C8: Chemical Analysis Flashcards
Define a pure substance:
A chemically pure substance is a single element or compound. It contains only one substance
Formulation [definition]:
A mixture that has been designed as a useful product
How are formulations made?
By mixing the components in carefully measured quantities to ensure that the product has the required properties
What are the types of formulations? [7]:
- Fuels
- Cleaning agents
- Paints
- Medine
- alloys
- Fertilisers
- Food
Working out purity [2]:
- Pure substances have exact and specific boiling and metal points
- The closer the values of an experiment to those in a data book the greater the purity of a sample
Boiling point [definition]:
The temperature at which liquid turns into gas
Melting point [definition]:
The temperature at which a solid turns into a liquid
Impure substance [definition]:
Made up of more than one substance
More impurities in a sample will…[3]:
- Increase the range of temperatures at which a sample will melt or boil
- Decrease the melting point
- Increase the boiling point
The components in formulations [2]:
- In a formulation, each component helps to decide what the mixture’s overall properties are.
- To make sure that a formulation does what it is supposed to, each chemical component must be present in a precisely measured quantity.
Distilled vs still water [2]:
- Distilled water is chemically pure as it has no mineral ions in it
- Still water is chemically impure
Chromatography [definition]:
Chromatography is a process that separates a mixture into its different components
The two phases in chromatography [2]:
- Substances are picked up and carried by a mobile phase (liquid or gas).
- The mobile phase then moves through a stationary phase (solid or viscous liquid).
Separation of substances in chromatography [2]:
- A substance moves far if it’s more attracted to the mobile phase
- A substance doesn’t move far if it’s more attracted to the stationary phase
Chromatography equation:
. Distance moved by the substance
R𝒻 = ——————————————————-
Distance moved by the solvent
How many chromatography spots are produced by pure samples, and why? [2]:
- The definition of a chemically pure substance is that it consists of only a single element or compound.
- This means that pure samples will only ever produce 1 chromatography spot regardless of solvent identity.
Which substance will travel more quickly in a chromatogram?
The substance which has a greater attraction for the mobile phase will travel more quickly
What type of technique is chromatography?
A separation technique
What is a chromatogram?
Where the results of chromatography are displayed
In chromatography, the number of spots produced by a mixture can vary depending on…
which solvent is used
Testing for hydrogen [3]:
- The test for hydrogen uses a burning splint held at the open end of a test tube with gas
- If the gas is hydrogen, a “squeaky pop” sound will be produced
- This noise is generated because hydrogen burns rapidly in the presence of oxygen to give H₂O
Testing for Oxygen [2]:
- Insert a glowing splint into a test tube that contains a gas
- If the gas is oxygen, the splint will relight
Testing for Carbon dioxide [2]:
- Take an aqueous solution of limewater (calcium hydroxide) and bubble through the gas
- If the gas is carbon dioxide, the limewater solution will turn from clear to cloudy
Testing for Chlorine [2]:
- Insert damp litmus paper into a test tube that contains a gas
- If the gas is chlorine, the litmus paper will bleach and change colour from red to white
Which gas is being tested for if you insert a glowing splint into a test tube?
Oxygen
What colour will damp litmus paper turn if it comes into contact with chlorine?
White
What happens if carbon dioxide is bubbled through limewater?
If carbon dioxide is bubbled through limewater, the solution will turn from colourless to cloudy
What are flame ions used to identify?
Metal ions (cations)
Cu²⁺(copper) flame test:
Green flame.
Ca²⁺(calcium) flame test:
Orange-red flame
Na⁺(Sodium) flame test:
Yellow flame
K⁺(potassium) flame test:
Lilac flame
Li⁺(Lithium) flame test:
Crimson flame
Flame test steps [2]:
- Wet the tip of a glass rod and dip it in a salt
- Place the tip of the glass rod in the flame
Equipment for flame tests [3]:
- Glass rod/ nichrome wire loop
- At least 4 different metal salts
- Bunsen burner
Why is it problematic for interpreting the results of a flame test if a sample is made up of multiple ions?
If the sample consists of a mixture of metal ions, the flame colours of some may be masked, which can lead to incorrect interpretations
Metal hydroxides [2]:
- Sodium hydroxide solutions can be used to identify some metal ions(cations)
- Sodium hydroxide is added to a solution of the metal ion to be tested, a solid precipitate is formed and can be used to identify the metal ions
Coloured precipitates in sodium hydroxide tests [3]:
- Copper(II) [
- Iron(II) [Fe²⁺]
- Iron (III) [Fe³⁺]
Which precipitate produced is reddish-brown in sodium hydroxide tests?
Fe³⁺
Which precipitate is light green and slowly turns brown(looks dirty green) in sodium hydroxide tests?
Fe²⁺
Which precipitate is light blue in sodium hydroxide tests?
Cu²⁺
What are the white precipitates produced in sodium hydroxide tests? [3]:
- Al³⁺
- Ca²⁺
- Mg²⁺
How does one know that the precipitate produced is Al³⁺?
It dissolves in excess sodium hydroxide solution
How do you distinguish between Mg²⁺ and Ca²⁺? [3]:
- Both Mg²⁺ and Ca²⁺ are insoluble in excess sodium hydroxide
- By doing the flame test you can find out which is which
- When burning Ca²⁺ it produces a orange-red flame. Whereas Mg²⁺ produces a white flame
Testing for Carbonates [3]:
- CO₃²⁻ ions are characteristic of all carbonates.
- A reaction between a carbonate and a dilute acid gives a salt, carbon dioxide and water.
- As carbon dioxide is produced, we can use the standard carbon dioxide test to work out if an unknown substance is a carbonate.
The products of a reaction between a carbonate and a dilute acid [3]:
- A salt
- Water
- Carbon dioxide
