The Acidic Environment

Contextual OutlineAcidic and basic environments exist everywhere. The human body has a slightly acidic skin surface to assist in disease control and digestion occurs in both acidic and basic environments to assist the breakdown of the biopolymers constituting food. Indeed, microorganisms found in the digestive system are well adapted to acidic or basic environments. Many industries use acidic and basic compounds for a wide range of purposes and these compounds are found in daily use within the home. Because of this, an awareness of the properties of acids and bases is important for safe handling of materials. Currently, concerns exist about the increased release of acidic and basic substances into the environment and the impact of these substances on the environment and the organisms within those environments. This module increases students understanding of the history, nature and practice of chemistry, the applications and uses of chemistry and implications of chemistry for society and the environment.

1. Indicators were identified with the observation that the colour of some flowers depends on soil compositionStudents learn to: classify common substances as acidic, basic or neutralAcids Change colour of indicator, litmus to red Are electrolytes Sour taste React with reactive metals (H2 + salt) React with carbonates and hydrogencarbonates (CO2, H2O, Salt) React with metal oxides (H2O, salt) React with metal hydroxides (H2O, salt)Bases Change colour of indicators, litmus to blue Are electrolytes React with acids (H2O, Salt) React with amphoteric metals (H2) Dissolve amphoteric metal hydroxidesAcidNeutralBase

HCl, used to clean bricksH2ONaOH, soap, polymers, drain cleaners

H2SO4, fertilisers, car batteriesCONH3, fertilisers, household cleaner

HNO3, pesticidesCa(OH)2, plaster and cement

CH3COOH, vinegarMg(OH)2, antacid

Citric Acid, fruits

Lactic Acid, milk and muscle tissue

identify that indicators such a litmus, phenolphthalein, methyl orange and bromothymol blue can be used to determine the acidic or basic nature of a material over a range and that the range is identified by change in indicator colourIndicates such as litmus, phenolphthalein, methyl orange and bromothymol blue can be used to determine the acidic or basic nature of a material. All indicators have their own range that is suitable to test. The range is identified by change in indicator colour. No single indicator can cover the entire 0-14 range.Universal indicator is a mixture of indicators.

identify and describe some everyday uses of indicators including the testing of soil acidity/basicityIndicators are used to test the pH of soil, affecting growth of plants and can change the colour of some flowers. It is also used for fish tanks and swimming pools, where the pH of the water is important.

Students: perform a first-hand investigation to prepare and test a natural indicator identify data and choose resources to further information about the colour changes of a range of indicators solve problems by applying information about the colour changes of indicators to classify some household substances as acidic, neutral or basic

