C8 Chemical Analysis Flashcards
What is a pure substance in chemistry?
pure substance is a material made up of only one type of element or compound, with no other substances mixed in. This means that its chemical composition is uniform throughout.
How can melting and boiling points be used to determine purity?
A pure substance has a fixed melting and boiling point. If a substance melts or boils over a range of temperatures, it is likely a mixture rather than a pure substance. For example, pure water boils at 100°C, but if impurities are present, the boiling point may be higher or lower.
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What is a formulation?
A formulation is a mixture of substances carefully designed to have specific properties for a useful purpose. Each chemical in a formulation has a particular function, and the ingredients are mixed in precise amounts to ensure the product works as intended.
Can you give examples of formulations?
Medicines – The active drug is mixed with other substances to control dosage and absorption.
Cleaning agents – Contain surfactants, fragrances, and preservatives.
Paints – Made from pigments, binders, and solvents.
Alloys – Mixtures of metals designed for strength and durability (e.g., steel, brass).
What is chromatography used for?
Chromatography is a technique used to separate mixtures of substances and identify unknown compounds. It is commonly used in forensic science, food testing, and medical research to analyze substances.
What are the two phases in chromatography?
The stationary phase – A solid or liquid that does not move (e.g., chromatography paper).
The mobile phase – A liquid or gas that moves and carries the substances with it (e.g., water or ethanol).
How does chromatography separate substances?
Substances move at different speeds because they have different solubilities and attractions to the stationary phase.
A substance that is more soluble in the mobile phase moves further up the paper.
A substance that is less soluble moves less far and stays near the baseline.
: How do you calculate the Rf value in chromatography?
.divide the distance travelled by the component by the distance travelled by the solvent
How can chromatography distinguish between pure and impure substances?
A pure substance produces a single spot in all solvents.
A mixture produces multiple spots, showing it contains more than one substance.
What is the test for hydrogen gas?
To test for hydrogen:
Collect the gas in a test tube.
Hold a lit splint at the open end.
If hydrogen is present, it will burn with a squeaky pop sound.
This sound is caused by the rapid combustion of hydrogen with oxygen, forming water.
What is the test for oxygen gas?
To test for oxygen:
Collect the gas in a test tube.
Insert a glowing splint (a splint that has been lit and then blown out so it’s still glowing).
If oxygen is present, the splint will relight.
Oxygen supports combustion, which is why the splint catches fire again.
What is the test for carbon dioxide gas?
To test for carbon dioxide:
Bubble the gas through limewater (calcium hydroxide solution).
If carbon dioxide is present, the limewater will turn milky (cloudy).
This happens because calcium carbonate (CaCO₃) forms a precipitate, making the solution cloudy.
What is the test for chlorine gas?
o test for chlorine:
Hold a piece of damp blue litmus paper near the gas.
If chlorine is present, the litmus paper will turn white (bleached).
Chlorine is a strong oxidizing agent, which destroys the dye in the litmus paper.
