C6- Chemical Synthesis

A brief summary of the 21st century science chemistry module C6- Chemical Synthesis

  • Created by: R_Hall
  • Created on: 23-06-11 09:55

The Chemical Industry

  • The chemical industry converts raw materials (crude oil, natural gas, air, minerals, water) into useful products.
  • The industry makes bulk chemicals on a scale of 1000's of tonnes (ammonia, NaOH, H2SO4, Cl, ethene).
  • Fine chemicals are made on a smaller scale (drugs and pesticides).
  • The part of the chemical works that produces the chemical is the plant.
  • People with many different skills are needed in the chemical industry (researchers, inventors, financial experts, engineers, transporters).
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Acids and Alkalis

  • Concentrated acids are dangerous, but dilute acids are needed for reactions in cells and harnessing energy from respiration.
  • Organic acids are molecular, molecules consisting of C, H and O atoms. The acidity arises from the H in the -COOH group.
  • H2SO4, HCl and HN03 acids come from inorganic or mineral sources.
  • Alkalis (NaOH, KOH) have a pH of above 7. They neutralize acids and are caustic; attack living tissues.
  • The pH scale is a number scale that shows the acidity or alkalinity of a solution in water. Indicators change colour to show whether a solution is acidic.
  • Acids react with metals to produce salt and hydrogen gas.
  • Acids react with a metal oxide or hydroxide to produce salt and water.
  • Acids react with carbonates to form a salt, carbon dioxide and water.
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Salts from Acids

  • When acids mix with water, they dissolve and react to produce hydrogen ions- ionic theory.
  • All acids contain H in their formulas; in organic acids, it is only the -COOH groups that ionize.
  • Strong acids (HCl, H2SO4, HNO3) ionize completely when they dissolve in H2O. Weak acids (organic acids) only ionize slightly.
  • Alkalis consist of metal ions and hydroxide ions; when they dissolve, they add hydroxide ions to water and make it alkaline.
  • During a neutralization reaction, the H ions from acid react with hydroxide ions from alkali to make water. The remaining ions make a salt.
  • Salts are ionic- consist of +ive metal ions (from metal oxide/hydroxide) and   -ive non-metal ions (from acid).
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Salts in our Lives

  • Soluble salts are used in our lives. For use in food and medicine, the salts have to be purified.
  • Kidneys remove toxic chemicals from blood; in case of kidney failure, dialysis machines do the job of the kidneys.
  • Inside the machine, the blood goes past a membrane- salts on other side of membrane pass into blood, toxic chemicals pass out of blood.
  • Calcium chloride is used as a dialysis salt. Too much or too little is harmful, needs to be balanced. The CaCl has to be pure and measured accurately.
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Purity of Chemicals

  • Suppliers of chemicals offer chemicals with a range of grades of purity.
  • There are 4 grades (technical, general, laboratory and analytical).
  • When deciding which grade to use, important to know-
  • - Amount of impurities.
  • - What the impurities are.
  • - How they can affect the process.
  • - Whether they will end up in the product, and if it matters.
  • Technicians can test the purity of an acid using a titration.
  • Steps in titration-
  • 1. Fill a burette with alkali (known concentration).
  • 2. Weigh a sample of acid and dissolve in water.
  • 3. Add indicator (phenolphthalein) to acid.
  • 4. Add alkali to acid, swirling. Stop adding when colour changes-end point.
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Rates of Reaction

  • Chemists measure the rate of reaction by finding the quantity of product produced or reactant used in a fixed time.
  • Average rate= change in the volume of product/ time take to happen.
  • Most rates of reactions change with time, fast at start but slows down.
  • Factors affecting rate of reaction-
  • - The concentration of reactants- higher the conc., the faster the reaction.
  • - The surface area of solid- smaller the surface area, faster the reaction.
  • - The temperature- higher the temperature, faster the reaction.
  • - Catalysts- speed up a chemical reaction.
  • A catalyst is a chemical that speeds up the reaction without being used in the process.
  • According to the collision theory, when molecules collide, some bonds between atoms break and some form, creating new molecules.
  • Any change that increases the number of successful collisions per second has an effect of increasing the rate of reaction.
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Chemical Quantities

  • Adding up the relative atomic masses for all the atoms in a formula of a compound give the relative formula mass.
  • Given the relative formula masses, it is possible to work out the reacting masses of the reactants and products.
  • The actual yield is the mass of a product after it is separated from the mixture, purified and dried.
  • The theoretical yield is the mass of a product expected if the reaction goes exactly as shown in the balanced equation. The actual yield is always less than the theoretical yield, because of by-products and loss of chemicals when moving from containers.
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Stages in Chemical Synthesis

  • Chemical synthesis is a way of making new compounds.
  • Making a sample of magnesium sulfate to react with an acid-
  • 1. Choosing the reaction- any of the characteristic reactions of acids to make salts.
  • 2. Risk assessment- to look for hazards arising from equipment or procedure.
  • 3. Working out the quantities to use.
  • 4. Carrying out the reaction in suitable apparatus under the right conditions- the reaction is fast enough at a temperature and is safe using the equipment.
  • 5. Separating the product from the reaction mixture. 
  • 6. Purifying the product.
  • 7. Measuring the yield and checking the purity of the product.
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