2. While we usually think of the air around us as neutral, the atmosphere naturally contains acidic oxides of carbon, nitrogen and sulfur. The concentrations of these acidic oxides have been increasing since the Industrial RevolutionStudents learn to: identify oxides of non-metals which act as acids and describe the conditions under which they act as acidsAcidic oxides react with water to form an acid. Eg. CO2 mildly acidic, SO2 and NO2, Most non-metal oxides except for CO, NO and N2O which are neutral. analyse the position of these non-metals in the Periodic Table and outline the relationship between position of elements in the Periodic Table and acidity/basicity of oxidesThe metals in group I & II form basic oxides. The basicity of these oxides increases down the group. Most non-metals other than the noble gasses form acidic oxides. The acidity of the oxide decreases down the group as the elements become more metallic in character. define Le Chateliers principleIf a chemical system at equilibrium experiences a change in concentration, temperature, volume, or partial pressure, then the equilibrium shifts to counteract the imposed change and a new equilibrium is established.Remember for equilibrium to be achieved, the system must be closed. This means chemicals are not being added or removed.At equilibrium, there is no change in macroscopic properties such as colour, temperature, pressure of gases concentration of reactants and products. The only movement is at the microscopic level and the movement of reactants to products is equal to the movement of products to reactants. identify factors which can affect the equilibrium in a reversible reactionAfter time=0, the chemical reaction takes place, the conc of reactants decreases and the conc of product increases with time. After 4 hours, the reaction reached equilibrium. At equilibrium, the rate of the forward reaction is the same as the rate of the reverse reaction so the concentration of reactants and products stay the same.Adding a CatalystThe catalyst speeds up both forward and reverse reactions, allowing the reaction to reach equilibrium faster. The position of the equilibrium doesnt change. At equilibrium, the conc of reactants and products are the same as for uncatalysed reaction.Changing the TemperatureIncreasing the temperature of a reaction mixture speeds up both the forward and reverse reactions.Exothermic(H2O(g) H2O(l) + energy)In exothermic reaction, heat is product. Increasing the temperature of an exothermic reaction favours the formation of reactants. The equilibrium conc of reactants will be higher at higher temperature and the equilibrium conce of products will be lower at higher temperature.Endothermic(energy + H2O(l) = H2O(g))In endothermic reaction, heat is reactant. Increasing the temperature of an endothermic reaction favours the formation of products. The equilibrium conc of products will be higher at higher temperature and the equilibrium conc of reactants will be lower at higher temperature.Change in Concentration(HCl + Mg -> MgCl2 + H2, 2H+ + Mg Mg2+ + H2)When reactants are added, there would be an instantaneous increase in the reactants followed by a readjustment as more products are formed according to Le Chateliers Principle. A new equilibrium position is reached where the conc of reactants and conc of products are more than initially.When pressure or volume is changed in gases, it reaches a new equilibrium position. When the pressure is increased, the reaction moves to the side with less moles and vice versa. If the no. of moles is the same, then the equilibrium position remains the same. When the volume of the system is halved, the concentration increases and a new position is reached where both of conc are greater. When the volume is doubled, the conc decreases by half and new equilibrium is reached that is less than the previous one. describe the solubility of carbon dioxide in water under various conditions as an equilibrium process and explain in terms of Le Chateliers principleCO2 CO2(aq) + H2O(l) H2CO3(aq) H+(aq) + HCO3-(aq)[exothermic]CO2 is acidic oxide, dissolves in water to produce H2CO3. Soft drinks (carbonated) are produced by dissolving CO2 in water at 400 500kpa. The water is supersaturated. When can/bottle is sealed, system stays that way at high CO2 gas pressure. At high pressure, equilibrium moves to the right so more is dissolved, increasing acidity. When uncapped/opened, the equilibrium moves to the left and CO2 comes out of solution, the acidity decreases as less CO2 is dissolved. When adding another acid into the system, the H+ ions of the new acid increases the concentration of H+ ions in solution, pushing the equilibrium left. Therefore, if acid added, then CO2 comes out of solution ie. Goes flat faster.When the temperature is increased, as it is an exothermic reaction, the equilibrium moves to the left according to Le Chateliers principle to reduce the effect. Therefore, as temperature is increased, more gas comes out of solution. Similarly, if the system is cool, then more CO2 is dissolved in solution. identify natural and industrial sources of sulfur dioxide and oxides of nitrogenSulfur DioxideNatural sources 2/3 of SO2 come from natural sources such as volcanoes and hot geothermal springs. Bacteria may decompose organic matter to produce H2S which is oxidises to SO2.Industrial burning of fossil fuels and extraction of metals from sulphide ores (smelting)Oxides of Nitrogen3 main types: Nitrous oxide NO2Nitric oxide NONitrogen dioxide NO2Natural sources lightning N2 (air)> NO2. Combustion in high temperatures bushfires.Industrial sources power stations (combustion and high temperature), cars, trucks. describe, using equations, examples of chemical reactions which release sulfur dioxide and chemical reactions which release oxides of nitrogenSulfur DioxideBurning of coal for electricity. Coal contains sulfur mainly as metallic sulfides (eg. FeS2). When burnt, the sulfur combines with oxygen in the air to form SO2. Some coals have a higher sulfur content than others. Australia has a lower sulfur coal.S in compounds + O2 (g) -> SO2 (g)4FeS2 (s) + 11O2 (g) -> 2Fe2O3 (s) + 8SO2 (g)Crude oil and natural gas also contain sulfur compounds most of which are extracted at the refinery and used to produce sulphuric acid. However, some SO2 is also produced when crude oil products and natural gas are burnt.Metal sulfides are found naturally and used to extract metals. The metal is roasted in air. This produces SO2 and the metal or metal oxide. 2ZnS (s) + 3O2 (g) -> 2ZnO (s) + 2SO2 (g)Bacterial decomposition also produces H2S (rotten egg gas). This oxidises to SO2.2H2S (g) + 3O2 (g) -> 2SO2 (g) + 2H2O(g)

