c3 quantitative chemistry Flashcards
(32 cards)
what does the conservation of mass state?
no atoms are destroyed or made during a reaction, therefore the mass of the product equals the mass of reactants.
what is the relative formula mass of a compound?
the sum of relative atomic masses of the atoms in the numbers shown in the formula
what should the RFM be in a balanced equation?
balanced on both sides
how can you calculate percentage mass of an element in a compound?
(Ar x number of atoms in the element // Mr of compound) x 100
what is the mass of one mole in a substance numerically equal to?
the substance’s relative formula mass
what is avogrado’s constant?
6.02x10^23
why is avogrado’s constant used?
the mass of that number of atoms or molecules of any substance is exactly the same number as the relative atomic mass or relative formula mass of the element/ compound
what can the measurement of amounts in moles apply to?
atoms, molecules, ions, electrons, formulae and equations
how to calculate the number of moles in a substance?
mass of element or compound (g) // Mr of element or compound
why might the mass increase in a reaction?
one of the reactants is a gas and all the products are solid, liquid or aqueous
— before the reaction, the gas is floating in the air , so its not contained in the reaction vessel, therefore it is not counted for its mass
— then in the products, it becomes contained inside the reaction vessel
why might the mass decrease in a reaction?
one of its products is a gas and all the reactants are solid, liquids or aqueous
— the reactants where contained in the reaction vessel
— if the vessel isnt enclosed, the gas product can escape, decreasing the mass
how can masses of products or reactants be calculated?
using a balanced equation
how to determine the amount of moles in a reaction?
look at the BIG number at the front of the compounds or elements. only in a balanced equation
what is a limiting reactant?
the reactant which is completely used up in a chemical reaction
what is an excess reactant?
the reactant which is still left over after the chemical reaction
why would a scientist use excess of one reactant in a chemical reaction?
to ensure that the other reactant is completely used up
what is the relationship between the limiting factor and product formed?
they are directly proportional
how to calculate the mass of a product formed?
1) write out a balanced equation
2) work out the relative formula masses of the reactant and product wanted
3) find out the number of moles in the substances you know the mass of
4) use the balanced equation to work out how many moles there’ll be of the other substance. thats how many moles of product will be made of this many moles of reactant
5) use the number of moles to calculate the mass
what can the concentration of a solution be measured in?
mass per given volume of solution
what is concentration?
the amount of substance in a certain volume of a solution
what is the relationship between the solute added and the concentration?
the more solute added, the higher the concentration. they are proportional
how to calculate the concentration of a solution in g/dm^3 ?
mass of solute (g) // volume of solvent (dm^3)
how to calculate the concentration of a solution in mol/dm^3 ?
moles of solute // volume of solvent (dm^3)
why is it not possible to obtain the calculated amount of a product?
1) the reaction may not go through completion as it is reversible
2) some of the product may be lost when separated from the reaction mixture
3) some reactants may react in different ways different to the expected reaction
