- 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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- 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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