DOCSLIB.ORG

Class X Ch.3 Acid Base and Salt

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Class X Ch.3 Acid Base and Salt Class x ch.3 Acid base and salt An acid is defined as a substance whose water solution tastes sour, turns blue litmus red and neutralizes bases. A substance is called base if its aqueous solution tastes bitter, turns red litmus blue or neutralizes acids. Salt is a neutral substance whose aqueous solution does not affect litmus solution Salts that Produce Basic Solutions When dissolved in water, a basic salt yields a solution with pH greater than 7.0. LEARNING OBJECTIVES Distinguish basic salts from non-basic salts KEY TAKEAWAYS Key Points In acid – base chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. Basic salts contain the conjugate base of a weak acid, so when they dissolve in water, they react with water to yield a solution with pH greater than 7.0. Key Terms basic salt: the product of the neutralization of a strong base and a weak acid; its anion is the conjugate base of the weak acid In acid-base chemistry, a salt is defined as the ionic compound that results from a neutralization reaction between an acid and a base. As such, salts are composed of cations (positively charged ions ) and anions (negative ions), and in their unsolvated, solid forms, they are electrically neutral (without a net charge). The component ions in a − − salt can be inorganic; examples include chloride (Cl ), the organic acetate (CH3COO ), − 2− and monatomic fluoride (F ), as well as polyatomic ions such as sulfate (SO4 ). The Reaction of a Basic Salt in Water There are several varieties of salts, and in this section we will consider basic salts. What makes a basic salt basic? It is due to the fact that the anion in the salt is the conjugate base of a weak acid. For a generalized anion B–, the net ionic reaction is: B−(aq)+H2O(l)⇌BH(aq)+OH−(aq)B−(aq)+H2O(l)⇌BH(aq)+OH−(aq) An example of a basic salt is sodium bicarbonate, NaHCO3. The bicarbonate ion is the conjugate base of carbonic acid, a weak acid. Therefore, it reacts with water in the following fashion: HCO−3(aq)+H2O(l)⇌H2CO3(aq)+OH−(aq)HCO3−(aq)+H2O(l)⇌H2CO3(aq)+OH−(aq ) Because it is capable of deprotonating water and yielding a basic solution, sodium bicarbonate is a basic salt. Other examples of basic salts include: Calcium carbonate (CaCO3) Sodium acetate (NaOOCCH3) Potassium cyanide (KCN) Sodium sulfide (Na2S) Notice that for all of these examples, the anion is the conjugate base of a weak acid (carbonic acid, bisulfate (second dissociation step of sulfuric acid), acetic acid, hydrocyanic acid, hydrogen sulfide). Conjugate Bases of Weak vs. Strong Acids Keep in mind that a salt will only be basic if it contains the conjugate base of a weak acid. Sodium chloride, for instance, contains chloride (Cl–), which is the conjugate base of HCl. But because HCl is a strong acid, the Cl– ion is not basic in solution, and it isn’t capable of deprotonating water. Sodium Bicarbonate: Because the bicarbonate ion is the conjugate base of carbonic acid, a weak acid, sodium bicarbonate will yield a basic solution in water. Salts that Produce Acidic Solutions When dissolved in water, acidic salts form solutions with pH less than 7.0. LEARNING OBJECTIVES Explain the formation of acid salts and their effects on a solution’s pH. KEY TAKEAWAYS Key Points Acid salts contain a hydrolyzable proton in the cation, anion, or both; for instance, the salt ammonium bisulfate (NH4HSO4) contains an acidic proton in both the cation and the anion. To determine the acidity / alkalinity of a hydrolyzable anion, compare the Ka and Kb values for the ion; if Ka > Kb, the ion is acidic; if Kb > Ka, the ion is basic. Key Terms acid salt: a salt that yields a solution with pH less than 7.0 hydrolyzable: capable of dissociating in water Salts With a Hydrolyzable Cation When dissolved in water, acidic salts will yield solutions with pH less than 7.0. This is due either to the presence of a metal cation that acts as a Lewis acid (which will be discussed in a later concept), or, quite commonly, due to a hydrolyzable proton in the cation or the anion. Salts with acidic protons in the cation are most commonly ammonium salts, or organic compounds that contain a protonated amine group. Examples include: + ammonium (NH4 ) + methyl ammonium (CH3NH3 ) + ethyl