2. Chemical Analysis Flashcards
(37 cards)
What is a pure substance?
A pure substance is one that is made up of just one compound. That substance can be either an element or a compound.
What is a fixed point?
The melting and boiling points of an element or a compound are called its fixed points.
How can you distinguish between pure and impure substances?
Pure elements and compounds melt and boil at specific temperatures. The smaller the deviation, the purer the substance.
What is the difference between a chemically pure substance and everyday pure substance?
In everyday language, a pure substance can mean a substance that has nothing added to it. However, there is no ‘milk’ compound, so milk is not chemically pure but a mixture.
What is a formulation?
A formulation is a mixture that has been designed to produce a useful product.
How are formulations made?
Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties.
What are examples of formulations?
Fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.
What might a medicinal formulation contain?
Medicinal products often contain between 5-10% of the active drug, along with colours, sweeteners, smooth coatings, fillers and other compounds.
What does paint contain?
Pigments, a binder, and a solvent.
What does washing up liquid contain?
Surfactant, water, colouring and fragrances, rinse agent.
What is chromatography and what is it used for?
Paper chromatography is used to separate mixtures of soluble substances and can help identify unknown substances.
What are the two different phases of chromatography?
Stationary phase (does not move) and mobile phase (moves).
How does paper chromatography separate mixtures?
Separation depends on the distribution of substances between the phases.
How can you use chromatography to distinguish between pure and impure substances?
A pure substance will produce one spot on the chromatogram, while a mixture will separate into different spots.
How do you calculate the Rf value?
Distance travelled by substance / distance travelled by solvent.
Why are Rf values useful?
Different compounds have different Rf values in different solvents, which can help identify the compounds.
How can you identify unknown substances using chromatography?
By comparing them with known substances based on the number of spots and their distances.
How do you test for hydrogen?
Hold a burning splint at the open end of a test tube of the gas. A squeaky pop sound indicates hydrogen.
How do you test for oxygen?
Insert a glowing splint into a test tube of the gas. The splint relights in oxygen.
What 3 things do you need for fire?
Heat, oxygen, and fuel.
How do you test for carbon dioxide?
Use an aqueous solution of calcium hydroxide. The limewater turns milky when carbon dioxide is present.
How do you test for chlorine?
Use damp litmus paper. The litmus paper bleaches and turns white in chlorine gas.
What are flame tests used for?
They can be used to identify some metal ions (cations).
What colour flame does lithium produce?
Crimson.
