Quantitative Chemistry Flashcards
What is the Relative Atomic Mass and its symbol?
The Ar of an element is a weighted mean mass of the isotopes of an element compared with that of the C (12) Isotope, which has a mass of exactly 12.
What is the Relative Molecular Mass and its symbol
The Mr of a substance is the sum of the masses of all the atoms present in the formula of that element or compound. It is used when calculating the mass of a covalent compound.
What is the relative Formula Mass and its symbol
The Mr of a substance is the sum of the masses of all the atoms present in the formula of that element or compound. It is used when calculating the mass of a ionic compound.
How to calculate the percentage of an element in a compound?
% of an element = Total mass of element in the compound/ Mr X 100
Calculate the percentage by mass of oxygen in MgSO4
First calculate the Mr: 24 + 32 + (4x16) = 120
There are four oxygen atoms so the mass of the oxygen is 4x16 = 64 So:
% of O in MgSO4 = 64/120 x100
= 53.3% (You don’t need to memorise this its just an example)
What is the mole?
The relative formula mass of a substance in grams
How many particles is in one mole of a substance?
One mole of a substance is 6.02 X 10 (to the power of 23)
It is obtained by weighing out RAM or FRM in grams
What is the equation to find the mole of a substance?
Moles = Mass of substance/Ar or Mr
Mass of substance must be in grams
Ar for elements
Mr for compounds
What is the equation to find the Mass of a substance?
Mass = mole x Ar or Mr
Mass of substance must be in grams
Ar for elements
Mr for compounds
How to use ratios to interpret quantitive equations
Too annoying to explain look in book idiot
Why can we interpret chemical reactions quantitatively?
As no atoms are made or lost
What is the percentage yield of a chemical reaction?
Percentage yield of a chemical reaction shows how much product was actually made compared with the amount of product that was expected.
What is the equation to find the percentage yield?
percentage yield =
Actual yield of desired product / Theoretical yield of desired product X 100
Why is the percentage of a product less than 100%
- Loss of product in separation from the reaction mixture
- Side reactions
- Reaction may be reversible and not go to completion
What is water of crystallisation
Water that is chemically bonded into the crystal structure
What does Hydrated mean?
Solid crystals contains water of crystallisation
What does dehydration mean?
Means removal of water of crystallisation
What is an anhydrous substance?
The substance does not contain water of crystallisation
What is the degree of Hydration?
The number of moles of water of crystallisation chemically bonded in 1 mole of the compound.
What is the empirical formula?
The simplest whole number ratio of the atoms of each element in a compound.
What is the molecular formula?
The actual number of atoms of each element in a molecule
How do you calculate the percentage of water of crystallisation in a compound?
% water of crystallisation =
degree of hydration X Mr of water / Mr of the compound X 100
What is the method to find the % of water of crystallisation in magnesium sulfate crystals?
- Place a small amount of the magnesium sulfate crystals in a boiling tube. Place a dry piece of cobalt chloride paper at the neck of the boiling tube. Heat the crystals and record observations
- Record the mass of a crucible
3.Weigh out about 5g of the magnesium sulfate crystals
- Heat the crystals for 5 minutes. Now reweigh using filter paper on the balance.
- Continue to heat the salt for a further 5 minutes until you get a constant mass.
- Draw a diagram of the apparatus
- Work out the % of water of crystallisation
- Work out the theoretical % of water of crystallisation if the formula is MgSO4.7H20
What is thermal decomposition?
The breakdown of a solid using heat and can be completed to completion by heating to a constant mass