ammonium (CH3CH2NH3 ) + anilinium (C6H6NH2 ) An example of an acid salt is one containing any of these cations with a neutral base, such as ammonium chloride (NH4Cl). Salts With Hydrolyzable Protons in the Anion Acid salts can also contain an acidic proton in the anion. Examples of anions with an acidic proton include: – bisulfate (HSO4 ) – dihydrogen citrate (H2C6H5O7 ) – bioxalate (HO2C2O ) Each of these anions contains a proton that will weakly dissociate in water. Therefore, salts containing these anions—such as potassium bisulfate—will yield weakly acidic solutions in water. Determining Acidity or Alkalinity of a Hydrolyzable Ion – From the previous concept, we know that salts containing the bicarbonate ion (HCO3 ) – are basic, whereas salts containing bisulfate ion (HSO4 ) are acidic. We determine whether the hydrolyzable ion is acidic or basic by comparing the Ka and Kb values for the ion; if Ka > Kb, the ion will be acidic, whereas if Kb > Ka, the ion will be basic. Anilinium chloride: Anilinium chloride is an example of an acid salt. The NH3+ group contains an acidic proton capable of dissociating in solution; therefore, a solution of anilinium chloride in pure water will have a pH less than 7. Overview of the Acid-Base Properties of Salt Some salts, such as ammonium bicarbonate (NH4HCO3), contain cations and anions that can both undergo hydrolysis. LEARNING OBJECTIVES Predict the pH of a solution of a salt containing cations and anions, both of which participate in hydrolysis. KEY TAKEAWAYS Key Points Basic salts result from the neutralization of a strong base with a weak acid. Acid salts result from the neutralization of a strong acid with a weak base. For salts in which both cation and anion are capable of hydrolysis, compare Ka and Kb values to determine the solution ‘s resulting pH. Key Terms neutralization reaction: a reaction between an acid and a base in which water and a salt are formed hydrolysis: a reaction with water in which chemical bonds break salt: in acid-base chemistry, one of the products in a neutralization reaction Summary of Acidic and Basic Salts As we have discussed, salts can form acidic or basic solutions if their cations and/or anions are hydrolyzable (able to react in water). Basic salts form from the neutralization of a strong base and a weak acid; for instance, the reaction of sodium hydroxide (a strong base) with acetic acid (a weak acid) will yield water and sodium acetate. Sodium acetate is a basic salt; the acetate ion is capable of deprotonating water, thereby raising the solution’s pH. Acid salts are the converse of basic salts; they are formed in the neutralization reaction between a strong acid and a weak base. The conjugate acid of the weak base makes the salt acidic. For instance, in the reaction of hydrochloric acid (a strong acid) with ammonia (a weak base), water is formed, along with ammonium chloride. The ammonium ion contains a hydrolyzable proton, which makes it an acid salt. Salts in Which Both Ions Hydrolyze The following is a more complicated scenario in which a salt contains a cation and an anion, both of which are capable of participating in hydrolysis. A good example of such a salt is ammonium bicarbonate, NH4HCO3; like all ammonium salts, it is highly soluble, and its dissociation reaction in water is as follows: NH4CO3(s)→NH+4(aq)+HCO−3(aq)NH4CO3(s)→NH4+(aq)+HCO3−(aq) However, as we have already discussed, the ammonium ion acts as a weak acid in solution, while the bicarbonate ion acts as a weak base. The reactions are as follows: NH+4(aq)+H2O(l)⇌H3O+(aq)+NH3(aq)Ka=5.6×10−10NH4+(aq)+H2O(l)⇌H3O+(aq)+N H3(aq)Ka=5.6×10−10 HCO−3(aq)+H2O(l)⇌H2CO3(aq)+OH−(aq)Kb=2.4×10−8HCO3−(aq)+H2O(l)⇌H2CO3(a q)+OH−(aq)Kb=2.4×10−8 Because both ions can hydrolyze, will a solution of ammonium bicarbonate be acidic or basic? We can determine the answer by comparing Ka and Kb values for each ion. In this case, the value of Kb for bicarbonate is greater than the value of Ka for ammonium. Therefore, bicarbonate is a slightly more alkaline than ammonium is acidic, and a solution of ammonium bicarbonate in pure water will be slightly basic (pH > 7.0). In summary, when a salt contains two ions that hydrolyze, compare their Ka and Kb values: If Ka > Kb, the solution will be slightly acidic. If Kb > Ka, the solution will be slightly basic. .
