Write an account of buffer solutions.
F7 Essay Writing (Buffer Solution) Q. Write an account of buffer solutions. Guidelines: In your answer you should consider, giving examples, (a) definition (b) their compositions --- weak acid and its salt (acidic buffer), e.g. CH3COOH / CH3COONa --- weak base and its salt (basic buffer), e.g. NH3 / NH4Cl (c) how they work --- equilibrium shift after addition of a small amount of strong acid / strong base to buffer, --- resistance to pH change upon addition of small amount of acid / base (d) their applications --- for checking indicator solution and calibrating pH meters --- for controlling solution pH for chemical / biochemical reactions, --- for preserving food (e) their importance in nature --- maintenance of blood pH __________________________________________________________________________ ~ Sample Essay ~ A buffer solution is one which resists changes in pH when small amounts of acid or alkali is added to it. It plays an important role in chemical processes where it is essential that a fairly constant pH is maintained. Buffer solutions could be classified into two types, namely acidic buffer and basic buffer solutions. Acidic buffer solutions An acidic buffer solution is one which has a pH less than 7. They are commonly made from a weak acid and its sodium salt. A mixture of ethanoic acid and sodium ethanoate solutions is a typical example.
Revision notes - Test For Gases and Ions
Tests for Gases Name Formula Test Observations Hydrogen H2 Ignite gas. Squeaky pop is heard. Oxygen O2 Place a glowing splint in a sample of the gas. The glowing splint relights. Carbon dioxide CO2 Bubble gas through limewater (saturated solution of calcium hydroxide) A solution turns from colourless to cloudy. A white (milky) precipitate of calcium carbonate forms which is sparingly soluble. Ammonia NH3 Test for gas using damp red litmus paper. Litmus paper turns blue. Chlorine Cl2 Test 1 Test for gas using damp litmus paper (red or blue) Chlorine bleaches the litmus paper very quickly. Test 2 Test for gas using moist starch-iodide paper. The paper turns blue-black. Test 3 Pass gas through a solution of a bromide. The solution turns from colourless to orange. Test 4 Pass gas through a solution of an iodide. The solution turns from colourless to brown (possibly with a black precipitate, iodine). Nitrogen dioxide NO2 Not many tests for this gas. The gas is brown. Sulphur dioxide SO2 Test 1 Bubble gas through a solution of potassium dichromate (VI) dissolved in sulphuric acid. The solution turns from orange to green. Test 2 Bubble gas through a solution of potassium manganate (VII) dissolved in sulphuric acid. The solution turns from purple to colourless. Tests for Ions Ion Formula Test Observations Carbonate CO32- Test 1
Heat of Neutralization. Objective: To investigate the enthalpy changes () of various acid-base neutralizations.
Title: Heat of Neutralization Objective: To investigate the enthalpy changes () of various acid-base neutralizations. Chemicals and Apparatus: .0M hydrochloric acid, ~1.0M sodium hydroxide solution, one thermometer, one polystyrene foam cup with lid, two pieces of 50.00 burette, two filter funnels, one piece of 25.00 pipette, pipette filler and a 100 beaker. Background: All chemical reactions involve energy changes. The study of energy changes is an important part of chemistry. Fundamental to the thermo-chemistry is the law of conservation of energy, which states that energy is neither created nor destroyed, but can be converted from one form to another. An exothermic reaction is one in which stored chemical energy is converted to heat energy (heat is released to the surroundings), conversely an endothermic reaction is one in which heat energy is converted to chemical energy (heat is absorbed into the system). The enthalpy (H) of a substance, sometimes called its heat content, is an indication of its total energy content. The equation for calculating the enthalpy change (heat change) is given by ?H = -m x c x ?T where m is the mass of the sample, c is the specific heat capacity of the sample and ?T is the change in temperature. The sign for ?H indicates the direction of heat flow, positive for endothermic processes and negative for exothermic processes. In this
Ozone chemistry speech. Today, I am here to inform you that an ozone hole has been detected over Antarctica and the concentration of ozone will continue to decrease across the globe if the emission of ODCs, such as CFCs, does not reduce.
