Quantative Chemistry Flashcards
How do you find the percentage of an element?
N x Ar/Mr x 100
Calculate the % of sodium in sodium oxide (Na2O)
2 x 23/62 x 100 = 79.19
We need to find the atomic mass of sodium which is 23.
But the Mr of the compound Na2O is 62 since 23x2+16 = 62
Then multiply by a hundred.
What is the avogadro number?
6.02x10*23
What is the equation for the mole concept (avogadro constant)
Number of molecules/particles
Number of moles Avogadro constant
How do you know what to solve for in the questions you will be given
If they’re asking to calculate the number of molecules/ particles: Avogadro constant
If they’re asking you to calculate the concentration of a solution in mol/dm3 and g/dm3: Mass/vol Mass
Conc Vol
If they’re asking you to calculate the maximum/minimum mass of a compound: find the moles, the ratio, then calculate the mass.
If they’re asking you to calculate the volume of gases in a reaction:
Volume
Mole Molar volume
How to calculate enthalpy change and energy released?
EC = Q/ moles
Q= M x C x RT
Q: energy released
M: mass of water heated
C= specific heat capacity of water
RT: rise in temperature
What is always the heat capacity of water?
4.2 Joules
How to calculate final temp for measuring enthalpy?
Final temp- intital temp
What is the molecular and emrpicsl formula?
Molecular- actual number of atoms present in a molecule.
Emprical formula- simplified number of atoms present in a molecule
How do you find the proportion of iron In iron oxide?
mass of iron/ Mr of the whole compound
What happens when the outer shell electron is close to the nucleus in metals and non metals-
Metals-
If the outer shell electron is close to the nucleus , the electron will be harder to lose due to the stronger electrostatic forces between the positive nucleus and negative electrons. Leading to a decreased reactivity for metals. Example- lithium has 2 energy levels.
Non metals-
If the outer shell is close to the nucleus, an electron will be easily gained due to the stronger electrostatic attraction between the nucleus and the electron to be gained. Increasing reactivity of metals.
Suggest how the apparatus could be modified to reduce
heat loss.
It can be covered with a lid
What is combustion?
Burning of something in the presence of oxygen
Suggest why it is important to mix the chemicals
thoroughly.
So all the SUBSTANCES react
How can the negative sign in bond dissociation energy state it’s an exothermic reaction ( -180 kg/mol) =
This states it’s an exothermic reaction because there is more energy released in the products than absorbed in the reactants
