quantitative chemistry Flashcards
conservation of mass and balanced equations
- no atoms lost or made during a chemical reaction
- mass of products = mass of reactants
relative formula mass
- sum of the relative atomic masses of atoms in numbers shown in formula
e.g HCl = 1 + 35.5 = 36.5
relative formula mass in balanced chemical equation
sum of rfm of reactants in quantities show = sum of rfm of products in quantities shown
mass only changes when a reactant or product is a gas
- gas has been released into atmosphere
estimations of uncertainty
whenever a chemical measurement is made there is always some uncertainty about result obtained
moles equation
moles = mass / rfm
moles = mol
mass = g
rfm = g mol-1
avogadro’s constant
number of atoms, molecules or ions in a mole of a given substance
6.02 x 10^23
limiting reactants
- reactant used up / not in excess since it limits the amount of products
- if used, amount of product produce is restricted to amount of excess reactant that reacts with limiting one
what is concentration measured in?
- g/dm3
mass of solute in a given volume of a known concentration equation
mass = concentration x volume
a smaller volume or larger mass of solute gives a…
higher concentration and vice versa
percentage yield calculation
percentage yield = amount of product produced / max amount of product possible x 100
why is it not always possible to obtain the calculated amount of a product?
- reaction may not go to completion because it is reversible
- some products are lost when it is separated from the reaction mixture
- some reactants may react in different ways to expected reactions
yield
amount of product obtained
atom economy equation
rfm of desired product from reaction / sum of rfm of all reactants x 100
what is atom economy?
measure of the amount of starting materials that end up as useful products
why is atom economy important?
- important for sustainable development and economic reasons to use reactions with high atom economy
what are some reasons why a particular reaction pathway is chosen/not chosen
- atom economy
- yield
- rate
- equilibrium position
- usefulness of by-products
volume of gas equation (at room temp)
moles x 24
mass of gas(g)/rfm of gas(dm3) x 24
at the same temp and pressure…
equal numbers of moles of any gas will occupy the same volume
volume of 1 mol of any gas at rtp
room temp and pressure = 20oc and 1 atm is 24dm3
concentration equation (moles and volume)
conc = moles / vol
