12. Experimental Techniques + Chemical Analysis Flashcards
What can time be measured with?
Time can be measured using a stopwatch or stop-clock which are usually accurate to one or two decimal places
What unit is used for time?
The units of time normally used are seconds or minutes although other units may be used for extremely slow reactions (e.g. rusting)
What can temperature be measured with?
Temperature is measured with a thermometer which can normally give readings to the nearest degree Celsius
Digital thermometers are available which are more precise than traditional thermometers
How do traditional thermometers work?
Traditional thermometers rely upon the uniform expansion and contraction of a liquid substance with temperature;
Is a traditional or a digital thermometer more accurate?
Traditional thermometers tend to be more accurate than digital thermometers which often need to be re-calibrated
What unit is used for temperature?
degrees Celsius (ºC)
What can mass be measured with?
Mass is measured using a digital balance which normally give readings to two decimal places. These must be set to zero before use
What unit is used for mass?
The standard unit of mass is kilograms (kg) but in chemistry grams (g) are most often used
What can the volume of a liquid be measured with?
The volume of a liquid can be determined using several types of apparatus, depending on the level of accuracy needed
What apparatus can be used for approximate volumes?
For approximate volumes where accuracy isn’t an important factor, measuring cylinders are used. These are graduated (have a scale so can be used to measure)
What is the most accurate way of measuring a fixed volume of a liquid?
Using a pipette
What is the most accurate way of measuring a variable volume of a liquid?
Burette
How can a the volume of a gas be measured?
The volume of a gas sometimes needs to be measured and is done by collecting it in a graduated measuring apparatus
What apparatus is used in measuring the volume of a gas?
A gas syringe
What determines whether the graduated cylinder is inverted or can be used upright?
A graduated cylinder inverted in water may also be used, provided the gas isn’t water-soluble
If the gas happens to be heavier than air and is coloured, the cylinder can be used upright
When is paper chromatography used?
This technique is used to separate substances that have different solubilities in a given solvent (e.g. different coloured inks that have been mixed to make black ink)
How is the paper set up?
paper chromatography
A pencil line is drawn on chromatography paper and spots of the sample are placed on it.
Why is pencil, not pen used to draw a line? (paper chromatography)
Pencil is used for this as ink would run into the chromatogram along with the samples
What is the paper lowered into?
paper chromatography
The paper is then lowered into the solvent container
What is important to remember when lowering the paper into the solvent?
(paper chromatography)
making sure that the pencil line sits above the level of the solvent so the samples don’t wash into the solvent container
How does the solvent travel up the paper?
paper chromatography
The solvent travels up the paper by capillary action, taking some of the coloured substances with it
What causes the different substances to travel at different rates and what does this from?
(paper chromatography)
Different substances have different solubilities so will travel at different rates, causing the substances to spread apart.
What correlation is there between the solubility of a substance and the distance it travels?
(paper chromatography)
Those substances with higher solubility will travel further than the others
What does paper chromatography show?
This will show the different components of the ink / dye
If substances are the same, will they produce the same chromatograms?
YES
If two or more substances are the same, they will produce identical chromatograms
What will happen to a substance during paper chromatography if it is a mixture?
If the substance is a mixture, it will separate on the paper to show all the different components as separate spots
How can you tell the difference between a pure and impure substance using paper chromatography?
An impure substance will show up with more than one spot, a pure substance should only show up with one spot
What is the difference between the boiling point of pure substances and mixtures?
Pure substances melt and boil at specific and sharp temperatures
Mixtures have a range of melting and boiling points as they consist of different substances that melt or boil at different temperatures
How can an unknown pure substance be identified?
An unknown pure substance can be identified by experimentally determining its m.p and b.p and comparing to data tables
Why do mixtures melt over a range of temperatures?
Mixtures melt over a range of temperatures as they contain two or more substances
What does a pure substance consist of?
A pure substance consists of only one substance and contains nothing else.
Where and why is it important to have pure substances?
To have a pure substance for food and drugs is very important as impurities could be dangerous even in small amounts
What is routinely assessed during the production of food and drugs?
Melting and boiling point analysis is routinely used to assess the purity of food and drugs
What are Retention Factor (Rf) values used to identify?
