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History of table of Elements
Periodic Table of Elements The periodic table of elements or less commonly know as Mendeleev's table is a chart of all the chemical elements. This important discovery was credited to a Russian chemist named Dmitri Mendeleev. It was discovered when Dmitri was trying to teach his class a way to learn the elements faster and easier. He wrote down the name of the element as well as the atomic number and atomic weight on pieces of paper. He laid all the known elements down on a table and looked for similarities among them. He put them from lowest atomic mass to the highest. Once he had them in order he noticed that some elements were missing. From the information he had gained he could figure out the unknown elements masses. He then could figure out the atomic masses of the unknown elements by averaging the atomic masses of the elements above and below the unknown element. From the table he had just made he could figure out the atomic mass, melting point, density, appearance, formula of chloride, and formula of oxide of the missing elements. Astonishingly his predictions were later found true. Before Dmitri Mendeleev, a French noble prominent named Antoine-Laurent de Lavoisier had made a similar type of table. In 1789 he had grouped 33 elements into gases, metals, non-metals, and earths. Although this was a great leap in chemistry it wasn't the best. Over the years chemists
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
Finding out how much acid there is in a solution
Finding out how much acid there is in a solution? Plan: In this experiment, I will be trying to find out the concentration of a solution of sulphuric acid, in the chemical reaction of sodium carbonate and sulphuric acid. I will be able to determine the concentration of sulphuric acid, by using a method called titration, which involves an alkali. I will need to prepare a solution of a base (sodium carbonate solution). The alkali helps to determine how much acid was necessary to neutralise the alkali. This would help to calculate the concentration of the acid. The formula for this chemical reaction is: Na2 CO3 (aq) + H2SO4 Na2SO4 (aq) + H2O (l) + CO2 (g) The strength/weakness of the acid and alkali affects the neutralisation of the reaction. Ph is considered here. PH is the measurement of how much H+ ions and OH- ion a substance contains. The more positively charged hydrogen ions there are, the more acidic it is. If there is more negatively charged hydroxide ions present, it is more of an alkaline. H + + OH - H2O Acid Vs Bases/Weakness and Strengths: The strength of an acid depends on the amount of it, which has reacted with water to produce ions. The concentration defines how much of the initial acid is dissolved in the solution. When an acid reacts with water, a hydrogen ion is transferred to a water molecule. This produces a hydroxonium ion
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
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:
Electrochemistry Experiment. Objective: To investigate the effect of change in lead(II) ion concentration on the potential of the Pb2+(aq) ∣Pb(s) electrode
Tsuen Wan Public Ho Chuen Yiu Memorial College Form 6 Chemistry Practical Experiment 15: Electrochemistry Date of experiment: 8/4/2011 Introduction: Redox reactions are reactions where the oxidation states of the atoms change. The atoms are either oxidized or reduced, depending if they lose or gain electrons. Electrochemical cells are devices that cause a current from redox reactions. It is set up so that electrons lost from one of the reagents can travel to another reagent. This creates a voltage, which is also known as the electric potential difference. This voltage can be read if a high-resistance voltmeter or multimeter is connected to the circuit Salt bridge is used to allow migration of ions between two electric cells to maintain neutrality of solutions. It is usually made up of a filter paper moistened with an inert solution or an inert solution/gelatine salt bridge to prevent oxidation of certain ions. This experiment is divided into 2 parts: part A and part B. Part A Objective: To investigate the effect of change in lead(II) ion concentration on the potential of the Pb2+(aq) |Pb(s) electrode Introduction: This experiment investigates the e.m.f. of the cell: Cu(s) |Cu2+(aq) |Pb2+(aq)|Pb(s) Keeping the ion concentration in the copper electrode system constant(1M) and varying the ion concentration in the lead electrode system, the effect of change in
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
