Reaction Calculations Flashcards
What is the molecular formula ?
formula that shows the number and type of each atom in a molecule
What is the empirical formula ?
simplest whole number ratio of atoms of each element present in one molecule or formula unit of a compound
E.g. the empirical formula of ethanoic acid is CH2O
What is the gas equation?
PV = nRT
(Pa) (m3) = n (8.31 mol/K) (K)
What avogadro’s number?
Number of particles equivalent to relative atomic mass/molecular mass of substance
E.g 6.02 x 10^23 = 12g of Carbon-12
Gas volume EQUN?
No. moles = volume of gas (dm3)/ molar gas volume (dm3)
- at room temp/pressure , molar gas volume = 24 dm3
- at standard temp/pressure molar gas volume = 22.4dm3
PRACTICAL : making a standard solution
- Weigh out precise amount of solid
- Add to a small volume of water/pre dissolve solid
- Transfer to volumetric flask
- Rinse the beaker with water/add washings to the volumetric flask
- Make up to SCRATCH mark with water - use pipettes t be precise
SWIRL FLASK
PRACTICAL : titrations
- Measure known volume of a solution with volumetric PIPETTE /put into conical flaks
- Other solution in burette (at 0.00 cm3)
- Few drops of indicatorto solution
- Open tap on burette/solution is added to conical flask until changes colour
- Slow down before end point (add dropwise)
- Repeat until concordant resultsreached (within 0.2 cm3 of each other)
Systematic errors?
errors that occur as a result of a faulty or poorly designed experimental procedure
E.g no reading burette at eye level
- repeating doesn’t remove these errors
Percentage uncertainty equn?
(Absolute uncertainty / measured value ) x 100
- times ans by 2 if read instrument 2 times etc
% yield equn?
% yield = (actual yield / theoretical yield) /100
- use moles
Atom economy equn?
Atom economy = (Mr of desired product / sum of Mr of all reactants ) x 100
Molar volume of a gas meaning?
Volume occupied by one mole of a gas at specified temp/pressure
Percentage purity equation?
(Actual mass/ expected mass ) x 100
Avogadro’s constant equation?
No. Moles = no. Particles / Avogadro’s constant
dm3 to m3 ?
Divide by 1000
Problem with using water of crystallisation method?
If value of crystallisation is greater than expected - suggest compounds underwent further decomposition
If value is less than expected - not all water molecules driven off during heating
PRACTICAL: Determining molar volume of gas
Use HCl and sodium carbonate
1. Measure out fixed vol of HCl into conical flask
2. Add known mass of sodium carbonate to conical flask
3. Immediately connect the gas syringe
4. All reaction to complete/ record vol of CO2 produced
- Repeat with different masses of sodium carbonate
Can use delivery tube/measuring cylinder full of water/measure displacement of water
Use :
Plot graph of vol of CO2 produced against mass of NaCO3
Volume of CO2 produced/moles of sodium carbonate = molar gas volume
Assumptions when using gas syringe/delkivery tube method to find molar volume of gas ?
- amount of gas lost between adding sodium carbonate/connecting gas syringe or delivery tube is negligible
- delivery tube/syringe set up is airtight so no gas lost
- reaction is complete
