Chemistry mid-years

• Pure substances are substances containing only one type of particle
• A saturated solution is a solution with as much dissolved solute as possible at a particular temperature. There must be some undissolved solute present
• Diffusion is when particles move from an area of high concentration to one of low concentration until evenly spread
• A white ring of ammonium chloride is seen in a sealed tube when hydrogen chloride gas and ammonia gas diffuse towards each other. The ring forms slightly closer to the hydrogen chloride side
• Hydrogen chloride + ammonia —> ammonium chloride
• HCl + NH3 —> NH4Cl
• Gases diffuse more quickly than liquids because the particles have more energy and are less dense. The more dense the gas is, the slower it diffuses
• if the surface area increases, the number of available particles increases leading to more successful collisions per second and an increase in rate of reaction
• The reaction between marble chips and hydrochloric acid is used to show the affect of surface area on rate of reaction
• CaCO3 (s) + 2HCl (aq) --> CaCl2(aq) + CO2(g) + H2O(l)
• Calcium carbonate + hydrochloric acid —> calcium chloride + carbon dioxide + water
• Concentration is a measure of the number of solute particles in a particular volume of solution
• Pressure is a measure of the number of gas particles in a particular volume of space
• An increase in gas pressure leads to an increase in concentration
• If the concentration increases, the number of available particles increases leading to a greater number of successful collisions per second and an increased rate of reaction
• Activation energy is the energy needed to start a chemical reaction by breaking reactant bonds
• If the temperature is increased, the particles have more kinetic energy and move around more so collide more often. Also, a greater proportion of the particles collide with an energy in excess of the activation energy
• A catalyst is a substance that speeds up a chemical reaction without being used up
• a catalyst provides a surface whereupon reactants are held in position so that the orientation is correct for the bond breaking and forming
• a catalyst provides an alternative reaction pathway of lower activation energy
• sodium thiosulfate and hydrochloric acid react to form sulfur
• 78% of the air is nitrogen
• 21% of the air is oxygen
• 0.9% of the air is argon
• 0.03% of the air is carbon dioxide
• Oxygen is extracted from the air by the fractional distillation of liquefied air
• The percentage of oxygen in the air can be determined by measuring the volume of air removed when iron is allowed to rust in a closed environment
• The percentage of oxygen in the air can be determined by passing air repeatedly over heater copper and measuring the change in air volume
• you can make oxygen by rapidly decomposing Hydrogen Peroxide (H2O2) using the catalyst Manganese dioxide to form water and oxygen gas
• Hydrogen peroxide —> water + oxygen
• Water will turn anhydrous copper (II) sulfate from white to blue