SNC2D Grade 10 Academic Science Chemistry – Acids and Bases

Thanks, Tony!

Chemistry: Chapter 6 Notes

 

Chapter 6.1—Identifying Acids and Bases

  • acids and bases are 2 particular type s of compounds
  • many of the substances you encounter each day can be classified either as acid/base
  • acids include edible acids (citrus fruits and their citrus acid), vinegar, fermentation of fruit juices to make wine
  • bases include the making of soap, other household cleaning products, baking soda
  • some acids and bases are safe to eat, while others are deadly and highly corrosive

 

ACIDS

  • an acid is a compound that produces hydrogen ions (H+(aq)) when dissolved in water
  • some acids are safe to eat (citric acid, acetic acid in vinegar), while others aren’t
  • many acids are corrosive and will react with metals
  • aqueous solutions of acids conduct electricity current, because of the ions present in the solution
  • when an acid dissolves in water, it reacts with water to form ions (in a process called ionization)
    • ex: when hydrogen chloride is bubbled through and dissolved in water to form ions, the hydrogen ions and chloride ions separate
      • HCl(aq) H+(aq) + Cl– 
  • acids in nature:
    • whip scorpion sprays a mist of acetic acid from rear of abdomen in self-defence
    • limestone caves occur when CO2 dissolves in rainwater to form carbonic acid, making the rain acidic; acidic water reacts with limestone, slowly dissolving it, and eventually, the rain caves large caverns in regions that have thick layers of limestone
    • hydrangea flowers produce different colour flowers based on acidity of soil
    • when you are bitten by an ant or brush against tiny hairs on a stinging nettle plant, you feel a stinging pain which is the formic acid (the acid dissolves the ends of the nerves in your skin, causing pain)

 

NAMING ACIDS

  • binary acids are composed of 2 elements—hydrogen and a non-metal
    • ex: when hydrogen chloride is dissolved in water, a binary acid HCl(aq) is formed
    • to name a binary acid according to the classical method
  1. write the root of the non-metal name
  2. add the prefix “hydro-“ to the root name
  3. add the ending “-ic acid” to the root name

 

Formula Classical Name IUPAC Name Uses
HF(aq) hydrofluoric acid aqueous hydrogen fluoride manufacturing aluminum/uranium; etching glass
HCl(aq) hydrochloric acid aqueous hydrogen chloride producing plastic; processing metals
HBr(aq) hydrobromic acid aqueous hydrogen bromide extracting metal ore
HI(aq) hydroiodic acid aqueous hydrogen iodide taking part in chem. reactions to make new compounds

 

 

  • an oxoacid is an acid composed of hydrogen, oxygen and another element
    • ex: formed between hydrogen and polyatomic ion (that contains oxygen)
    • to name an oxoacid using the classical method:
  1. write the name of the anion, without the “-ate” or “-ite” ending
  • exceptions: sulfur (use “sulfur-“); phosphorus (use “phosphor-“)
  1. if the anion name ended in “-ate” replace it with “-ic” at the end of the name
  2. if the anion name ended in “-ite”, replace it with “-ous” at the end of the name
  3. add the “acid” to the end of the name

 

Formula Classical Name IUPAC Name Uses
H2SO4(aq) sulphuric acid aqueous hydrogen sulfate in car batteries; in acid precipitation
H2SO3(aq) sulphurous acid aqueous hydrogen sulfite disinfecting and bleaching
HNO3(aq) nitric acid aqueous hydrogen nitrate producing explosives; fertilizers
H3PO4(aq) phosphoric acid aqueous hydrogen phosphate making fertilizers, soaps, and detergents
HClO3(aq) chloric acid aqueous hydrogen chlorate produces explosives and matches
H2CO3(aq) carbonic acid aqueous hydrogen carbonate naturally in water; in carbonated sinks

 

 

WRITING CHEMICAL FORMULAS FOR ACIDS

  • steps:

 

