Chapter 3 Flashcards
Define Relative Molecular Mass (Mr)?
The mass of a molecules relative to 1/12th the mass of 12carbon atom
What is the relative formula mass used for?
Ionic compounds and giant structures
Define relative formula mass?
Mass of a formula unit relative to 1/12th mass of a 12carbon atom
How are the relative molecular mass and relative formula mass calculated?
By adding up the relative atomic masses of a compound
Define the term ‘MOLE’
The mole is the amount of substance that contain 6.02X10^23 particles, known as Avogadro’s constant Na.
What is the Molar Mass equal to?
Mass of 1 mole of substance (gmol-1)
What does N=m/Mr mean?
Number of Moles= Mass/ Molar Mass
How can you calculate the number of moles using Avogadro’s constant?
Number of Moles= Number of Particles/ 6.02X10^23
When can the amount of individual atoms/ ions in a substance be found?
If the amount of a pure substance is known
Define empirical formula?
Simplest whole number ratio of atoms of each element in a compound
Define Molecular formula?
Actual number of atoms of each element in a compound
What are the 4 steps to calculating the empirical formula?
- Find the mass of each element
- Find the number of Moles (n=m/mr)
- Find the ratio of moles by dividing each by the smallest value
- Apply to molecular formula
What are the three steps of finding the molecular formula from the empirical formula and molar mass?
- Find the empirical formula mass of the compound
- Divide the Mr by the empirical formula mass
- Multiply each subscript by the number calculated in Step 2.
What is a hydrated salt?
Some ionic solids containing water, WATER OF CRYSTALLISATION, as part of their structure.
How is water of crystallisation shown in an equation and what does it mean?
using a ‘.’ which effectively means ‘+’
How can water of crystallisation be removed and what are the products?
The water of crystallisation can be driven off by heating to leave an anhydrous salt.
Define the water of crystallisation
Water molecules bonded into a crystalline structure
What is a hydrated salt?
A crystalline compound containing water molecules
What is a anhydrous salt?
A crystalline compound without water molecules
What is the concentration of a solution?
The amount solute in a given volume of solvent
What is the equation to calculate the number of moles using concentration?
Number of Moles = Concentration X Volume
How many cm3 in 1 dm?
1000cm^3 = 1 dm^3
What is a standard solution?
A solution of known concentration is called standard solution
What is the Molar Gas volumes Vm?
Is the volume occupied by 1 mole of ANY gas at RTP.
What is the value of Vm?
24 dm^3
What are the values for RTP?
20’ and 101 Kpa
What is the equation for calculating Moles of Gas?
Moles of Gas= Volume of gas (dm3)/ Molar Volume (dm3)
How many cm3 is in 1 litre?
1000 cm3= 1 litre
How many particles are in 1 moles of any gas?
6.02X10^23 particles
How does temperature effect the volume of gas occupied?
The hotter the gas, the faster the particles are moving because of increased kinetic energy and so the more volume they will occupy.
How does pressure effect the volume of gas occupied?
The higher the pressure, the more compressed the gas will be and the less volume it will occupy
How does amount of gas effect the volume of gas occupied?
The more gas particles there are, the more voulme they will occupy.
What four features do molecules in an ideal gas equation have?
- Random motion
- Elastic collision
- Negligible size
- No intermolecular forces
What is the equation for the ideal gas equation?
pV=nRT
What is the unit for the p in pV=nRT?
Pa
What is the unit for the V in pV=nRT?
m^3 (1m3= 10^3 dm3= 10^6 cm3)
What is the unit for the N in pV=nRT?
Number of moles
What is the unit for the R in pV=nRT?
Gas constant = 8.314 jmol-1k-1
What is the unit for the T in pV=nRT?
In Kelvin, (C’ + 273)
What are the two assumptions the Real Gas Equation relies on? When are these true?
- Forces between gas particles are negligible
- Gas particles have negligible size compared to the size of their container
These are true at low pressures and high temperatures.
What is the non-ideal gas equation?
(P+ N^2a/V^2) (V-b) = nRT
Define stoichiometry
The ratio of the amount, in moles, of each substance in a chemical reaction
What are the three steps to calculating quantities from amount and equations?
- Find the number of moles for one substance
- Use the mole ratio from the stoichometry to find out how many moles the other substance will produce.
- From this number calculate the mass/volume/ concentration of the desired substance.
How can you identify what metal is in a unknown compound?
By how much hydrogen gas it produces in excess acid
Define the term Percentage Yield
The actual mass of product obtained expressed as a percentage
What is the equation for calculating Percentage Yield?
(Actual yield of product/ Theoretical Yield of Product) X100
What 3 reasons are there for why percentage yield is usually less than 100%?
- Incomplete reaction
- Side reactions occurring
- Loss of product during separation/ purification stage.
Define Atom Economy
A measure of the amount of starting reactants that become useful products
What is the equation for calculating Atom economy?
(Sum of molar masses of desired product / Sum of molar masses of all products) X100
What are 5 other factors they take into account to judge the cost effectiveness and sustainability of the reaction/ process?
- How “green” the process is
- How cheap the raw materials are
- How much energy is required for the process itself
- The atom economy of the process
- How can waste products be delt with
What is a limiting reagent?
The reactant used up first in a chemical reaction. It limits how much product can be made.
What is the excess reagent?
The reactant, of which, there is a quantity of left over unused after a chemical reaction.
When are excess reagents added sometimes?
To speed up reactions
Should the excess reagent be cheap/ expensive?
Cheap and/or recyclable
What is the role of the excess reagent in the product?
None, it should be easily isolatable from the products once the reaction is complete.
Where is the number of moles of the limiting reagent used?
In calculating the theoretical yield of product
