11 Chemistry - Stoichiometry Flashcards
Define: mole / avogadro’s constant
(6.02X10^23) things
How many molecules 1 mole of hydrogen gas has?
(6.02X10^23)
How many moles is:
a) 3.01 X 10^23 =
b) 18 X 10^22 =
a) 0.5 moles
b) 0.299 moles
how many
_________ = moles
avogadro
How many is:
a)2.8 moles of h2?
a) 1.6856 x 10^24
moles x avogadro = how many
If I have 0.5 moles of CuSO4
a) how many molecules of copper sulphate are there?
b) how many oxygen atoms are there?
a) 0.5(avogadros) = 3.01x10^23
b) (3.01x10^23) x 4 = 1.204 x 10^24
What is the atomic mass (Ar) of an atom equal to?
It is equal to the mass on grams of one mole of that element
eg. copper, Cu, has an atomic mass of 64, this means one mole of Cu is 64g
What is the molecular mass (Mr) of a compound equal to?
It is equal to the mass of one mole of a compound
eg. NaCl Na = 23 Cl = 33.5
so NaCl = 23+33.5
= 58.5g is the mass of one mole of NaCl
Find the mass of one mole of:
a) methane CH4
b) Ethanic acid CH3COOH
c) Glucose
a) 16g
b) 60g
c) 180g
Equation for moles and mass
mass mass
Moles = _______ moles formula mass
Ar or Mr
What is concentration?
The amount of solute in a given volume of solution
What is the unit for concentration?
mol dm^-3 or (mol/dm^3)
What is the equation for concentration?
moles vol(dm^3)
concentration = \_\_\_\_\_\_\_\_ moles 24dm^3
volume(dm^3)How much is 1 dm^3?
1 litre
At room temp, what is the volume of 1 mole of any gas?
24dm^3
At 0°C, what is the volume of 1 mole of any gas?
22.7dm^3
Equation for moles in gases
volume volume
moles of gas = ________ moles 24dm^3
24dm^3
equation of combustion
something + 2oxygen –> carbon dioxide + water
If i burnt 10g of methane, what mass of oxygen would be needed?
1) 10/16 = 0.625 moles of methane
2) We know from the combustion equation that every 1 molecule of methane reacts with 2 of oxygen
so, 0.625 x 2 = 1.25 moles of oxygen
3) moles x Mr = mass
1. 25 x 32 = 40g of oxygen
What are all equations that link moles, to mass, to gas volume, to concentration?
mass volume moles
moles Mr moles 24dm^3 concentration 24dm^3
What does an acid + base give?
Give an example with hydrochloric acid and sodium hydroxide
acid + base = neutralisation
hydrochloric acid + sodium hydroxide = water + salt
What is the relative atomic mass (Ar)?
the weighted average of all isotopes of an element, compared to carbon 12
What is relative formula mass (Mr)?
the combined mass of the atoms in a compound, compared to carbon 12
What do these symbols mean?
a) (g)
b) (s)
c) (aq)
d) (l)
a) (g) gas
b) (s) solid
c) (aq) aqueous - dissolved in solution
d) (l) liquid
What does limiting reagent and excess reagent mean?
Limiting - the one you have less of, the one that is all used up, how much is produced depends on it
Excess - the one you have more of, still some left at then end but in smaller amount
What are the ionic charges of metals?
always +ive group number (except transition metals)
eg. Na+ Al3+
What are the ionic charges of non-metals?
always -ve
charge = 8 - goup number
eg. O2- Cl-
What are the charges for these polyatomic anions?
a) CO3
b) SO4
c) OH
d) NO3
e) PO4
f)NH4 (cation)
a) CO3 2-
b) SO4 2-
c) OH -
d) NO3 -
e) PO4 3-
f)NH4 (cation) +
What is empirical formula
simplest ratio of the atoms in a compound
what is molecular formula
actual ratio of atoms
eg. C6 H12 O6
How do you determine empirical formula?
1- start with no. in grams
if it is % the total mass is 100g, so then the masses = %
2-convert each mass into moles
3-divide each mole by the smallest no. of moles calculated
4-round to the nearest whole number, this is the ratio
how do you convert empirical formula to molecular?
1- calculare mass of empirical formula
2- divide molar mass of compound by mass of empirical formula to find ratio
3- multiply all atoms by this ratio
done
how do you find the relative atomic mass from percent abundance?
1- each exact atomic weight is multiplied by the percent abundance (as decimal, e.g. 23.2% = 0.232)
2- Add all results together
eg Carbon
Mass no. = 12
Exact weight = 12.000000
% abundance = 98.90
Mass no. = 13
Exact weight = 1.000000
% abundance = 1.10
solution:
(12.000000) (0.9890) + (1.000000) (0.0110) = 12amu
Boron has an atomic mass f 10.18amu
however no single boron atom has a mass of 10.10 amu
how do you explain this?
10.18 is the average mass
some atoms have less and some have more but the average turns out to be 10.18