Step Example

Carbonic Acid

  1. determine if it is a binary acid, or an acid containing a polyatomic ion
name ends in “-ic acid” and doesn’t begin with “hydro-“, it is a polyatomic ion that ends in “-ate”
  1. identify the chemical formula for the polyatomic ion
the formula for the carbonate ion is CO32-
  1. determine how many hydrogen ions are required so that the net charge of the acid is 0
because each hydrogen ion has a 1+ charge, 2 hydrogen ions are needed to cancel out the 2- charge of the carbonate ion
  1. write the chemical formula
H2CO3

 

 

BASES

  • is a compound that forms hydroxide ions (OH(aq)) when dissolved in water
  • common household examples include soap, baking soda, and antacids
  • although some bases are safe to consume/be in contact with, many bases are not
    • some people mistakenly think that acids are dangerous, and bases are not; truth is that both acids and bases can cause severe chemical burns
  • properties of bases are a bitter taste and a slippery feel
  • aqueous solutions of bases conduct electric current because of the ions in solution
    • when a base dissolves in water, the ions separate from one another, and hydroxide ions are released into the water in a process called dissociation
    • ex: when sodium hydroxide dissolves in water, the ions separate
      • NaOH(aq) Na+(aq) + OH(aq)

 

NAMING BASES

  • many bases are ionic compounds composed of metal ions and hydroxide ions
  • their names and chemical formulas are written using the same rules as ionic compounds
    • some bases have a common name found on consumer products
  • naming examples:

 

 

Formula Chemical Name Common Name Uses
NaOH sodium hydroxide Iye, caustic soda drain/oven clears; used to make paper, glass and soap
Mg(OH)2 magnesium hydroxide Milk of Magnesia in laxatives and antacids
Ca(OH)2(aq) calcium hydroxide lime water for soil and water treatment

 

 

  • sodium hydroxide is one of the most important chemicals in industry; sodium chloride is typically mass-produced by a method called the chlor-alkali process
    • sodium hydroxide is produced simultaneously with chlorine has (another important chemical in industry)
    • 2NaCl(aq) + 2H2O(l) 2NaOh(aq) + Cl2(g) + H2(g)

 

WRITING CHEMICAL FORMULAS FOR BASES

  • writing the chemical formula for a base are the same for writing chemical formulas for an acid
  • to write the chemical formula for a base, you must make sure to include enough hydroxide ions in the formula so that the total charge of the compound is 0
  • steps:

 

Step Example

aqueous potassium hydroxide

  1. identify the cation and anion
metal cation is potassium, while anion is hydroxide
  1. determine the ion charge of the cation and anion
ion charge of the cation is (+1), and the ion charge for anion is (-1)
  1. determine the correct subscripts for the chemical formula
I need one cation to balance out my one anion
  1. write the chemical formula
KOH

 

 

Chapter 6.2—The pH Scale and Indicators

THE pH Scale

  • is a numerical scale from 0-14 that is used to classify aqueous solutions as acidic, basic, or neutral; it measures the concentration of hydrogen ions in a solution
  • if the pH is BELOW 7, it’s an acid (1-3 is strong acid; 4-6 is weak acid)
    • this means there are many more hydrogen ions in the solution than hydroxide ions
    • the lower the pH, the more acidic the solution (a lemon at pH2 is more acidic than milk at pH6)
    • high in hydrogen but low in hydroxide ions
  • if the pH is ABOVE 7, it’s a base (8-10 is weak base; 11-14 is strong base)
    • this means there are more hydroxide ions than hydrogen ions in the solution
    • the higher the pH, the more basic the solution (oven cleaner at pH13 is more basic than eggs at pH 8)
    • high in hydroxide by low in hydrogen ions
  • if the pH is EXACTLY 7, it’s neutral
    • falls in the middle of the pH scale
    • the solution is neither acidic nor basic
    • this means there is a same number of hydrogen and hydroxide ions in the solution
    • pure water has a pH of 7, as do solutions of some compounds (sodium chloride)
    • equal number of hydroxide and hydrogen ions

 

DIFFERENCES IN pH Values

  • the concentration of hydrogen ions associated with a value on the pH scale differs from the value above it or below it by a power of 10
    • for example, a solution that is pH4 has a concentration 10 times greater than a solution that’s pH5

