C12 - Chemical Analysis Flashcards
What is chemical analysis?
All the instruments and methods we use to separate and identify different substances
In chemistry, what is a pure substance?
Something that contains ONLY ONE type of compound or element
What are so examples of pure substances?
Pure water - only H2O molecules
Pure Sodium Chloride
What is an example of an impure substance?
A mixture of Water and Sodium Chloride (salt)
What are the BPs + MPs of pure substances?
They melt and boil at specific temperatures
What is an example of a physical test for water?
If it boils at 100°C, we can conclude that its pure water
What are the BPs + MPs of impure substances (mixtures)?
Melts and boils over a range of temperatures
What are formulations?
Mixtures that have been prepared using a specific formula
Formulations are mixtures that have been prepared using a specific formula.
What does this then mean?
They contain precise amounts of different components
They have a particular function
What are examples of formulations?
Medicines
Fuels
Alloys
Food
What is paper chromatography used for?
Separating different dyes in an ink
How do you test for chlorine gas?
Take a piece of blue litmus paper and dampen it
Then add it to your sample gas
If chlorine is present, the paper will turn from BLUE 🔵 to WHITE⚪️
Why when testing for chlorine gas, the dampened blue litmus paper temporarily turns red?
The chlorine dissolves in the water on the damp paper and forms hydrochloric acid
Because HCL is acidic, it turns the blue litmus paper RED
What precautions must you take when testing for Chlorine gas?
Chlorine gas is poisonous so you must wear a mask or do the experiment in a fume cupboard
How do you test for oxygen?
Place a glowing splint into your sample gas
If the gas is oxygen, the splint will relight
How do you test for hydrogen gas?
Hover a burning splint over your sample gas
If its hydrogen gas, you will hear a ‘POP’ sound
How do you test for Carbon Dioxide?
Using a delivery tube, Bubble your gas sample through a separate test tube of calcium hydroxide (lime water)
If CO2 is present, it will cause the calcium hydroxide to go cloudy ☁️
Why does the calcium hydroxide solution turn cloudy when carbon dioxide is present?
Carbon dioxide + calcium hydroxide reacts to form calcium carbonate.
CaCO3 is a white solid that cant dissolve and makes the solution appear cloudy
How do you test for Carbonates?
A carbonate + an acid —> salt + carbon dioxide + water
Add dilute HCL to a test tube of carbonates
Run the gas produced into a solution of calcium hydroxide using a delivery tube
If the calcium hydroxide turns cloudy, carbon dioxide is present
Meaning a carbonate is present
How do you test for Sulfates?
Add dilute HCL to your sample solution to remove any unwanted carbonate and sulfite ions
Add barium chloride solution. If the solution forms a white precipitate, Sulfate ions are present
Why must you add Hydrochloric acid to remove any Carbonate ions and sulfite ions when testing for sulfates?
Carbonates and Sulfites can also react with barium to produce a white precipitate
This will confuse our results
How do you test for Halide Ions?
Add dilute NITRIC acid to remove any unwanted Carbonates and Sulfites
Add Silver Nitrate.
If halide ions are present, The silver ions react with the halide ions to form a precipitate
What do the Halide Ions consist of?
Chloride ions
Bromide ions
Iodide ions
When a test for halide ions are positive, which precipitate do chloride ions form?
A white Precipitate
When a test for halide ions are positive, which precipitate do Bromide ions form?
A Cream precipitate
When a test for halide ions are positive, which precipitate do iodide ions form?
A Yellow precipitate
