C2-ELEMENTS,COMPOUNDS AND MIXTURES Flashcards
what is relative atomic mass
the mean mass of an atom of an element compared of 1/12 the mass of a carbon 12 atom
how can masses of atoms be described
relative atomic mass
mass rules of atoms in terms of carbon relative atomic mass(12.0)
-less mass than a carbon 12 atom if its A is below 12
-more mass than a carbon 12 if its A is about 12
what is relative formula mass
mean mass of a unit of substance compared to 1/12 the mass of a carbon 12 atom
periodic table shows:
the relative atomic masses of the elements.The bottom number in each box is the A,for that elements atoms
what does a chemical formula tell you
-how many atoms of each element that there are in a substance.
for eg- H20 is 2 hydrogens and 1 oxygen
how do you calculate relative formula mass
-write down the A’s of each substance
-times by how many of each substance there is in the chemical formula given
-multiply these values
what is an empirical formula
shows the simplest whole-number ratio of the atoms of each element in a compound.
how to calculate empirical formula
-find highest common factor
-divide the chemical formula by the highest common factor
-write down the empirical formula
What does a balanced chemical equation show
the formulae and number of units for all the substances in a reaction.
what does pure mean
describes natural substances that have not been processed or changed
what is a mixture
A mixture contains two or more substances not chemically combined together
what is a compound
A pure substance made from more than one type of element chemically bonded together
how are mixtures useful
as you can deliberately choose different substances to mix and in result produce desired properties
What is an alloy
a mixture of a metal with one or more other elements.
for e.g.-most jewellery are made from copper and gold mixed together ad pure gold is very soft
What is the melting point
The temperature at which a substance changes from a solid to a liquid
What is the melting point of a pure substance like
A single temperature
for e.g. 17 degrees Celsius
What is the melting point of an impure substance like
-less than that of the pure substance
-often melts over a range of temperatures.Not just one
for e.g. 12-16 degrees Celsius
how can you determine purity using melting point
the greater the difference between the measured melting point for a substance and its accepted melting point,the lower its purity is likely to be
how do you determine melting point
-by heating it
-you can measure it at which it melts or measure the temperature at regular time intervals and plot a graph
what should you make sure to do when measuring melting point
-heat the substance slowly
-stir the substance as it melts
why must you heat slowly and stir substance
-allows temperature of whole sample to increase
-mixing ensures that the entire sample is at the same temperature
-improves the accuracy of a measurement of the melting point of a sample
what is a solution
one substance dissolves into another
solvent and solute
-solute is the substance that dissolves
-solvent is the substance it dissolves in
what happens when a particle dissolves
the substances separate and become completely mixed with the particles of the solvent
soluble and insoluble
-if a substance can dissolve in a particular solvent, it is soluble in that solvent.
-if it can’t-it is insoluble in that solvent.
-substances can be soluble in one solvent but insoluble in another solvent.
For example,nail varnish dissolves in nail-varnish remover but not in water.
FILTRATION
-separates an insoluble substance in the solid state from substances in the liquid state
-filter paper has tiny holes-when u filter a mixture of sand and water , the water molecules are small enough to pass through,sand cannot
-sand (residue) stays in the filter paper while the water (filtrate passes through)
Crystallisation
slowly heating a solvent and forming regularly shaped crystals
-heat until becomes saturated solution(when no more solute can be dissolved at that temperature)
-crystals will start to form,so let it cool and as solution cools the solubility of solute decreases, so more crystals form.
-you can separate from the remaining solution using filtration
-dry in a warm oven or by patting with filter paper
what does a water bath do
heats solutions slowly-enables regular crystals to form on crystallisation.
Simple distillation
-separates a solvent from a solution by relying on the solvent to have a much lower boiling point that the solute
-when heated,solvent escapes in gas state after evaporating.
-then cooled and condensed back into liquid state by a condenser(piece of apparatus kept cold using a flow of cold water)
how is simple distillation useful
if you want to purify a substance
also can provide purified water for chemisits
Fractional distillation
-separating mixtures of liquids
-heat up mixture
-when boiling point is reached, will rise and condense into pure liquid
-if others by chance evaporate,will be caught by glass rods in fractional column and it it cooler than their boiling point,so will condense into a liquid and go back into the mixture.
what is each substance separated by fractional distillation called
fractions-they are just a part of the original mixture
how does the fractioning column improve the separation of the mixture
it has a large surface area on which the vapours can continually condense.
what happens to the column during frac distillation
the column becomes hottest at the bottom and coolest at the top
chromotography- the two chemical phases
stationary(does not move)
mobile(does move)
What is a phase
a substance in the soliq,liquid or gas state
in paper chromotography
-the stationary phase is absorbent paper
-the mobile phase is is a solvent in a liquid state
how is thin-layer chromotography worked