These values are used to identify the components of mixtures
Is the Rf value of a particular compound always the same?
Yes
What does calculating Rf values allow scientists to do?
Calculating the Rf value allows chemists to identify unknown substances because it can be compared with Rf values of known substances under the same conditions
How do you calculate the Rf value?
Retention factor = distance moved by compound ÷ distance moved by solvent
Does the Rf value have units?
NO
- The Rf value is a ratio and therefore has no units
When are locating agents used and what do they do?
paper chromatography
Locating agents are substances which react with the sample and produce a coloured product which is then visible
What substances are hard to see using paper chromatography?
What is used to solve this problem?
invisible samples such as proteins
A locating agent
When is the locating agent applied to the chromatogram?
The chromatogram is treated with the agent after the chromatography run has been carried out, making the sample runs visible to the naked eye
What does the choice of the method of separation depend on?
the nature of the substances being separated
What is one similarity between all separation methods?
All methods rely on there being a difference of some sort, usually in a physical property such as b.p., between the substances being separated.
To separate mixtures of solids, what differences can be used to carry this process out?
Differences in density, magnetic properties, sublimation and solubility can be used
If using a difference in solubility to separate a mixture of solids, what must be taken into account?
For a difference in solubility, a suitable solvent must be chosen to ensure the desired substance only dissolves in it and not other substances or impurities
What are immiscible liquids?
two or more liquids which do not mix together
How can immiscible liquids be separated?
Immiscible liquids can be separated using a separating funnel or by decanting (pouring carefully)
When is filtration used?
Used to separate an undissolved solid from a mixture of the solid and a liquid / solution ( e.g. sand from a mixture of sand and water
- What is placed in the funnel?
(filtration)
Filter paper is placed in a filter funnel above another beaker
- What is poured into the funnel?
filtration
Mixture of insoluble solid and liquid is poured into the filter funnel
- How does the filter paper allow filtration to be carried out?
Filter paper will only allow small liquid particles to pass through as the filtrate
- What is left behind in the filter paper and funnel?
filtration
Solid particles are too large to pass through the filter paper so will stay behind as a residue
When is crystallisation used?
Used to separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold (e.g. copper sulphate from a solution of copper (II) sulphate in water)
- What is the first step of crystallisation?
The solution is heated, allowing the solvent to evaporate to leave a saturated solution behind
- How can you test the solution to see if it’s saturated?
crystallisation
Test if the solution is saturated by dipping a clean, dry, cold glass rod into the solution. If the solution is saturated, crystals will form on the glass rod
- What is done with the saturated solution?
crystallisation
The saturated solution is allowed to cool slowly and solids will come out of the solution as the solubility decreases, and crystals will grow
- How are the crystals collected?
crystallisation
Crystals are collected by filtering the solution
- What is done with the collected crystals?
crystallisation
They are then washed with cold, distilled water to remove impurities and allowed to dry
When is simple distillation used?
Used to separate a liquid and soluble solid from a solution (e.g. water from a solution of saltwater) or a pure liquid from a mixture of liquids
- What is the first step in simple distillation?
The solution is heated and pure water evaporates producing a vapour which rises through the neck of the round-bottomed flask
- What happens to the vapour?
fractional distillation
The vapour passes through the condenser, where it cools and condenses, turning into pure liquid H2O which is collected in a beaker
- What happens after all the water is evaporated from the solution?
(crystallisation)
After all the water is evaporated from the solution, only the solid solute will be left behind
When is fractional distillation used?
Used to separate two or more liquids that are miscible (can mix) with one another (e.g. ethanol and water from a mixture of the two)
- To what point is the solution heated?
F distillation
The solution is heated to the temperature of the substance with the lowest boiling point
- Which substance will rise first and what will happen to it?
(F distillation)
This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker
- Once this substance is fully evaporated, what is left behind?
(F distillation)
All of the substance is evaporated and collected, leaving behind the other components(s) of the mixture
Lithium (Li+)
Crimson
Sodium (Na+)
Yellow
Potassium (K+)
Lilac
Calcium (Ca2+)
Brick Red
Barium (Ba2+)
Apple Green
What three ions form a white precipitate when reacted with sodium hydroxide solution?
