Amount of Substance - Chapter 2 Flashcards
What is the valency of an atom in a molecule
The valency in a molecule can be taken as the number of bonds which that atom forms in the compound
What is the valency of an ion
The valency of an ion in an ionic compound is equal to the charge on the ion
For metals
Valency =
valency = group number
For Non-metals
Valency =
Valency = (8-group number)
Formula of Ammonium
NH4 +
Formula of Hydrogencarbonate
HCO3 -
Formula of Hydroxide
OH -
Formula of Phosphate
PO4 3-
Formula of Carbonate
CO3 2-
Formula of Hydrogensulphate
HSO4 -
Formula of Nitrate
NO3 -
Formula of Sulphate
SO4 2-
What is a chemical equation
It is an equation that tells us what is happening in a reaction
What are word equations
They are qualitative
May include state symbols
e.g. hydrogen + fluorine -> hydrogen fluoride
What are balanced symbol equations
They are quantitative Obey the law of conservation of mass Tell us the number of moles of each substance involved May include symbol equations e.g. H2 + F2 -> 2HF
What are balanced symbol equations sometimes called
Stoichiometric equations
What elements exist as diatomic molecules
Hydrogen Oxygen Nitrogen Fluorine Chlorine Bromine Iodine Astatine
What is the equation for % of substance in a compound
Mr of substance/Mr of whole compound x100
What is the chemical formula of a compound
It is a representation of the composition of a compound
What are the 2 types of formula
Empirical formula
Molecular formula
What is the empirical formula
The simplest ratio of atoms of each element in a compound
What is the molecular formula
The actual numbers of atoms of each element in a molecule
Can ionic compounds have molecular formulas
No and they dont apply
How do you convert empirical formula to molecular formula
Take the Mr of empirical formula and divide it by the Mr of the molecule and times each atom by that number.
How to find formula of compound with the reactants
Calculate moles of each reactant and divide both by the smaller answer
Find ratio and then put it together into an equation
How to find formula of reactant from the products
Calculate moles of the elements in the reactant
Divide by smallest and find ratio and put into equation
How to find formula of reactant through the weights of multiple products
Find moles of elements in the reactant and then the weights
Use weights to find the unknown weight of third element
Calculate moles and find ratio
Put it into a formula
What is a relative mass
It is a comparative value which is a mass compared to some standard mass
What is relative atomic mass, Ar
It is the average mass of an atom of an element on a scale where an atom of carbon-12 is exactly 12
Equation for relative atomic mass
(% x mass) / 100
What is relative molecular mass, Mr
It is the average mass of a molecule of an element or compound on a scale where an atom of carbon 12 is exactly 12
What is relative formula mass, Mr
It is the average mass of a formula unit on the scale where an atom of carbon 12 is exactly 12
Equation for relative molecular and formula masses
(number of atoms x mass)
What is a mole
A mole of a substance is 6.02 x1023 particles of it
What is avogadros number
6.02 x10 23
What is one mole of a substance
One mole of a substance is its Ar or Mr in grams
Why do we need moles
Because when we talk about equal amounts in chemistry we mean equal numbers of particles and not equal masses
Equation for number of moles
moles = mass / Mr
What is the equation for number of particles
No of particles = moles x Avogadro’s number
What is a reading
A reading is a value found from a single judgement when using a piece of equipment
What is the uncertainty in a reading
It is at least + - 1/2 of the smallest division on the equipment
What is a measurement
It is a value found from the difference between the judgements of two readings
What is the uncertainty in a measurement
It is at least + - 1 of the smallest division on the equipment
What is the equation for % uncertainty
overall uncertainty/value x100
How do you construct an ionic equation
Split up the compounds into ions if substance is a liquid in aqueous state
Remove spectator ions
What salts and hydroxides are soluble
All sodium, potassium and ammonium salts All nitrates Most chlorides, bromides and iodides Most sulphates Sodium, potassium and ammonium hydroxides
What salts and hydroxides are insoluble
Silver and lead chlorides, bromides and iodides Lead and barium sulphate Calcium sulphate is sparingly soluble Most other carbonates Most other hydroxides
What is a soluble salt
It is one which will dissolve in water at room temperature
What is an insoluble salt
It is one which will not dissolve in water at room temperature
What is a sparingly soluble salt
It is one which will dissolve slightly in water
What do chemical equations refer to quantity in
moles
What is a tonne converted into kg and g
1000 kg
1,000,000 g
What does it mean when a substance is in excess
It is when more of a substance is used than needed so not all of it will react
What is the limiting reagent
The reactant that is not in excess
What is the equation for percentage yield
actual yield/theoretical yield x100
What does percentage yield measure
The efficiency of the chemical process
What is the equation for atom economy
Total Mr of desired product/Total Mr of reactants (or products) x100
What does atom economy measure
What proportion of the products of a reaction are the desired product and how much is waste
What does the volume of a gas depend on
The temperature
The pressure
number of moles of it
Under the same conditions what will 1 mole of two gases share
the same volume
What id the ideal gas law equation
PV = nRT Pressure in Pa Volume in m3 Number of moles Gas constant 8.31 J/K/mol Temperature in Kelvin - degrees + 273
What is the conversion from cm3 to m3 and dm3 to m3
x10-6
x10-3
What does the concentration of a solution tell us
How much solute is dissolved in a known volume of solution
How do you convert from mol/dm3 to g/dm3
multiply by the Mr
What is the equation for concentration
moles/ volume (dm3)
moles x1000/volume (cm3)
What is a titration
It is a procedure where a solution of known concentration is used to determine an unknown concentration
What is the percentage error of a pipette
0.05/25 x100 = 0.2%
What is the percentage error of a burrette
0.15/average titre x100
What is the percentage error of a 1 and 2 decimal point weigher
0.1/mass weighed x 100
0. 01/mass weighed x 100
What is the percentage error of a volumetric flask
0.5/250 x 100 = 0.2%
What is a back titration
It is a procedure which involves reacting a known mass of an insoluble solid with a known excess of an acid or alkali so that some will be left over
