section 1 Principles of chemistry Flashcards
what are the 3 different forms of material?
solid
liquid
gas
in a solid the particles don’t …………..
move
the hotter the particles are the ………………… they move
faster
do liquids have a definite shape or volume?
volume
in gases particles move in a ……………… motion
random
what is the process where a solid is cooled to make a gas called?
subliming
what is condensing and evaporating?
condensing - cooling a gas to a liquid
evaporating - heating a liquid to a gas
what does ammonia and HCL create in a glass tube?
a white ring of ammonium chloride
what is in a nucleus of an atom?
protons and neutrons
where are electrons in an atom?
on the outer shells
what is the mass number?
the number of protons and neutrons
what is the atomic number?
the number of protons or electrons
what is a molecule?
a group of atoms
elements consist of ………………. atom
one type
how are compounds bonded?
chemically
what is filtration used to separate?
insoluble solids from liquid
what is used to separate a soluble solid from a solution?
crystallisation
what are the four steps to separate rock salts
grinding
dissolving
filtering
crystallisation
what is chromatography used for?
identifying dyes
what are the 2 types of distillation and what are they used for?
simple - separate solution
fractional - separate a mixture of liquids (crude oil)
what is group 1, 0 and 7 on the periodic table called?
1 - alkali metals
0 - noble gases
7 - halogens
how many electrons can go on each shell?
2 on the first then 8 on every other one
what is ionic bonding?
transfer of electrons to form ions
giant ionic structures have a …….. melting and boiling point
high
what is covalent bonding?
sharing electrons
how can covalent bonding be shown?
dot and cross diagram
what type of bonding has a very strong attraction?
covalent
is there charged ions in a giant covalent structure?
no
giant covalent structures ……………………. electricity
don’t conduct
give 2 examples of giant covalent structures
diamond
graphite
What type of attraction is there between ionic bonding and what does that give the compounds?
Strong electrostatic bond between the oppositely charged ions giving a high melting and boiling point
How are covalent bonds held together?
Strong attraction between the shared electron and the nuclei of the atoms involved
Explain the attraction in a simple molecular substance
Atoms within a molecule are very strong
Attraction between molecules are very week ( intermolecular)
Melting and boiling points are low
Explain covalent structures
Lots of strong covalent bonds - takes a lot of energy to break
Don’t conduct electricity
Insoluble in water
Eg diamonds and graphite
Compounds with ionic bonding always have ………… And ions are held to get her in a ………………
Giant ionic structures
Closely packed 3d lattice by attraction between oppositely charge ions to
Ionic compounds have a …….. Melting and boiling point because ………………
High
Electrostatic attraction is very strong
Lattices with higher charged ions will ..….…
Have higher Melting and boiling points
Explain the structure of a diamond
Each carbon forms four covalent bonds
Hardest natural substance
Explain the structure of graphite
Each carbon forms three covalent bonds creating layers which can slide over each other
Free electrons so only non metal with conducts electricity
The higher the ionic charge the higher the …..
Melting and boiling points
What is an ionic crystal?
A giant three-dimensional lattice structure held together by the attraction between the oppositely charged ions.
What is unique about simple molecular structures?
They can be Gases or liquids or solids with low melting points.
Why do simple molecular structures have low melting points?
Because the have weak molecular forces which are easy to break.
Why do giant covalent structures have high melting points?
Because there a strong covalent bonds between the positive and negative ions which are hard to break.
Draw a diagram of the position of atoms in
a) diamond
b) graphite
a) each carbon atom is bonded to another four carbon atoms.
b) - 2 hexagonal layers
- weak forces between the layers
- each carbon atom is bonded to another three carbon atoms
- delocalised electrons which can move between the layers.
How do the uses of diamond and graphite depend on their structures?
Diamond is very strong and hard to break and so is used for cutting.
Graphite has weak forces between layers meaning it can slide and so is used as a lubricant.
Explain conductivity and malleability of metals in terms of structure and bonding.
Metals form a lattice arrangement and are hard to break due to the strong attraction between the delocalised electrons and positive ions. So they can conduct when solid and are malleable as ions form layers.
If an atom gains an electron it has what charge?
If an atoms loses an electron it has what charge?
Negative.
Positive.
What is an isotope?
Different atomic forms of the same element with the same number of protons but different number of neutrons.
The periodic table is an arrangement of elements in what order?
In order of atomic number.
The group of an element represents the number of…..
