CHAPTER 3 - AMOUNT OF SUBSTANCE Flashcards
What is amount of substance?
A quantity used to count the number of particles in a substance
What is avogadro’s constant?
The number of particles in each mole of carbon-12
how do you calculate moles
Mass - g
————————————
Molar mass (mr) -g mol-1
Define molecular formula
The number of atoms of each element in a molecule
What is empirical formula?
The simplest whole-number ratio of atoms of each element in a compound
Define relative molecular mass
Compares the mass of a molecule with the mass of an atom of carbon-12
Define relative formula mass
Compares the mass of a formula unit with the mass of an atom of carbon-12
What is water of crystallisation?
Water molecules that are bonded into the crystalline structure of a compound
What are 2 assumptions that are made about the hydrated copper sulphate equation (water of crystallisation) ?
- Assumes all water is lost - salt changes colour but only surface is seen / some water may be left inside
- Assumes there is no further decomposition- some salts decompose further when heated / difficult to judge when no colour change has been seen
Define concentration of a solution
The amount of solute, in moles, dissolved in each 1dm3 of solution
How do you calculate concentration?
N (moles) = c (Moldm-3) x v (dm3)
What is a standard solution?
A solution of known concentration
How is a standard solution prepared
Dissolve exact mass of solute in solvent and making up solution to an exact volume
How do you work out mass concentration?
Mass concentration (gdm-3) = n (moles) x mol concentration (moldm-3)
When do equal volumes of different gases contain the same number of molecules?
At the same temperature and pressure
What is molar gas volume (Vm) ?
The volume per mole of gas molecules at a stated temperature and pressure
How do you calculate molar gas volume (dm3) ?
n = v dm3
————
24.0
How do you calculate molar gas volume (cm3) ?
n = V cm3
————
24 000
What are the assumptions made for the molecules making up an ideal gas?
- random motion
- elastic collisions
- negligible size
- no intermolecular forces
What is the ideal gas equation?
pV = nRT
- p = pressure (Pa)
- V = volume (m3)
- n = amount of substance (mol)
- R = ideal gas constant (8.314 mol-1k-1)
- T = temperature (K)
How do you convert dm3 or cm3 into m3 ?
dm3
———
1000
cm3
—————
1,000,000
How do you convert MPa and kPa to Pa ?
kPa x 1000 =Pa
MPa x 1,000,000 =Pa
How do you convert degrees Celsius to kelvin?
temp ( in celsius) + 273 = K
What is stoichiometry of a reaction?
The balancing numbers give the ratio of the amount , in moles , of each substance.
