quantitative chem Flashcards
(29 cards)
what is the law of conservation of mass?
-no atoms are lost or made during a chemical reaction so the mass of the product equals the mass of the reactants
what kind of ions do metals form?
-positive ions
what kind of ions do most non-metals form?
-negative ions
what ions do transition metals form
-several different ions
key fact about ions
-the ions a metal or non metal forms is based on their group
-oxygen which is a non-metal and in group 6 forms a O²⁻ ion
-magnesium which is a metal in group 2 forms Mg²⁺ ion
what is a key rule of ionic compounds ?
-the charges on the ions have to cancel out to leave an overall charge of zero
why are you never allowed to change the small numbers in a chemical formula?
-this produces a different molecule.
what is the definition of (relative formula mass Mr)
-the sum of the relative atomic masses of the atoms in the numbers shown in the formula
what are 2 key facts about relative formula mass?
-no units
-never involves big numbers
equation for calculating percentage by mass of an element
(total relative atomic mass of the atoms of that element/relative formula mass of compound) x 100
what is the equation for that links moles, mass and relative atomic mass?
-moles=mass (g) / relative atomic mass. ( Ar)
what is the equation that links moles, mass and relative formula mass
-moles = mass (g) / relative formula mass Mr
what is Avogadro’s constant?
-6.02 × 10²³
what is the limiting reactant?
what is the excess reactant?
-the reactant that is fully used up
-the reactant that is not used up
2 definitions of concentration?
-mass of a solute in a given volume of solution
-number of moles in a solute of a given volume of solution
what is a solute?
-a chemical that is dissolved in a solvent
2 equations for concentration + units
-concentration ( g/dm³) = mass (g) / volume (dm³)
-concentration (mol/dm³) = moles/volume (dm³)
how do we increase the concentration?
-increasing the mass of the solute and keeping the volume the same
how do we decrease the concentration?
-increasing the volume of the solution and keeping the mass of the solute the same
what are three reasons why it is not always possible to achieve 100% yield in a chemical reaction?
-some of the product may be lost when separated from reaction mixture
-some of the reactants may react in different ways to the expected reaction so we do not get the product we expect
-reversible reactions may not go to completion
equation for percentage yield
(mass of the product actually made/maximum theoretical mass of product) x 100
why can we not achieve greater than 100% yield?
-that would mean we had created atoms
what is atom economy?
-a measure of the amount of starting materials that end up as useful products
what are two advantages of atom economy?
-minimises the production of unwanted products, so we save money
-increased sustainability by not wasting resources
