Topic 2 - States Of Matter And Mixtures Flashcards
Describe the arrangement, movement and relative energy of a solid
Arrangement - close together, regular pattern
Movement - vibrate about fixed positions
Relative energy - least stored energy
Describe the arrangement, movement and relative energy of a liquid
Arrangement - close together, random
Movement - move around each other
Relative energy - mid stored energy
Describe the arrangement, movement and relative energy of a gas
Arrangement - far apart, random
Movement - fast in all directions
Relative energy - most stored energy
What happens during a state change? (Interconversion)
- energy is transferred to or from the particles
- the arrangement of the particles change
- the movement of the particles change
What are the names of the state changes? (Eg solid -> gas)
Gas to liquid - condensing Gas to solid - deposition Liquid to solid - freezing Liquid to gas - evaporating or boiling Solid to liquid - melting Solid to gas - sublimation
What happens at a substances melting point?
At its melting point, a substance begins to:
- melt if energy is transferred to the particles
- freeze if energy is transferred to the surroundings
What happens at a substances boiling point?
At its boiling points, a substance begins to:
- boil if energy is transferred to the particles
- condense if energy is transferred to the surroundings
Why does a substance evaporate?
A substance evaporates if it changes from a liquid to a gas below its boiling point:
- particles with high enough energy leave the surface of the liquid
- the remaining particles have less energy
- the liquid cools down unless it is heated
How do you predict the state of matter from given data?
A substance is a:
- solid below its melting point
- gas above its melting point
- liquid between its melting and boiling points
What is the difference between pure substances and mixtures?
A PURE substance contains only one element or compound eg
- pure hydrogen contains only hydrogen molecules
- pure water contains only water molecules
PURE usually means nothing else has been added to the substance
Mixtures are IMPURE as they contain different elements and/or compounds. The components of a mixture are NOT chemically joined together
Define an element
An element is a substance that consists only of atoms with the same atomic number (same number of protons in their nucleus) eg:
- hydrogen is an element because its atoms all have one proton in their nucleus
- oxygen is a different element because its atoms all have eight protons
What is the difference between an element and a compound
A COMPOUND is a substance that consists of atoms of two or more different elements, chemically joined together eg:
- water is a compound because it consists of hydrogen atoms and oxygen atoms chemically joined together
This is different to an element as it is two or more elements
What is the difference between pure melting points and mixture melting points?
Pure substances have sharp melting points on graphs however mixtures melt over a range of temperatures.
Explain how you use simple distillation to separate a solvent from a solution
Simple distillation works because the solute in the solution has a much higher boiling point than the solvent.
When the solution is heated:
- the solvent boils
- solvent vapour passes into the condenser
- the vapour is cooled and condensed back to the liquid state
The solution becomes more concentrated during simple distillation because the solute stays behind.
How do the apparatus in simple distillation work? (Condenser)
The condenser has two tubes, one inside the other:
- cold water runs through the space between the two tubes, keeping the condenser cold
The cooling water doesn’t mix with the substance being separated
Why does fractional distillation work to separate a liquid from a mixture of miscible liquids (liquids that mix completely with each other) ?
Fractional distillation works because the liquids in the mixture have different boiling points:
When the mixture is heated:
- the mixture boils
- hot vapour rises up the fractionating column
- vapour condenses when it hits the cool surface of the column and drips back
- the fraction with the lowest boiling point reaches the top of the column first
- its vapour passes into the condenser
If you carry on heating, vapours from fractions with higher boiling points pass to the condenser
Why does filter paper help in filtration?
Filtration works because the filter paper has tiny pores. These are:
- large enough to let water molecules through
- small enough to stop insoluble solid particles going through
How and why do you use filtration?
Filtration is used to seperate an INSOLUBLE substance from a LIQUID or a SOLUTION
There are two reasons for doing this:
- To purify a liquid or a solution by removing solid impurities from it, eg sand from sea water
- To seperate the solid you want from the liquid it is mixed with e.g to separate crystals from a solution after crystallisation
How does crystallisation work (method) and what does it produce?
You can use crystallisation to produce solid crystals from a solution
In crystallisation:
- the solution is heated to remove enough solvent to produce a saturated solution (one that cannot hold any more solute)
- the saturated solution is allowed to cool
- crystals from in the solution
- the crystals are separated from the liquid and dried
Why does CRYSTALLISATION work?
