Chemistry Calculations Flashcards
What information does the atomic number provide?
The number of protons and electrons in an element
Why must the number of protons be equal to the number of electrons?
So it isn’t positively charged or negatively charged, so it’s neutral
What information does the mass number provide?
No. of protons +No. of neutrons = mass number
It’s a representation of the mass
What’s an isotope?
Isotopes are atoms which contain the same number of protons but different numbers of neutrons.
What particles are in the nucleus of an element?
Proton
Neuton
What’s a definition of an element?
An element contains only one type of atom
What’s a definition of an compound?
A compound is a substance that is made of two or more different elements which are chemically bonded together.
What is formed when atoms form chemical bonds by losing or gaining electrons ?
They form electrically charged atoms called ions
How do you calculate relative atomic masses(RAM or Ar)?
100
Define RAM:
The average mass of an atom of an element taking into account the ISOTOPE MASSES AND ABUNDANCES.
When calculating ram what figures do you need?
The different isotope masses
Abundances %
How do you calculate relative formula masses(RFM or Mr)?
You break up the formula in elements
(Mass of E1 x amount of E1)+(Mass of E2 x amount of E2)+…..
Formula of hydroxide:
_
OH
Formula of sulphate:
2-
SO
4
Formula of carbonate:
2-
CO
3
Formula of hydrogen carbonate:
_
HCO
3
Formula of nitrate:
_
NO
3
Formula of ammonium:
+
NH
4
How do you calculate percentage compositions (%compositions)?
You need to have the RFM/Mr
(Mass of E1 x amount of E1)
—————————-
RFM
What do you need to work out the empirical formula?
A percentage or mass of the elements and RAM of the elements
How do you calculate the empirical formula?
1)for each element do:
% or mass
————
RAM
2)then divide through by the smallest value from 1
3)the answer from two should give you an integer ratio or a .5 which would mean you have to double all the numbers
4)you then write out the formula using the element symbols and the ration as small numbers
How do you calculate the molecular formulae?
You need to have the empirical formula first
1)you work out the RFM of your empirical formula
2)then you have the RFM of a substance
3)RFM of the substance
————————-
RFM of the empirical formula
4)you then with what answer you get from 3 times the ratio of the empirical formula by it and then write the formula with the ratio you just calculated
How do you find a formula of a hydrated compound?
You need to have the mass of the compound and of the water
1)for both the compound and water you do
Mass
——————–
RFM of the compound
2)then divide through by the smallest
3)you will have to get a integer ratio from the answers to 2
4)you then write out the formula with the ratio before the compounds, you write:
_Formula of compound. _Water
Describe an experiment of magnesium reacting with oxygen:
- weigh the crucible and lid
- put the magnesium in the crucible with the lid on and weigh it
- heat the magnesium opening the lid occasionally to let oxygen in
- once the magnesium has stopped flaring leave the lid off
- after 5 mins weigh the crucible with its lid on and content
- heat again and re weigh until a consistent mass is reached
How do you determine whether the results are reliable?
We can’t say how reliable our results our because we only did the experiment once we could make it more reliable by doing it more times and getting an average
Once you have done an experiment of a reaction between magnesium and oxygen how do you calculate the percentage mass of oxygen?
Mass of magnesium
100-(——–––————- x100)
Mass of MgO
How do you calculate the percentage of a compound in a chemical formula?
RFM of compound
——————————x100
RFM of chemical formula
How do you calculate the amount of moles of a substance?
Mass
Moles = ——–
Mr
When you have a equation what numbers represent the mole ratio numbers?
The big number before each substance shows the mole ratio
How do you calculate mass from equations?
1) write the mole ratio of the balanced word equation
2) calculate RFM
3) do mass divided by RFM to give you the number of moles
4) do the RFM(of the substance you’re trying to find the mass of)x moles according to the mole ratio of the equation
How do you work out percentage yields?
Actual yield x 100
————————
Theoretical yield
When finding a mystery element what do you try and work out?
The RAM
