compounds Flashcards
chemical formulae
letters which represent the elements in the compound and numbers which tell us how many atoms of each element there are
example of chemical formulae
K2SO4
what are the elements with a 2 in their formula
-hydrogen H2
-nitrogen N2
-oxygen, O2
-fluorine, F2
-bromine, Br2
-chlorine, Cl2
-iodine, I2
what are compounds
they are substances which are made of two or more different types of atom that are chemically joined
what are the properties like in compounds
the compound has completely different properties to its constituent elements
Carbon dioxide
CO2 1 carbon, 2 oxygen
methane
CH4 1 carbon, 4 hydrogen
sulphur dioxide
SO2 1 sulphur, 2 oxygen
water
H2O 2 hydrogen, 1 oxygen
ions
is an atom/ molecule that has a different number of protons to electrons, so it has a different charge.
metal atom ions
need to lose electrons to gain full outer shells
non metal ions
need to gain electrons
hydrogen charge
+1
oxygen charge
-2
nitrogen charge
-3
fluorine charge
-1
relative molecule mass
it is a measure of the total mass of all the atoms in a molecule
what is relative molecule mass abbreviated to
RMM or M
how do you find the RMM
by adding all the Ar ( relative atomic mass) values in a molecule together
percentage composition?
the percentage by mass of an element in a compound
how do you work out percentage composition
% of element= Ar x number of atoms / RMM of compound
How are mixtures separated
filtration
evaporation
chromatography
distillation
distillation
used to separate mixtures of liquids that boil at different temperatures
method of distillation
- solution is heated
- the liquid with the lowest boiling point will boil first and evaporate
- meaning it will be easier for the liquids to separate
- this all showing that it has a low boiling point
chromatography
is used to separate a mixture of substances that have different solubilities
how do you calculate the Rf value
distance travelled by ink / distance travelled by water
how does the solubility of the ink effect chromatography
the more soluble the dye id the further it will travel up the paper
what does the Rf value tell you about the chromatography paper
the bigger the Rf value, the further up the paper the ink has travelled the value will never be bigger than 1
method of chromatography
- set up apparatus
- on chromatography paper draw a line with pencil and a dot in the middle with an ink pemn
- fold paper over wooden splint so the tip reaches water
- take splint out and let it dry
what colour would the chromatography paper be with an ink dot
blue and purple
Separating mixtures with evaporation
heating the solution until the solvent evaporates and turns into gas leaving behind the solid residue
filtration method
- crush the solid using a pestle and mortar
-put solid into beaker and add 50cm3 of water and stir well - filter the mixture into a conical flask using a funnel and filter paper
- once all collected put in evaporating basin
- place over bunsen burner until all evaporated
what are the changes that could happen in chemical reactions
- change colour
- give off gas
- get hot
- get cold
- give out light
- make smells
- form solids( precipitates)
colour changes
A colour change might take place when two substances react. It can also happen when a compound is broken down by heating it
effervescence
which a reaction in a liquid produces bubbles of gas
precipitation
Some liquids react together to produce an insoluble solid. This is called a precipitation reaction and the solid formed is called a precipitate.
temp change
Chemical reactions can take in energy or release energy, often in the form of heat. This causes a change in temperature.
exothermic temp change
the reactants hold more energy than the products, so exothermic reactions release energy in the form of heat.
Exothermic reactions can be identified by an increase in temperature.
endothermic temp change
Endothermic actions take in heat. So endothermic reactions can be identified by a decrease in temperature.
reactants
they are the starting substances
products
the new substances formed in a reaction
what is the first stage in a chemical reaction
bond between the atoms in the reactants are broken
second stage of a chemical reaction
the atoms re-organise
third stage of a chemical reaction
new bonds are made between the atoms in the products
symbol equations
uses the formulae of the reactants and products to show what happens in a chemical reaction
how do you calculate percentage yield
actual yield / theoretical yield X 100
balanced equation
is where there is the same number of atoms of each element on each side of the equation
what charge are group 1 metals
1+
what charge are group 2 metals
2+
what charge are group 6 elements
2-
what charge are group 7 elements
1-
what is 1 mole - avogadro constant
6 X 10,23
the mass of 1 mole of an element
is the same as the atomic mass of the element
the mass of 1 mole of a molecule
is the same as the molecular mass
moles equation
mass / Ar or Mr
mass equation
moles X Ar or Mr
empitical formula
simplest formula of a compound
