Topic 1 - Key Concepts in Chemistry Flashcards
Balance: Fe + Cl2 -> FeCl3
2Fe + 3Cl2 -> 2FeCl3
What is a hazard?
Anything that has the potential to cause harm or damage
What is an oxidising substance?
A substance which provides oxygen which allows other materials to burn more fiercly
Give an example of an oxidising substance?
Liquid oxygen
What is the oxidising symbol?
A ball on fire
What is a harmful substance?
A substance that can cause irritation, reddeing or blistering of the skin
Give an example of a harmful substance?
Bleach
What is the harmful symbol?
An exclamation mark
What did John Dalton describe atoms as?
Solid spheres
What is the mass of an electron?
0.0005
What does the nuclear symbol of an atom tell you?
The atomic number and mass number
What are isotopes?
Different forms of the same element with the same number of protons but a different number of neutorns
What is relative atomic mass?
The average mass of one atom of the element, compared to 1/12 the mass of one atom of carbon-12
What is the important details in the RAM definiton?
Average mass one atom compared to mass one atom carbon-12
How can you calculate isotopic abundances?
Multiply each RIM by its isotopic abundance and add up all the results
Divide by the sum of the abundances
Boron has two isotopes, Boron-10 and Boron-11
Given that the relative abundance of Boron-10 and Boron-11 are 4 and 16, work out the RAM of Boron
(10x4)+(11x16) / (16+4) = 10.8
Bromine has an atomic number of 35 and has two stable isotopes Bromine-79 and Bromine-81
Given that 51% of bromine atoms are Bromine-79 and 49% are Bromine-81
Work out the RAM of bromine
Give your answer to the nearest whole number
(.51x79)+(.49x81) = 79.98
= 80
What does each group represent?
Atoms with the same number of electrons in their outer shell
What does each period represent?
Atoms with the same number of shells
If elements are in the same group, what is similar about them?
Similar chemical properties
Based on its position in the periodic table, would you expect the chemical properties of potassium to be more similar to those of sodium or calcium?
Explain your answer
Sodium as they are both in the same group (Group 1) and elements in the same group have similar chemical properties`
Give the electronic configuration of aluminium
Atomic number = 13
2,8,3
In which group and period of the periodic table would you expect to find the element with the electronic configuration 2.8.8.2?
Group 2, Period 4
What are ions?
Charged particles
When do anions form?
When atoms gain electrons
When do cations form?
When atoms lose electrons
What is the chemical formula of calcium nitrate?
Ca2+ + NO3-
Ca(NO3)2
What is the formula of the ionic compound, lithium oxide?
Li+ + O2-
Li2O
What happens when a metal and non-metal react together?
The metal atom loses electrons to form a cation whilst the non-metal gains these electrons
What is ionic bonding between?
Nonmetals and metals
Describe, in terms of electron transfer, how sodium and chlorine react to form sodium chloride?
Sodium loses its one outer electron to chlorine
Describe, in terms of electron transfer, how potassium and chlorine form potassium chloride
Potassium loses its one outer electron to chlorine
What structure do ionic compounds have?
A giant ionic lattice
What are the properties of ionic compounds?
High melting and boiling point
Inconductive when solid
Conductive when molten or in solution
Give the models that can be used to show structures?
2D representations
Dot and cross diagrams
3D models
Ball and stick models
What are the advantages to using 2D representation?
Simple
Shows what atoms are connected
Shows how the atoms are connected
What are the disadvantages to using 2D representation?
Doesn’t show the shape
Doesn’t show the size
What are the advantages to dot and cross diagrams?
Shows how compounds or molecules are formed
Shows where the electrons in the bonds or ions come from
What are the disadvantages to dot and cross diagrams?
Doesn’t show the size
Doesn’t show it’s arranged
What are the advantages to 3D models?
Shows the arrangement of ions
What are the disadvantages to 3D models?
Doesn’t show the inner layer of the substance
What are the advantages of ball and stick models?
Great to visualise structure
What are the disadvantages of ball and stick models?
Makes it look like there are big gaps between the atoms
Doesn’t show the correct scale
Explain why calcium chloride, an ionic compound, has a high melting point?
A lot of energy is needed to break the strong attraction between the ions/the strong ionic bonds
What is a covalent bond?
A strong bond that forms when a pair of electrons is shared between two atoms`
What are the typical sizes of simple molecules?
10^-10
What are the properties of simple molecular substances?
Low melting/boiling point
Unconductive
Some are soluble, some aren’t
How does size of a simple molecular substance affect it’s mp/bp?
The bigger the molecule, the strength of the intermolecular force increases so more energy is needed to break them so the melting and boiling point increases
Why are mp/bp so low in simple molecular substances?
Because in order to melt or boil the compound you only need to break these feeble intermolecular forces and not the covalent bonds
What is a polymer?
A molecule made up of long chains of covalently bonded monomers
What is a monomer?
A small molecule that when joined together makes a polymer
Explain why oxygen is a gas at room temperature?
Because the intermolecular forces between molecules of oxygen are weak and don’t need much energy to break meaning the boiling point is below the temperature of room temperature
Explain why N2 doesn’t conduct electrically?
