The history of the atom
[Type text] Shafaq Zahid The history of the atom Over the span of hundreds of years science has advanced tremendously improving our understanding of what makes up the world we live in. The atom is one of sciences important findings and has had a changing history of new discoveries, always altering the way we see things. In the early 1800s a man called John Dalton made an atomic theory with predictions about atoms. He stated that atoms are tiny particles that make up elements and that they are indivisible. We now know that there are in fact smaller particles inside the atom, but at this stage it was assumed that the atom was the smallest. He also said that all atoms of a given element are the same and atoms of one element are different from those in every other element. This meant that every different element had its own unique type of atoms. (Dalton also developed the first table of atomic masses) As the years went on a scientist called JJ Thomson discovered the electron by using cathode ray tubes. This discovery proved that there was an even smaller particle inside the atom itself, disproving one of Dalton’s theories and improving our understanding about elements and atoms. JJ Thomson created the famous plum pudding atom model which shows an atom made up of negative electrons moving about in a ‘sea’ of positive charge, thus making the atom neutral with no overall
Redox titration of copper evaluation
Redox Titration of Sodium Thiosulphate against Copper (II) Sulphate My results from this titration can be seen in the table below: Rough st 2nd 3rd Final Reading/cm3 29.30 25.25 30.40 28.80 Initial reading/ cm3 05.05 0.80 6.20 4.55 Titre/ cm3 24.25 24.45 24.20 24.25 The concordant results I will be using in my calculation are the titres from my 2nd and 3rd titration as there are within 0.01 cm3 of one another. To calculate the average titre I will use the following method: Average Titre = (24.20 + 25.25) 2 = 24.225 cm3 In this titration there are two half equations that are involved, the first is when the copper (II) sulphate is added to the potassium iodide: 2Cu2+ + 4I- --> 2CuI + I2 The second half equation takes place when the sodium thiosulphate is titrated into the solution containing the Cu2+ and iodine: I2 + 2S2O32- --> S4O62- + 2I- As I need to find the concentration of the Cu2+ I have to look at both half equations to find the ratio of Cu2+ to S2O32-, which is 1:1. This is because in each step of the reaction there are 2 moles of each. This will mean that the number of moles of Cu2+ will be the same as the number of moles of S2O32-: n = c x v n of S2O32- = 0.102827763 x 24.225 1000 = 2.491002571 x 10-3 mol n of Cu2+ = 2.491002571 x 10-3 mol Now that I have the number of moles of Cu2+ I can
Comparing the enthalpy changes of combustion of different alcohols
Unit 1.4b Aim: Comparing the enthalpy changes of combustion of different alcohols Introduction: I am going to investigate the difference in enthalpy of combustion for a number of different alcohols. My aim is to find out the best fuel out of the five alcohols. I will calculate the value for enthalpy change by burning different fuels to heat a specific amount of water using the fact that 4.2J of energy are required to raise the temperature of 1g of water by 1°C. I will also produce a wide range of results and compare them to calculate their enthalpy change of combustion. Background information: The enthalpy change of combustion is the energy transferred to and from the surroundings at a constant pressure, when one mole of fuel burns completely. The symbol is ?H. The chemical reactions that release energy to their surroundings are called exothermic and the energy that transferred to them from the surroundings is called endothermic. ?H = ?H products - ?H reactants The units are kilojoules per mole (kJmol-1) Exothermic Ref: http://www.s-cool.co.uk/a-level/chemistry/chemical-energetics/revise-it/enthalpy-changes Exothermic reactions are more common. An example of exothermic reaction is: photosynthesis in plants where the energy comes from the sunlight. Energy cannot be destroyed but it can transfer from one form to another. The total energy of a system of reacting
Chemical Bonding
