C3-quantitative chemistry

• is the Mr of a compund always greater than the Ar of any of the elements in that compound

  yes as you find the Mr by adding up the Ar of each element so it must be greater
• the Ar of oxygen is 16 and the Ar of nitrogen is 14. find the Mr of nitric oxide, NO.

  14+16=30

  theres only one atom of each element in the formula, so just add the Ar values together
• how do you calculate the percentage mass of an element in a compound

  multiply the Ar of the element by the number of atoms of that element in the formula of the compound. then divide the compounds Mr and multiply by 100
• the formula of the compound of sulfur hexaflouride is SF6

  calculate the Mr of sulfur hexafluoride. Ar of F=29 and Ar of S = 32

  19x6=114

  114+32=146
• the Mr of methane, CH4 is 16, the Ar of carbon is 12

  what is the percentage mass of carbon in methane

  12/16=0.75

  0.75x100=75%
• what does it mean by the term conservation of mass?

  it means the total mass of the products in a reaction will always be equal to the total mass of the reactants, this is because no atoms are ever destroyed or created during a reaction
• how do you find concentration of a solution in g/dm3

  divide the mass of solute in grams by the volume of the solution in dm3
• what is the mass of sodium sulfate is there in 100cm3 of sodium sulfate solution if the solution has a concentration of 5g/dm3

  100cm3=100/1000=0.1dm3

  concentration = mass / volume

  5 x 0.1 = 0.5g
• what is the concentration in g/dm3 of the solution formed when 15g of potassium nitrate are dissolved in 250cm3 of water

  250 / 1000 = 0.25

  concentration = mass / volume

  15 / 0.25 = 60g/dm3