Quantitative Chemistry Flashcards
What is an isotope of an element?
Atoms of the same element with the same number of protons and electrons but with a different number of neutrons e.g. carbon-13.
What is a mole? How do you calculate it?
Relative formula mass in grams - calculated with Mass (g) / Ar or Mass (g) Mr.
What is Avogadro’s constant?
6.02 x10^23 - there is always this may atoms, molecules or ions in the mole of any substance.
What is a limiting reactant? How can it be recognised?
The limiting reactant is the reactant that gets used up first and limits the product of the reaction. (The excess reactant is the reactant that is in excess i.e. the other reactant.) The limiting reactant can be worked out from the ratio of the moles an the multipliers. Example: there are 4 burger buns and only 3 patties. Therefore the patties are the limiting reactants because only 3 burgers can be made.
What is yield?
The mass of product produced.
What is the percentage yield and how is it calculated?
Percentage of actual yield as compared to maximum theoretical yield.
(Actual mass of products produced / theoretical mass of products) x 100
What are some reasons that percentage yield is not 100%?
- The reaction is reversible
- The reactants may be impure
- There may be by-products (unwanted or unexpected products)
- Some of the products may be left in the apparatus
What is atom economy and why is it useful?
Atom economy is the extent to which the atoms in the reactants end up in the desired product. it is important because it maximises profits that companies make and helps reduce pollution and reduce the amount of energy used.
How can we calculate atom economy?
(Mr of desired product / Mr of total reactants) x 100
How many cm^3 are in 1 dm^3?
1000
How do we calculate concentration of a solution?
Concentration (g/dm^3) = Mass of solute (g) / volume of solvent (dm^3)
How can we increase concentration?
- Adding more solute and dissolving it in the same volume of solvent
- Evaporating off some of the water so the same mass of solute is in a smaller volume of solvent.
What is a titration?
The experiment used to determine the exact volume of acid and alkali needed to neutralise with each other.
What is the curved surface of a liquid called and how do we properly read it?
Meniscus - liquid sticks to the surface of the surface of the cylinder. Read from the bottom of the meniscus with eye level with the meniscus.
What are concordant results?
Precise results that are within 0.1 of each other.