Load more

Recommended publications
  • CO2 Capture from Flue Gas Using Amino Acid Salt Solutions
    CO2 capture from flue gas using amino acid salt solutions Jacco van Holst, Patricia. P. Politiek, John P. M. Niederer, Geert F. Versteeg* University of Twente, Faculty Science and Technology (UT TNW), P.O. Box 217, 7500 AE Enschede, The Netherlands Abstract An initial kinetic study was performed on the reaction of CO2 with various potassium amino acid salt solutions at 298 K. Kinetics were measured at 0.5 kmol/m3, reason for which only apparent ki- netic constants are presented. The results were compared with the work of Kumar et al. [1] and Penny and Ritter [2]. Keywords: CO2, flue gas treatment, kinetics, potassium amino acid salt solutions Introduction One of the most alarming global environmental problems of today is the increase of the natural greenhouse effect. This problem is mainly caused by the increasing atmospheric carbon dioxide concentration due to the burning of fossil fuels for power generation. To reduce these problems, the carbon dioxide emissions from flue and fuel gases produced in combustion and gasification proc- esses in power plants have to be decreased by efficiency improvements and carbon dioxide capture. The removal of acid gases such as carbon dioxide, H2S or COS by absorption in aqueous alkanola- mine solutions is widely used in the chemical industry. Carbon dioxide reacts with primary and sec- ondary amines, reaching an equilibrium of carbamate, bicarbonate, and carbonate species. The ini- tial absorption reaction is the formation of the carbamate, which can then undergo hydrolysis to the bicarbonate and, if conditions such as pH are suitable, the carbonate species. The degree of hydroly- sis of the carbamate is determined by parameters such as amine concentration, solution pH, and the chemical stability of the carbamate [3].
    [Show full text]
  • SALTS of FATTY ACIDS
    SALTS of FATTY ACIDS Prepared at the 33rd JECFA (1988), published in FNP 38 (1988) and in FNP 52 (1992). Metals and arsenic specifications revised at the 55th JECFA (2000). An ADI 'not specified' was established at the 33rd JECFA (1988) SYNONYMS INS No. 470 DEFINITION These products consist of calcium, potassium or sodium salts of commercial myristic, oleic, palmitic, stearic, acids or mixtures of these acids from edible fats and oils. The article of commerce can be further specified by: - saponification value, - solidification point for the fatty acids obtained from the salts, - iodine value, - residue on ignition including assay of the cation, and - moisture content Assay Not less than 95% total fatty acid salts, dry weight basis DESCRIPTION Hard, white or faintly yellowish, somewhat glossy and crystalline solids or semi-solids or white or yellowish-white powder FUNCTIONAL USES Anticaking agent, emulsifier CHARACTERISTICS IDENTIFICATION Solubility (Vol. 4) Potassium and sodium salts are soluble in water and ethanol; calcium salts are insoluble in water, ethanol and ether Test for cations Heat 1 g of the sample with a mixture of 25 ml of water and 5 ml of hydrochloric acid. Fatty acids are liberated, floating as a solid or oil layer on the surface which is soluble in hexane. After cooling, aqueous layer is decanted and evaporated to dryness. Dissolve the residue in water and test for the appropriate cation. Fatty acid composition Using the Method of Assay, identify the individual fatty sample. The fatty acid(s) in primary abundance should conform to those declared on the label of the product PURITY Free fatty acids Not more than 3% Measure free fatty acids as directed in the method Free Fatty Acids.