Bonding By Hollie Scorer Ionic Bond An ionic bond is the electrostatic attraction that forms between oppositely charged ions. Ionic compounds are electrically neutral, it is held together by the attraction between the opposite charges of cations and anions. There are various types of ionic bonds that can be formed by the transfer of electrons an example of this is calcium chloride. In this compound calcium has two electrons on its outer shell, the chlorine atom has seven outer electrons. If the calcium atom transfers two electrons, one to each chlorine solution it becomes a Ca2+ ion with the stable configuration of an inert gas in this case its argon. At the same time each chlorine, having gained one electron becomes a Cl¯ ion, also with an inert gas configuration. Calcium chloride, CaCl2 www.bbc.co.uk/.../img/gcsechem_102.gif Ionic bonds are formed between metal atoms which lose electrons the reason for this is the low first ionization energy metals have. The energy required to remove electrons from metals to attain a noble gas structure is considerably low. Ionic bonds also occur in non-metal atoms which gain electrons the reason for this is the group 7 atoms have a strong electron affinity. Covalent Bond A covalent bond is formed by the sharing of valence electrons rather than by transfer, the bonds are formed between non-metal atoms. An example of this is
Hydrolysis of an ester
A-Level Chemistry Coursework: Hydrolysis of an ester Ying-Jun Ng For the hydrolysis of methyl benzoate, care must be taken throughout the procedure as a number of dangerous substances are being used. During the procedure a labcoat, goggles, and gloves must be worn throughout. Specific safety instructions for chemicals or procedures are explained in the step that they are introduced. Observations, readings, and necessary safety precautions are discussed in the same order as the procedure was carried out in. . Safety: Methyl benzoate is harmful is inhaled or is it gets into contact with the skin or eyes or if swallowed. So it is necessary to carry out the entire procedure in a well-ventilated area and gloves and goggles must be worn. Sodium hydroxide is a caustic soda and so is not very dangerous however regular safety precautions (goggles, labcoats and gloves) and care is still carried out to prevent spillages. Ethanol is highly flammable and dangerous substance as it contains methanol. Therefore, it should not come into direct contact with any flame. It is harmful it swallowed, inhaled or comes into contact with skin. Observations: Methyl benzoate is originally a transparent liquid however the addition of the sodium hydroxide, ethanol and anti bumping granules turns the liquid cloudy. 2. Safety: As a Bunsen burner is being used a heat mat should be placed
Gas Behaviours and the Weather
Gas Behaviour and the Weather The atmosphere above the Earth's surface consists of a mixture of gases called air. By learning about the nature, concepts and laws of gases, the changes in the atmosphere can be monitored and future weather events can be predicted. The accuracy of these predictions however, is questionable as the gas laws are only accurate for ideal gases. The air in the atmosphere is not an ideal gas and therefore, there are many variables that must be taken into account when predicting and measuring temperature, pressure, volume, and density of the atmosphere's air. Pressure can be defined simply as the amount of force applied to a unit area of surface (Princeton University - WordNet, 2010). Air pressure is the weight of the air pressing down on Earth. Weight is the measure of the amount of force pushing down on Earth due to gravity. Therefore, measuring the weight of the air pressing down on Earth measures the amount of force applied to the Earth's surface and thus, the pressure. Air pressure also relates to the density of the air and the height above the Earth's surface from where it is being measured (see Passante, 2006). The lines on the weather map (Fig. 1) represent the variations in pressure from region to region shown in 'isobars'. Temperature is a measurement of the speed of the molecules' movement in a substance. The more energy the molecules
How does aspirin work?