It works because:
- The solubility of the solute decreases as the saturated solution cools
- crystals form from the excess solute
What is SOLUBILITY?
Solubility is the mass of solute that dissolves in a given volume of solvent at a given temperature
Explain the two phases in CHROMOTOGRAPHY
- STATIONARY phase - a substance that does not move
2. MOBILE phase - a substance that moves through the stationary phase - the solvent
What happens during CHROMOTOGRAPHY?
- each soluble substance in the mixture forms bonds with the two phases
- substances that form stronger attractive forces with the stationary phase stay at the bottom
- substances that form stronger attractive forces with the mobile phase move towards the top
A student wants to produce some copper sulfate crystals from copper sulfate solution. She heats the solution in an evaporating basin to remove some of the water.
Describe the steps that she should then take to obtain dry crystals of copper sulfate.
(3 marks)
She should let the solution cool down so that crystals form. She should then decant the remaining liquid and dry the crystals in an oven.
(DECANTING - pouring the liquid away carefully so that the solid stays behind)
Outline one method to produce dry copper chloride from a mixture of broken glass, dust and copper chloride powder.
(4 marks)
Add water to dissolve the copper chloride. (1)
Filter to remove the glass and dust. (1)
Heat the filtrate to produce copper chloride crystals (by crystallisation) (1)
Pat the copper chloride crystals dry with filter paper/put them in a warm oven. (1)
How do you use and do paper CHROMOTOGRAPHY?
Firstly, drops of the different samples are put onto the paper and allowed to dry.
The bottom of the filter paper is used and dipped into a solvent (this can be water or something the samples will dissolve in).
The different compounds in a sample dissolve to different extents in the solvent. More soluble compounds are carried up the paper faster than less soluble ones, so the compounds separate out.
What can you use a CHROMATOGRAM for?
- to distinguish between pure and impure substances (a pure substance will produce one spot)
- identify a substance by comparing its pattern of spots with those of a known substance
- identify substances using Rf values
Explain the stages in water treatment to make waste and ground water potable
- SEDIMENTATION - large insoluble particles sink to the bottom of a tank
- FILTRATION - small insoluble particles are removed by filtering through beds of sand
- CHLORINATION - chlorine gas is bubbled from the water to kill microbes
Describe how sea water can be made potable
This can be achieved by using simple distillation:
- filtered sea water is boiled
- the water vapour is cooled and condensed to form distilled water
We do this because sea water contains dissolved salts and their concentration is too high to drink it safely. These dissolved salt are removed by distillation but the distilled water still contains dissolved gases from the air
What must drinking water have to be to be potable (safe for drinking) ?
- low levels of contaminating substances
- low levels of microbes
Explain why water used for chemical analysis must not contain any dissolved salts? (3 marks)
Dissolved salts could react with the substances used in the analysis. A product formed in the reaction could interfere with the analysis, giving a false result. If the water used does not contain any dissolved salts, this will not happen.
Advantages and disadvantages of simple distillation of sea water?
+ uses a plentiful raw material
+ produces pure water
+ kills microbes in the sea water
- needs a lot of energy to heat the water
Explain the method and apparatus of paper CHROMOTOGRAPHY to investigate the composition of ink
Using eye protection, chromotography paper, boiling tube with bung, dropping pipette, pencil and rubber, solvent for mobile phase.
Draw a pencil line near the bottom of the chromotography paper. Apply a small spot of ink, and then place the paper into a boiling tube containing a little solvent. Replace the bung and allow the solvent to travel through the paper.
A student uses simple distillation to purify the solvent a sample of ink, the method he uses is as follows:
- add some ink to a boiling tube, then fit a delivery tube and bung
- hold the boiling tube with a test tube holder
- heat the ink using a roaring Bunsen burner flame until it is dry
- collect the water vapour in a test tube
State two ways of improving his method using the same essential equipment. (2 marks)
Two of the following at one mark each:
- clamp the boiling tube
- use a blue flame with the air hole half open
- do not heat to dryness
- put the test tube in a beaker of cold/iced water
How do you find the Rf value from chromotography data?
Rf = distanced travelled by spot / distance travelled by solvent
( / = divided by)