Al3+
Ca2+
Mg2+
What substance that forms a white precipitate dissolves in excess sodium hydroxide solution?
Al3+
How can you distinguish between the white precipitate formed by Ca2+ and Mg2+?
Flame Test
What three ions form a coloured precipitate when reacted with sodium hydroxide?
Cu2+
Fe3+
Fe2+
Fe2+
Light green -> brown
Light green -> brown
Fe2+
Fe3+
Reddish brown
Reddish brown
Fe3+
Cu2+
Light blue
Light blue
Cu2+
Crimson
Lithium (Li+)
Yellow
Sodium (Na+)
Lilac
Potassium (K+)
Brick Red
Calcium (2+)
Apple Green
Barium (2+)
Test for carbonates
Add dilute acid, if it fizzes and produces CO2 it is a Carbonate.
Test for halides (Bromine, Chlorine, Iodine)
Add dilute nitric acid.
Add silver nitrate. If a precipitate forms it is a halide.
ALWAYS ADD THE ACID FIRST.
Chloride
White
White
Chlorine
Bromine
Cream
Cream
Bromine
Iodine
Yellow
Yellow
Iodine
Test for Sulfates
Add hydrochloric acid (do this first to remove carbonate ions that would otherwise form a precipitate).
Add barium chloride solution.
If a white precipitate forms it is a sulfate. the precipitate formed is Barium Sulfate.
4 techniques for separating mixtures
> Filtration
Crystallisation
Distillation
Chromatography
When is filtration used?
Used to separate substances that are insoluble in a particular solvent from those that are soluble.
Crystallisation
> Water is evaporated through heating in an evaporating dish on a water bath. (gentler form of heating)
When small crystals begin to form, heat is removed and solution is left to evaporate at room temperature. This last step should take place in a flat bottomed or petri dish to increase surface area for evaporation.
Distillation
> Solution is heated until the substance with the lower boiling point evaporates.
Gas gets passed into a condenser and is surrounded with cold water.
A pure, liquid substance will come out.
Chromatography
The process whereby small amounts of dissolved substances are separated by running a solvent along a material such as absorbent paper.
R(f) Retention Factor
Distance a spot has been carried above the baseline/ distance of the solvent front.
Benefits of modern chromatography methods
> Highly accurate and sensitive
Quicker
Enable very small samples to be analysed
Benefits of classic chromatography methods
> Less expensive
Don’t take the special training required by modern techniques.
Results of modern chromatography can often only be interpreted in comparison with data from known substances.
Gas chromatography
> Sample mixture is vaporised.
a ‘carrier gas’ moves the vapour through the coiled column.
Compounds that are more attracted to the material in the column will take longer to come out (have a longer retention time).
Substances can be identified by comparing their retention time to that of known substances.
Mass Spectrometry
A machine that can be used to analyse small amounts of a substance to identify it and find its relative molecular mass.
Where is the molecular ion peak located on a graph?
The last peak on the right as you look at a mass spectrum.
apparatus suitable for measuring time
stopwatch
apparatus suitable for measuring time
thermometer
apparatus suitable for measuring mass
digital mass balence
suitable apparatus for measuring volume
volumetric pipette
burette
measuring cylinder
gas syringe
advantages of stopwatch
measures up to 0.01 s
digital
advantages of volumetric pipette
measured a fixed volume of liquids ACCURATELY
measures up to 0.1cm3
more accurate than measuring cylinder
disadvantages of volumetric pipette
hard to use
only measures fixed volume
advantages of gas syringe
easy to set up
keeps gas dry
disadvantages of gas syringe
limited gas collected
delicate and expensive
advantages of thermometers
measures to the nearest degree
measures to the nearest degree
measures up to 0.01 cm3
more accurate than a beaker
advantages of a beaker
holds verities of volumes
assists chemical procedures that involve heating
heating
stirring
disadvantages of burette
hard to read
larger compared to a pipette
advantages of burette
contains propper volume readings of VARIABLE VOLUMES
measures to nearest 0.1cm3
accurate
what is a solvent
solvent as a substance that dissolves a solute
what is a solute
solute as a substance that is dissolved in a
solvent
what is a solution
solution as a mixture of one or more solutes
dissolved in a solvent
what is a saturated solution
saturated solution as a solution containing
the maximum concentration of a solute
dissolved in the solvent at a specified
temperature
what is residue
residue as a substance that remains after
evaporation, distillation, filtration or any
similar process
what is a filtrate
filtrate as a liquid or solution that has passed
through a filter
What materials do you need for an acid–base titration
(a) burette
(b) volumetric pipette
(c) suitable indicator
Describe how to identify the end-point of a
titration using an indicator
end point is determined by change of colour
methyl orange: orangy in acid yellow in base
define a locating agent
it is used in colourless substances to spot he different compounds in the colourless solution
the one that is the highest on the paper is??
