C3: Moles and Mass Flashcards
revise moles, masses and Mr as well as basic calculations
What is Relative atomic mass?
the average number of all the isotopes of that element (Ar)
what is relative formula mass?
the Ar of all the compounds added up
how do you calculate percentage mass of an element from a molecular formula?
(Ar of element*number of element) / (Mr of whole compund) * 100
what is a mole
a unit of measuring the amount of chemical
how many particles does one mole of substance contain?
avogadro’s constant: 6.02*10^23
atomm, molecules or ions
what is the mass of one mole of substance equal to?
the relative formula mass in grams of the substance
what are the four steps to calculate the mass or moles of reactants or products?
1) write out balanced equation
2) find moles of known substance (mol=mass/mr)
3) find moles of unknown substance using molar ratio
4) find mass of unknown substance. (mass=moles*mr)
what is the law of conservation of mass?
no atoms are gained, created, lost or destroyed in a chemical reaction. hence the mass of the reactants will equal the mass of products
what is the exception to the law?
when one of the reactants or products is a gas - it can escape easily and is difficult to measure i.e: oxidation or thermal decomposition
how can you prove the law?
comparing the mass of (balanced) reactnts and products or comparing the moles
