Flashcards
What is an atom?
an atom is the smallest part of an element that can exist
What is an element?
an element is a substance of only one type of atom
How are the elements listed and approximately how many are there?
- listed in the periodic table
- about 100 of them
Elements can be classified into two groups based on their properties; what are these groups?
metals and non-metals
elements may combine through chemical reactions to form new products; what are these new substances called?
compounds
What is a compound?
two or more elements combined chemically in fixed proportions which can be represented by formulae
Do compounds have the same properties as their constituent elements?
no, they have different properties
What is a mixture? Does it have the same chemical properties as its constituent materials?
A mixture consists of two or more elements or compounds not chemically combined together; it does not have the same chemical properties.
What are the methods through which mixtures can be separated? Do they involve chemical reactions?
Filtration, crystallisation, simple distillation, fractional distillation and chromatography; they do not involve chemical reaction.
Describe and explain simple distillation
Simple Distillation is used to separate liquid from a solution - the liquid boils off and condenses in the condenser. The thermometer will read the boiling point of the pure liquid. Contrary to evaporation, we get to keep the liquid.
descirbe and explain crystallisation/evaporation
Evaporation is a technique for separation of a solid dissolved in a solvent from a solvent. The solution is heated until all the solvent evaporates; the solid stays in the vessel.
Crystallisation is similar, but we only remove some of the solvent by evaporation to form a saturated solution. Then we cool down the solution. As we do it, the solid starts to crystallise, as it becomes less soluble at lower temperatures. The crystals can be collected and separated from the solvent via filtration.
describe and explain fractional distillation
Fractional distillation is a technique for separation of a mixture of liquids. It works when liquids have different boiling points.
The apparatus is similar to the one of simple distillation apparatus, with the additional fractionating column placed on top of the heated flask.
The fractionating column contains glass beads. It helps to separate the compounds. In industry, mixtures are repeatedly condensed and vapourised. The column is hot at the bottom and cold at the top. The liquids will condense at different heights of the column.
Describe and explain filtration
Filtration is used to separate an insoluble solid is suspended in a liquid. The insoluble liquid (called a residue) gets caught in the filter paper, becasue the particles are too big to fit through the holes in the paper. The filtrate is the substance that comes through the filter paper.
Apparatus: filter paper + funnel
Describe and explain chromatography
Chromatography is used to separate mixture of substances dissolved in a solvent.
In paper chromatography, we place a piece of paper with a spot containing a mixture in a beaker with some solvent. The bottom of the paper has to be in contact with the solvent. The solvent level will slowly start to rise, thus separating the spot (mixture) into few spots (components).
What is a separating funnel?
A separating funnel is an apparatus for separating immiscible liquids. Two immiscible liquids of different densities will form two distinct layers in the separatory funnel.
We can run off the bottom layer (the liquid with greater density) to a separate vessel.