 

DETERMINING THE pH OF A SOLUTION

  • there are several methods that can be used to determine the pH of a solution
  • a pH meter determines pH by using an electronic pH probe—the probe uses the electrical properties of a solution to determine pH
  • litmus paper is an example of a pH indicator (a substance that changes colour to show the concentration of hydrogen ions and hydroxide ions in a solution)
    • litmus solution is often dried onto thin paper strips and comes in red and blue
    • using a strip of red and blue litmus paper, you can determine whether a solution is acidic, basic or neutral
    • blue litmus paper turns red in an acidic solution, and red litmus paper turns blue in a basic solution
    • in a neutral solution, neither type of litmus paper changes colour
    • using only litmus paper is not sufficient to precisely determine the pH of a solution
  • universal indicator and pH paper—to more accurately determine the pH of a solution, several indicators that cover the pH range must be used
    • universal indicator is a mixture of several indicators that produce a different colour at different pH levels
    • pH paper is prepared by soaking strips of paper in universal indicator and then allowing them to dry—a drop of solution to be tests is placed on the pH paper
  • examples of tests:

 

Indicator Colour in Acid Colour in Base Colour in Neutral
red litmus paper red blue red
blue litmus paper red blue blue
neutral litmus paper pink blue purple
phenolphthalein colourless pink colourless
universal indicator (order of Rainbow) red (strong), orange, yellow (weak green (weak), blue, purple (strong) yellow/green

 

 

  • specific indicators can also be used, which change colour within a small range of pH values; by testing a solution with several different indicators, you can more accurately determine the pH of a solution

 

Indicator pH Range in Which Colour Changes Colour Change as pH Increases
methyl orange 3.2-4.4 red to yellow
methyl red 4.8-6.0 red to yellow
bromothymol blue 6.0-7.6 yellow to blue
phenolphthalein 8.2-10.0 colourless to pink
indigo carmine 11.2-13.0 blue to yellow

 

 

pH INDICATORS IN NATURE

  • there are many substances that contain natural acid-base indicators

 

 

 

 

 

Plant Colour of Indicator
Acid Neutral Base
apple red grey-purple green
cabbage juice blue purple red
blueberry red purple blue
cherry red red-purple blue-green
grape red purple blue-green
pomegranate red purple blue-green
raspberry red red purple pale green

 

 

ACIDS AND BASES: SIMILARITIES AND DIFFERENCES

 

Property Acids Bases
Taste sour bitter
What Does the Substance React With?
  • metals to give H2 gas
  • compounds with carbonates and bicarbonates to give CO2 gas
  • proteins to break them down into smaller molecules

 

Touch many acids will burn your skin bases feel slippery, and many can burn skin
Indicator Tests turns blue litmus paper red turns red litmus paper blue
Electrical Conductivity conducts electricity conducts electricity
pH less than 7 greater than 7
Production of Ions in water form H+(aq) ions when dissolved in water forms OH(aq) ions when dissolved in water, as well as CO3-2 and HCO3

 

 