the most soluble
what does it mean if the spot doesnt move from the pencil start line?
insoluble
what does it mean if there are two spots in the same height?
theyre the same compound as the same compound have the same solubilty
why is the substance that travels the furthest is also the more soluble?
because it implies that it is the least attracted to the paper so it just moves upwards
state the Rf value formula
distance moved by spot/ distance moved by solvent
what does it mean if we get a number over 1 when calculating the rf value?
that it’s not right!! it’s always under 1
What is filtration
used to separate an insoluble solid from a liquid
What is the name of the first group?
Alkali Metals
What are the four characteristics of group 1?
more reactive as they go down
Softer as they go down
density increases as they go down
melting point increases as they go down
What is the equation for any metal with water?
2X +2H2O => 2XOH + H2
What is the name of group 2?
Alkali Earth Metals
Name 6 properties of transition metals
they have high melting points
hard tough and strong
react slowly w oxygen and water
iron is used for building/ copper is used for electrical cables
transition metals form colored compounds
some are catalysts
Give 4 properties of metals?
Malleable
ductile
Conductors of heat
Conductors of electricity
Give 2 things that metals form
Positive ions
Basic oxides
Give 4 properties of non- metals
brittle
non- ductile
insulators of heat
insulators of electricity
Give 2 things that non- metals form.
Negative ions
Acidic oxides
Name all the elements of group 7 and their state
F GAS
Cl GAS
BR LIQUID
I SOLID
At SOLID
Show the trends of Halogens
Get darker in color as they go down
Become less reactive as they go down
Melting/Boiling point increases as they go down
Show the trends of noble gases
Boiling point increases as they go down
The atoms increase in size and mass as they go down
density of mass increases as they go down
What are the uses of helium and why?
Fill balloons and airships
Because it is lighter than air and does not burn
What are the uses of neon and why?
advertising signs
Glow when a current is passed through them
What are the uses of argon and why?
Filler in tungsten bulbs
Protect melted that are being welded
unreactive
What are the uses of Krypton and why?
Used in lasers and car head lamps
Unreactive/inert
Used in lasers and car head lamps
Unreactive/inert
Used in light house lamps, lights in hospital operating room
Glow when a current is passed through them
What is the bonding between Non- metal and non- metal?
covalent
Metal and metal?
Metallic
Non metal and metal?
Ionic
What are the two physical properties of flerovium?
High melting point
Malleable
Write a chemical equation for the reaction of calcium with cold water.
Ca+2H20 => Ca(OH)2 + H2
Give 2 observations when potassium is added to cold water
Moves around
Flame
Describe a test for hydrogen
Test: Lit splint placed on mouth of apparatus
Result: You hear a pop
One physical property that is similar for both cobalt and potassium
They are both conductors of electricity
State one physical property that is different for cobalt and potassium
They have different melting points
State the formula for lithium ion
Li+
State the formula for nitride ion
N3-
Predict three physical properties of vanadium which are typical of transition elements
High melting points
Strong
Hard
What is the color of flame for Lithium?
Red
What is the color of flame for Sodium?
Yellow
What is the color of flame for Potassium?
Lilac
What is the color of flame for Copper?
Blue - Green
What is the anion test for chloride?
Add nitric acid then silver nitrate solution
What is the result of the anion test for chloride?
