c3- quantitative chemistry

• Who first attempted the elements of the periodic table?

  Newlands, Mendeleev
• How did Newlands and Mendeleev arrange the elements?

  by arranging them in order of their atomic mass
• Describe Newlands' periodic table

  → elements arranged in order of atomic mass

  → recognised every element had similar properties to the element 8 places along

  → some elements placed in incorrect groups
• Describe Mendeleev's periodic table

  → elements arranged in order of atomic mass

  → recognised physical/chemical properties of an element were related to their atomic mass

  → left space for yet undiscovered elements and predicted their properties
• What were the disadvantages of the early periodic tables?

  incomplete, some elements placed in incorrect groups
• What effect did the discovery of sub-atomic particles have on the periodic table?

  table was arranged in order of atomic (proton) numbers, all elements were placed in correct groups
• Why do elements in the same groups have similar properties?

  they have the same number of electrons in their outer shells
• What do we call the elements in group 1?

  alkali metals
• List the properties of alkali metals

  → metals with low density

  → react with non-metals to form ionic compounds

  → compounds formed are white solids that dissolve in water to form colourless solutions

  → react with water, releasing hydrogen

  → form hydroxides that dissolve in water to form alkaline solutions
• What can we say about the reactivity of group 1 (alkali) metals?

  the further down the group an element is, the more reactive the element (and the lower its melting/boiling point)
• List properties of transition metals compared with group 1 (alkali) metals

  → most have higher melting points and densities

  → are stronger and harder

  → are much less reactive (don't react as vigorously with water or oxygen)
• List properties of transition metals

  → have ions with different charges

  → form coloured compounds

  → useful as catalysts
• How do group 7 elements (halogens) react with metals?

  form ionic compounds in which the halide ion carries a charge of -1
• What can we say about the reactivity of group 7 elements (halogens)?

  the further down the group an element is, the less reactive the element (and the higher its melting/boiling point)
• What displacement occurs among halogens?

  a more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt
• What is shielding?


  when electrons in inner shells weaken the attraction between electrons in the outer shell
• What can we say about the gain/loss of electrons compared with the height of the energy level of the outer electrons?

  the higher the energy level of the outer electrons:

  → the more easily electrons are lost

  → the less easily electrons are gained
• What is hard water?

  water containing dissolved compounds, usually of calcium or magnesium
• Describe the two types of hard water

  permanent hard water remains hard when it is boiled, temporary hard water is softened by boiling
• What does temporary hard water contain?

  hydrogencarbonate ions (HCO3- )
• Why does temporary hard water soften when heated?

  the hydrogencarbonate ions decompose on heating to produce carbonate ions which react with calcium and magnesium ions to form precipitates
• Give two disadvantages of using hard water

  → more expensive because more soap is needed

  → scale produced by hard water reduces efficiency of appliances such as kettles
• Give two advantages of using hard water

  → calcium compounds are good for the development and

  maintenance of bones and teeth

  → can help reduce heart disease
• Describe the reaction of hard and soft water with soap

  soft water forms lather with soap, hard water forms scum with soap so more soap is needed to form lather
• How can we soften permanently hard water?

  by removing the dissolved calcium and magnesium ions
• Describe two ways of softening hard water

  → adding sodium carbonate (which reacts with the calcium/magnesium ions to form a precipitate of calcium/magnesium carbonate)

  → using commercial water softeners (such as ion exchange columns containing hydrogen ions or sodium ions, which replace the calcium and magnesium ions when hard water passes through the column)
• What must drinking water for humans contain?

  sufficiently low levels of dissolved salts and microbes
• Why do we purify drinking water?

  to improve taste and quality
• Name two methods of water purification

  filter cartridges (small scale), water treatment (large scale)
• What do filter cartridges contain to purify water?

  → activated carbon: reduces chlorine levels/organic impurities

  → ion exchange resin: removes calcium, magnesium etc. ions

  → silver: stops growth of bacteria within filter
• How is drinking water purified in a treatment facility?

  1. water passed through filter beds to remove any solids

  2. water purified using chlorine
• Why is chlorine added to drinking water?

  to reduce microbes
• What is water fluoridation?

  the addition of fluoride to a water supply to reduce tooth decay
• Give two advantages of water fluoridation

  reduces tooth decay, strengthens teeth
• Give two disadvantages of water fluoridation

  excess of fluoridated water can cause problems with thyroid bones, you cannot consent to drinking fluoridated water
• How do we calculate the energy transferred in a reaction?

  Q= mc ΔT

  
  

  Q = energy transferred

  m = mass of liquid heated

  c = specific heat capacity

  ΔT = change in temperature
• What method do we use to determine the amount of energy released when substances burn

  simple calorimetry
• What can we use calorimetry for?

  comparing the amount of energy released by fuels and foods
• What does the energy change of a solution (in an insulated container) during a reaction tell us?

  the amount of energy released or absorbed in the chemical reaction
• What can simple energy level diagrams show?

  → the relative energies of reactants and products

  → the activation energy

  → the overall energy change of a reaction