C4- Chemical calculations Flashcards
what is relative atomic mass
Relative atomic mass = the average mass of all the isotopes of an element, relative to C-12
what is mass number
Mass number = the total amount of protons+neutrons
what does Aᵣ mean
Ar = relative atomic mass - (for a single atom)
what does Mᵣ mean
Mr = relative molecular mass (for a compound)
what does mole mean
A mole is a measurement for a certain number of atoms/particles/molecules
We call this number Avagrado’s constant
what is Avagrado’s constant
Avagrado’s constant = 6.02x10^23
What formula would you use to calculate mass from moles?
Mr x Mole = Mass
what is percentage yield
Percentage yield = the mass of product that a chemical reaction produces
what is the formula to calculate percentage yield
Actual mass of products / Max theoretical mass of products
why will percentage yield never be 100%
5 points
Factors why percentage yield won’t be 100%
1)reactants may give unwanted products
2)reversible reactions
3)Product may be lost in handling or apparatus
4)Reactants may not be not pure
5)Products may be lost from separating from mixture
what is atom economy
Atom economy = the extent to which the atoms in the starting materials end up in the desired product.
why is atom economy less than 100%
3 points
Reasons why atom economy is less than 100%:
1)More than one product, where the extra products are not desirable
2)The more ‘waste’ products, the lower the atom economy
3)The Haber process is an example of a reaction with 100% atom economy - it has only one product (ammonia)
why do we want a higher atom economy
We want a higher atom economy as:
1)it is greener (more sustainable)
2)more efficient
3)Reactions with a lower atom economy wastes materials, and money
what does concentration mean?
Concentration = how much of a mass there is in a set amount of liquid
what is the equation for concentration
concentration = mass/volume
n=c X v
!FACT!
If the question doesn’t mention anything, you need to use grams, and dm^3
!FACT!
Your mass and volume can be in any units - you just need to adapt the unit of your concentration accordingly
what is the conversion between cm–>decimetres
cm—>dcm=/10
how do air bags work?
How do air bags work:
There are chemicals in air bags that react to give off just the right amount of N2 for it to be a cushion
what is molar gas volume
Molar gas volume = volume of gas for 1 mole of any gas
The molar gas volume - is 24dm^3
how do you find out number of moles in a gas?
Number of moles of gas = volume of gas (dm^3) / 24dm^3
what is 1atm
1atm is a measure of pressure, and it’s our normal day to day pressure. 1 atmosphere is 101kPascals (Pa) which is the normal unit of pressure