Oxides of Nitrogen (NOx) nitric oxide (NO) a colourless gas, a neutral oxide - nitrogen dioxide (NO2) a brown gas, an acidic oxideLightning at very high temperature generated by lightning, atmospheric oxygen and nitrogen react to produce nitric oxide which then reacts slowly with more atmospheric oxygen to produce nitrogen dioxide.N2 (g) + O2 (g) heat lightning-> 2NO(g)2NO(g) + O2 (g) -> 2NO2 (g)Also in industries where high temperatures are generated. About 86% of total NOx come from vehicle exhausts. NO is formed when nitrogen and oxygen react at high temperatures. NO2 is produced by the oxidation of NO. The rate of NO2 formation depends on the concentration of NO in the air. Up to 10% of total NOx is NO2.NOx is also derived from other sources, including industries, electrical power production and oil refining. Nitrous oxide is produced by certain bacteria. The amount of nitrous oxide produced in this way has increased as nitrogenous fertilizers provide more nitrogen. assess the evidence which indicates increases in atmospheric concentration of oxides of sulphur and nitrogenNote that in Australia NOx and SOx have remained fairly constant over the past decade. It has also stabilised in Europe but is increasing in Asia particularly China due to rapid industrialisation.EvidenceAssess

The effects of acid rain, erosion of marble and limestone buildings, forests and aquatic organisms. This has increased in recent times.This is indirect and qualitative evidence. It is a good indicator of levels of NOx and SOx in the air.

Increase of acidity in lakesNot good evidence. Indirect but quantitative. Might be from other sources like soil, surface runoff or organisms in the lake, not necessary NOx and SOx.

Higher atmospheric concentrations of SO2 and NOx measuredSolid, direct, quantitative. Only started measuring in 1970s, nothing else to compare this evidence to. Not good indicator of increased levels.

Now find higher atmospheric concentrations of SO2 and NOx in industrial areas.Direct and quantitative. But comparison not good for increased levels over time. Difference between industrialised areas and other areas not difference between time frames.

Heavy acidic smogs London 1952, Los Angeles and Tokyo in 1960sVisual pollution, able to be seen. Good evidence, direct and quantitative. Smog wasnt there before, good comparison to times past.

Overall assess:Up until the 1970s, the evidence are all indirect and mostly qualitative. After the 1970s, we start directly measuring the concentration of SOx and NOx, this is quantitative. However, these new quantitative measurements cannot be compared to the qualitative evidence, so the levels of NOx and SOx in the air cannot be certain. calculate volumes of gases given masses of some substances in reactions, and calculate masses of substances given gaseous volumes, in reactions involving gases at 0C and 100kPa or 25C and 100kPa explain the formation and effects of acid rainRain or precipitation that is more acidic than normal rain is referred to as acid rain. Normal rain is slightly acidic because of carbonic acid in the rain, formed with the CO2 in the air. Primarily, moisture in the air react with SO2 and NOx to form H2SO4 and HNO3 acids. The presence of SO2 and NOx in the air can be caused by natural events such as volcanic eruptions, forest fires, lightning bolts and bacterial decomposition. Industries also contribute to this, including power-generating plants, ore smelting, motor vehicles and industrial furnaces.Acid rain can dissolve valuables minerals in the soil. Severe acid rain can damage the protective layer on leaves. Aquatic organisms are affected by the increased acidity in their habitats. Acid rain can also damage man-made buildings and monuments. The food chain can also be affected by bioaccumulation of heavy metals washed into the river by acid rain. Acidic water can dissolve metal piping.

Students: identify data, plan and perform a first-hand investigation to decarbonate soft drink and gather data to measure the mass changes involved and calculate the volume of gas released at 25C and 100kPa analyse information from secondary sources to summarise the industrial origins of sulphur dioxide and oxides of nitrogen and evaluate reasons for concern about their release into the environmentSome industrial sources of SO2 include the burning of coal and natural gas, the refining of crude oil and smelting. NO2 is generated in power stations and car engines, where high temperature and combustion occurs. SO2 contribute greatly to the quality of air. Excessive SO2 in the air can cause respiratory problems. People with asthma can experience symptoms after exposed to SO2 after 10 minutes. In others, SO2 can cause the inflammation of the respiratory tract, induce coughing and muscus. Cardiac problems can also be related to increased levels of SO2. These problems are evident in that on days where the concentration of SO2 in the air is high, more people are admitted to hospitals for cardiac and respiratory problems than days with low concentrations.At a concentration of 200 g/m3, NO2 is a toxic gas. In asthmatic children, high and constant exposure to NO2 is believed to lead directly to increased chances of asthma attacks and bronchitis. Also in children, excessive exposure to NO2 can contribute to reduced lung function or the lung not developing fully. SO2 and NO2 in the air can also react with the water particles in the air to form sulfuric acid, which can precipitate in the form of acid rain. Acid rain can cause damage to buildings, water bodies with changed pH and increase corrosion in places. It is damaging to the environment as the wax protective layers on leaves of plants can be corroded away by acid rain, and also causes deforestation. Changed pH in water bodies can pollute our water sources and affect aquatic life. Small pH changes can cause organism migration and large changes can cause death and abnormalities in some organisms. Acid rain can also change soil acidity, which affects plant growth. Important human monuments can be corroded, especially sandstone structures.The release of SO2 and NO2 into our environment is a large problem and raises concern. Its effects range from affecting the human health, destroying natural habitats, cause organism death and corrode important structures in the world.

