Chemistry

• Physical change


  Main difference from chemical change
• Chemical change


  Apparent change in mass even though mass cannot be created or destroyed
• Possible cause of apparent change in mass in a chemical reaction
• Collision theory


  Two things that must happen for two particles to react
• Activation energy


  Diagram showing what it means
• Monitoring the rate of a reaction


  • The rate changes as the reaction proceeds
  • Easy ways to monitor the change
• Reaction of marble (calcium carbonate) with hydrochloric acid

  1. Reaction starts straight away

  2. Reaction can be monitored by measuring volume of gas formed

  3. Reaction can be monitored by measuring change in mass of reaction flask
• Apparatus used to measure volume of gas produced


  • Conical flask with hydrochloric acid, marble chips added, stopper fixed, stopclock started
• 0.5 moldm


  Concentration of hydrochloric acid
• 2.0 moldm


  Concentration of hydrochloric acid
• Using dilute and concentrated solutions in a reaction


  • Fig. 6.8
• Developing practical skills


  • Dilute hydrochloric acid
  • Gas syringe
  • Calcium carbonate (marble chips)
• Experiment with hydrochloric acid and calcium carbonate


  • Fig. 6.9
• Safety note: Eye protection should be worn and great care taken in supporting and using the gas syringe, especially if the plunger may be pushed out completely
• Investigating how the concentration of hydrochloric acid affects the rate of its reaction with calcium carbonate (marble chips)

  1. Place 40 cm3 of 0.2 mol/dm3 hydrochloric acid in the conical flask

  2. Add 10 cm3 of distilled water

  3. Carefully weigh 5 g of calcium carbonate (an excess) into a small beaker

  4. Add the calcium carbonate to the flask

  5. As soon as the marble chips are added, start timing the reaction
• A solution that has a pH less than 7 is considered an acidic solution.
• A solution that has a pH greater than 7 is considered a basic (alkaline) solution.
• The pH scale ranges from 0-14, where 0 is very acidic, 7 is neutral, and 14 is very alkaline.
• Acids can react with metals to produce hydrogen gas and salts.
• Strong acids like sulfuric acid or nitric acid will always react with metals, while weaker acids like citric acid or lactic acid might not react at all.
• Acids can react with metals to produce hydrogen gas and salt.
• Bases can react with acids to form salts and water.
• Bases can react with acids to form salt solutions and water.
• Strong acids dissociate almost completely into their component ions when they dissolve in water.
• When an acid reacts with a metal, it produces hydrogen gas and a salt.
• Weak acids only partially ionize in water.
• Metallic oxides can also react with acids to form salts and water.
• Metallic oxides are bases because they contain metal cations and oxygen anions.
• Bases are substances that contain OH- ions and have a pH greater than 7.
• Bases have the ability to accept protons.
• Base + Acid → Salt Solution + Water
• Weak acids only partially ionize in solution.
• Carbonates react with acids to form carbon dioxide, water, and the corresponding salt.
• Salt + Acid → Salt Solution + Water
• When a base reacts with water, it produces OH- ions which increase the concentration of hydroxide ions in the solution.
• Ammonia reacts with acids to form ammonium salts and water.
• The pH scale is used to measure the concentration of H+ ions in an aqueous solution.
• Metal Oxide + Acid → Metal Hydroxide + Salt
• A neutral solution has a pH value of 7.
• The reaction between an acid and a base is called neutralization.