White Precipitate forms
What is the anion test for Bromide?
Add nitric acid then silver nitrate solution
What is the result of the anion test for bromide?
Cream precipitate forms
What is the anion test for iodide?
Add nitric acid then silver nitrate solution
What is the result of the anion test for iodide?
Yellow precipitate forms
What is the anion test for Nitrate?
Add Aluminium foil and sodium hydroxide solution and heat
What is the result of the anion test for nitrate?
Ammonia gas is given out
turns red litmus blue
What is the anion test for Sulfate?
Add hydrochloric acid then barium nitrate solution
What is the result of the anion test for sulfate?
White precipitate forms
What is the anion test for Sulfite?
Add hydrochloric acid and warm gently
What is the result of the anion test for sulfite?
Sulfur Dioxide produced
Turns acidified potassium permanganate form purple to colourless
What is the anion test for carbonate?
Add hydrochloric acid
What is the result of the anion test for carbonate?
Bubbles seen
Gas turns lime water milky
What is the test for oxygen?
What is the result?
Put a glowing splint to the test tube
Splint relight
What is the test for Hydrogen?
What is the result?
Put a lighted splint to the test tube
Goes pop
What is the test carbon dioxide?
What is the result?
Bubble through lime water
turns milky
What is the test for Ammonia?
What is the result?
Hold damp red litmus at mouth of the test tube
Turns litmus paper blue
What is the test for Chlorine?
What is the result?
Hold damp blue litmus at mouth of the test tube
Turns damp litmus red then white
What is the test for sulfur dioxide?
What is the result?
Add acidified potassium permanganate
Turns from purple to colorless
What is effect if ammonium is added to aqueous sodium hydroxide?
When heated ammonia gas given off- turns litmus blue
What is the effect if copper is added to aqueous sodium hydroxide?
Pale blue precipitate forms
Precipitate does not dissolve in excess
What is the effect if Iron (II) is added to aqueous sodium hydroxide?
Pale green precipitate forms
Precipitate does not dissolve in excess
What is the effect if Iron (II) is added to aqueous ammonia?
Pale green precipitate forms
Precipitate does not dissolve in excess
What is the effect if Iron (III) is added to aqueous sodium hydroxide?
Red brown precipitate forms
Precipitate does not dissolve in excess
What is the effect if Iron (III) is added to aqueous ammonia?
Red brown precipitate forms
Precipitate does not dissolve in excess
What is the effect if Aluminium is added to aqueous sodium hydroxide?
White precipitate forms
precipitate does dissolve in excess
What is the effect of Aluminium in aqueous ammonia?
White precipitate forms
precipitate does dissolve in excess
What is the effect of Zinc in aqueous sodium hydroxide?
White precipitate forms
Precipitate does dissolve in excess
What is the effect of zinc in aqueous ammonia?
White precipitate forms
Precipitate does dissolve in excess
What is the effect of calcium in aqueous sodium hydroxide?
White precipitate forms
Precipitate does not dissolve in excess
What is the effect of calcium in aqueous ammonia?
No precipitate forms
What is the effect of chromium in aqueous sodium hydroxide?
Green precipitate forms
Precipitate does not dissolve in excess
What is the effect of chromium in aqueous ammonia?
Grey green precipitate
Insoluble in excess
Which is the only alkali gas?
Ammonia
What are ions?
Ions are atoms or molecules that cave a positive or negative charge
What is the charge of a proton?
1+
What is the charge of a neutron?
0
What is the charge of an electron?
-1
Why do isotopes have the same chemical properties?
Because they have the same number of electrons in their outer shell.
What are the metal ions you can test for using a flame?
Lithium Li+
Sodium Na+
Potassium K+
Calcium Ca²+
Barium Ba²+
Copper (II) Cu²+
What flame color does lithium Li+ have?
Red
What flame color does sodium Na+ have?
Yellow.
What flame color does potassium K+ have?
Lilac.
What flame color does lithium Li+ have?
Red.
What flame color does calcium Ca²+ have?
Orange-red.
What flame color does barium Ba²+ have?
Light-green.
What flame color does copper (II) Cu²+ have?
Blue-green.
What are the anions?