3. Acids occur in many foods, drinks and even within our stomachsStudents learn to: define acids as proton donors and describe the ionisation of acids in waterH atom contains 1 proton and 1 electron. H+ is just a proton. A proton and a hydrogen ion are the same and can be represented by H+. An acid is then a proton donor. When acid molecule contacts water, it can ionise and donate a proton to the water molecule.HCl(g) + H2O(l) -> H3O3(aq) +Cl-(aq)Free H+ does not exist in aqueous solution, it forms hydronium ion H3O+.When an acid molecule is placed in water, it can ionise, releasing a proton and forming a negative ion. The proton, H+, can attach to a water molecule, H2O, forming what is called a hydrated hydrogen ion or hydronium ion, H3O+.Note base is a proton acceptor. identify acids including acetic (ethanoic), citric (2- hydroxypropane-1,2,3- tricarboxylic), hydrochloric and sulfuric acidAcetic (ethanoic)

Citric (2- hydroxypropane-1,2,3- tricarboxylic)

describe the use of the pH scale in comparing acids and basesThe pH scale is used to compare the concentration is H+ ions in solutions of acids and bases. The pH scale normally extends from 0-14, where 0 is acidic, 7 is neutral and 14 is basic.If a strong acid has a concentration greater than 1 mol/L, the pH is less than zero. Similarly, a strong base solution with a concentration greater than 1 mol/L has a pH greater than 14. Most solutions lie between pH 0 to 14. There are several methods to estimate pH including litmus paper, universal indicator (combination of indicators) which is observed through colour-change. More precisely, a pH metre is used or a data logger with a pH probe. describe acids and their solutions with the appropriate use of the terms strong, weak, concentrated and diluteConcentrated and dilute acidsThese terms describe the amount of acid dissolved in the solution.Concentrated acid an acid solution that has a high concentration of solute and low solvent.Dilute acid an acid solution that has a low concentration of solute and high solvent.Strong and Weak AcidsThese terms describe the degree of ionisation of the acid molecules.Strong acid an acid that is completely ionised.Weak acid an acid that is not completely ionised. identify pH as -log10 [H+] and explain that a change in pH of 1 means a ten-fold change in [H+]pH = -log [H+]pH01234567891011121314

H+10010-110-210-310-410-510-610-710-810-910-1010-1110-1210-1310-14

A change in pH of 1 means a change in H+ by a factor of 10. compare the relative strengths of equal concentrations of citric, acetic and hydrochloric acids and explain in terms of the degree of ionisation of their moleculesBy comparing the hydrogen ion concentration or the pH of acidic solutions of the same concentration of the degree of ionisation can be calculated. Eg. Acids of equal concentration (0.01molL-1)NameFormula[H+]pH

Hydrochloric AcidHCl0.0102.00

Ethanoic AcidCH3COOH4.1710-143.38

Citric AcidHOOCCH2COHCOOHCH2COOH2.7410-32.56

HCl has the greatest ion concentration and the greatest degree of ionisation. It is the strongest acid. HCl and CH3COOH are monoprotic while citric acid is triprotic. describe the difference between a strong and a weak acid in terms of an equilibrium between the intact molecule and its ionsA strong acid is one that ionises completely. That is, the equilibrium lies to the right. The ions are present in a much higher concentration than the intact molecule. Eg. HCl, HBr, HNO3.A weak acid does not ionise completely. Equilibrium lies to the left. Ions at a lower concentration than the intact molecule. Eg. CH3COOH, citric acid, H2CO3, H2S

