chemical analysis Flashcards
What are the 2 things a pure substance can be?
-Single element
-Single compound
In terms of boiling and melting point, what is the difference between pure substances and impure substances?
Pure substances = -melt at a specific fixed temperature
-specific boiling point
Impure substances = melt an boil over a range of temperatures
What is the definition of formulation?
A formulation is a mixture that has been designed as a useful product.
What are examples of formulations?
Fuels
Cleaning products
Paints
Medicines
Alloys
Fertilisers
Food
What is the process when forming a formulation?
In a formulation, the quantity of each component is carefully measured so that the products has the properties we need.
What does paper chromatography allow us to separate?
Allows us to separate substances based on their different solubilities
What is the stationary phase in chromatography?
The paper because it does not move.
What is the mobile phase in chromatography?
The solvent because it does move!
In chromatography, pure substances will produce how many spots?
A single spot
In chromatography, compounds in a mixture separate into?
May separate into different spots depending on the solvent.
In chromatography, what does it mean if your a more soluble substance?
Travel further up the paper.
In chromatography, why do we draw our starting line in pencil?
In we drew the line in pen, the pen ink would move up the paper, with solvent.
TRUE OR FALSE? Can use chromatography to identify an unknow substance?
True.
How do we find the RF of the unknow substance?
Rf=
Distancemovedbythechemical
———————————————–
Distancemovedbythesubstance
Why might we need to repeat “using paper chromatography to identify an unknow substance” using a different solvent?
Several different substance could have the same Rf value. We might need to repeat this experiment using a different solvent
What if in “using paper chromatography to identify an unknow substance” , the substance has never been analysed?
Then there will not be an RF value on the database.
What is the process for “Required Practical 6: Chromatography”?
- We have a sample of food colouring which is a mixture of chemicals. We call this “U” for unknown. We also have 4 food colourings that it could contain. We label these A-D.
- We use a ruler to draw a horizontal pencil line on the chromatography paper. The line should be about 2cm above the bottom of the paper.
- We know mark 5 pencil spots at equal spaces across the pencil line. Leave 1cm clear at each side.
- Use a capillary tube to put a small spot of each of the know food colours and the unknown colour onto the pencil spots. Keep the spots small to prevent spreading into each other.
- Pour water (solvent) into a beaker to a depth of 1cm.
- We attach the paper to a glass rod using tape and lower the paper into the beaker. The bottom of the paper should dip into the water.
-MAKE SURE THE PENCIL LINE WITH THE SPOTS OF INK MUST BE ABOVE THE SURFACE OF THE WATER.
-AND THE SIDES OF THE PAPER SHOULD NOT TOUCH THE SIDES OF THE WALLS OF THE BEAKER(IF THAT HAPPENS THEN THAT WILL INTERFERE WITH THE WATER MOVES.
-AND FINALLY PUT A LID ABOVE TO REDUCE EVAPORATION OF THE SOLVENT
- At this stage the colour will move up the paper. We need to be sure not to move the beaker. Once done carefully remove the paper from the chromatography paper from the beaker when then water has travelled 3/4 up. We use a pencil to mark when the water has reached.
- Hang the paper up to dry.
Calculate Rf values
Measure the distance moved by each dye and the distance moved by the solvent.
Use the formula:
𝑅𝑓=
Distancemovedbychemical
——————————————
Distancemovedbysolvent
Test for hydrogen
The test for hydrogen uses a burning splint held at the open end of a test tube of the gas. Hydrogen burns rapidly with a pop sound.
Test for oxygen
The test for oxygen uses a glowing splint inserted into a test tube of the gas. The splint relights in oxygen.
Test for carbon dioxide
The test for carbon dioxide uses an aqueous solution of calcium hydroxide (lime water). When carbon dioxide is shaken with or bubbled through (by a plastic pipette) limewater the limewater turns milky (cloudy).
Test for chlorine
The test for chlorine uses litmus paper. When damp litmus paper is put into a beaker with chlorine gas the litmus paper is bleached and turns white