Chapter 6.3—Reactions of Acids and Bases

ACID-BASE NEUTRALIZATION

  • neutralization is the reaction of an acid and a base to produce a salt and water
  • example: hydrochloric acid and sodium hydroxide (base) react: HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)
    • forms a double displacement reaction, in which the ions of the reactants which places to form new compounds
    • water is formed as the hydrogen ions of the acid and the hydroxide ions of the base combine
      • H+(aq) + OH(aq) HOH(l); HOH is the same as HHO or H2O
    • the remaining ions (Na and Cl) formed a salt (any ionic compound that is neither an acid nor a base is salt)
      • in most cases, the salt formed by a neutralization reaction is soluble in water and will not form a precipitate
  • it doesn’t matter whether the acid is added to the base or the base added to the acid; either way, the removal of both hydrogen and hydroxide ions form water, causes the mixture to approach pH 7
  • if the right amounts of acid and base react, the resulting solution will be neutral
  • antacids is an application of neutralization—the lining in your stomach secrets HCl(aq) which helps break down food in the digestion process
    • some people suffer from excess production of HCl which can cause heartburn (a burning sensation in the stomach that can extend up through the chest area into the esophagus/throat)
    • common treatment of heartburn is the use of antacids; they have the ability to neutralize the acid
    • antacids have an ingredient that is a base to help increase the pH of the gastric juices
    • common base in antacids are Mg(OH)2 and Al(OH)3
  • in March 2007, a railroad tanker derailed, spilling 150 000 litres of sulphuric acid into the Blanche River; an important step in the clean-up was adding a base (calcium hydroxide) to neutralise the acid
    • H2SO4(aq) + Ca(OH)2(aq) CaSO4(aq) + 2H2O(l)
    • when an acid spill occurs, a quick response is critical to minimize the size of spill by containing the spilled acid and stopping any leaks from containers (like overturned tankers)
    • neutralizing the acid and warning/evacuating people in the area help prevent injuries
    • cleaning up the spill doesn’t prevent harm to the environment (after Blanche River spill, fish died) 

 

ACID PRECIPITATION

  • rainwater is naturally acidic, and normally has a pH of around 5.6; this acidity is the result of carbon dioxide in the air dissolving in and reacting with water to form carbonic acid
    • CO2(g) + H2O(l) H2CO3(aq)
      • similar synthesis reactions of other non-metal oxides form additional acids, which lower pH of rainwater even more
  • high temperatures in a car’s engine causes nitrogen and oxygen to react and form several different nitrogen oxides; these oxides can react with water to form acids
    • NO2(g) + H2O(l) HNO3(aq)
    • catalytic converters help decrease the amount of nitrogen oxides that enter the atmosphere, but they don’t eliminate the nitrogen oxides completely
  • another major contributor to acid precipitation is sulfur oxides, which come from industrial processes (ores smelted in Sudbury region contain sulfur, which forms sulfur dioxide during the smelting process); also produced during the combustion of fossil fuels that contain sulfur (coal and natural gas)
    • S8(s) + 😯2(g) 8SO2(g)
      • sulfur dioxide can react with additional oxygen to form sulfur trioxide, which in turn can react with water to form sulphuric acid
      • 2SO2(g) + O2(g) 2SO3(g)                     then                        SO3(g) + H2O(l) H2SO4(aq)

 

EFFECTS OF ACID PRECIPITATION

  • Eastern Canada is especially sensitive to the effects of acid precipitation—in provinces that are part of the Canadian Shield (Ontario), the soils and waterways lack a natural ability to fight the damage caused by acid precipitation
    • these areas contain mostly granite rock, which doesn’t provide a source of basicity
      • in Western Canada, there are more limestone-based rock, which has a natural basicity (reducing effects of acid precipitation)
  • the change in pH of a lake/river water can be abrupt, as the rushing waters of the snowmelt which could hold deadly does of acid drain into the waterway
    • mass fish kills can occur because of acidic pollutants that have collected in the snow that had melted
      • fish may gradually disappear from a lake/stream as the environment becomes less tolerable
  • a healthy lake/stream can support a variety of organisms than an acidified one
    • as a lake/stream becomes more acidic, many types of tiny organisms begin disappearing(these organisms are food sources for fish and other animals)
    • as pH decreases, fish have trouble reproducing; a decreased fish population affects animals that depend of fish as a food source

 

REDUCING EMISSIONS THAT CAUSE ACID PRECIPITATION

  • scientists are working to solve environmental challenges caused by acid precipitation—one solution is to reduce emissions that cause acid precipitation
  • sulfur oxides are a major contributor to acid precipitation—one way to reduce it is to use scrubbers on smokestacks of industrial plants that burn coal
    • nearly all coal contain sulfur as a contaminant—when the coal burns the sulfur contaminant also burns, forming sulphur dioxide (SO2)
      • calcium carbonate is added to the coal and air as they enter the furnace’ while the coal burns in the air, it forms carbon dioxide and sulfur dioxide
      • the calcium carbonate decomposes into carbon dioxide and calcium oxide;; some of the sulfur dioxide reacts with the calcium oxide forming calcium sulphite
      • unreacted sulfur dioxide enters the wet scrubber, where a slurry of calcium oxide in water is sprayed; most of the remaining sulfur dioxide will form Calcium sulphite, which would mix with water to become a slurry that is discarded