    [Show full text]
  • DP70460.Pdf (4.893Mb)
    HEAT CHAHGES ACCGKPABYIIJG ABSGRFTIOH EQUILIBRIA IB SOLTJTIQH. D. C. UCETSBVAUfER C h e w . LD Sill ,/V\7 od L VVC\ I If) <2 D-C. C o ' :o Thesim submitted to the Faculty of the Graduate School of the TJnivsrsity of Maryland in partial fulfillment of the requirements for the degree of Doctor of Phil­ osophy* A 1 9 fc 6 .. UMI Number: DP70460 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI DP70460 Published by ProQuest LLC (2015). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 ACKHQWLXDGMEHT The writer wishes to express hie appreciation and thaiifcs to Dr* Hell S. Gordon, Head of the Depart­ ment of Chemistry of the University of Maryland who dlreetcd this work and gate helpful suggestions and advice* TABLE OF G CH U M S X* Introduct 1 q h -—-*——— «*►»»««*«*»*«»»*— «■»»*-«««»»» x . Historical He view-----— ----- —■—— — — Z Heat of Absorption of Liquids art Gases- 1 4 Heat of Coagulation --- -- ™ -i^ * General Methods and Materials--— — — — — 2H of G els— 38H ----- - --- — ;S6 ------ Froeebnre——— ——-——32 If# Experiiaenial Hes’nlts-— --— — — — — ---- g*> T. Hubimavy C oixdua i OHS— —— — -— —— 61 FX* Lit eratare Gi ted :——— Introduction Adscript ion has for a long time teen a well recognised phenomenon and numerous investigations have been mad® on the nature and magnitude of the energy changes involved* Some of the measurementa on the adsorption of gases have shown ti&se changes to be enormous.
    [Show full text]
  • United States Patent Office Patented July 18, 1972 1
    3,677,770 United States Patent Office Patented July 18, 1972 1. 2 It will be apparent that those fusible sugars which may 3,677,770 be employed have a melting or fusion point below their CARBONATED CANDY Frank Witzel, Spring Valley, N.Y., assignor to decomposition temperature, and that no substantial de Beech-Nut, Inc., New York, N.Y. composition occurs at the melting or fusion temperature No Drawing. Filed Oct. 7, 1970, Ser. No. 78,910 which would interfere with fusion, melting, or solidifica Int, Cl, A23g 3/00 tion on cooling. U.S. C. 99-134 R 2 Claims Although as will be apparent from this disclosure, the fusible sugars which may be used in the practice of this invention include those which have a melting or fusing ABSTRACT OF THE DISCLOSURE 0 point which falls within a wide range, the preferred mate rials will be those having a melting or fusing point at The off-taste present in effervescent hard candy due to temperatures of from slightly above room temperature unreacted food acidulant as well as salt formed by the to about 300 F. (149 C.). reaction of the efferverscent factors, i.e., leavening agent The fusible sugars which may be employed in the prac and acidulant, is overcome by incorporating a small tice of this invention include sugars and their derivatives amount of a saccharin into the candy. such as sugar alcohols and sugar acids. Typical fusible monosaccharide sugars include glucose, fructose (levu lose), invert sugar (chemically equal parts of glucose BACKGROUND OF THE INVENTION and fructose), arabinose, etc.
    [Show full text]
  • Metals and Acids Key Revision Facts • to Test for Hydrogen Gas- Place a Lighted Spill Near the Gas and Hear a ‘Squeaky Pop’
    Metals and Acids Key Revision Facts • To test for hydrogen gas- place a lighted spill near the gas and hear a ‘squeaky pop’. • Potassium, sodium and magnesium are all examples of reactive metals. • Copper, lead and gold are all examples of unreactive metals. • When reactive metals are placed in acids they will react violently with lots of gas given off. Unreactive metals do not react with the acid. • The equation for the reaction between a metal and an acid is: metal + acid salt + hydrogen Zn + HCl sZnCl + H • State symbols Solid (s) Liquid (l) Gas (g) Aqueous - a substance dissolved in water (aq) • Magnesium and iron filings react vigorously with air • Group 1 metals react with water to produce hydroxides and hydrogen. • sodium + water sodium hydroxide + hydrogen • Some metals like magnesium react slowly with cold water but will react quickly with steam. • The reactivity series lists in order, how reactive metals are: K Potassium Most reactive Na Sodium Ca Calcium Mg Magnesium Al Aluminium Zn Zinc Fe Ferum Increasingly reactive Sn Tin Pb Lead Cu Copper Hg Mercury Ag Silver Least Au Gold reactive Metals and Acids Key Revision Facts • A more reactive metal will displace a less reactive metal from its compound for example • Magnesium + copper sulphate Magnesium sulphate + copper • Metals below carbon in the reactivity series can be extracted from its ore by heating it with carbon • Ceramic materials are compounds for example silicates and metal oxides • Polymers are long chain molecules. • Wool is an example of a natural polymer. • Polyethene is an example of a synthetic polymer.
