Ch2.1 Atoms and Reactions Flashcards
Define relative isotopic mass
The mass of an atom of an isotope compared with one-twelfth of the mass of an atom of carbon-12
Define relative atomic mass
The weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12
Define relative molecular mass
The weighted mean mass of a molecule compared with one-twelfth of the mass of an atom of carbon-12
Define relative formula mass
The weighted mean mass of a formula unit compared with one-twelfth of the mass of an atom of carbon-12
How do you know the isotopic mass of an isotope?
It is the mass number (protons and neutrons, electrons are ignored)
What is the term relative molecular mass used for?
Simple molecules eg. CO2
What is the term relative formula mass used for?
Compounds with giant ionic or giant covalent structures
Describe how atomic masses are measured and how this unit is used
Atomic masses are measured using a unit called the unified atomic mass unit (u). The mass of an atom of carbon-12 is 12u so the mass of one twelfth of an atom of carbon-12 is 1u
What is assumed when measuring atomic masses?
That protons and neutrons have a mass of 1u each and the mass of electrons is neglected as they make such a tiny contribution
Define ‘amount of substance’
The quantity whose unit is the mole. Chemists use ‘amount of substance’ as a means of counting atoms
What is the unit and symbol for ‘amount of substance’?
unit: mol.
symbol: n
Define ‘a mole’
The amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope
How are the mole and atomic mass of an element related?
The mass of 1 mole of any element is the same mass as its relative atomic mass in grams
Define molar mass, give an example (carbon) and give its unit
The mass per mole of a substance eg. carbon has a molar mass of around 12g/mol
unit: g/mol or g mol⁻¹
Define ‘The Avogadro Constant’, give its symbol and give its value
The number of atoms per mole of the carbon-12 isotope
Symbol: Nᴀ
Value: 6.022 x 10²³
What equation links moles, molar mass and mass?
Mass = Moles x Molar mass OR m = n x M
What equation links moles, number of particles and Avogadro’s constant?
Number of particles = Moles x Avogadro constant OR
x = n x Nᴀ
What is a compound? Give example of water
A substance made of two or more different types of atoms which are bonded together in set, fixed proportions eg. water always has 2 hydrogen atoms per oxygen atom
What is an empirical formula? Give example of ethane
It tells you the simplest ratio of the numbers of each type of atom in a compound eg. ethane is C₂H₆ so the empirical formula is CH₃
How do you calculate an empirical formula?
- Find molar ratios
- Divide values by the smallest molar ratio
- Form ratio in formula
How do you calculate a molecular formula?
- Find the mass of one unit of the empirical formula
- Find out how many units of the empirical formula are in the molecular formula
- Multiply this value into the empirical formula and scale it upwards accordingly
What equation links moles, molar mass and mass?
Moles = mass ÷ molar mass
What equation links moles, volume and molar volume?
Moles = volume ÷ molar volume
What equation links 24.0 dm³/mol, volume in dm³ and moles?
Moles = volume in dm³ ÷ 24.0dm³/mol
What equation links moles, 24 000 cm³/mol and volume in cm³?
Moles = volume in cm³ ÷ 24 000 cm3/mol
What equation links moles, volume and concentration?
Moles = concentration x volume
How much room does 1 mole of any gas take up at room temperature or pressure?
24.0 dm³ or 24 000 cm³
What is room temperature?
25°C or 298K
What is room pressure?
101 325 Pa (100 000 Pa)
How do you work out the percentage yield of a product? (equation)
(actual amount of product (mol) ÷ theoretical amount of product (mol)) x 100
What are some reasons of why yields in a reaction may not be 100%?
- equilibrium, reaction may not go to completion
- by products may be produced
- impure reactions
- reactants/products left over in apparatus
- separation and purification may lead to loss of product
How is the theoretical mass of a product calculated?
comes from the balanced chemical equation as well as (mol = mass ÷ Mr)
How is the actual mass of a product calculated?
The physical mass is calculated by weighing it
What is the definition of atom economy?
A form of percentage yield used to determine the efficiency of production of desired products
What is the formula for atom economy?
(molecular mass of desired product / sum of molecular masses of all products) x 100
What type of reaction always has an atom economy of 100%?
Addition reactions
Which types of reactions are always less than 100%?
Substitution reactions and elimination reactions
What are alkalis?
Soluble bases
Name some common acids and their formulas
- hydrochloric acid (HCl)
- sulfuric acid (H₂SO4)
- nitric acid (HNO₃)
- ethanoic acid (CH₃COOH)
Name some common alkalis and their formulas
- sodium hydroxide (NaOH)
- potassium hydroxide (KOH)
- ammonia (NH₃)
How do acids behave i aqueous solutions?
