1.3 Amount of substance Flashcards
Avogadro constant
6.022 x 10^23
The number of atoms in 12g of C12
Number of particles
No of particles = moles x avagadro constant
Relative atomic mass
Average mass of one atom of an element compared to 1/12th mass of C12 atom
Relative molecular mass
Average mass of one molecule compared to 1/12th mass of C12 atom
Moles=
Mass/Mr
Percentage yield
Actual yield/theoretical yield x 100
Why do scientists want a high percentage yield?
It increases the amount of product that is made from the same amount of reactants
How can percentage yield be increased?
Improvements to experimental technique
Atom economy
Mass of desired products/total mass of reactants x 100
Why do scientists want a high atom economy?
Increases the mass of atoms in the reactants that are turned into products
Reduces the amount of waste
Concentration equation
Moles/volume
Concentration
The amount of a solute dissolved in a known volume of solvent
Concordent
Within 0.1cm3 of each other
Steps to make up a standard solution (titration)
- Weigh sample bottle containing solid on a balance
- Transfer to beaker and reweigh sample bottle
- Record mass difference
- Add distilled water
- Stir with a glass rod until all is dissolved
- Transfer to volumetric flask using a funnel, include washings
- Make up to 250cm3
- Shake
Improvements to titration accuracy
- Remove air bubbles from burette tap to ensure the volume is correct
- Remove the funnel used before starting the titration as solution drops could affect the burette reading
- Swirl the conical flask to ensure all reactants have reacted and not left on the sides of the flask
