M2 - Amount of Substance Flashcards
Amount of substance and the mole, Determination of formulae, Moles and volumes and Reacting quantities
How is the molecular formula found?
Find empirical formula.
Divide molar mass of a molecule by molar mass of empirical formula.
Multiply empirical formula by the result.
What is the equation for the number of moles of a substance?
n=m/Mr
n - number of moles (mol)
m - mass (g)
Mr - molar mass (g/mol)
Define empirical formula (1)
Simplest whole number ratio of atoms
What is the percentage yield?
The actual yield divided by the theoretical yield expressed as a percentage.
(actual yield / theoretical yield ) X100
What is the concentration of a solute?
The amount of solute (in moles) dissolved in each 1dm^3 of solution
What is the value of gas molar volume at room temperature and pressure?
1 mole of any gas takes up 24 dm^3/mol at rtp
What is gas molar volume?
The volume per mole of a gas.
Measured in dm^3/mol
What are the benefits of a high atom economy?
Produce a larger proportion of desired products and few waste products.
Important for sustainability, the best use of natural resources.
How is the empirical formula found?
E Element
M Mass or %
--- ----------------
M Molar mass
A Answer (moles)
------------------------
Smallest answer
R RatioWhat is atom economy?
The molar mass of desired product divided by the sum of the molar masses of all products expressed as a percentage.
(mr of desired products/ mr of total products) X100
What is a titration?
A technique used to accurately measure the volume of one solution that reacts exactly with another solution.
D
When can a mean titre be worked out?
When two or more concordant results are obtained.
What is relative formula mass?
The weighted mean mass of the formula unit of a compound compared with 1/12th of an atom of carbon-12
What is stoichiometry?
The balancing numbers giving the ratio of the amount, in moles, of each substance in a balanced equation.
A
What is the empirical formula?
The simplest whole-number ratio of atoms of each element in a compound.
What is the equation to calculate moles of a gas at RTP?
n = v / 24
molar gas volume = 24 (dm^3/mol)
n - number of moles (mol)
V - volume (dm^3)
C
What are titrations used for?
titrations are used for Finding the concentration of a solution.
Identification of unknown chemicals.
Finding the purity of a substance.
What are the standard conditions for temperature and pressure?
T = 298K or 25C
P = 1atm or 100kPa
101kPa or 1 atm of pressure
What is the limiting reagent?
The reactant that is not in excess.
What is the molecular formula?
The number of atoms of each element in a molecule.
D
What is the equation for finding a solution’s concentration?
c=n/v
c - concentration (mol/dm^3)
n - number of moles (mol)
v - volume (dm^3)
In hydrated salts, what is the name given to water molecules?
Waters of crystallisation
Why is the theoretical yield so hard to achieve?
The reaction is incomplete.
Competing side reactions giving different products.
Loss of product in handling and purification.
Reversible reaction.
B
What is a mole?
The amount of any substance containing as many particles as there are particles in 12g of the carbon-12 isotope.
What is relative molecular mass?
The mass of a molecule compared with the mass of an atom of carbon-12.
Explain what is meant by molecular formula (1)
Number and type of atoms making up a molecule
C
What are concordant results?
Within 0.10 cm^3 of each other.
What are the assumptions made about an ideal gas?
Random motion
Elastic collisions
Negligible size
No intermolecular forces
What is Avogadro’s Constant?
The number of atoms in one mole of the carbon-12 isotope. found in data sheet 6.02X10^23
Outline the steps to prepare a 250 cm3 standard solution
step 1: find mass of chemical compound you want
step2:
weigh the solid and then
dissolve it, with stirring, in distilled water
pour solution into a 250cm3 volumetric flask
rinse beaker with distilled water into the flask
add distilled water to flask - bottom of meniscus on graduation line
place stopper on flask and invert
B
What is meant by the term mole? (1)
Amount of substance that has the same number of particles as there are atoms in 12g of carbon 12
What is the ideal gas equation?
State the standard units for each.
pV=nRT p - pressure (Pa) V - volume (m^3) n - number of moles (mol) R - gas constant, 8.314 (J/mol/K) T - temperature (K)
What term is given to the .n H2O part of a formula? (1)
Waters of crystallisation
What are the balanced equations used to find?
The quantities of reactants required to prepare a required quantity of a product.
The quantities of products that should be formed from certain quantities of reactants.
B
C