- acids release H+ ions (protons)
eg. HCl(g) –> H+(aq) + Cl-(aq)
What characteristic do strong acids have?
They are very good at giving up H+ ions (protons). This means they fully ionise/dissociate in water (or almost fully)
What do weak acids do in water?
They don’t fully ionise/dissociate. When they give up their protons they quickly take them back afterwards- strong acids don’t do this
How do alkalis behave in aqueous solutions?
Alkalis are a special type of base that dissolve in water to form OH-(aq) ions
eg. NaOH(s) + aq –> Na+(aq) + OH-(aq)
How do acids and alkalis behave when in the same solution?
The H+ ions and OH- ions react to form water
What difference is there in the equation for how ammonia (a weak base) behaves in water?
There is a double headed arrow because it accepts its ions back whilst giving off new ones
What is an amphoteric substance?
Substances that can behave as acids and bases eg. amino acids
Why are amino acids amphoteric substances?
They have an amino group which is able to accept a proton and a carboxylic acid group which is able to donate a proton
What features do salts have?
- the positive ion in a salt is usually a metal ion or ammonium ion (NH₄+)
- the negative ion is derived from an acid
- the formula for a salt is the same as the parent acid except that an H+ ion is replaced by the positive ion
What is a hydrated salt?
A salt containing water. Sometimes when salts form there are water molecules loosely attached to the ions in the crystal
How is the number of water molecules involved in a hydrated salt shown?
In a dot formula
eg. NaCl.5H₂O
How is an anhydrous salt formed?
A hydrated salt is heated to the point the water molecules are driven off and the compound that is left is an anhydrous salt
What is water of crystallisation?
Water molecules in a hydrated salt
Describe method of working out mass of water in a hydrated salt (not titrating)
- mass of empty crucible
- mass of crucible and hydrated salt
- heat until constant mass
- mass of crucible and anhydrous salt
- mass of hydrated salt - mass of anhydrous salt = mass of water
What are the 3 types of acid that can exist and what is the difference between them?
- monobasic/monoprotic: one acid molecule donates one proton eg. HCl
- diabasic/diprotic: one acid molecules donates two protons eg. H₂SO₄
- tribasic/triprotic: one acid molecule donates three protons eg. H₃PO₄
Name some general bases
- metal oxides
- metal hydroxides
- ammonium hydroxide
- metal carbonates
- ammonia
What do bases and acids produce in neutralisation reactions?
A salt and water
What do an acid and metal oxide react to produce?
Salt and water
What do an acid and metal hydroxide react to produce?
Salt and water
What do an acid and ammonium hydroxide react to produce?
Salt and water
What do an acid and metal carbonate react to produce?
Salt, water and carbon dioxide
In what type of reaction do metals react with acids and what is produced?
They react together in redox reactions and produce a salt and hydrogen
What do redox reactions involve?
Both reduction and oxidation processes
Define oxidation in terms of electrons
Loss of electrons
Define reduction in terms of electrons
Gain of electrons
Define an oxidising agent in terms of electrons
A species that removes electrons from another
Define a reducing agent in terms of electrons
A species that gives electrons to another
What happens to the oxidation number of a substance that is oxidised in a reaction?
It increases
What happens to the oxidation number of a substance that is reduced in a reaction?
It decreases
What is a disproportionation reaction?
Where one substance is reduced and oxidised in the same reaction
Which element is the turning point for where max oxidation numbers of metals start to decrease again?
Mn - manganese
In, non-metals what is the general range of what their oxidation numbers can be?
Their group number to their group number minus 8
eg. chlorine is in group 7 so oxidation numbers could be from +7 to -1
What is the formula for the ideal gas equation?
PV = nRT
P- pressure (Pa)
V- volume (m³)
n- moles of gas
R- gas constant (8.31 ish)
T- temp (K)
What assumptions are made in the ideal gas equation?
- there is no intermolecular forces in gases
- all particles are the same size
What is the oxidation state of any element?
0
What is the oxidation state of group 1 elements?
always +1
What is the oxidation state of group 1 elements?
always +1
What is the oxidation state of group 2 elements?
always +2
What is the oxidation state of fluorine?
always -1
What is the oxidation state of hydrogen?
- usually +1
-1 when in metal hydrides eg. NaH
What is the oxidation state of oxygen?
- usually -2
- +2 in F₂O
- -1 in peroxides
What is the sum of the oxidation numbers equal to?
The charge of the ion or zero if it’s an uncharged compound
What are Roman Numerals used for in chemistry?
Used to show oxidation states of transition metals
eg. Fe²⁺ in FeO is iron (II) oxide
Fe³⁺ in Fe2O3 is iron (III) oxide
What is an oxyanion? Give examples
Negative ions containing an element and oxygen and usually ending in ‘ate’
- NO₂⁻ = nitrate (III)