 

RENEWING ACIDIFIED LAKES

  • another way to address acid precipitation is to attempt to reverse its effect
    • liming is the application of basic materials (typically lime-based) to renew acidified lakes and regions)
      • like giving a lake a giant antacid tablet
      • calcium carbonate is most commonly added to water to raise pH
  • as long as acidic water continues to enter the lake, the pH will drop again, and the lake will require continuous liming treatments
  • liming can cause problems—it increases calcium content and some species and insects are sensitive to calcium levels
  • preventing acid precipitation by using catalytic converters, scrubbers and new technologies is a better solution than fixing the aftermath of the problem

 

ACID LEACING AND METALS

  • smelters create acids as a by-product of the smelting process; however, acids are also an important part of refining metals
    • ex: copper and nickel need acids in the refinement process, as the acid reacts with the metals to form soluble compounds
  • the acidic solution containing the soluble metal salt is separated from the unwanted sold materials and the metals are later recovered from the solution
    • the properties of acids and metals allow acid leaching to be used to extract desired metals from ores’ these same properties create environmental problems
  • at many mining sites, you can see tailing piles (tailings are materials both solid and liquid that are left after the desired product (copper, nickel, gold) is removed from an ore
    • these piles are stored in above-ground facilities where they’re exposed to air and water
  • sulphide compounds in the tailing can form acids as they react with water and oxygen—if not contained, the resulting acids could cause run-off that can harm the local environment
    • acids can also leach metals from tailings, which could contaminate the area around tailing pile
  • acid leaching can be used to clean up soils that have been contaminated by toxic metals
    • first step is to remove any solid metal from contaminated soil, reducing the amount of acid needed to treat soil
      • the metal removed can be sent to smelter to be melted down
    • the soil is then treated with acid in order to leach out ,metal ions and any small pieces of metals
    • once the metal has been dissolved in the acid, it is recovered through precipitation; chemicals that form solid precipitates with the metal ions are added to the solution
    • after the precipitation, liquid component is recycled and used in leaching process again, while solid component containing the metal is collected for appropriate disposal
    • this process is expensive, so therefore preventing contamination in the first place is the best solution

 

Handout—Behaviour of Acids and Bases in Water

  • a water molecule is like a small magnet—one end is slightly positive, and one end is slightly negative
    • because water has slightly opposite charges at different ends, it will attract to different parts of compounds (slightly positive hydrogen will attract to negative ions, while slightly negative oxygen will attract to positive ions)
      • the slight charges of water can cause some ionic compounds to break apart and float freely in the solution (aka ionization)
  • acids in water—most acids are covalent compounds, and have polarity like water molecules
    • ex: water breaks apart hydrogen chloride as the hydrogen is attracted to negative end of water, while chlorine is attracted to positive end
      • hydrochloric acid is ionized
  • bases are generally ionic compounds, and they easily split by water (they dissociate)
    • ex: sodium hydroxide will dissociate in water (positive sodium will attract to negative oxygen, while negative hydroxide will attract to positive hydrogen)

 

Handout—Acid-Base Neutralization 

  • acid-base neutralization is a special type of double displacement
    • one acid and one base are the reactants
    • the products are water and an ionic salt (basically any ionic compound)
  • neutralization general equation:
    • acid(aq) + base(aq)  water(l) + salt(aq)
  • neutralization when the base contains carbonate/bicarbonate (the carbonate and bicarbonate break down after to form CO2)
    • acid(aq) + base (that has carbonate/bicarbonate)(aq)  water(l) + ionic salt(aq) + carbon dioxide(g)
      • example: HCl(aq) + NaHCO3(aq)  H2O(l) + NaCl(aq) + CO2(g)
    • the bicarbonate (HCO3) or carbonate (CO3) break down to form CO2