ERT ORAL SCRIPT (Year 2004- Channel 7 news, slide 1) Breaking news in LA today is that the new movie premier The Day After Tomorrow is actually based on a true event that happened in 1986 at an international conference on climate change. However, it was not global warming leading into an ice age that was discussed, but (slide 2) the discovery of the ozone hole that biologically dangerous ultraviolet (UV) radiation cannot be completely absorbed to preserve the life forms on Earth. Thankfully, unlike the movie, 24 countries agreed to abide to the Montreal Protocol on substances that deplete the ozone layer, which aimed to gradually phase out all ozone-destroying chemicals, ODCs for short. Although measures have been taken, the ozone layer will not recover until the middle of this century as most ODCs have a lifetime of 20 to 100 years. Here coming up, is an extract from a video of the conference. (Year 1986, slide 3) Ladies and gentlemen, I am Professor Rowland. Today, I am here to inform you that an ozone hole has been detected over Antarctica and the concentration of ozone will continue to decrease across the globe if the emission of ODCs, such as CFCs, does not reduce. USA: The CFCs' industry is worth 8 billion dollars per year. I understand. The chemical is ideal for many purposes as it is used as a solvent and cleaning agent in the electronic industry, a non-toxic
Reactions of aldehydes and ketones. The purpose of this experiment is to compare some reactions of ethanal and propanone.
Date: 8/11/2011 Exp. No.: 25 Title: Reactions of aldehydes and ketones Aim: The purpose of this experiment is to compare some reactions of ethanal and propanone. Introduction: In this experiment, ethanal and propanone were chosen as they are relatively safe. The structures of the 2 compounds are as follow: Ethanal Propanone In this experiment, we are going to investigate the following reactions of these 2 compounds: . Addition 2. Condensation 3. Oxidation 4. Iodoform reaction Apparatus and chemicals: Apparatus: Safety spectacles, hot water bath, cold water bath, test tubes, beakers Chemicals: Saturated hydrosulphite solution , 2,4-dinitrophenylhydrazine solution, 0.1M potassium dichromate solution, 1M sulphuric acid, Fehling's reagent (Fehling solution A + Fehling solution B), 0.05M Silver nitrate solution, 2M sodium hydroxide solution, 2M ammonia solution, iodine solution 10% (in KI(aq)) Procedures: Part 1: Addition reaction with sodium hydrogensulphite . About 2 cm3 of saturated sodium hydrogensulphite solution was added into a test tube. 2. The test tube was put into a cold water bath. 3. Similar volume of ethanal was added drop by drop into the test tube. 4. The experiment was repeated using propanone instead of ethanal. Part 2: Condensation reaction with 2,3-dinitrophenylhydrazine . About 1 to 2 drops of ethanal was added
Determining the concentration of acid in a given solution
Determining the concentration of acid in a given solution Planning 4 I have been given a sample of sulfuric (VI) acid solution with a concentration between 0.05 and 0.15 mol dm-³. I am going to find out the accurate concentration of the sulfuric acid. To find out the concentration of the acid I will react it with a known volume and concentration of a base and see how much base was needed to neutralise the acid. The acid is a strong acid which means that I know all the H+ ions have been disassociated and are in the solution. The H+ ions will react with the OH- ions in the alkali which will neutralise the solution. I am provided with solid, hydrated sodium carbonate with the formula Na2CO3·10H2O.1 This is a readily available base and I can dilute it down to achieve the concentration I want to react with the acid. The formula of the reaction that will take place is H2SO4 (aq) + Na2CO3 (aq) --> Na2SO4 (aq) + CO2 (g) + H2O (l) So 1 mole of H2SO4 reacts with 1 mole of Na2CO3. A titration will give me the most reliable and accurate results with the available equipment. To do my titration I will need: A Burette 7 I will need a burette to add the sodium carbonate to the sulfuric acid solution. The burettes provide me with very accurate results of volume of solution added. The class set of burettes measure 50cm3. I want to do a titration
UV-Visible Spectrophotometry
