fea p1,2 Flashcards
what does Avogadro’s constant represent?
the number of atoms per mole of the carbon-12 isotope
how do you calculate the mass of 1 mole of an element?
mass of 1 mole = relative atomic mass in grams
equation linking moles, mass and mr?
moles (mol) = mass (g) / molar mass (g mol-1)
what is an empirical formula?
simplest whole number ratio of atoms of each element present in a compound
how do you calculate empirical formula?
set mass to percentage, vice versa (must add to 100)
divide the amount of each element by its mr
divide the answers by the smallest value obtained
ratio!
what is Avogadro’s law?
under the same temperature and pressure, one mole of any gas would occupy the same volume
how much volume does a gas occupy at room temp and pressure?
24 dm3 or 24000 cm3
molar gas volume
the volume per mole of gas molecules
why do different gas particles occupy the same volume?
the gas particles are very spread out, hence the individual differences has no effect
how do you calculate moles when gas volume is given?
moles = volume (dm3) / 24
moles = volume (cm3) / 24000
what are the ideal ways in which gases behave?
continuous motion
no intermolecular forces experienced
exert pressure when they collide with each other or container
no kinetic energy lost in collisions
when temp increases, kinetic energy of gases increase
ideal gas equation and units
pV = nRT
pressure (Pa)
volume (m3)
temperature (K)
1 atm = ? Pa
1 atm = 101325 Pa
how do you convert from *C to K?
+ 273
what does concentration of a solution mean?
amount of solute dissolved in 1 dm3 of solvent
equation linking moles, conc and volume
moles = concentration (moles dm-3) x volume (dm3)
what is a standard solution?
a solution of known concentration
how do you prepare a standard solution?
1 weigh solute using weigh by difference method
2 dissolve solute in beaker using the solvent
3 pour solution into volumetric flask
4 rinse the beaker using the solution (e.g. distilled water) and add to flask
5 add solvent to flask until it reaches graduation line
6 mix solution thoroughly
concentrated
dilute
concentrated - large amount of solute per dm3 of solvent
dilute - small amount of solute per dm3 of solvent
percentage yield definition
efficiency of which reactants are converted into products
why might the percentage yield not be 100%?
reaction may be at equilibrium
reactants may be impure
side reactions could happen
reactants or products may be left behind when transferring
loss of products during separation and purification
percentage yield equation
percentage yield = actual amount of product (mol) / theoretical amount of product (mol) x 100
atom economy?
proportion of desired products compared with all the products formed in the reaction
atom economy equation?
atom economy = mr of desired product / sum of the mr of all products x 100
does 100% yield = 100% atom economy?
no, even if all the reactants are converted into products, not all products of the reaction will be required products
what type of reaction has 100% atom economy?
addition reactions (two or more reactants combined to form one product)
systematic error
same error appears in each measurement
what is the weighing by difference method?
1 measure mass of container
2 add chemical to container and weigh container
3 calculate mass of the chemical
4 transfer chemical and reweigh empty container
5 calculate the mass of chemical transferred
maximum error formula
uncertainty / total volume x100
e.g. 0.2 / 250 x 100 = 0.08%