Students: solve problems and perform a firsthand investigation to use pH meters/probes and indicators to distinguish between acidic, basic and neutral chemicals plan and perform a first-hand investigation to measure the pH of identical concentrations of strong and weak acids gather and process information from secondary sources to write ionic equations to represent the ionisation of acidsHydrobromicHBr(l) + H2O(l) -> H3O+(aq) + Br (aq)NitricHNO3(l) + H2O(l) -> H3O+(aq) + NO3 (aq) SulfuricH2SO4(aq) + H2O(l) -> H3O+(aq) + H+(aq) + SO42(aq)H3O+ + HSO4 + H2O -> 2H3O+ + SO42Sulfuric acid is a diprotic acid because each molecule can release up to two protons.EthanoicCH3COOH(l) + H2O(l) -> H3O+(aq) + CH3COO(aq)Phosphoric acid is called a triprotic acid because each molecule can release up to three protons.H3PO4 + 3H2O -> 3H3O+ + PO43 use available evidence to model the molecular nature of acids and simulate the ionisation of strong and weak acidsModel kits and pen caps. gather and process information from secondary sources to explain the use of acids as food additivesAcids used to improve taste, make the food sour, drinks and sweetsPreserve food bacteria cant survive in acidic environment eg. Canned fruits and vegetables, picklesPrevents spoilage by oxidation, antioxidantDietary reasons-Vitamin CFood additives

NameFormulaFor

Acetic AcidCH3COOHPreserve food (pickling), flavouring

Citric AcidCH2COOHCOHCOOHCH2COOHFlavouring and preservative (anti-oxidant)

Malic AcidCH2COOHCHOHCOOHFlavouring

Tataric AcidCHOHCOOHCHOHCOOHFlavouring, preservative, antioxidant, rising agent

Lactic acidCH3CHOHCOOHProduction of dairy products

Phosphoric acidH3PO4Acidulation of soft drink, manufacture of cheese

Propanoic acidCH3CH2COOHControls bacteria and mould growth

Ascorbic acid (vitamin C)CH2OHCHOH(C4H3O4)Antioxidant to prevent spoilage, added to increase vitamin C in many foods

identify data, gather and process information from secondary sources to identify examples of naturally occurring acids and bases and their chemical compositionAcids

NameFormulaWhere occur

Citric acidCH2COOHCOHCOOHCH2COOHCitrus fruits, vegetables

Malic AcidCH2COOHCHOHCOOHApples, cherries

Tataric AcidCHOHCOOHCHOHCOOHGrapes and pineapples

Benzoic acidBenzene COOHPrunes, plums cranberries

Bases

NamesFormulaWhere occur

Calcium CarbonateCaCO3Limestone and marble

Calcium magnesium carbonateCaCO3MgCO3dolomite

process information from secondary sources to calculate pH of strong acids given appropriate hydrogen ion concentrations

4. Because of the prevalence and importance of acids, they have been used and studied for hundreds of years. Over time, the definitions of acid and base have been refined outline the historical development of ideas about acids including those of: Lavoisier Davy ArrheniusScientist(s)Acid definitionBase definitionNotesWhy the theory was modified

Lavoisier(1780s)Acids contained oxygen, which made them acidicIt was observed that non-metal oxides reacted with water to form acidic solutionsMetal oxides are not acidic and HCl did not have oxygen.

Davy(1815)Acids all contained hydrogen.Bases react with metals to form salts.Observed known acids contain H that could be replaced by metal. 1830, 10 more acids with no H discovered.Doesnt explain why substances without H are acidic.

ArrheniusAn acid produces H+ ions when dissolved in waterA base produced OH- when dissolved in water Observed in electrolysis on acids that H2 produced at cathode, therefore must contain ions. Thought stronger acids ionised more than weak acids. This theory explains neutralisation, the OH- and H+ forms water. Interpreted property of acids.The theory is too restrictive and doesnt allow for other solvent. Narrow definition of bases doesnt allow for basic metal salts and acidic non-metal salts.Doesnt explain amphoteric substances.

outline the Brnsted-Lowry theory of acids and basesIndependently but simultaneously proposed that acids are proton donors and bases are proton acceptors. Acid if it has greater tendency to give protons than solvent. Base if has greater tendency to accept proton than solvent.The Acidic Environment2013

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HA + H2O => H3O+ + A-HCl(g) + H2O(l) => H3O+(aq) + Cl-(aq)B + H2O => HB+ + OH-NH3(g) + H2O(l) => NH4+(aq) + OH-