Asthma In America, more than 80 billion aspirin tablets are consumed each year. Aspirin is a trade name for acetyl salicyclic acid and is effective as an analgesic, antipyretic, and anti-inflammatory drug. History Aspirin's predecessors, derivatives of salicylic acids, have been used to treat a variety of conditions for more than 2,500 years. The Greek physician, Hippocrates (400BC), recommended the use of willow bark (a natural source of salicylates) to ease pain during childbirth. This use of salicylates was also advocated by Galen, a second century Roman physician, and mentioned in medical texts of the Middle Ages and Renaissance. In 1757, Reverend Edward Stone conducted the first scientific study of natural sources of salicylates and wrote about the success of willow bark in the cure of fevers and aches. Leroux showed in 1829, that salicin is the active agent in willow and was first extracted by Fontana and Brugnatelli. Salicin was concerted into Salicylic acid by the Italian chemist Piria in 1839. It was synthesised by a process discovered by Kolbe and Lautemann in 1860 which led to the introduction of Salicylic acid and sodium salicylate (forerunners of aspirin) for treatment of fever and arthiritis. However, these compounds were toxic to the stomach and caused diarrhoea and vomiting. German chemist Felix Hoffmann was set the task by Arthur Eichengrun of Friedrich
Atmospheric Pollution
Open Book-Coursework Introduction This open book report is about atmospheric pollution, and I will be mostly focusing on photochemical smog. Photochemical smog is a thick haze in the troposphere and is very dangerous. It is caused by reactions in the atmosphere between sunlight and pollutants from motor vehicles and industries. Formation of Photochemical smog Primary and secondary pollutants with the help of sunlight form photochemical smog. A primary pollutant is an air pollutant emitted directly from a source (motor vehicles or industries). Examples of primary pollutants include NOx gases, SOx gases, COx gases and also hydrocarbons. Secondary pollutants are formed when primary pollutants, undergo further reactions and are not emitted directly into the atmosphere. An example of a secondary pollutant is ozone. The Formation of primary pollutants Primary pollutants are formed in the combustion of fuel in a coal-fired station. The output pollutants produced by coal fired stations are, sulphur oxides, nitrogen oxides and carbon dioxide. Sulphur is found in coal. When coal burns the sulphur compounds are oxidised so convert into sulphur oxide gases. Nitrogen oxide emissions can be produces in two ways. Firstly, most fuels contain compounds of nitrogen as it is formed by proteins. When nitrogen combusts, the nitrogen compounded are oxidised giving us NOx gases. The other
Assessed Practical (Skill P)
AS - Assessed Practical (Skill P) The aim of this experiment is to find out which reaction is correct for the thermal decomposition of copper carbonate out of the following two equations. 2CuCO3(s) ==> Cu2O(s) + 2CO2(g) + 1/2O2(g) CuCO3(s) ==> CuO(s) + CO2(g) Avagadro's constant states that one mole of gas under standard conditions will fill 24dm3 under standard conditions so it is possible to find the amount of gas evolved by measuring the volume. From this it is also possible to find which version of the reaction has taken place. How much copper carbonate should be used? The first equation will produce more gas so that is the maximum amount to be taken into account when deciding how much copper carbonate needs to be used. If one mole of copper carbonate is used then one mole of CO2 and 0.25 moles of O2 will be evolved. This will occupy 30dm3 in total. One mole of copper carbonate has a mass of 123.664g. Because most gas syringes are 100cm3 the amount of gas evolved needs to be less than this. To make the experiment such that 60cm3 will be evolved the mass of copper carbonate needs to be divided by 500. Having 60cm3 gas evolved will leave room in the gas syringe in case the conditions are not perfect for the experiment. If the volume was calculated so that 90cm3 gas would be evolved there is a chance that the gas syringe would not be able to take it. 30000/500 = 60
Spectroscopy
Chemistry Unit 2 Spectrometry Katie Bennett Spectrum Definition: The several coloured and other rays of which light is composed, separated by the refraction of a prism or other means, and observed or studied either as spread out on a screen, by direct vision, by photography, or otherwise. Introduction to Spectroscopy Spectroscopy is a complex art - but it can be very useful in helping scientists understand how an object like a black hole, neutron star, or active galaxy is producing light, how fast it is moving, and even what elements it is made of. A spectrum is simply a chart or a graph that shows the intensity of light being emitted over a range of energies. Spectra can be produced for any energy of light - from low-energy radio waves to very high-energy gamma-rays. Spectra are complex because each spectrum holds a wide variety of information. For instance, there are many different mechanisms by which an object, like a star, can produce light - or using the technical term for light, electromagnetic radiation. Each of these mechanisms has a characteristic spectrum. . The Electromagnetic Spectrum White light (what we call visible or optical light) can be split up into its constituent colours easily and with a familiar result - the rainbow. All we have to do is use a slit to focus a narrow beam of the light at a prism. This set-up is actually a basic spectrometer.