Chloride Cl⁻
Carbonate CO₃²⁻
Bromide Br⁻
Iodide I⁻
Sulfate SO₄²-
Sulfite SO²⁻ ₃
Nitrate NO₃⁻
How do you test for Chlorine Cl⁻ and what is the test result (anion)?
Acidify with dilute nitric acid, then add aqueous silver nitrate (white ppt).
How do you test for Carbonate CO₃²⁻ and what is the test result (anion)?
Add dilute acid, then test for carbon gas (effervescence, carbon dioxide produced).
How do you test for Iodide I⁻ and what is the test result (anion)?
Acidify with dilute nitric acid then add aqueous silver nitrate (yellow ppt).
How do you test for Sulfate SO₄²- and what is the test result (anion)?
Acidify with nitric acid then add aqueous barium nitrate (white ppt).
How do you test for Sulfite SO₃²⁻ and what is the test result (anion)?
Add a small volume of acidified aqueous potassium manganate (VII)
(the acidified aqueous potassium manganate (VII) changes color from purple to colorless).
How do you test for Nitrate NO₃⁻ and what is the test result (anion)?
Add aqueous sodium hydroxide to aluminium foil and warm carefully (ammonia produced).
What are the aqueous cations?
Aluminum Al3+
Ammonium NH₄⁺
Calcium Ca²+
Chromium Cr3+
Copper (II) Cu²+
Iron (II) Fe²+
Iron (III) Fe3+
Zinc ²+
What is the effect of aqueous sodium hydroxide and aqueous ammonia on Aluminum Al3+ (cation)?
Sodium hydroxide: White ppt, soluble in excess giving a colorless solution.
Ammonia: White ppt, insoluble in excess.
What is the effect of aqueous sodium hydroxide on Ammonium NH₄⁺(cation)?
Sodium hydroxide: Ammonia produced on warming.
What is the effect of aqueous sodium hydroxide and aqueous ammonia on Calcium Ca²+ (cation)?
Sodium hydroxide: White ppt, insoluble in excess.
Ammonia: no ppt or a very slight white ppt.
What is the effect of aqueous sodium hydroxide and aqueous ammonia on Chromium Cr3+ (cation)?
Sodium hydroxide: Green ppt, soluble in excess.
Ammonia: Green ppt, insoluble in excess.
What is the effect of aqueous sodium hydroxide and aqueous ammonia on Copper (II) Cu²+ (cation)?
Sodium hydroxide: Light blue ppt, insoluble in excess.
Ammonia: Light blue ppt soluble in excess, giving a dark blue solution.
What is the effect of aqueous sodium hydroxide and aqueous ammonia on Iron (II) Fe²+ (cation)?
Sodium hydroxide and Ammonia: Green ppt, insoluble in excess ppt turns brown near the surface on standing.
What is the effect of aqueous sodium hydroxide and aqueous ammonia on Iron (III) Fe3+ (cation)?
Sodium hydroxide and Ammonia: Red-brown ppt, insoluble in excess.
What is the effect of aqueous sodium hydroxide and aqueous ammonia on Zinc ²+ (cation)?
Sodium hydroxide and Ammonia: White ppt, soluble in excess giving a colorless solution.
What are the gases you can test for?
Ammonia NH₃
Carbon Dioxide CO₂
Chlorine Cl₂
Hydrogen H₂
Oxygen O₂
Sulfur Dioxide SO₂
What is the test and test result for Ammonia NH₃?
Turns damp red litmus paper blue.
What is the test and test result for Carbon Dioxide CO₂?
Turns limewater milky.
What is the test and test result for Chlorine Cl₂?
Hold damp blue litmus at mouth of the test tube
Turns damp litmus red then white
What is the test and test result for Hydrogen H₂?
Pops with a lighted splint.
What is the test and test result for Oxygen O₂?
Relights a glowing splint.
What is the test and test result for Sulfur Dioxide SO₂?
Turns acidified aqueous potassium manganate (VII) from purple to colourless.
What is a mixture?
Two or more substances mixed together but not chemically combined.
NOTE - The chemical properties of each substance in a mixture are unchanged.
How do we know if a substance is pure?
