ChemistryU8- Chemical Analysis Flashcards
What is meant by pure substances?
A substance made up of only 1 element or compound
What is the test for pure water?
We measure the boiling points and melting points- so for pure water the melting point is exactly 0 degrees Celsius and the boiling point is exactly 100 degrees Celsius.
What does anhydrous mean?
A substance containing no water
What is the test for water?
Turns white anhydrous copper sulfate a blue colour
The melting/ boiling points of compounds are called fixed points- how do we identify and differentiate mixtures and pure substances?
Use their fixed points data
1- Why do melting and boiling points differ for mixture? 2- What do impurities do to the MP and BP of a substance?
1- Fixed points vary due to mixture composition
2- Lower the melting point but raise boiling points
What is the correlation between MP and BP for pure substances?
Range of melting points and boiling points are very narrow
How do the graphs for melting points of impure and pure substances differ? Draw the graphs and label the axis’s
Pure substances have a sharp melting point but mixtures melt over a range of temperatures. This difference is most easily seen when the temperature of a liquid is measured as it cools and freezes. With pure substances the change of state to a liquid stays at a straight horizontal line at the same temperature but with impure substances its a curve.
1- Define solvent
2- Define solute
1- the liquid in which a solute is dissolved to form a solution.
2- component in a solution, dissolved in the solvent.
What is a formulation?
Useful mixtures that have been designed to make useful products and they carry out specific functions
Why are formulations important?
They work to perform a specific function and allow us to use active drugs effectively and safely.
Give 4 ingredients that can be added to a formulation and state its purpose
Pigment- Visual aesthetics
Solvent/ water- Makes the formulation more dilute and gives a desired consistency
Binder- Binds everything together so its useable
Flavouring- Makes the formulation better tasting and enjoyable for children or even adults.
Give 3 examples of formulations
Any 3 from: pesticides, detergents, fertilisers, fuels, skincare, pharmaceutical drugs, cosmetics, paint etc
What percentage of an active drug is allowed to be used?
5-10% of the active drug
What is Chromatography?
A physical separation technique used to separate a mixture. Remember this means no chemicals are used and no new substances are produced
Whats the pattern for melting and boiling of impure substances?
Over a range of temperatures
Describe the melting and boiling point of a pure substance using a graph
Start with ice and increase temperature then at around 0 degrees Celsius, the temperature stays still and this is the melting point. Then the temperature increases again but comes to a standstill at 100 degrees Celsius and stops rising as this is the boiling point- as both BP AND MP are fixed temperatures we know the water is pure.
Why must we carefully measure the quantities of a formulation?
So that the product we are designing has the properties we need
How do our substances separate in Paper Chromatography?
Based on their different solubilities
More soluble= further distance and less soluble= shorter distance
In Chromatography, what is the paper and the solvent called?
The paper is the stationary phase as it doesn’t move
The solvent is the mobile phase as it does move
Describe a 6 mark Chromatography Experiment ( 10 steps)
1) Get Chromatography paper and draw a straight pencil line on the bottom of the paper (2 cm from base).
2) Get your ink/colouring and place dots of each substance on the line at equal distances apart (1cm) using a capillary tube and label them (A-Z)
3) Place the bottom of the chromatography paper in solvent making sure the solvent is 1cm below the pencil line.
5) Pour a solvent into a beaker
6) Attach the paper using a glass rod
7) Place chromatogram in beaker until the bottom of the paper touches the solvent BUT make sure the ink is not touching the water and put a lid on the beaker to reduce EVAPORATION
8) capillary action will draw up the solvent.
9) Remove chromatogram and draw a solvent line at the top of the paper to see how far the solvent reached
10) Dry the paper
In a Chromatography experiment, why do we use pencil and not pen?
Pencil is insoluble in water whereas pen dissolves in water (soluble).
When we see 1 spot after chromatography experiment, what does this mean? and what about 2 or more spots
The substance is pure and not a mixture- but if there was 2 spots+ the substance is a mixture
Why does Chromatography work?
The chemical in the mixtures will be attracted to the stationary phase ( the paper) to different extents- so chemicals that strongly attach to the paper do not move far but chemicals that are weakly attracted will move further up.
How do pure chemicals and chemicals in a mixture differentiate in solvents?
Pure chemicals produce a single spot in all solvents
Chemicals in mixtures separate into different spots depending on the solvent
What is the equation for retention factor?
distance travelled by component/ distance travelled by solvent
What does the Rf value tell us about the solubility of a separated component?
larger Rf value means the component is more soluble and smaller Rf value means the component is less soluble
How would you measure Rf values?
measure distance of ink on pencil line to how far ink went and divide it by the distance between the pencil line and solvent line.
What does it mean if a component stays on the pencil line and doesn’t move?
The component is insoluble
What is a capillary tube?
A very thin glass tube which uses capillary action to draw liquids in
In the Chromatography required practical- why mustn’t the sides of the paper touch the sides of the beaker?
It can interfere the way the water moves
In chromatography, when spots line up it means…
they contain the same substance
How do we identify the chemicals in colours?
Calculate the Rf values and look up Rf value in a data base to identify the chemical
What the units for Rf value?
TRICK QUESTION! there are no units for retention factor
What are the 2 problems with using Rf values to identify chemicals?
different chemicals could have the same Rf values so we need to repeat the experiment using different solvents to narrow it down. Also if chemicals have never been analysed before, they wont appear on the database
Describe the test for hydrogen
We light a burning splint and as hydrogen burns rapidly it produces a pop sound
Describe the test for oxygen
We place a glowing splint into the tube of oxygen and the splint relights
Describe the test for carbon dioxide
Limewater is an aqueous (water) solution of calcium hydroxide. Draw some Co2 into a pipette and bubble the gas into the limewater. If c02 is present, the limewater will turn cloudy after repeating this
Describe the test for chlorine
Insert damp litmus paper into the mouth of a test tube. Chlorine will bleach the litmus paper and turn it white.
What colour is litmus paper originally?
blue
Why does the hydrogen test produce a squeaky pop?
Hydrogen is highly flammable so the pop is like a mini explosion!
Balance and displace the chloride: Mg + HCL
Mg +2HCL —– mgCL2 +h2
What is limewater and state the formula?
Calcium hydroxide CA(OH)2
Why does the limewater turn cloudy?
because a calcium carbonate precipate is formed
What is the 2nd reaction for the test of carbon dioxide?
Light a lit splint near the gas in question and if the match is extinguished the gas is C02 as the C02 displaced oxygen and prevented combustion!
What do we use to produce oxygen?
Hydrogen Peroxide —- O2 and H20
What safety precautions should we take when working with Chlorine? ( level of usage)
Dont use too much chlorine as its toxic!
Why is calculating Rf values important?
Rf values are specific to the compounds and allow us to identify unknown substances or compounds
Why does chromatography work?
Chemicals will separate due to their attraction to the mobile and stationary phases. Molecules that are more soluble in the solvent have a higher attraction to the mobile phase so move up faster. And molecules less soluble in the solvent are more attracted to the stationary phase and do not move up as fast
How can we tell via chromatography if there is the same element in 2 different mixtures?
They will have the same Rf value and will move up the solvent at the same rate/distance