    [Show full text]
  • Ph Calculations
    03.10.2018 pH calculations MUDr. Jan Pláteník, PhD Brønsted-Lowry concept of acids and bases • Acid is a proton donor • Base is a proton acceptor + - HCl(aq) + H 2O(l) H3O (aq) + Cl (aq) Acid Base Conjugate Conjugate acid base + - H2O(l) + NH 3(aq) NH 4 (aq) + OH (aq) AcidBase Conjugate Conjugate acid base 1 03.10.2018 Which of the following are conjugate acid-base pairs? A) HCl, NaOH - B) H 2O, OH 2- C) H 2SO 4, SO 4 - D) H 2SO 3, HSO 3 - E) HClO 4, ClO 3 + F) H 3C-NH 2, H 3C-NH 3 Autoionization of water Water is amphoteric as it can behave both as acid and base + - 2 H 2O(l) H3O (aq) + OH (aq) Ion-product constant for water: + - + - Kw = [H3O ][OH ] = [H ][OH ] In pure water at 25 ºC: [H +] = [OH -] = 1.0 × 10 -7 mol/L -7 -7 -14 2 2 Kw = (1.0 × 10 mol/L)×( 1.0 × 10 mol/L) = 1.0 × 10 mol /L Constant! 2 03.10.2018 pH Activity = f . c + pH= -log 10 (activity of H ) f is activity coefficient, pOH= -log (activity of OH -) f<1, 10 c is molar concentration Ion-product of water (constant!): pH + pOH = 14 E.g.: pH=7 (neutral): [H +] = 10 -7 M = 0.0000001 mol/L pH=1 (acidic): [H +] = 10 -1 M = 0.1 mol/L pH=13 (alkaline): [H +] = 10 -13 M = 0.0000000000001 mol/L Strong acid E.g. HCl, HNO 3, H 2SO 4 In aqueous solution fully dissociates to H + and A − pH of strong acid can be calculated as pH = −log (f × [H +]) For HCl: [H +]= [HCl] + For H2SO 4: [H ]= ~ [H2SO 4] nd + -2 (2 H does not fully dissociate, Kd= ~10 ) 3 03.10.2018 Calculating the pH of strong acid solutions Example: Calculate the pH of 0.06 mol/L HCl.
    [Show full text]
  • Understanding Acidity of Molten Salt Hydrate Media for Cellulose
    Understanding Acidity of Molten Salt Hydrate Media for Cellulose systems, which indicate that the main effect of a salt on the rate stems from the effect on the Hydrolysis by Coupling Kinetic Studies, Electrolyte Solution Modeling, acidity rather than catalytic properties of the ions. Prior investigations suggest that in addition to 13 the nature of the salt, the mineral acid used to acidify the MSH plays a key role in cellulose and C-NMR Experiments dissolution and reactivity.[1,6] It has been proposed that a synergistic effect between LiBr and H2SO4 renders this system more reactive than HCl acidified MSH. Similar to the effect of the Natalia Rodriguez Quiroz, Dionisios G. Vlachos* salt, we found that the effect of different acids on the reactivity could be attributed to their effect Chemical and Biomolecular Engineering Department, University of Delaware, on the overall acidity. However, as seen in Figure 2b, different acid-salt pairs will result in a 150 Academy St., Newark, DE 19716 (USA) different acidity based on (1) the strength of the acid that will contribute to the initial proton *[email protected] concentration (2) the interactions between the salt and the acid that can affect the speciation of the acid in solution and therefore the proton concentration. Lastly, we assessed the calculated pH values in concentrated LiBr solutions experimentally by extending the 13C-NMR method Introduction developed by Farcasiu[7] for the calculation of Hammett acidity of super acids, to concentrated Homogeneous chemo-catalytic systems play an important role in biomass upgrading. inorganic salt solutions. Figure 2c shows good agreement between the OLI calculated pH and Recently, the depolymerization of lignocellulosic biomass in concentrated metal salts and more the experimentally measured pH in different salt solutions.
