Quantitative chemistry Flashcards
What is the conservation of mass?
total mass of the product=total mass of reactant
mass is conserved because no atoms are lost
half equation
used to show what happens to one reactant in a chemical reaction
Fe–Fe 2 + 2e-
iron atoms loses two electron
What is the relative formulae mass?
relative formulae mass is relative atom mass (top number)
CO2 (12 x 1 ) + (16 x 2) = 44
Ca(NO3)2 40 + (14 x 2) + ( 16 x 6)=164
What is Avogadro’s constant and give an example?
6.02 x 10 23
EXAMPLE
Na2O
3 moles so 3 x 6.02 x 10 23=1.806 x10 24
Number of moles=Mass/relative atomic mass
EXAMPLE-calculate the number of atoms in 28g of lithuim Li=7
28/7=4 4 x 6.02 x 1023=2.408 x 10 24
What is the equation for Moles?
Number of moles=Mass/relative atomic mass
EXAMPLE-120g of calcium. How many moles of calcium have you ben given. Ar for CA=40
120/40=3moles
Limiting reactant example
How many moles of copper will be produced if we used 0.5 moles of copper sulphate and 1 mole of magnesium? Calculate the mass of copper produced
CuSO4 + Mg— MgSO4 + Cu
0.5 x 63.5=31.75g
Moles of gas
Volume=amount(mol) x 24dm3
Calculate the volume of 51g of ammonia gas NH3=17
moles=mass/ar
51/17=3
3 x 24=72dm3
Concentration
Concentration= mol/volume
A solution of sodium nitrate has a conc of 0.8 mol/dm3.Clculate the mass of sodium nitrate in 0.5dm3.MR NaNO3=85
moles=conc x voulme
moles = 0.8 x 0.5 = 0.4
mass=moles x Ar
0.4 x 85=34g
Titeration
17cm3 of hydrochloric acid were required to neutralise 25cm3 of sodium hydroxide.(conc of 0.1 mol) Calculate conc of acid. Mr HCl=36.5
HCl +NaOH–HaCl + H2O
HCL
C= (0.0025/0.017)=0.147 mol/dm3
n=0.0025
V= 0.017 DM3
NaOH
C=0.1 MOL/DM3
N= (0.1 X 0.025=0.0025)
V=0.025 DM3
0.147 x 36.5= 5.366g
n=c x v
What are the first steps of titeration?
1)Wash and rinse the pipette with the alkali being used
2)Measure the volume (25cm3) of sodium hydroxide solution using a pipette into a
conical flask
What is percentage yield?
Can’t always get 100% yield
- Some product may be lost
- Reversible reaction may not go to completion
- Reaction may react in different ways
What is the Percentage yield calculation?
Percentage yield= mass of product actually made/Maximum theoretical product x 100
What is the calculation for atom economy?
Atom economy= relative formulae mass of desired product/ sum of all relative formulae mass of all product reactant x 100
What factors do you consider when choosing a reaction pathway?
Important factors to consider when choosing a reaction pathway include
- atom economy
- Cost of reactant
- % yield
What is the difference between limiting reactant and excess?
Fully used up-Limiting reactant
Not used up-excess reactant
What is an ionic equation?
used to simplify complicated equations
show the species(different atoms,molecules or ions involved in a reaction) involved
spectator ions ( ions are not involved with the reaction)are not included
Give an example of an ionic equation?
AgNO3 + NaCl—AgCl +NaNO3
silver nitrate +sodium chloride – silver chloride
IONIC EQUATION:
Ag+(aq) + cl-(aq)—AgCl(s)
What is an apparent change in mass?
happens when a reaction is carried out in a non-closed system and includes a gas that can enter or leave
Give an example of apparent change in mass
when mg is burned in air it forms magnesium oxide so the mass of the solid increases because oxygen has a mass
if the mass of oxygen is included the total mass of all the reactants is equal to the total mass of all the product
How do you calculate the mass of a reactant or product from a balance equation?
Al2O3—2Al + 1 1/2 O2
calculate the mass of AL2O3 needed to produce 540g of 2Al
amount of aluminium=540/27=20mol
amount of aluminium oxide required=20/2=10mol
formulae mass of aluminium oxide= (27 x2)+(16 x 3)=102
mass of aluminium oxide needed=10 x 102=1020g
What do you add to the sodium hydroxide in the conical flask?
3) Add 5 drops of indicator such as methyl orange to the conical flask
4) Place the flask on a white tile so colour change can be seen clearly
What acid do you add to the alkali?
6) Place the sulfuric acid in burette that has been washed and rinsed with acid
7) Add the acid to the alkali until the solution is neutral.Once we see a colour change(yellow-red) add the acid drop by drop until the solution is neutral
Why is it important to mix the acid and alkali?
8) Important to swirl the solution to make sure the acid and alkali mix
9) Read the volume of acid added from the burette
What do you do once you have done the practical?
10) Repeat the titration x2 take the mean for the final volume
11) Calculate the mean volume of acid added
