow reactions to occur in cells under much less severe conditions than would otherwise be required.<\/p>\n<p>The rate of a reaction is the amount of change from reactant to product over a given period of time. When these quantities are plotted on a graph, the slope of the line indicates the reaction rate. The rate of a chemical reaction is increased by adding a catalyst that reduces the activation energy, thereby lowering a barrier to the chemical reaction. For example, hydrogen peroxide breaks down to form hydrogen and oxygen. The rate of reaction can be measured by measuring the amount of oxygen produced. Adding a catalyst, such as many transition metals, causes hydrogen peroxide to break apart faster.<\/p>\n<h3>Summary<\/h3>\n<ul>\n<li>Matter is conserved in chemical reactions.<\/li>\n<li>The SI unit for the amount of a substance is the mole (mol), which is equal to units.<\/li>\n<li>The molar mass of a substance is the mass, in grams, of one mole of its atoms or molecules.<\/li>\n<li>A solution consists of two or more components, a solvent and one or more solutes.<\/li>\n<li>Ionic compounds dissociate in aqueous solution.<\/li>\n<\/ul>\n<\/section>\n<p><!-- CONTENT ENDS HERE --><\/p>\n<div class=\"advance\"><a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/biology\/basic-chemistry-part-i\">\u2b05 Previous Lesson<\/a> <a class=\"button\" href=\"http:\/\/americanboard.org\/Subjects\/biology\/basic-science-core\">Workshop Index<\/a> <a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/biology\/earth-science\">Next Lesson \u27a1<\/a><\/div>\n<p><a class=\"backtotop\" href=\"#title\">Back to Top<\/a><\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>\u2b05 Previous Lesson Workshop Index Next Lesson \u27a1 Basic Chemistry, Part II Objective In this lesson, you will review chemical reactions; the concept of the mole as a unit of measurement and how to use it; the properties of chemical solutions and how they are classified; and how absorption or energy release are related to [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-22","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/americanboard.org\/Subjects\/biology\/wp-json\/wp\/v2\/pages\/22","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/americanboard.org\/Subjects\/biology\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/americanboard.org\/Subjects\/biology\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/americanboard.org\/Subjects\/biology\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/americanboard.org\/Subjects\/biology\/wp-json\/wp\/v2\/comments?post=22"}],"version-history":[{"count":23,"href":"https:\/\/americanboard.org\/Subjects\/biology\/wp-json\/wp\/v2\/pages\/22\/revisions"}],"predecessor-version":[{"id":1060,"href":"https:\/\/americanboard.org\/Subjects\/biology\/wp-json\/wp\/v2\/pages\/22\/revisions\/1060"}],"wp:attachment":[{"href":"https:\/\/americanboard.org\/Subjects\/biology\/wp-json\/wp\/v2\/media?parent=22"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}