Includes effect of solvent, applies to non-aqueous solutions too. Explains why some salts act as acids and others act as bases and how some substances are amphoteric. In this theory, every acid has a conjugate base. An acid or a base can be an ion. To be an acid, substance must contain H atom.Eg. H2O(l) + H2O(l) => H3O+(aq + OH-(aq)Acidity doesnt depend on the structure of the substance butt on its properties relative to those of the solvent or other reactant in the solution. Hydrolysis of salts that produce pHs different from 7 is acid/base reaction. describe the relationship between an acid and its conjugate base and a base and its conjugate acidConjugate means to be linked with something, so a conjugate base is the base linked with the acid and vice versa. In the Bronsted-Lowry theory, every acid has a conjugate base that has the same formula but one less proton and therefore one less charge than the acid. Every base has a conjugate acid that has one more proton and one more change than its base. HCl + H2O => H3O+ + Cl-NH3 + H2O NH4+ + OH-CH3COOH + H2O H3O+ + CH3COO-CO32- + H2O HCO3- + OH- identify a range of salts which form acidic, basic or neutral solutions and explain their acidic, neutral or basic natureSalts are formed when acids react with bases. A salt is an ionic compound formed from a cation other than H+ and an onion other than OH- or O2-. The pH of aqueous salt solutions is not always 7. Some salts form basic solutions and are called basic salts. Other form acidic solutions and are acidic salts and those that are neutral form neutral solutions. The Bronsted-Lowry theory provides the explanation for this. It is because many of the anions or cations can act as acids or bases. Hydrolysis is a Bronsted-Lowry reaction of an ion with water to give excess H+ or OH-. Basic Anions:Hydrolysis of basic anions:CH3COO-(aq) + H2O CH3COOH + OH-CN- + H2O HCN + OH-HCO3- + H2O H2CO3 + OH-CO32- + H2O HCO3- + OH-Basic anions are those that react with water to form OH-. The presence of OH- results in basic solution. Basic anions are from weak acids. Only small amount of basic anion reacts with water because acid formed is stronger than water.

Acidic Anions: (typically contain H+ and are conjugate bases of strong acids)HSO4- + H2O SO42- + H3O+HCO3- is basic as it more readily accepts protons than donates them. It comes from a weak acid.

No Basic Cations

Acidic Cations NH4+ + H2O NH3 + H3O+Equilibrium lies to the left because H3O+ stronger acid than NH4+ and NH3 is stronger base than H2O. Final solution is mildly acidic.

Generally:Strong acid + Strong base => Neutral Salt + waterWeak acid + Strong base => Basic Salt + waterStrong acid + Weak base => Acidic Salt + waterWeak acid + Weak base => Neutral salt + water identify conjugate acid/base pairsAcidConjugate Base

HClCl-

HNO3NO3-

H2SO4HSO4-

HSO4-SO4-

NH4+NH3

CH3COOHCH3COO-

H2OOH-

BaseConjugate Acid

OH-H2O

H2OH3O+

CN-HCN

NH3NH4+

S2-HS-

CO32-HCO3-

Strong acids have weak conjugate bases. Moderately weak acids have moderately weak conjugate bases. Weak acids have strong conjugate bases.

Strong Acids: HCl, H2SO4, HNO3Weak Acids: CH3COOH, HNO2, H2CO3, HFStrong Bases: NaOH, KOHWeak Bases: NH3, NH4OH identify amphiprotic substances and construct equations to describe their behaviour in acidic and basic solutions identify neutralisation as a proton transfer reaction which is exothermic describe the correct technique for conducting titrations and preparation of standard solutionsA titration is an experimental procedure that mixes a solution of known concentration and a solution of unknown concentration until they neutralise. The concentration of the second solution can then be calculated. It is a quantitative volumetric analysis.Primary Standard SolutionRequirements: Have a known formula and be very pure Should not absorb or lose moisture from or to the air Soluble Relatively high formula mass to minimise weighing errors HCl and H2SO4 unsuitable as conc. Varies from batch to batch. NaOH unsuitable as absorbs water Na2CO3 used for basic and Oxalic acid used for acidic1. Weigh out exact amount of solid using electronic balance (heat to remove water)2. Place solid in a beaker and mix with distilled water3. Pour solution into a volumetric flask with a funnel4. Rinse beaker and funnel with distilled water in a wash bottle so all solution goes into the flask5. Fill the flask up to exactly 250ml6. Shake/invert the volumetric flash so the mixture is well mixed7. Place the stopper on the flask when storing to prevent evaporation

Titration1. Rinse a conical flask with distilled water, a bulb pipette with primary standard and the burette with secondary standard2. Draw out exactly 25ml of primary standard with pipette and place in conical flask3. Add 3 drops of suitable indicator and swirl4. Fill the burette with secondary standard and record initial reading5. Drip secondary standard into the conical flask whilst swirling the flask to mix6. Once the indicator changes colour, stop the burette immediately7. Read and record the final burette reading8. Calculate