    [Show full text]
  • The Preparation and Properties of the Neutral Ammonium Salts of Organic Acids
    742 LEROY MCMASTER. is seen to be 12.2, in good agreement with Kopp’s number. The atomic volume of divalent carbon in the carbon monoxide is 23. It is interest- ing to note that, if acetylene be assumed to have a divalent and a tetra- valent carbon atom, i. e., the acetylidene structure, its atomic volume agrees exactly with that found experimentally. We have endeavored to produce addition compounds of acetylene and hydrobromic at low temperatures. Acetylene is quite soluble in this acid, but solutions containing even 50% of acetylene show no tendency to pre- cipitate compounds at temperatures as low as -115’. With liquids having high vapor pressures at their freezing points, such as hydrobromic and hydriodic acid, but particularly with acetylene, the phenomenon of freezing and boiling occurring simultaneously is shown in a striking way. Liquid acetylene in a sealed tube can be supercooled about 5’. As crystallization takes place the remaining liquid boils furiously. MCGILLUNIVERSITY. [CONTRIBUTIONFROM THE CHEMICALLABORATORY OF WASHINGTONUNIVERSITY. ] THE PREPARATION AND PROPERTIES OF THE NEUTRAL AMMONIUM SALTS OF ORGANIC ACIDS. BY LEROYMCMASTER. Received January 31, 1914. As stated in two previous papers,’ most of the ammonium salts of organic acids described in the literature are the acid salts instead of the neutral salts Many of the “neutral” salts purchased have also been found to be “acid.” This is due to the fact that they have been pre- pared by neutralizing the aqueous solution of the organic acid with am- monia water or ammonium carbonate and the solution allowed to evaporate to crystallization. The salts thus formed are generally hydrolyzed and the acid salt results.
    [Show full text]
  • Final Copy 2020 05 12 Leen
    This electronic thesis or dissertation has been downloaded from Explore Bristol Research, http://research-information.bristol.ac.uk Author: Leendertz-Ford, Anna S T Title: Anatomy of Seventeenth-Century Alchemy and Chemistry General rights Access to the thesis is subject to the Creative Commons Attribution - NonCommercial-No Derivatives 4.0 International Public License. A copy of this may be found at https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode This license sets out your rights and the restrictions that apply to your access to the thesis so it is important you read this before proceeding. Take down policy Some pages of this thesis may have been removed for copyright restrictions prior to having it been deposited in Explore Bristol Research. However, if you have discovered material within the thesis that you consider to be unlawful e.g. breaches of copyright (either yours or that of a third party) or any other law, including but not limited to those relating to patent, trademark, confidentiality, data protection, obscenity, defamation, libel, then please contact [email protected] and include the following information in your message: •Your contact details •Bibliographic details for the item, including a URL •An outline nature of the complaint Your claim will be investigated and, where appropriate, the item in question will be removed from public view as soon as possible. ANATOMY OF SEVENTEENTH-CENTURY ALCHEMY AND CHEMISTRY ANNA STELLA THEODORA LEENDERTZ-FORD A dissertation submitted to the University of Bristol in accordance with the requirements for the degree of Doctor of Philosophy in the Faculty of Arts, School of Philosophy.
    [Show full text]
  • Title Students' Understanding of Acid, Base And
    Title Students’ understanding of acid, base and salt reactions in qualitative analysis Author(s) Kim-Chwee Daniel Tan, Ngoh-Khang Goh, Lian-Sai Chia and David F. Treagust Source School Science Review, 84(308), 89-97 Published by The Association for Science Education This document may be used for private study or research purpose only. This document or any part of it may not be duplicated and/or distributed without permission of the copyright owner. The Singapore Copyright Act applies to the use of this document. Students' understanding of ;ed towards materials, acid, base and salt ing young people and 'dialogue and debate' reactions in qualitative e and particle physics. analysis jal exhibits at school neighbouring schools, Kim-Chwee Daniel Tan, Ngoh-Khang Goh, Lian-Sai Chia :recent Awards can be and David F. Treagust Conventional methods of teaching QA do not seem to help students understand the reactions involved. This new instructional package may help. The topic qualitative analysis (QA) is an important specified in the syllabus. J\s students are assessed >\RC component of the national grade I 0 chemistry mainly on their written observations, the main ~hysics and Astronomy practical examinations in Singapore. During the emphasis of QA practical work is getting correct esearch Council practical examinations, grade 10 students ( 15- to 17- results and writing 'standard' observations. Thus, years-old) are required to carry out a series of many students merely follow instructions given in the procedures using chemicals. apparatus and worksheets, and seldom think about what they are appropriate techniques. They also need to observe and doing (Tan et ul., 2001 ).
