Foundation: C8 - Chemical Analysis Flashcards
Pures substances are substnace that only contain one type of _____ or ______
Element
Compound
Melting and boiling point can be used to determine if a substance is pure. Explain why.
If a substance is pure it will melt and boil at specific temperatures.
If it melts or boils above or below this temperature it is not pure (contains impurities).
What is a formulation?
- A mixture with specific proportions/concentrations of some of the components.
- For example, milk is a mixture but chocolate milkshake is a formulation as it has specific concentrations of some of the components.
Which of the following are formulations?
- Petrol
- Crude oil
- Sea water
- 0.5 M hydrochloric acid
- Paint
- Orange juice (staright from an orange)
- Perfume
- Steel
- Petrol
- 0.5 M hydrochloric acid
- Paint
- Perfume
- Steel (it’s an alloy which is a mixture of metals with specific proportions of some of the components)
What is chromatography used for?
Seperating different substances (solutes) in a mixture (e.g seperating different chemical in ink or food dye)
Chromatography:
What are the two phases called in chromatography?
What is each pahse made from?
Mobile phase: A solvent (e.g water)
Stationary phase: Usually a solid (e.g paper)
Chromatography:
During chromatography some substances move further along the stationary phase (e.g paper) than others, explain why this happens?
Substances that are more soluble move further because they spend longer in the mobile phase.
Chromatography:
In the image shown (the right part of it) , how many substances did the ink contain? How can you tell?
3 (or more): Because there are 3 spots
Chromatography:
In the image shown, which substance (purple, blue or red) was the most soluble? How can you tell?
Blue: It travelled the furthest
Chromatography:
In the image shown, which substance (purple, blue or red) would have the highest Rf value?
Blue
Chromatography:
In the image shown, which substance (purple, blue or red) was the least soluble? How can you tell?
Red: It travelled the least far
Chromatography:
In the image shown, which substance (purple, blue or red) would have the lowest Rf value?
Red
Chromatography:
Chromatography was used to seperate the substances in four different inks. What can you conclude about the substances in the four inks from looking the chromatogram below?
- Ink 1, 2 and 3 contained 1 substance.
- Ink 1, 2 and 3 contained different substances
- Ink 4 contained 2 substances.
- The substance in ink 1 was the least soluble.
- The substance in ink 3 was also in ink 4.
- The substance in ink 3 was the most soluble substance.
In the exam they often show you examples of people doing chromatography where they have made mistakes.
What are the common types of mistakes they show? Why are these mistakes a problem?
- The line is drawn in ink: Ink is soluble
- The solvent is above the start line (spots of ink/dye): The ink or dye ill move into the solvent not up the paper.
- The wrong solvent (e.g water instead of ethanol) is used: The substances are insoluble in the solvent.
Chromatography:
Rf value =
Rf value = distance travelled by substance ÷ distance travelled by solvent
Chromatography:
- How do you measure distance travelled by a substance in chromotography?
- What units do they normally ask you to use in the exam?
- Measure from the start line to the middle of the spot.
- mm
Chromatography:
- How do you measure distance travelled by the solvent?
- What units do they normally ask you to use in the exam?
- Measure from the start line to the solvent front.
- mm
Describe the test you would use to identify if a gas is Chlorine.
- Place a damp piece of litmus paper in the gas.
- If chlorine is present the limus paper will turn white
Describe the test you would use to identify if a gas is oxygen.
- Place a glowing splint in the gas
- If the gas is oxygen the splint will relight
Describe the test you would use to identify if a gas is hydrogen.
- Place a burning splint in the gas.
- If it’s hydrogen you wil hear a squeaky pop.
Describe the test you would use to identify if a gas is carbon dioxide?
- Pass/bubble the gas through limewater.
- If the gas is carbon dioxide it will go a milky colour.
Triple:
Describe how to test for carbonate (CO32-) ion.
- Add dilute acid.
- Test if the gas produced is carbon dioxide (which is made if carbonate ions are present).
- Pass the gas through limewater.
Triple:
Describe how to test for sulfate (SO42-) ions?
- Add 2 drops of dilute hydrochloric acid
- Add 2 drops of barium chloride
- A white precipitate will form if sulfate ions are present
Triple:
Describe how to test for chloride (Cl-), bromide (Br-) and iodide (I-) ions.
- Add 2 drops of dilute nitric acid
- Add 2 drops of silver nitrate
- Chloride ions: GIve a white precipitate
- Bromide ions: Give a cream precipitate
- Iodide ions: Give a yellow precipitate
Triple:
What type of ions give a crimson flame?
- Lithium (Li+)
Triple:
What type of ions give a yellow flame?
- Sodium (Na+)
Triple:
What type of ions give a lilac flame?
- Potassium (K+)
Triple:
What type of ions give an orange-red flame?
- Calcium (Ca2+)
Triple:
What type of ions give an green flame?
- Copper (Cu2+)
Triple:
Describe how to test for metal ions using the flame test.
- Use a clean nichrome wire loop
- Dip the loop in the sample (salt or solution)
- Record the colour of the flame
Triple:
Describe how to test for metal ions using sodium hydroxide.
- Add a few drops of sodium hydroxide to a solution containing the unidentified ions.
- Different metal ions will give different colour precipitates.
Triple:
- When sodium hydroxide is added to a solution what colour precipitate is given if calcium (Ca2+), magnesium (Mg2+) or aluminium (Al3+) ions are present?
- How can you distiguish the aluminium ions from the calcium and magnesium ions?
- White
- If you keep adding sodium hydroxide the white precipitate eventually redissolves with aluminium ions.
Triple:
When sodium hydroxide is added to a solution what colour precipitate is given if copper (II) (Cu2+) ions are present?
Blue
Triple:
When sodium hydroxide is added to a solution what colour precipitate is given if Iron (II) (Fe2+) ions are present?
Green
Triple:
When sodium hydroxide is added to a solution what colour precipitate is given if iron (III) (Fe3+) ions are present?
Brown
Triple:
Why do ions emit light when heated?
- As ion is heated electrons gain energy
- They become exited/move to a higher energy level
- When electrons move back to their original energy level, energy is released as light.
Triple:
Why do different ions emit different wavelengths of light when heated?
They have different charges (e.g Li1+ and Be2+)
or
Different electron arrangements (e.g Ca2+ and Mg2+)