Electrons in their outer shell.
The noble gases (group 0) are a family of inert gases which means….. because…..
They don’t react
Because they have a full outer shell so they don’t need to give up or gain electrons.
Oxidation is…..
Reduction is…..
The loss of electrons.
The gain of electrons.
Ions are formed when…..
Atoms lose or gain electrons to form charged particles (ions).
Groups 1 and 2 elements are most likely to form…..
Groups 6 and 7 elements are most likely to form…..
Positive ions (cations).
Negative ions (anions).
What do the following state symbols mean?
s) (g
(l) (aq)
(s) solid
(l) liquid
(g) gas
(aq) dissolved in water / aqueous solution
What is an electric current?
A flow of electrons or ions.
Why do covalent compounds not conduct electricity?
Because they have no free electrons and no ions.
Why do ionic compounds only conduct electricity when molten or in solution?
Because the ions aren’t free to move until then.
What does electrolysis involve?
The formation of new substances when ionic compounds conduct electricity.
Write the ionic half equations representing the reactions at the electrodes in aluminium extraction.
Positive electrode: 2O2- ➡️ O2 + 4e
Negative electrode: Al3+ + 3e ➡️ Al
Why is molten cryolite used in the extraction of aluminium from purified aluminium oxide?
Impure aluminium oxide (bauxite) has a much too high melting point so it is dissolved in cryolite to reduce the melting point which reduces the energy costs to melt it.
Why does the anode (positive electrode) need to be replaced?
The O2 produced at the anode reacts with the carbon electrode and produces CO2 which is a gas and so the anode needs replacing every three weeks.
What is a major factor in electrolysis?
The cost of electricity.
What are the rules for writing half equations?
- match two elements you are using with H+ and OH- by their charges.
- at negative electrodes, only the least reactive positive ion (on the reactivity series) will attract so work out which one is least reactive.
- at positive electrodes, Halides (group 7 ions) attract first.
THEN WRITE EQUATIONS.
How can mixtures be separated?
Distillation, fractional distillation, filtration, crystallisation and paper chromatography.
How is carbon dioxide produced?
By reacting calcium carbonate with dilute acid
Or by thermal decomposition of metal carbonates.
How is oxygen produced in the lab?
By using hydrogen peroxide which splits up into water and oxygen and the reaction is sped up by using manganese oxide as a catalyst.
Describe the properties of carbon dioxide.
More dense than air
Slightly soluble in water.
Explain the uses of carbon dioxide.
Slightly soluble in water - so used to make fizzy drinks fizz.
More denies than air - so is used in fire extinguishers as sinks into flames and stops oxygen getting to them.
What is covalent bonding?
When atoms share electrons with each other to get full outer shells. This is called a covalent bond. They have a strong attraction between them.
What is a metal?
A giant structure of positive ions surrounded by a sea of delocalised electrons.
How would you calculate the RAM of the sample with this information?
A sample of copper contains 69% copper-63 and 31% copper-65.
(69 x 63) + (31 x 65) = 6362 / 100
If there is no percentage abundance in a sample when working out RAM what do you do?
Do normal multiplications in brackets and add them together as normal. Then add up numbers in place of percentages (this number will replace the “divided by 100” in usual calculations to work out RAM). Divide your answer from the brackets addition by the sum of the numbers in place of percentages.
How do you work out relative formula mass (Mr) from relative atomic mass (Ar)?
Add up the relative masses of each atom.
e.g. Mr of CO2:
C= 12 O2= 16 x 2 = 32
12 + 32 = 44
What is a mole?
A measure of an amount of substance.
What is the equation linking moles, mass and RAM?
Moles = mass / RAM
How do you find the maximum possible mass of a compound, known as ‘reacting masses’?
e. g. Compound = MgO which can be produced from 500 kg of MgCO3.
1) write equation
MgCO3 = MgO + CO2
2) work out the relative mass of each compound in the equation
MgCO3 ➡️ MgO + CO2
84 40 44
3) write 500kg under MgCO3 and work out how many times the relative mass needs to be multiplied to get to 500 (in this case 84 x 6 = 500)
MgCO3 ➡️ MgO + CO2
84 40 44
x6
500
4) multiply next compounds mass (in this case MgO’s: 40) by same number to get the answer.
MgCO3 ➡️ MgO + CO2
84 40 44
x6 x6
=500 =240kg
What are the steps to finding the empirical formula?