Name: Chu Ka Ki Student No.: 50555542 Group: 1 Date: 17-02-2005 Experiment: 2 BCH 2004 Principle of Analytical Chemistry Lab Report (Report One) Title: UV-Visible Spectrophotometry Aim: To determine phosphate composition in cola beverages by UV-Visible spectrophotometry and pH titrimetry. Introduction: UV-Visible spectrophotometry is one of the most important methods for the chemical analyze. Ultraviolet-Visible spectroscopy or Ultraviolet-Visible spectrophotometry (UV/VIS) involves the spectroscopy of photons (spectrophotometry). It uses light in the visible and adjacent near ultraviolet (UV) and near infrared (NIR) ranges. In this region of energy space molecules undergo electronic transitions. The method is used in a quantitative way to determine concentrations of an absorbing species in solution, using the Beer-Lambert law: where A is the measured absorbance, I0 is the intensity of the incident light at a given wavelength, I is the transmitted intensity, L the length of the cell, and c the concentration of the absorbing species. For each species and wavelength, ? is a constant known as the extinction coefficient. The absorbance A and extinction ? are sometimes defined in terms of the natural logarithm instead of the base-10 logarithm. Methodology: Colorimetric Analysis: At the beginning, 4cm3 decarbonated cola was transferred into a 100cm3
Enthalpy of formation of calcium carbonate
EXPERIMENT 6 Enthalpy of formation of calcium carbonate Objective To determine the enthalpy of formation of calcium carbonate Procedures A. Reaction of calcium with dilute hydrochloric acid . 1.0909 g of calcium metal was weighed out accurately. 2. 100 cm3 of approximately 1 M hydrochloric acid was pipetted.and placed in a plastic beaker. 3. The initial temperature of the acid was determined 4. The weighed calcium was added into the acid and stirred thoroughly with the thermometer until all the metal had reacted. 5. The maximum temperature attained by the solution was recorded. 6. The experiment was repeated with 1.0538g calcium metal. Results: Experiment no. 2 Mass of Ca used/ g .0909 .0538 Initial temp. of solution/ ? 27 26 final temp. of solution/ ? 55 52 Temperature change/ ? 28 26 Calculations and Discussion: . What does the term "heat of formation" of a substance mean? Heat of formation refers to the heat change when one mole of a substance is formed from its constituent elements is their standard states under standard conditions. 2. What are "standard conditions" for thermochemical calculations? Standard conditions is defined as elements or compounds appear in their normal physical states at a pressure of 1 atm (101325 Nm-2/760mmHg) and at temperature of 25 oC (298 K).Moreover, the solution should have unit activity(1mol dm-3 ). 3. Write
Determination of a Rate Equation
Determination of a Rate Equation Introduction: The rate of reaction is the rate of depletion of reactants or the formation of a product during a chemical reaction. It is expressed by units of concentration over the time taken for the reaction to take place. (Avogrados, 2010) Aim: To plan and carry out an experiment involving a graphical method to determine how the concentration of each component affect the rate of reaction in this reaction: 2HCl + Na2S2O3 --> 2NaCl + SO2 + S + H2O Background Information: Sodium thiosulphate and hydrochloric acid are both clear colourless solutions. They react together according to this equation: 2HCl + Na2S2O3 --> 2NaCl + SO2 + S + H2O When these solutions are mixed together, a yellow precipitate, sulphur, is produced. This causes the mixture to appear cloudy. The faster the rate of the reaction, the faster the solution appears cloudy. There are four basic factors that affect the rate of a reaction namely: Temperature, concentration/ pressure (in gases), physical state/ surface area of the reactants and the presence or absence of a catalyst [(Think Quest, 2008) and (WebChem, 2005)] Basic Idea: * Two sets of experiments will be carried out. In each case, the concentration for a single reactant will be varied * All other factors should remain constant * Conical flask containing the mixed reactants will be placed on a paper
Analysis of sulphur dioxide content in wine.doc
Analysis of sulphur dioxide content in wine Objective To determine the amount of sulphur dioxide, an antioxidant, present in wine by using volumetric analysis. Principle All free SO2 molecules is first convert into SO32- by NaOH solution: SO2 + 2OH- › SO32- + H2O Acidification of the solution liberates all SO2: 2SO32- + 2H+ › 2SO2 + 4H2O which is then titrated with 0.0057M iodine solution in which starch is used as end-point indicator: SO2 + I2 + 2H2O › 2HI + H2SO4 Chemicals white wine (carbonated), 1M NaOH, 2M H2SO4, 0.0057M I2, starch solution Apparatus volumetric apparatus, pipette, measuring cylinder, dropper, white tile Procedure 1.> Find out the volume of wine from the label on the bottle. 2.> Pipette 25cm3 of white wine into a conical flask. 3.> Add about 12cm3 of 1M NaOH and stand for about 15 minutes. 4.> Add about 10cm3 of 2M H2SO4 to the mixture and then few drops of starch solution as indicator. Quickly, titrate the mixture with 0.0057M iodine solution. 5.> Record the titre required to produce pale blue colour. 6.> Repeat steps 2-5 for 2-3 times. Data Analysis Trial st 2nd Final reading /cm3 3.05 2.80 26.30 Initial reading /cm3 0.25 9.70 23.25 Volume of I2 added /cm3 2.80 3.10 3.05 Average volume of I2 added /cm3 3.075 Concentration of I2 solution: 0.0057 M
