chemistry OCR-open book 2008
Section1: Discuss with the use of examples the main difference between Alpha decay and Beta decay: An alpha particle consists of 2 protons and 2 neutrons (He- nucleus), which is emitted as the nucleus looses 2 protons and 2 neutrons to become more stable. In this process a new chemical element is produced and this process is called transmutation, and this is a spontaneous reaction. For example the decay of Uranium-238 into Thorium- 234 E.g. 1 Beta decay: A beta- particle is a high energy electron, emitted when a neutron in the nucleus decay to form a proton and an electron. E.g. 1 E.g. 2 The differences between alpha and beta decay: Alpha decay Beta decay It's a form a nuclear fission reaction, where the atom splits in to two daughter nuclei. An energetic negative electron is emitted, producing a daughter nucleus of one higher atomic number and the same mass number. Alpha decay is restricted to heavier elements; an element only emits an alpha particle is it atomic number is less than 82. Beta particle is emitted when a heavy element decays with atomic number of above 82 decays. Alpha radiation reduces the ratio of protons to neutrons in the parent nucleus. A beta particle is emitted when there is too many neutrons, a neutron decays into a proton, an electron and an antineutrino. Difference between nuclear fission reaction and
Electrochemical Cells
Electrochemical Cells Tam Paul-Worika Contents Aim of the Investigation.....................................................3 Background.....................................................................3 * Redox Reactions * Electrochemical Cells * Salt Bridge * Nernst Equation Plan.................................................................................5 * Equipment * Risk Assessment * Instructions * Making the solutions Analysis...........................................................................7 Evaluation......................................................................17 Aim of the Investigation In my investigation, I will observe how changing the concentration of a solution can affect the electrode potential in an electrochemical cell. I will also see if there is a trend when the concentration is changed. Background Redox Reactions Redox reactions are reactions where the oxidation states of the atoms change[1]. The atoms are either oxidised or reduced, depending on if they lose or gain electrons. Electrochemical Cells Electrochemical cells (also known as Galvanic cells or Voltaic cells[2]), are devices that cause a current from chemical reactions. These reactions occur through redox. An electrochemical cell is set up so that the electrons lost from one of the reagents can travel to another reagent. This creates a voltage, which
Stereochemistry of Butenedioic acid
Name: Tonny, Chan Kar Yu, Student ID: 10297729 Date of Experiment: 19th February 2005, Group: B1 Title: Stereochemistry of Butenedioic acid Objective: To study the interconversion of two geometric isomers, maleic acid (cis isomer) to fumaric acid (trans isomers), the differences in physical properties between this pair of cis-trans isomers and determine the stereochemistry of addition of bromine to butenedioic acid. Chemicals and Apparatus: 2 grams of maleic acid, 10 cm3 of concentrated hydrochloric acid, 10 cm3 of bromine water1, one 50 cm3 beaker, one 100 cm3 beaker, one 250 cm3 beaker, one 10 cm3 measuring cylinder, one piece of spatula, one piece of water glass, one glass rod, a few pieces of filter paper, a set of Buchner funnel, a filter flask with side tube, three glass capillary tubes, a set of melting point apparatus, one long hollow glass tubing, one electronic balance, one heater and the oven Background: Stereochemistry is always encountered throughout organic chemistry. And stereochemistry isomerism can be divided into two classes, geometrical isomerism and optical isomerism. Although these categories are not mutually exclusive, it is not uncommon to find compounds that exhibit only one or the other of the two types. Most geometrical isomers result from cyclic systems or restricted rotation about double bonds. The preparation of fumaric acid by
Making Aspirin
In this task we were asked to synthesise aspirin from salicylic acid (2 - hydroxybenzoic acid) and ethanoic anhydride (CH3COOCOCH3) in a laboratory scale and prepare a pure silver chloride sample from the solutions of silver nitrate (AgNO3) and sodium chloride (NaCl) of known concentrations. Now I am going to describe the preparation of these two items and estimate the purity of one of my samples. Preparation of aspirin: Now I am going to explain the preparation of the aspirin; Materials : (a) ethanoic acid (b) ethanoic anhydride (c) salicylic acid (d) water cooled condenser (e) filter paper (f) Buchner funnel (g) vacuum oven (h) melting point recorder machine etc. Procedure ) Firstly we mixed 5 ml of ethanoic acid with 5 ml of ethanoic anhydride in a 50 ml round bottomed flask. 2) After that we added 5 g of 2- hydroxybenzoic acid and a few anti - bumping stones . 3) Then we attached a water cooled condenser and reflux the mixture for 30 minutes over a Bunsen and gauze. 4) Then we pour the mixture slowly into 100 ml of cold water which is being stirred vigorously. 5) After that we removed the 2 - ethanoyloxybenzoic acid by filtration through a Buchner funnel. 6) Then we removed the product from the fume cupboard and dried it in a vacuum oven at about 80 degree Celsius. 7) Then we weight the dried product and recorded its melting point. Chemical reaction:
Investigation of Enzyme Activity
An Investigation of Enzyme Activity with different Substrate Concentrations. Aim To investigate how different concentrations of substrate affects the rate of enzyme activity. Objective My objective is to determine how different concentrations of substrate, affects the rate of enzyme activity. I will do this by using different concentrations of Hydrogen Peroxide, and mixing it with the enzyme catalyse. Then I will measure how much gas is produced. Theory What is an Enzyme? Enzymes are proteins which are biological catalysts. A catalyst in chemical terms substantially reduces the energy barrier which exists between atoms and which prevents the atoms from getting close enough to react and form a bond with one another. An enzyme lowers the energy of activation of a reaction but the catalyst is not changed in any way in the process .Therefore, when the atoms of molecules are acted upon by enzymes, an identical reaction occurs as would have occurred without the enzyme but, the energy hill required to overcome the getting-close barrier, is much, much smaller than would have been true without the enzyme's help. The structure of the enzyme is such that atoms of molecules can get close enough to interact, but the energy required to allow this closeness is relatively small. Its like going into an empty closet with someone relative to going into an empty auditorium with someone.
An investigation into the efficiency of alcohols as fuels.
Joe Taylor 11T Chemistry coursework An investigation into the efficiency of alcohols as fuels Planning The aim of the experiment is to investigate the use of five alcohols as fuels. The combustion of alcohols is exothermic, meaning that when burnt they give off more heat than they take in. This makes them useful as fuels, and many countries are adopting alcohol fuels, for example Brazil. Therefore it seems useful and topical that the efficiency of the alcohols should be investigated. The alcohols methanol, ethanol, propan-1-ol and propan-2-ol will be tested. In order to evaluate the efficiency of these alcohols as fuels, their enthalpies will be investigated. Alcohols are perfect for testing, as they are all liquids with the same weight. Therefore weight is not a variable, and it is only the heat given off that is to need be considered. From previous organic chemistry studies the structures and formation of alkanes, alkenes and alcohols were known, along with the energy values for the bonds within alcohols themselves. This allowed for the creation of the bond energy table below. Bond Bond Energy (kJmol-1) C-H 435 O=O 497 C=O 803 H-O 464 C-C 347 C-O 358 These are the alcohol's formulae: Methanol: CH3OH Ethanol: C2H5OH Propan-1-ol: C3H7OH Propan-2-ol: C3H7OH Pentanol: C5H11OH Each of these reacts with Oxygen (0=0) in combustion For a pictorial
Objective To find out the equilibrium constant, Kc, for the reaction below, using acid hydrolysis:
Determining an Equilibrium Constant Objective To find out the equilibrium constant, Kc, for the reaction below, using acid hydrolysis: Principle Although the hydrolysis of ethyl ethanoate is very slow, by using dilute hydrochloric acid as catalyst, the above equilibrium can be attained in 48 hours. After 48 hours, the reaction mixture can then be titrated with standard sodium hydroxide solution. Finally, the equilibrium concentrations of four components below and hence, Kc of hydrolysis of CH3COOCH2CH3 can then be calculated: Chemicals 2M HCl, 1.0335M NaOH, ethyl ethanoate, phenolphthalein indicator Apparatus 5 small reagent bottles, 5ml pipette & filler, burette, measuring cylinder, conical flask, electronic balance, stand, white tile Procedure -- Preparation, allow reaching equilibrium position 1.> Label 5 reagent bottles & their stoppers as 1A, 1B, 2, 3 and 4. 2.> Weigh each reagent bottles with their stoppers and record their corresponding masses in Table 3. 3.> Pipette 2M HCl into each bottles, using measuring cylinders to transfer ethyl ethanoate into bottles 2,3,4 and water into bottles 3,4 according to the amount shown in Table 1. Table 1 shows the amount of chemicals added: Reagent bottle's number A B 2 3 4 Volume of HCl(aq) added /cm3 5.0 5.0 5.0 5.0 5.0 Volume of CH3COOCH2CH3(l) added /cm3 - - 5.0 4.0 2.0 Volume of H2O(l) added /cm3
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.
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