- write the 2 elements you are given in a table of two columns.
- write their masses (which you are given) underneath.
- write their RAM underneath (using periodic table).
- calculate the number of moles in each (mass / RAM).
- divide each number of moles by the smallest one.
- then multiply the numbers you get by their elements in that collumn
e. g. Na = 2, O = 1 and write empirical formula: Na2O.
Describe experiments to investigate the movement of particles.
- potassium manganate + water.
- ammonia + hydrogen chloride.
- bromine gas + air.
What are the differences between elements, compounds and mixtures?
Elements consist of one type of atom only.
Compounds are made up of two or more elements, chemically joined.
A mixture has no chemical bonds between the different parts of the mixture.
What is an atom?
The smallest particle of an element that can take part in a chemical reaction.
How would you work out the molecular formula of a molecule?
e.g. A molecule that has an empirical formula of C4H3O2 and a relative molecular mass if 166.
- find the relative formula mass of the empirical formula (C4H3O2)
(12 x 4) + (1 x 3) + (16 x 2) = 48 + 3 + 32 = 83g.
- relative molecular mass is 166, so there are 166 / 83 = 2 empirical units in molecule.
- molecular formula must be empirical formula x 2 = C8H6O4.
What is the atomic number?
The number on the bottom of the element in the periodic table.
The number of electrons or protons an atom of that element has.
What is the relative atomic mass number?
The number on the top of each element on the periodic table.
The number of protons + neutrons each atom of that element has.
What does RTP stand for and what actually is it?
Room temperature and pressure.
Room temperature: 25 degrees C.
Pressure: 1 atmosphere.
What occupies 24dm3 at room temperature and pressure?
Avogadro’s Law
1 mole of any gas.
What is the equation that links volume with moles of a gas, that you would use when given the number of moles or volume of a gas to workout out the missing component?
Volume (must be in dm3) = number of moles x 24.
V = n x 24.
Remember: Very Naughty 24.
Rearrange to suit information and question given.
How would you convert cm3 to dm3?
1 dm3 = 1000 cm3.
So divide the number of cm3 by 1000 = same number of dm3.
cm3 ➡️ dm3 = / 1000
dm3 ➡️ cm3 = x 1000
How would you calculate the percentage yield of a reaction?
% Yield = (actual mass made / mass that could have been made) x 100
How would you work out the number of moles with the concentration of a substance and the volume?
Number of moles = concentration x volume
Or vise versa.
Concentration = number of moles / volume
Volume = number of moles / concentration.
How would you carry out acid-alkali titrations?
- use fixed volume pipette and a pipette filler to measure 25cm3 of alkali
- add alkali to conical flask with 3 drops of indicator
- fill burette with acid
- use burette to slowly add acid to alkali, and stir as you go
- add extremely slow near neutralisation point
- indicator changes colour when all alkali has been neutralised
- record volume of acid used to neutralise alkali
- repeat
How would you do titration calculations?
e.g. 25cm3 of hydrochloric acid was neutralised by 40cm3 of sodium hydroxide with a concentration of 0.5 mol/dm3, what is the concentration of the acid?
- make a table with two collumns and three rows, with ‘c’, ‘v’, and then ‘n’ on each row in order at the side.
- the acid and alkali compounds go in the two collumns, one in each at the top.
- fill in the information you know from the question in the table (remember, volume must be in dm3 and concentration must be in mol/dm3)
- you will be given 2 pieces of information for one compound and only one piece of information from the other, workout the number of moles using the equation n = c x v for the compound you know most about.
- look at the equation for the reaction, write near it the ratio of each compound to eachother in that reaction.
- if the ratios are the same for the two compounds you have, they have the same number of moles, if not x2, x4, /2, /4 accordingly. You now know the number of moles for both.
- reverse the equation n = c x v to find the last missing piece of information in the table.
- figure out the answer to the question from your table.
What does enthalpy mean?
Energy
How would you do bond energy calculations?
- all information is given, so use it
- apply information in table stating energy amounts for each bond to the amount of that particular bond in the equation.
- to work out overall energy change for the reaction, use the equation 🔺H = energy in - energy out
(🔺H = energy needed to break - energy made) - workout if equation is exothermic or endothermic, a negative 🔺H means an exothermic reaction.
What do these symbols mean:
🔺H?
Ea?
🔺H = energy change Ea = activation energy
How would you calculate the ‘amount’ of a solute?
Amount = volume x concentration.