Pure substances have a sharp melting point and boiling point whereas if a substance is impure, the impurities will have an effect on the melting and boiling point.
FURTHER EXPLAINATION : Pure water has an exact boiling point of 100°C whereas impure water could have a boiling point of 103°C.
Why is purity important (for consumption)?
Medical drugs and food additives must be pure to avoid harming people. To have a pure substance for food and drugs is very important as impurities could be dangerous even in small amounts
A solution contains a solid dissolved in a solvent. Which is the solute and which is the solvent?
The dissolved solid is called the solute and the liquid that dissolves the solid is the solvent.
Define filtration.
Separating a solid from a liquid by using filter paper (the precipitate is insoluble).
What is the filtrate and what is the residue?
The solution which passes through the filter paper is called the filtrate and the solid that stays on the filter paper is called the residue.
Define decanting.
To gradually pour another liquid from one container into another in order to separate out sediment.
What is centrifugation/ what is the use of a centrifuge machine?
The separation of a solid from a liquid by rapid spinning during the solid collects at the bottom of the test tube - the liquid can then be decanted off carefully.
What is crystallization?
The formation of crystals when a saturated solution is left to cool.
If you were to have produced a soluble salt, how would you separate this salt from the solution that it was dissolved in?
Warm the solution in an open container allowing the solvent to evaporate, leaving a saturated solution..
Allow this solution to cool.
The solid will come out of the solution and crystals will start to grow, these can be collected and allowed to dry.
What is simple distillation?
Used to separate a liquid and soluble solid from a solution or a pure liquid from a mixture of liquids.
When does simple distillation work?
Works when the liquids have different boiling points.
What is the sequence of events in distillation?
Heating → evaporating → cooling → condensing.
How do you separate ethanol and water?
Ethanol has a lower boiling point than water (ethanol boiling point 78°C VS water boiling point 100°C) so it evaporates first. The ethanol vapor is then cooled and condensed inside the condenser to form a pure liquid.
How does the fractional distillation of crude oil (petroleum) and products for fermentation work?
The oil is heated in the fractionating column and the oil evaporates and condenses at a number of different temperatures.
The many hydrocarbons in crude oil can be separated into fractions each of which contains molecules with a similar number of carbon atoms.
The fractionating column works continuously, heated crude oil is piped in at the bottom. The vaporized oil rises up the column and the various fractions are constantly tapped off at the different levels where they condense.
The fractions can be processed to produce feuls and feedstock for the petrochemical industry.
NOTE - The separation of the components in petroleum is achieved by fractional distillation on an industrial scale.
What is fractional distillation used for?
Used to separate two or more liquids that are miscible with one another.
What are the steps to separating liquids using fractional distillation?
The solution is heated to the temperature of the substance with the lowest boiling point.
This substance will rise and evaporate first, and vapors will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker.
All of the substance is evaporated and collected, leaving behind the other components.
What are the steps to separating liquids using simple distillation?
The solution is heated and pure water evaporates producing a vapor which rises through the neck of the round-bottomed flask.
The vapor passes through the condenser, where it cools and condenses, turning into pure water which is collected in a beaker.
After all the water is evaporated from the solution, only the solid solute will be left behind.
What can simple distillation be used to do?
Simple distillation can be used to separate the products of fermentation, such as alcohol and water.
How can immiscible liquids (oil and water) be separated?
Immiscible liquids can be separated using a separating funnel or by decanting.
Appropriate apparatus for measuring:
Time.
Temperature.
Mass.
Volume.
Time = stopwatch/ clock.
Temperature = thermometer.
Mass = balance.
Volume = measuring cylinder/ burette/ pipette.
What is paper chromatography used for?
Used to separate mixtures and give information to help identify substances.
What does paper chromatography involve?
Involves a stationary phase and a mobile phase.
How do you carry out paper chromatography?
Place substances on line near bottom of the paper.
- Place in solvent and observe how far the substances travel up the paper.
What does paper chromatography separation depend on?
Separation depends on the distribution of substances between the phases.
What is the formula for Rf value?
Rf value = distance moved by substance ÷ distance moved by solvent.
