C12 Chemical Analysis Flashcards
What is a pure substance?
A pure substance is a single element or compound, not mixed with any other substance.
They melt and boil at specific temperatures, which can be used to distinguish pure substances from mixtures.
How can pure substances be distinguished from mixtures?
By their specific melting and boiling points.
Pure substances will have consistent melting and boiling points, unlike mixtures.
What is the everyday definition of a pure substance?
A substance that has had nothing added to it, thus unadulterated and in its natural state, e.g., pure milk.
This aligns with the scientific definition but may vary in context.
What is a formulation?
A formulation is a mixture that has been designed as a useful product.
Formulations are carefully measured to ensure the product has the required properties.
Give examples of formulations.
- Fuels
- Cleaning agents
- Paints
- Medicines
- Alloys
- Fertilisers
- Foods
What is chromatography used for?
To separate mixtures and provide information to help identify substances.
It involves a stationary phase and a mobile phase.
What does the Rf value represent?
Rf value = distance moved by substance ÷ distance moved by solvent.
It helps in identifying compounds based on their movement in different solvents.
What happens to compounds in a mixture in chromatography?
They may separate into different spots depending on the solvent.
A pure compound will produce a single spot in all solvents.
What is paper chromatography?
An analytical technique that separates compounds by their relative speeds in a solvent as it spreads through paper.
The more soluble a substance is, the further up the paper it travels.
What does the term ‘pigment’ refer to?
A solid, coloured substance.
Pigments are often separated in chromatography.
How can hydrogen gas be tested?
By using a burning splint held at the open end of a test tube of the gas, which creates a ‘squeaky pop’ sound.
This indicates the presence of hydrogen as it burns rapidly.
What indicates the presence of oxygen gas?
A glowing splint inserted into a test tube of the gas will relight.
This test is commonly used to confirm oxygen.
How can carbon dioxide be tested?
By bubbling the gas through limewater (calcium hydroxide), which will turn milky (cloudy).
This is a classic test for carbon dioxide.
What is the test for chlorine gas?
Damp litmus paper will be bleached and turn white when exposed to chlorine gas.
This reaction indicates the presence of chlorine.
What is the purpose of a flame test?
To identify the presence of certain metal ions based on the color of the flame produced.
Which color indicates the presence of sodium ions in a flame test?
A bright yellow flame.
True or False: A flame test can be used to identify all metal ions.
False.
What color does lithium produce in a flame test?
Crimson red.
Fill in the blank: The flame test is most effective for detecting __________ ions.
alkali and alkaline earth metal
Which metal ion produces a green flame during a flame test?
Copper(II) ions.
What is the primary method to test for metal hydroxides?
Adding a few drops of a strong acid to observe effervescence.
True or False: All metal hydroxides are soluble in water.
False.
What is the test for carbonates?
Adding dilute acid and observing the production of carbon dioxide gas.
Which gas is produced when carbonates react with acid?
Carbon dioxide (CO2).
Fill in the blank: The presence of __________ can be tested using barium chloride solution.
sulfates
What is the expected result when testing for halides with silver nitrate?
A colored precipitate forms.
What color precipitate does silver chloride produce?
White precipitate.
Which halide produces a cream precipitate with silver nitrate?
Bromide.
What color is the precipitate formed with silver iodide?
Yellow precipitate.
True or False: The sulfate test requires the use of hydrochloric acid.
True.
What indicates a positive test for sulfates?
The formation of a white precipitate of barium sulfate.
What is the common reagent used to test for sulfates?
Barium chloride solution.
Fill in the blank: The test for __________ involves adding silver nitrate to a solution and observing for precipitate formation.
halides
What is the first step in performing a flame test?
Clean a platinum or nichrome wire loop.
Why is it important to use a clean wire loop for a flame test?
To avoid contamination and ensure accurate results.
What happens when a carbonate reacts with an acid?
It produces carbon dioxide, water, and a salt.
True or False: All metal hydroxides are bases.
True.
Which type of ions can be identified using the flame test?
Mainly alkali and alkaline earth metal ions.
What is the role of hydrochloric acid in the sulfate test?
To remove carbonate impurities that could interfere with the test.
Fill in the blank: The reaction of a halide with silver nitrate forms a __________.
precipitate
What visual change occurs during the carbonate test?
Bubbles of carbon dioxide gas are produced.
