CHAPTER 3 - AMOUNT OF SUBSTANCE Flashcards
What is the Avogrado constant?
6.02 x10^23
The number of partices in each mole of Carbon-12
What is the equation to calculate moles?
Mass (m)/Molar mass (Mr)
(Mr M(e)n)
(Worked equation page 23)
What is molecular formula?
Number of atoms of each element in a molecule
What is empirical formula
Simplest whole-number ratio of atoms of each element in a compound
What is relative molecular mass?
Compares the mass of a molecule with the mass of an atom of carbon-12
What’s relative formula mass?
The mass of a formula unit compared with the mass of an atom of Carbon-12
Describe the practical method to find out the formula of a hydrated salt
Weigh an Empty crucible
Add hydrated salt into the weighed crucible. Weigh the crucible and the hydrated salt
Using a pipe-clay triangle, support the crucible containing the hydrated salt on a tripod.
Heat the crucible and contents gently for about one minute, then heat strongly for a further three minutes
Leave the crucible to cool. Then weigh the crucible and anhydrous salt
How to work out the formula of a hydrated salt
Calculate the amount, in mol, of anhydrous CuSO4.
Calculate the mass and amount, in mol, of water
Find the smallest whole-number ratio
Write down the value of x and the formula of hydrated CuSO4
(worked example pg 24)
What are two assumptions that have been made during the calculation of Formula of Hydrated salt (Water of Crystallisation)
1 - All of the Water has been lost
2 - No further Decomposition
A student carried out an experiment to calculate the water of crystallisation of two hydrated salts. For the first salt, the student did not remove all the water of crystallisation. For the second salt, the student removed all of the water of crystallisation but unfortunately the salt composed further.
For each salt, explain whether the students calculated value of x, the number of water molecules in the formula unit, would be greater or smaller than the actual value of x in data books
The first salt would not lose all H2O so x would appear to be smaller than it should be
The second salt loses more mass than just water so x would appear to be greater than it should be
Unit conversions Between a cubic centremetre to millilitre
to Cubic decimetre to litre
1 cm3 = 1ml
1000ml = 1 litre
1dm3 = 1000ml = 1 Litre
How would you work out the Concentration of a solution
c = n/V
(worked solution page 26)
What is a standard solution?
A solution with a known concentration
What is molar gas volume?
he volume per mole of gas molecules at a stated temperature and pressure
What does RTP mean?
Room Temperature and Pressure
What is RTP values?
20 degrees celsius
101 kPa (1 atm) pressure
What is Vm at RTP?
24.0 dm3mol-1
What is the ideal gas equation?
pV = nRT
P = Pressure
V = Volume
n = Moles
R = Gas constant = 8.31
T = Temperature in Kelvin
(Worked example page 29)
What are the assumptions for the Ideal gas equation?
Random Motion
Elastic Collisions
Negligible size
No Intermolecular Forces
Describe an experiment to find a relative molecular mass
Add sample of volatile liquid to a small syringe via a needle
Weigh small syringe
Inject the Sample into a gas syringe through the self-sealing rubber cap. Reweigh the small syringe to find the mass of the volatile liquid added to the gas syringe.
Place gas syringe in a boiling water bath at 100 degrees C. The liquid vaporises producing a gas. The pressure is recorded.
What is Stoichiometry?
The balancing of numbers to give the ratio of the amount, in moles, of each substance
Describe the method of Identifying an unknown metal
Set Up Gas syringe attached to a beaker,
Weigh Sample of metal and add to flask
Using a measuring cylinder, add 25.0cm3 of 1M HCl (dilute) (an excess) to the flask and quickly replace the bung.
Measure the maximum volume of gas in the syringe
(Worked example page 34)
What is Theoretical Yield
The maximum possible amount of product in a reaction
Why is the Theoretical yield so difficult to achieve?
The Reaction may not have gone to completion
Other reactions (side reactions) may have taken place alongside the main reaction
Purification of the product may result in loss of some product
Some of the Products may have escaped
What is Actual Yield
The actual amount of product collected from experiment
How would you calculate percentage yield?
Percentage yield = Actual yield/ Theoretical yield x 100
(worked example page 35)
What is the limiting reagent?
The reactant that is not in excess and will be completely used up during he reaction
What is Atom economy?
A measure of how well atoms have been utilised
Why are reactions with high atom economies beneficial?
Produce large proportion of desired products and few unwanted waste products
Important for sustainability as they make but use of natural resources
How would you calculate atom economy?
Atom economy = Sum of molar masses of desired products / Sum of molar masses of all products x 100
(worked example page 36)
