quantitative chem

• relative formula mass (Mr)

  the sum of the relative atomic masses of the elements as given in the formula for any non-molecular compound
• % mass of an element in a compound

  (relative atomic mass (Ar) x number of atoms of that element / relative formula mass (Mr)) x 100
• relative atomic mass (Ar)

  the measure of the mass of one atom of a particular element (nucleon number)
• difference between atomic mass and relative atomic mass

  - atomic mass is the actual mass of an individual atom, whereas relative atomic mass is an average of the masses of all the isotopes of an element

  - atomic mass is a specific value, whereas relative atomic mass is a relative value
• atomic weight


  the number of protons plus the number of neutrons of an atom
• atomic number


  the number of protons in the nucleus of an atom
• atomic mass


  the weighted average of the masses of the isotopes of an element
• the mole is simply the name given...


  to an amount of a substance
• mole


  the SI base unit used to measure the amount of a substance
• one mole of any substance is...

  an amount of that substance that contains an Avogadro number of particles
• Avogadro's constant


  number of molecules in 1 mole = 6.022 × 10²³
• why is the Avogadro's constant used?

  The mass of this number of atoms or molecules of any substance is exactly the same number of grams as the relative atomic/formula mass of an element/compound
• in more simple terms, one mole of any substance is...

  its relative formula mass in grams

  (e.g. carbon has an Ar of 12, so one mole of carbon is exactly 12g)
• one mole of atoms/molecules of any substance...

  will have a mass in grams equal to the relative formula mass
• number of moles (mol) =

  mass (g) / relative formula mass (Mr)
• mole formula triangle

  
• in a chemical reaction...

  mass is always conserved
• during a chemical reaction, ... atoms are destroyed and ... atoms are created


  no, no
• because of the law of conservation...

  no mass is lost or gained
• if the mass in a reaction changes...

  it is because a gas is involved and the reaction took place in an unsealed reaction vessel
• if the mass in a reaction increases...

  one of the reactants was a gas that's found in air and when it reacted it became a part of the product in the reaction vessel
• if the mass in a reaction decreases...

  one of the reactants has been turned from a solid/liquid/aqueous solution into a gas, a product, and escaped the reaction vessel
• why does gas escape if the reaction vessel isn't sealed?

  gas will expand to fill any container it's in, so if it's in an unsealed container, the gas expands out of the vessel and escapes into the air ground
• what are the big numbers in chemical equations?

  they are coefficients that multiply all the atoms in a formula, which also represent how many moles of each substance takes part/is formed in a reaction
• what are the small numbers in chemical equations?

  they are subscripts that depicts the number of atoms of the element present in the molecule
• reactions stop when...


  one reactant is used up
• the reactant that's used up after a reaction is called...

  the limiting reactant (because it limits the amount of product that's formed)
• any reactants that remain after a reaction stops is called....

  excess reactants
• excess reactants are present to ensure...


  that the other reactant is used up
• the amount of product formed is ... to the amount of limiting reactant

  directly proportional
• If you half the amount of the limiting reactant, how will the amount of product be affected?


  the product will also be halved
• the amount of product depends on...

  the limiting reactant
• more reactant particles = more...

  product particles
• One mole of any gas occupies...

  24dm³ at 20°C (room temperature)
• at the same temperature and pressure, equal number of moles of any gas will...


  occupy the same volume
• volume of gas (dm³) =

  (mass of gas (g)/Mr of gas) x 24
• volume of gas formula triangle

  
• concentration is a measure of...

  how much solute there is per volume of solution
• concentration


  the mass of solute in a given volume of solution, or mass/volume
• the more solute there is in a given volume...

  the more concentrated the solution