Different compounds have different Rf values in different solvents, which can be used to help identify the compounds. How?
Compounds in a mixture may separate into different spots depending on the solvent but a pure compound will produce a single spot in all solvents.
How will an impure substance show up on the paper and how will a pure substance show on the paper?
An impure substance will show up with more than one spot, a pure substance should only show up with one spot.
How will a mixture show up on the paper?
If a substance is a mixture, it will separate on the paper to show all the different components as separate spots.
How will two substances which are the same show up on the paper?
If two substances are the same, they will show up the same on the paper after carrying out the chromatogram.
What happens on the paper when the substance is more soluble?
The more soluble a substance is, the further up the paper it travels.
What are locating agents?
Locating agents are substances that react with the sample and produce a colored product which is then visible which allows for Rf values to be taken and molecules to be identified.
When is a chromatogram treated with a locating agent?
The chromatogram is treated with the agent after the chromatography run has been carried out, making the sample runs visible to the naked eye.
What are the examples of locating agents?
Ninhydrin used with proteins - breaks them down into amino acids and colors them purple.
UV light.
Carbonate (CO3^2-)
Add dilute acid.
- Effervescence, carbon dioxide is produced.
Chloride (Cl-) in solution
Acidify with dilute nitric acid, then add aqueous silver nitrate.
White PPT
Iodide (I-) in solution
Acidify with dilute nitric acid, then add aqueous silver nitrate.
Yellow PPT
Nitrate (NO3-) in solution
Add aqueous sodium hydroxide then aluminium foil. Warm carefully.
Ammonia is produced
Aluminium (Al^3+)
Adding:
1-Aqueous sodium hydroxide
2-Aqueous ammonia
1-White PPT, soluble in excess giving a colourless solution
2-White PPT, insoluble in excess
Ammonium (NH4+)
Adding:
1-Aqueous sodium hydroxide
2-Aqueous ammonia
1-Ammonia is produced on warming
2-No change
Calcium (Ca^2+)
Adding:
1-Aqueous sodium hydroxide
2-Aqueous ammonia
1-White PPT, insoluble in excess
2-No PPT, or a very slight white PPT
Copper(II) (Cu^2+)
Adding:
1-Aqueous sodium hydroxide
2-Aqueous ammonia
1-Light blue PPT, insoluble in excess
2-Light blue PPT, soluble in excess giving a dark blue solution
Iron(II) (Fe^2+)
Adding:
1-Aqueous sodium hydroxide
2-Aqueous ammonia
1-Green PPT, insoluble in excess
2-Green PPT, insoluble in excess
Zinc (Zn^2+)
Adding:
1-Aqueous sodium hydroxide
2-Aqueous ammonia
1-White PPT, soluble in excess giving a colourless solution
2-White PPT, soluble in excess giving a colourless solution
Ammonia (NH3)
Turns damp red litmus paper blue
Carbon dioxide (CO2)
Turns limewater milky
Chlorine (Cl2)
Bleaches damp litmus paper
Hydrogen (H2)
Gives a squeaky pop sound when a lighted splint is added to it
Iron(III) (Fe^3+)
Adding:
1-Aqueous sodium hydroxide
2-Aqueous ammonia
1-Red-brown PPT, insoluble in excess
2-Red-brown PPT, insoluble in excess
What is the effect if copper is added to aqueous ammonia?
Pale blue precipitate forms
adding excess precipitate dissolves giving a deep blue solution
Sulphate (SO3^2-) in solution
Acidify with dilute nitric acid, then add aqueous barium nitrate.
White PPT
What are the steps of separating undissolved solid from a liquid using filter paper?
Filter paper is placed in a filter funnel above another beaker.
The mixture of insoluble solid and liquid is poured into the filter funnel.
Filter paper will only allow small liquid particles to pass through in the filtrate.
Solid particles are too large to pass through the filter paper so will stay behind as a residue.
How do you test for Bromide Br⁻ and what is the test result (anion)?
Acidify with dilute nitric acid, then add aqueous silver nitrate (cream ppt).
Oxygen (O2)
Relights a glowing splint
disadvantages of a beaker
calculates an estimate not an accurate liquid volume
