Structure 1.4 Flashcards
What is a mole?
The amount of a substance that contains as many specified particles as there are atoms in exactly 12g of carbon-12
How many particles in one mole of a substance?
Avogardo’s Constant /
6.02 x 10^23
What is the equation that converts number of particles to number of moles?
number of moles (n) = number of particles (N) / avogardo’s constant (NA)
What is the formula for mole ratio?
Number of a specific particle per a specific substance
What is the relative atomic mass of an element (Ar)?
The weighted average of its isotopic masses, according to their relative abundances, relative to 1/12 of the mass of a carbon-12 atom.
What is the relative formula mass (Mr)?
The sum of the relative atomic masses of the atoms as given in the chemical formula of a species
What is the relative molecular mass (Mr)?
the mass of a molecule relative to 1/12 the mass of a carbon-12 atom
What is molar mass?
The mass of one mole of a substance (M, g mol-1)
What is the formula for converting mass to number of moles?
number of moles (n) = mass (m) / molar mass (M)
What does the empirical formula of a compound give?
The simplest ratio of atoms of each element present in that compound
What does the molecular formula of a compound give?
The actual number of atoms of each element present in a molecule
How can the molecular formula be found from the empirical formula?
(Molecular formula mass / empirical formula mass ) x empirical formula
What is the percentage composition by mass of a compound?
The proportion of the total mass of the compound accounted for by the mass of each element
What is the formula for percentage composition by mass?
%Element = m(element)/m(compound) x 100%
What is the formula for percentager composition by mass, using the chemical formula?
%Element = M(element) / M(compound) x 100%
How can the molar mass of a compound be found?
Adding the relative atomic masses of the elemtns in the compound
What is the molecular formula reserved for?
Covalent molecular species
With ionic substances, what is the empirical formula the same as?
the ionic formula
How can masses be used to find the empirical formula?
Objective: find the simplest whole number ratio of the number of moles of each element in a substance
steps
- Identify the mass of each element
- Calculate the moles of each element
- Divide by the smallest number of moles
- Find the simplest whole number ratio
- Find the EF
How can the percentage composition by mass be used to find the EF?
Assume the mass is 100g, and follow the normal steps
How is relative empirical formula mass (EFr) calculated?
Adding the relative atomic masses of the atoms in the empirical formula together
What is the IB Chemistry unit for quantifies volumes?
cm3 / dm3
1000 cm3 = 1 dm3
What is the formula for concentration as mass per volume?
C = m (g) / V (dm3)
What is the formula for concentration as moles per volume?
C = n (mol) / V (dm3)
What is molarity?
Molar cocentration
How to prepare a solution of a known concentration?
- Dispense the required mass of solid into a weighing bottle on a top-loading balance
- Record the mass of the weighing bottle and solid on an analytic balance
- Transfer the solid to a volumetric flask (size that is relevant to the amount of diluted solution desired)
using a funnel placed in the neck of a flask - Record the mass of the (now empty) weighing bottle on an analytical balance -> weighing by difference
- Add deionised water to the volumetric flask via the funnel until its about 1/3 full
- Stopper the flask and shake until the solid is dissolved
- Fill the flask to the calibration mark with deionised water, such as the meniscus sits on the line
- Stopper the flask and invert several times
When the dissolving of a 2.0 mol dm-3 sodium chloride occurs in a 1.0dm3 solution, what is the outcome?
2.0 mol of sodium
2.0 mol of chloride
(based on mole ratio)
What is the equation for the dissociation of badium hydroxide, Ba(OH)2?
Ba(OH)2 (s) -> Ba2+ (aq) + 2OH- (aq)
If 1.5 mol of Ba(OH)2 is dissolved in 1.0dm3 of solution, what are the products?
1.5 mol of Ba2+
3.0 mol of OH
What is the process for calculating the concentration of a compoent when mixing two or more solutions?
- Count the number of moles of the component, for all solutions
- Add the number of moles together
- Find the total volume of all solutions
- Use c = n/v to find
What is dilution?
The process of adding more solvent to a solution
What is the formula for the concentrations and volumes of a solution after a dilution?
C1 x V1 = C2 x V2
What theory explains the physical behaviour of ideal gases?
Kinetic molecular theory
What does kinetic molecular theory consist of?
- Total volume of gas particles is neglible compared to the volume of the gas
- Gas particles move randomly, in straight lines. Particles collide with the walls of the container and with each other, but collisions are elastic.
- forces of attraction between gas particles (and between gas particles and the walls) are negligible and can be ignored
- average kinetic energy of the particles is directly proportional to the absolute temperature of the gas
What are elastic collisions?
Collisions where the total energy of the colliding particles is the same before and after the collision
What is an ideal gas?
A hypothetical gas whose pressure-temperature-volume behaviour can be completely accounted for by the ideal gas equation
When do real gases deviate from ideal gas behaviour?
- when the pressure is high
- when the temperature is low
- when the gas molecules are polar and strongly attracted to each other
- when gas molecules are large
What is the ideal gas equation?
PV = nRT
P = pressure (kPa)
V = volume (dm3)
n = moles (mol)
R = gas constant
T = temperature (K)
What is the gas constant, R?
8.31 J mol-1 K-1
Why do real gases deviate from the ideal gas law most at high pressures?
Breaks the assumption of kinetic molecular theory that the volume of particles is neglible. Close enough for intermolecular attraction to occur
What is the equation for pressure?
pressure = force / area
What are the units for pressure?
1 Pascal = 1 N / 1m2
1 Kilopascal = 1000Pa
1 bar = 100 kPa
What is the pressure at sea level?
1 atmosphere = 101.3 kPa
What is the relationship between pressure and temperature?
As temperature increases, the speed and kinetic energy of the gas particles also increase. Thus, the particles collide with the will with greater force and more frequency, which increases the pressure
What is the relationship between pressure and moles?
As the number of moles increase (at a fixed volume), there are more particles to collide with the wall. This increase in frequency of collisions increases the pressure
What is the relationship between pressure and volume?
As the volume increases, the pressure decreased. This is because there are less gas particles per unit volume and thus, less frequent collisions which decreases the overall pressure
What is the combined gas equation?
(P1 x V1) / T1 = (P2 x V2) / T2
T must be in K
What is standard temperature and pressure (STP)?
0 degrees Celsius
100kPa
What is standard ambient temperature and pressure (SATP)?
25C
100kPa
What is Avogardo’s hypothesis?
Equal volumes of all gases at the same temperature and pressure contain the same number of molecules
What is molar volume?
Volume occupied by one mole of gas at a specified temperature and pressure.
What is the molar volume of an ideal gas at STP?
22.7 dm3 mol-1
What is the formula for calculating the number of moles of an ideal gas, from its known volume at STP?
n = V/Vm