IndicatorsStrong Acid + Strong Base use Bromothymol Blue (6.2 7.6)Strong Acid and Weak Base use Methyl Orange (3.1 4.4)Weak Acid and Strong Base use Phenophthaline (8.3 10.0)Weak Acid and Weak Base use Data Logger and change is too gradual to be seen qualitatively describe the effect of buffers with reference to a specific example in a natural systemA buffer is an aqueous solution that resists a change in pH when a small amount of a strong acid or strong base is added to it. It contains equal amounts of a weak acid and its conjugate base and is made by mixing equal parts of a weak acid and a salt of that acid or a weak base and a slat of that base.Note Just a weak acid on its own does not make a buffer because it will not dissociate enough to provide enough to provide enough basic ion so it is a mixture of a weak acid and a salt of that weak acid or a weak base and the salt of that weak.

Eg. Acetic acid and sodium acetate. pH around 4.6CH3COOH(aq) + H2O(l) CH2COO- + H3O+ [eq1]

This is possible because the weak acid and base are at equilibrium. When acid or H+ (H3O+) are added they react with the weak base to form more of its conjugate acid and the equilibrium shifts towards the weak acid right. Thus buffer resists the change in pH by removing strong acid from the solution.When more base or OH- are added then they react with the weak acid to form its conjugate base and the equilibrium moves to the left. Thus buffer has resisted the change in pH by removing strong base from the solution.H3O+ + CH3COO- => CH3COOH(aq) + H2O(l) [eq2 acid added, reverse of eq1]CH3COOH(aq) + OH- => CH3COO- + H2O(l) [eq3 base added, this is forward reaction of eq1]Because acetic acid is a weak acid, a change in the amount of acid present only producs a very small change in the hydrogen ion concentration and therefore there is only a small change in the pH.

Biological SystemsLiving things contain enzymes that are used to control metabolic rates of reaction. Enzymes are pH sensitive and so need to be at their optimum pH for metabolism. The pH in the body is maintained by buffers.Specific Example (learn equations)Blood is a buffered solution with a pH of 7.4 that maintains the pH of the blood between 7.35 and 7.45.When CO2 dissolves in the blood it forms carbonic acid, which ionises to form carbonate and H+. This happens as CO2 diffuses from the cells into the blood.CO2 (g) + H2O(l) H2CO3 (aq)H2CO2 (aq) H+(aq) + HCO-2 (aq)If more CO2 is added then more H+ ions will form, lowering the pH, but the equilibrium will move to the left to minimise the change.When CO2 leave the blood at the surface of the lungs the pH become higher but the equilibrium will move to the right to minimise the change.Students: gather and process information from secondary sources to trace developments in understanding and describing acid/base reactions choose equipment and perform a first-hand investigation to identify the pH of a range of salt solutions perform a first-hand investigation and solve problems using titrations and including the preparation of standard solutions, and use available evidence to quantitatively and qualitatively describe the reaction between selected acids and bases perform a first-hand investigation to determine the concentration of a domestic acidic substance using computer-based technologiesAttached Sheet analyse information from secondary sources to assess the use of neutralisation reactions as a safety measure or to minimise damage in accidents or chemical spillsAcids and bases are corrosive and if these chemicals are spilt, they must be cleaned up quickly before damages are done to spilt surfaces. Neutralisation is one way to minimise this damage. However, neutralisation is an exothermic reaction that can generate a lot of heat if a strong acid and a strong base is reacted together. Firstly, the spill is contained and soaked up with sand or vermiculite, it is then transported to a suitable location. For safety reasons, acids and bases should be weak ones or diluted ones before they are reacted together and a large amount of water needs to be present when reacting them together. For acid spillages, excess bases are added such as sodium carbonate:Na2CO3(s) + 2HCl(aq) => 2NaCl(aq) + H2O(l) + CO2(g)Sodium carbonate is a good base to use for acid spills as it is cheap, easy to clean up afterwards and does not pose a danger if used in excess. For spilt bases, weak acids are often used such as vinegar or benzoic acid and sometimes very dilute HCl or H2SO4NaHCO3(s) + NaOH(aq) => Na2CO3(aq) + H2O(l)Sodium hydrocarbonate is a very good neutraliser for both acids and bases as it is amphiprotic. Sodium hydrogen phosphate is also amphiprotic. Neutralisation reactions are exothermic reactions that produce some amount of heat, therefore, are not suitable to use for spillages onto the skin. If spilled onto skin, flush with water.Safety precautions that use neutralisation reactions include neutralising effluent discharges by factories into sewers. The government has strict regulations on the pH of effluents released into the sewer as a change of pH may affect the bacterial breakdown in the sewers.

