Amount of substance Flashcards
Calculating Water of crystallisation
3.210g of hydrated magneisum sulfate MgSO4xH2O was heated to make 1.567g of anhydrous magneisum sulfate. Find the value of x and hence give the formula of the hydrated salt
Set up a Mass, Mr, Moles table with the MgSO4 and H2O as a heading
Mass of MgSO4 has been given (1.567) minus that from 3.210 to get 1.643g of water
Divide the mass by the Mr on both sides
U get the moles from this which is 0.013 for MgSO4 and 0.091 for H2O
Divide by the moles on MgSO4 u get the ratio 1:7
7 is x in MgSO4xH2O
written as MgSO4.7H2O
. is important
What does anhydrous mean
Without water
In a titration 21.4 cm^3 of 0.2 moldm^-3 HCL was needed to neutralise 25cm^3 of NaOH. Calculate the Conc of NaOH
- Lay it out like a balancing equation so like this:
NaOH + HCl –> NaCl +H2O - Use the equation N(moles)=C (concentration moldm^-3) x V (volume dm^-3)
- In this question the volume of both is given and the conc is given for HCl
- Input the numbers in the equation and you get 0.0214 x 0.2=0.00428
- The molar ratio of the equation is 1:1 therefore the moles for NaOH is the same as HCl
- You already have the Volume of NaOH so rearrange the equation for conc and you get 0.00428/0.025= 0.17 mol
- Usually it is to 2DP
Formula for Moles (the one linking conc and vol)
Moles=Conc (moldm^3)x Vol (dm^3)
Can you substitute atom economy for percentage yield
No both are diff
Why is a high atom economy good
Better for enviornment
Less waste
More sustainable
Cheaper
What is the formula for atom economy
Mass of desired product/Total mass of reactants x100
What is the formula linking moles mass mr
Mass(g)= Mr x Moles (mol)
What is the ideal gas equation
pV=nRT
p=Pascals (Pa)
v= Metres^3 (m^3)
n=Moles(mol)
r=8.31 j/mol
t=Temperature (K) if its in *C then add 273
How much gas is made by 0.12g of magneisum ribbon and HCl at 298k + 100kPa (r=8.31)
- Lay the question out as a balanced equation like this:
Mg +2HCl –> MgCl2 +H2 - Mass=Mr x moles rearrange to mass/mr
- u have the mass of mg so divide it by the mr (0.12/24.3)=0.0050 mol
- Look at the molar ratio of the equation it is 1:2:1:1 both Mg andf H are 1 so therefore the same moles
5.substitute the ideal gas equation for volume = v=nRT/p= 0.005 x 8.31 x 298/100000 =0.000124
how do you convert 100m^3 to cm^3
x1,000,000
0.75 g of Calcium Carbonate reacts with 0.25 moldm^-3 sulfuric acid what volume of acid (in cm^3) will be needed to neutralise calcium carbonate
- Write out the equation CaCO3 + H2SO4 – CaSO4 + H2O +CO2
- Work out the moles
- moles = 0.75/100 =0.0075
- they are all in the same molar ratio
- volume = moles/conc 0.0075/0.25= 0.03 dm^-3
- convert to cm^3- 30cm^3
What do you do in doubt
Work out the moles
What is the unit of V in Ideal gas equation and convert cm^3 to it
METRES ^ CUBED
1m^3=1,000,000cm^3
How much cm in 1 dm
10 cm
How much is 100cm^2 in dm^2
1
How much is 1000cm^3 in dm^3
1000
Convert 1000 dm^3 into m^3
1m^3
What is avogodros number
6.022x10^23
Formula for moles from a gas
Volume(dm^3)=Moles x 24
Moles from a solid
Mass(g)=moles x RAM (g/mol^-1)
RAM is the bigger number on the atom
formula for Moles from solution
Moles=Conc(moldm^3) x vol (dm^3)
define empiracal formula
simplest whole number ratio of atoms in a compound
General method for empircal fomrula
Step 1 : Divide each mass (or % mass) by the atomic mass of the element
Step 2 : For each of the answers from step 1 divide by the smallest one of those
numbers.
Step 3: sometimes the numbers calculated in step 2 will need to be multiplied up to
give whole numbers.
These whole numbers will be the empirical formula