N2 molecules aren’t charged nor contain any free electrons or ions
What is a giant covalent structure?
A structure of atoms in which all are bonded to each other by strong covalent bonds
What are the properties of giant covalent structures?
Very high MP/BP
Don’t generally conduct
Aren’t soluble
Why do giant covalent structure have high MP/BP?
Because lots of energy is needed to break the covalent bonds
Give examples of carbon-based giant covalent structures
Diamond
Graphene
Graphite
What is diamond made up of?
A network of carbons that each form four covalent bonds
Give the properties of diamond
High MP
Very hard
Doesn’t conduct
Explain the properties of diamond
High MP as the bonds are take alot of energy to break
Very hard as the atoms are held in a rigid lattic structure by strong covalent bonds
Doesn’t conduct as no free electrons or ions
What are the uses of diamond?
To strengthen cutting tools (Eg. Saw teeth and drill bits)
What is graphite made up of?
Sheets of hexagonal carbon atoms forming three covalent bonds
Give the properties of graphite
Slippery and soft
High MP
Conductive
Explain the properties of graphite
Slippery and soft as there aren’t any covalent bonds between the layers
High MP as the bonds in the layers need loads of energy to break
Conductive as the delocalised electrons are free to move
What are the uses of graphite?
Lubricating material
Electrodes
What is graphene?
A single sheet of carbon atoms joined together in hexagons (a single layer of graphite)
What are fullerenes?
Molecules of carbon shaped like closed tubes or hollow balls
What can fullerenes be used to do?
Cage other molecules
Give uses of fullerenes and how they work?
Deliver drugs to the body as they can cage molecules
Industrial catalysts as they have a huge surface area
What is the formula for buckminsterfullerene?
C60
What is buckminsterfullerene?
A stable molecule that forms soft brownish-black crystals
What are the properties of nanotubes?
Conductive
High tensile strength
Give one use of graphite and state what property of graphite makes it suitable for this use?
Lubricant - It’s slippery and soft
Electrodes - Conducts electricity
What does metallic bonding involve?
Delocalised electrons
What type of structure are metals?
Giant
How are metallic structures held together?
By electrostatic forces of attraction between the delocalised electron and the metal ions
What produces all the properties of metals?
The delocalised electrons
What are the properties of metals?
High MP/BP Aren't soluble Dense Malleable Conductive
Why do metals have high MP/BP?
Because to overcome the electrostatic forces between the metal ions and the delocalised sea of electrons alot of energy is needed
Why are metals dense?
The metal ions are packed close together
Why are metals malleable?
Because in a pure metal atoms can slide over each other
Why can metals conduct?
Because of the delocalised electrons
What are the usual properties of non-metals?
Dull-looking
Brittle
Lower BP
Copper is a metallic element
State what property of copper makes it suitable for using in electricaal circuits and explain why it has this property?
It’s conductive because it will have a sea of delocalised electrons around it
Thomas has two samples of solids
One of the samples i metal
Solid A is shiny and conduct electricity whilst B is a white powder that only conducts electricity when dissolved in water
Predict with reasoning, whether solid A or solid B is likely to be the metal?
A, as it is shiny and conducts electricity
Metals conduct because of the sea of delocalised electrons
B isn’t a pure metal as it is soluble and metals can’t be dissolved in water
If the mass increases in a reaction, what has happened?
Gas from the environment has reacted with the reactants
If the mass decreases in a reaction, what has happened?
Some of the product is gaseous and it has diffused out
Why does gas escape vessels?
Because it will expand to fill any container it’s in, meaning if the vessel isn’t sealed the gas will expand out from the vessel
A student carries out a reaction which produces gas
Predict how the mass will change over the reaction
Explain your answer
As the reaction goes on the mass will decrease until one of the reactants is the limiting factor
Find the RFM of MgCl2
Mg = 24 Cl = 35.5
= 24 + 2(35.5)
= 24 + 71
= 95
Find the RFM of Ca(OH)2
Ca = 40 H = 1 O = 16
= 40 + 2(16 + 1)
= 40 + 2(17)
= 40 + 34
= 74
What is the empirical formula of a compound?
The smallest whole number ratio of atoms in the compound
Find the empirical formula of glucose?
C6H12O6
CH2O
How do you find the lowest whole number ratio?
Divide by the smallest number
Compound X has the empirical formula C2H6N
The Mr of the compound X is 88
Find the molecular formula of compound X
C2H6N
= 24 + 6 + 14
= 44
= 88 / 44
= 2
= 2 x C2H6N
= C4H12N2
Calculate the RFM of ethanol
C2H5OH
= 24 + 5 + 16 + 1
= 46
What is the empirical formula of a compound with the molecular formula C4H8Cl2?
C4H8Cl2
= 8 / 2
= 4
= 4 / 2
= 2
C2H4Cl
What is avogardo’s constant?
6.02 x 10^23
What is one mole of any atom or molecule equal to?
It’s Ar/Mr
How many atoms are there in 5 moles of oxygen gas?