5. Esterification is a naturally occurring process which can be performed in the laboratory describe the differences between the alkanol and alkanoic acid functional groups in carbon compoundsA functional group is an atom or group of atoms that reacts in a characteristic way in different carbon compounds.Alkanols (Alcohol)Alkanoic Acids

Functional GroupHydroxyl group(OH)Carboxyl Group(COOH)

General FormulaCnH2n+1OHROH where the R is the alkyl groupCnH2n+1COOHRCOOH where R is the alkyl group

Acid/BaseNeutralNot readily lose OH or HAcidIt can donate a proton, weak acid

SolublityOH group is polar, solubleForm hydrogen bonds in waterCOOH is polar, soluble, H-bond

PolarityPolar due to OH groupMore polar than alkanol because of COOH

MP and BPHigher MP or BP then similar alkane or alkene due to H-Bonding.Note: Alkane, alkene have weak dispersion forceHigher MP and BP than similar alkanol as it has more H-bonding.

identify the IUPAC nomenclature for describing the esters produced by reactions of straight-chained alkanoic acids from C1 to C8 and straight-chained primary alkanols from C1 to C8To name an ester the alkanol name with the ending changed from anol to yl then the acid name with the oic changed to oate explain the difference in melting point and boiling point caused by straight-chained alkanoic acid and straight-chained primary alkanol structuresStraight-chained means no branches on the hydrocarbon chainPrimary alkanol means the OH group is at the end of the hydrocarbon chain

The high MP and BP in alkanols is due to H-boning between the O in one molecule and the H of an OH in a nearby molecule.

The ability of the COOH group to be involved in two hydrogen bonds gives an alkanoic acid an even higher boiling point than that of a similar sized alkanol. Two h-bonds can occur between a pair of alkanoic acid molecules.

identify esterification as the reaction between an acid and an alkanol and describe, using equations, examples of esterificationAn acid, containing the COOH group can react with an alkanol, containing the OH group, to produce ester and water.

Eg Ethanoic acid and ethanol

The O in the water comes from the acidThe reaction is reversible and comparable quantities of alkanol, acid, ester and water are present at equilibrium. describe the purpose of using acid in esterification for catalysis explain the need for refluxing during esterificationEsterification is the reaction between an alkanol and an alkanoic acid. (example of condensations reaction, water condenses out) It is also an equilibrium reaction. It is a moderately slow reaction at room temperature. To speed up the reaction, a catalyst (concentrated H2SO4) is used and the reaction is heated. The H2SO4 also acts as a dehydrating agent, absorbing the water and forcing the equilibrium to the right, resulting in a higher yield.Heating the reaction speeds up the reaction but the volatile alcohol could escape. To prevent this, a condenser is placed on top of the flask so that any volatile components are cooled by the water in the condenser and runs back into the reaction. This is refluxing. Refluxing also improves the safety of the operation as the vapours are flammable.Because of the volatility, the reaction is carried out in a water bath and often on an electric hot plate. (if reflux is done correctly, there should be no vapour escaping, dont put as answer)Boiling chips are added for a greater surface area for the reason to boil, preventing bumping.The flask is not stoppered to prevent a build-up of pressure due to vapourisation. The reaction can be carried out in a fume cupboard to prevent inhalation and safety glasses are worn. The reaction can still take several hours to reach equilibrium. outline some examples of the occurrence, production and uses of estersEster3-methylbutyl ethanoate(or pentyl ethanoate)Benzyl ethanoate

Where OccurAlso known as Banana oilNaturally in the banana plant

Can be produced syntheticallyFound naturally in flowers (jasmine, ylang-ylang)

Sweet aroma used in perfume, candlesSolvent in plastics, resin, oils, lacquers

Equations(CH3)2CHCH2CH2OH + CH3COOH => CH3COOCH2CH2CH(CH3)2

3-methyl butan-1-ol + Ethanoic Acid => 3methylbutyl ethanoate

[sulphuric acid is catalyst]C6H5CH2OH + CH3COOH => C6H5CH2OOCCH3

Benzyl Alcohol + Ethanoic Acid => Benzyl Acetate

[sulphuric acid catalyst]

UseBanana food flavouringJasmine/peach scented deodorants and perfumes

Students: identify data, plan, select equipment and perform a first-hand investigation to prepare an ester using reflux process information from secondary sources to identify and describe the uses of esters as flavours and perfumes in processed foods and cosmeticsSee above