elements, compounds and mixtures Flashcards
(32 cards)
What is an element?
A substance made of atoms that all contain the same number of protons and cannot be split into anything simpler.
Examples include copper, iron, and magnesium.
How many elements are found in the Periodic Table?
118 elements.
What is a compound?
A pure substance made up of two or more elements chemically combined.
Examples include copper(II) sulfate (CuSO4), calcium carbonate (CaCO3), and carbon dioxide (CO2).
What is a mixture?
A combination of two or more substances (elements and/or compounds) that are not chemically combined.
How can mixtures be separated?
By physical methods such as filtration or evaporation.
What distinguishes a pure substance from a mixture in chemistry?
A pure substance consists of a single element or compound with no other substances.
What is an example of a pure substance?
Pure water, which contains only H2O molecules.
What is an example of a mixture?
Drinking water, which contains H2O molecules and additional substances like dissolved ions and chlorine.
What are the melting and boiling point characteristics of pure substances?
Pure substances melt and boil at specific and sharp temperatures.
What happens to impure substances in terms of melting and boiling points?
Impure substances have a range of melting and boiling points.
What technique is used to separate a liquid and soluble solid from a solution?
Simple distillation.
What is fractional distillation used for?
To separate two or more liquids that are miscible with one another.
What is filtration used for?
To separate an undissolved solid from a mixture of the solid and a liquid.
What is crystallisation used for?
To separate a dissolved solid from a solution when the solid is much more soluble in hot solvent than in cold.
What is paper chromatography used for?
To separate substances that have different solubilities in a given solvent.
What does a chromatogram display?
The visual output of a chromatography run showing separated components.
What does a pure substance produce on a chromatogram?
Only one spot.
What does an impure substance produce on a chromatogram?
More than one spot.
What is the retention factor (Rf)?
A ratio calculated by the equation: distance moved by substance / distance moved by solvent.
What does the Rf value indicate?
It helps identify the components of mixtures.
True or False: The Rf value depends on the solvent used.
True.
What happens when you change the solvent in chromatography?
The Rf value changes.
What is the boiling point of ethanol?
78 ºC.
What is the boiling point of water?
100 ºC.
