Chapter 3 Flashcards
Formula including moles, Mr and mass?
n = m/Mr Mol = mass in grams/ molar mass in g mol-1
Purpose of Avogadro’s constant
Number of atoms needed to have 12g of carbon-12
Huge number
What is unit for molar mass
G mol-1
Ionic equation method?
Difference between net and complete equation?
Balance equation, write correct formula/charge of each charge and how much there are, write aq after each ion, bring down s,l,g compounds unchanged.
Complete is everything same method as above
Net has repeated ions (spectator ions) removed
How do you get number of molecules of a compound?
Multiply avogadros constant with number of moles
Difference between molecular formula and empirical formula
Molecular shows number and type of atoms of each element in one molecule
Empirical is simplest whole number ratio of each element in compound
How do you workout empirical formula from data
Divide all mass by their Mr, divide smallest number to get ratios and then adjust to get whole numbers
What does volume of gas depend on
Temp and pressure
Pressure at room temp
101000 Pa
What is room temp
20 degrees c
Or 293 K
Convert from kelvin to degrees c
Minus 273
Molar volume of gas at RTP
24 dm3 mol-1
Or 24000 cm3 mol-1
How will a higher temp affect volume of gas
More kinetic energy so move further apart increasing volume of gas.
How will a higher pressure affect volume of gas
The forces of container push molecules closer together decreasing volume
Formula for volumes of gases not at RTP
Units
pV= nRT
Pressure in Pa Volume in m3 N is number of moles in mol R is gas constant 8.314 T is temp in kelvins K
M3 to dm3 to cm3
1m3
Is 1,000 dm3
Is 1,000,000 cm3
MgO exp
Why do you meed to raise the crucible
Needs oxygen from air to react with Mg
MgO exp
Purpose of breaking up MgO whilst hearing
To ensure all Mg reacts as theres increased surface area
MgO exp
Why does the formula show less oxygen than is present in pure MgO
Not all Mg reacts
Possible that Mg reacts with nitrogen from air too
MgO exp
Why does Mg reacts with O rather than N from air
O2 has double bond
N has triple bond
O requires less energy to break so it is easier
Concentration formula in g dm-3
Concentration in mol dm-3
Mass of solute in g divided by volume of solution in dm3
Replace mass of solute by number of moles
What is a hydrated salt?
Why is water trapped in salt?
During salt crystallisation from an aqueous solution some molecules of water is trapped within the solid lattice.
Water is a polar molecule
What is the water trapped in a hydrated salt called
Water of crystallisation
How do you remove the water in a hydrous salt ?
What is new substance called?
Heat the salt means water is removed from structure
An anhydrous salt
What is atom economy
Definition
Not formula
Way of measuring how much of your reagents makes useful products
Atom economy formula
Mr of useful product divided by total Mr of all products
Multiplied by 100 to get percentage
Percentage yield formula
Percent yield= actual yield divided by theoretical yield multiplied by 100
2 ways of lowering percentage uncertainty
Increase accuracy of measuring equipment
Increase overall mass of reagents used
Percentage uncertainty
Measurement has uncertainty of +/- 0.5
Reading of 15.7
0.5 / 15.7 * 100
