C2.1 Purity and separating mixtures Flashcards
What does relative atomic mass mean?
The mean mass of an atom of an element compared o 1/12 of the mass of a carbon atom
What does chemical formula tell you?
Tells you how many atoms of each element there are in a unit of a substance
What is an empirical formula
Shows the simplest whole number ratio of the atoms of each element in a compound
What is a pure substance
A pure element consists of only one element or compound
What is an alloy?
A mixture of a metal with one or more other elements.
What is the melting point of a substance?
The temperature at which it changes from the solid state to the liquid state
How would you know if a substance is impure using melting points
the melting point is less than that of the pure substance
Often melts over a range of temperatures not just one temperature
How does a solution form?
When one substance dissolves in another
What is a solute and solvent?
The substance that dissolves and the solvent is the substance it dissolves
What does it means when a substance is soluble?
when the substance can dissolve in a particular solvent.
How does filtration work?
Filtration separates an insoluble substance in the solid state from substances in the liquid state.It works because the filter paper has tiny, microscopic holes.When you filter a mixture of sand and water, water molecules are small enough to pass through the filter paper, but the large grains of in soluble sand cannot.The sand stays behind in the filter paper as the residue while the water passes through as the filtrate.Particles of a dissolved solute are also small enough to pass through filter paper
How does crystallisation work?
IF you heat a solution the solvent evaporates leaving the solute behind.If you heat the solution too strongly, you het a powder hut if uu allow the solvent to evaporate slowly you het regularly shaped crystals.
Crystillisation takes patience as you need to heat the solution gently until it becomes a saturated solution.Asolution is saturate when no more solute can be dissolved at that temperature Crystals start forming at this point. so you then let the solution cool slowly.As the solution cools, the solubility of the solute decreases so more crystals form
What does simple distillation separate?
Separates a solvent from a solution.
What does fractional distillation do
Separates two or more substances from a mixture in the liquid state
What stages does chromatography rely on
A stationary phase that does not move
A mobile phase that does move
What happens in paper chromatography
The stationer phase is absorbent paper
the mobile phase is a solvent in the liquid state such as water or propane
What does gas chromatography do
Separates the components of a mixture and also measures their amounts
What can you use to tell if a substance is pure
You can use paper chromatography or thin layer chromatography to tell if a substance is pure but thin layer chromatography has some advantages
it is quicker
It is more sensitive so a smaller sample can be used
there is a larger range of stationer phases and solvents to choose from
What separation method would you use for insoluble and soluble substances?
dissolving followed by filtration
What seperation method would you use for a solute dissolved in a solvent (a solution )?
Crystillisation to obtain the solute, simple distillation to obtain the solvent
What seperation method would you use to separate two or more substances in the liquid state?
fractional distillation
what seperation mixture would you use to separate coloured soluble substances
paper chromatography or thin layer of chromatography
Label the parts of the filtration method
Funnel
Filter Paper
Residue
Filtrate
What is an affinity?
natural attraction or force between things
What is the mobile phase in chrometography?
A gas or liquid that carries the component
What is stage 1 of chromatography?
A pencil line is drawn near the bottom of a piece of chromatography paper
Along this line evenly spaced crossess are drawn
What is stage 2 of chromatography?
A sample of the unknown food colouring to be tested is plaved on the first cross.
Samples of known food dye are placed on the other crossess
What is stage 3 of chromatography?
The bottom of the paper is placed in a solvent. Water and ethanol are often used as solvents.
What s stage 3 of chromatography?
The bottom of the paper is placed in a solvent. Water and ethanol are often used as solvents
What is stage 4 of chromatography?
The solvent travels up the paper and the dues travel with it.
The size of the molecules in each dye affects the distance travelled up the paper
What is stage 5 of chromatography?
Food colouring often contains a mixture of dyes.
These separate during chromatography and can be compared to known substances
What is the formula fo Retention Factor Values (RF)
Distance from the baseline to the solvent front