1 mol = 6.02 x 10^23
5 mol = 6.02 x 10^23 x 5 = 3.01 x 10^24
3.01 x 10^24 x 2
When reading mole questions what must you check?
The number of atoms in the molecule
What it’s asking you for (Atoms/Moles/Mass/Molecules)
When reading mole questions what must you check?
The number of atoms in the molecule
What it’s asking you for (Atoms/Moles/Mass/Molecules)
When reading mole questions what must you check?
The number of atoms in the molecule
What it’s asking you for (Atoms/Moles/Mass/Molecules)
What is the formula for number of moles?
Mass / Mr
State the equation relating moles, mass and Mr
Moles x Mr = Mass
How many magnesium atoms are there in 60 g of magnesium?
Mg = 24
Mass / Mr = Moles
60 / 24 = Moles
2.5 moles
- 5 x (6.02 x 10^23) =
- 505 x 10^24 =
Calculate the number of moles in 90g of water
H20
= 2 + 16
= 18
= 90 / 18
= 5 moles
How many molecules of ammonia are present in 3.5 moles of ammonia gas?
= 6.02 x 10^23 x 3.5
= 2.107 x 10^24
How many atoms are present in 81.4 g of calcium hydroxide?
Ca(OH)2 = 74
Mass / Mr = Moles
- 4 / 74 = Moles
- 1 Moles
= 1.1 x 6.02 x 10^23
= 6.622 x 10^23 molecules
= 6.622 x 10^23 x 5
= 3.311 x 10^24 atoms
How many moles are there in 66g of CO2?
CO2 = 44
Moles = Mass / Mr Moles = 66 / 44 Moles = 1.5 moles
What mass of carbon is there in 4 moles of carbon dioxide?
= 4 x 12
= 48 g
What is concentration?
The measure of how crowded things are
What is the concentration equation?
Concentration = Mass / Volume
25 g of copper sulfate is dissolved in 500 cm^3 of water
Whats the concentration?
= 500 cm^3
= .5 dm^3
= 25 / .5
= 50 g/dm^3
What mass of sodium chloride is in 300 cm^3 of solution with a concentration of 12 g/dm^3
300 cm^3 = 0.3 dm^3
C = M / V M = C x V M = 12 x .3 M = 3.6 g
Calculate the mass of 0.2 moles of potassium bromide
KBr = 119
Moles = Mass / Mr Mass = Moles x Mr Mass = 0.2 x 119 Mass = 23.8 g
0.5 moles of substance X has a mass of 87 g
Whats the RFM of X?
Moles = Mass / Mr Mr = Mass / Moles Mr = 87 / 0.5 Mr = 174
What mass of sodium hydroxide is contained in 200 cm^3 of a 55 g/dm^3 solution?
200 cm^3 = 0.2 dm^3
C = M / V M = C x V M = 55 x 0.2 M = 11 g
A sample of a hydrocarbon contains 36 g of carbon and 6 g of hydrogen
Work out the empirical formula of the hydrocarbon
36 g of C = 3 moles
6 g of H = 6 moles
3: 6
1: 2
CH2
Describe the experiment to calculate the empirical formula
Heat a crucible then leave it and weight it with its lid
Add some magnesium ribbon and reweigh it
Heat the crucible containing the magnesium, with the lid slightly off, for 10 minutes
Allow the crucible to cool and reweigh
When doing the experiment to calculate the empirical formula, why is the crucible heated at first?
To make sure its clean and to get rid of oil or water traces
When doing the experiment to calculate the empirical formula, why is the lid put where it is?
To prevent tiny bits of solid leaving the crucible but to allow oxygen to enter
A student heats 1.08 g of magnesium ribbon in a crucible so it completely reacts to form magnesium oxide
The total mass formed was 1.8g
Calculate the empirical formula
= 1.8 - 1.08
= 0.72 g
= 1.08 / 24
= 0.045 moles
= 0.72 / 16
= 0.045 moles
0.045:0.045
1:1
MgO
A 45.6 g sample of an oxide of nitrogen contains 13.9 of nitrogen
What is the empirical formula of the nitrogen oxide?
= 45.6 - 13.9
= 31.7 g oxide
= 31.7 / 16
= 1.98 moles
= 13.9 / 14
= 0.99 moles
0.99 : 1.98
1 : 2
NO2
What is the relation between the limiting reactant and the product?
Directly proportional
Why is the relation between the limiting reactant and the product direct?
If there is no limiting there will be no product
If you add more limiting there will be more product
What is the limiting reactant?
The reactant that is used up in a reaction
What is the ion for carbonate?
CO3^2-
What is the ion for sulfate?
SO4^2-
What is the charge of a group 6 element?
-2
Describe how ionic bonding occurs?
A non-metal is reduced by a metal which is oxidised
Why do ionic compounds conduct when molten or aqeous?
Because the ions are free at that point
Do simple molecular compounds have high or low boiling points?
Low as in order to boil the compound you only have to break the feeble intermolecular forces
Give a definition for the RFM of a compound?
The Ar of all the elements added together
Describe how to balance an equation using the masses of the reactants and products
Work out moles of each product and reactant and put into a whole number ratio