    [Show full text]
  • Experiment # 9: the Henderson-Hasselbalch Equation
    Experiment # 9: The Henderson-Hasselbalch Equation A buffer is commonly defined as a solution that resists changes in pH when a small amount of acid or base is added or when the solution is diluted with pure solvent. This property is extremely useful in maintaining the pH of a chemical system at an optimum value to appropriately influence the reaction kinetics or equilibrium processes. A buffer solution actually is a mixture of a weak acid and its conjugate base or a mixture of a weak base and its conjugate acid. The conjugate forms are commonly referred to as “salts”. For a typical weak acid, the dissociation equilibrium is represented as: + + Acid l H + Base; Ka = [H ] [Base] [Acid] according to the Bronsted-Lowry concept. If a pure weak acid is dissolved in a pure solvent the concentrations of H+ and conjugate Base will be equal, neglecting autoprotolysis of the solvent. Rearranging the dissociation constant equation and solving for [H+ ] gives: [H +] 1/2 = [Ka (Acid)] . If other factors governing conjugate base concentration are present in the system (either as added salt of the weak acid or as added base to partially neutralize the acid), the concentrations of H+ and conjugate Base will no longer be the same. Under these conditions, the equation for [H+ ] becomes: + [H ] = Ka [Acid]/[Base] = K [Acid]/[Base]. Taking negative logarithms of both sides of the above equation gives: + -log ([H ]) = -log (Ka ) – log ([Acid]/[Salt]) or pH = pKa – log ([Acid]/[Salt]). Upon inversion of the argument the last log term becomes positive, as: pH = pKa + log ([Salt]/[Acid]).
    [Show full text]
  • Ammonium Soaps
    United States Department of Agriculture Agricultural Marketing Service | National Organic Program Document Cover Sheet https://www.ams.usda.gov/rules-regulations/organic/national-list/petitioned Document Type: ☐ National List Petition or Petition Update A petition is a request to amend the USDA National Organic Program’s National List of Allowed and Prohibited Substances (National List). Any person may submit a petition to have a substance evaluated by the National Organic Standards Board (7 CFR 205.607(a)). Guidelines for submitting a petition are available in the NOP Handbook as NOP 3011, National List Petition Guidelines. Petitions are posted for the public on the NOP website for Petitioned Substances. ☒ Technical Report A technical report is developed in response to a petition to amend the National List. Reports are also developed to assist in the review of substances that are already on the National List. Technical reports are completed by third-party contractors and are available to the public on the NOP website for Petitioned Substances. Contractor names and dates completed are available in the report. Ammonium Soaps Crops 1 2 Identification of Petitioned Substance 3 4 Chemical Names: CAS Numbers: 5 Anhydrous Ammonium Soaps 84776-33-0 (Ammonium soaps of fatty acids C8 – 6 C18) 7 Other Name: 63718-65-0 (Ammonium nonanoate) 8 Ammonium Soaps 9 Ammonium Salt of Fatty Acids Other Codes: 10 Perlargonic Acid, Ammonium Salt EPA Registration No.: 66702-7-39609 11 (Ammonium soaps of fatty acids) 12 Trade Names: EPA PC Code: 031801 (Ammonium salts of fatty 13 Hinder® acids (C8 – C18) 14 15 16 Summary of Petitioned Use 17 18 Ammonium soaps have been approved by the United States Department of Agriculture’s (USDA) National 19 Organic Program (NOP) for a range of uses pertaining to crop production.
    [Show full text]