C1 - Atoms Flashcards
What does an atom consist of?
An atom has a tiny nucleus at the centre, surrounded by electrons
What does an atom consist of?
An atom has a tiny nucleus at the centre, surrounded by electrons
What is a compound?
A compound is made up of more than one type of element, that is chemically bonded
What is a mixture?
The substances can be elements, compounds, or both. consists of two or more different substances, not chemically joined together.
What is a mixture?
The substances can be elements, compounds, or both. consists of two or more different substances, not chemically joined together.
What is the periodic table?
The periodic table lists all the chemical elements, with eight main groups each containing elements with similar chemical properties.
Differences between compounds and mixtures
• compounds have a fixed composition
•mixtures have no fixed composition
•chemical reactions must be used to separate the elements in a compound
• different elements/compounds in a mixture can be separated more easily
•there are chemical bonds between atoms of different elements in a compound, but in a mixture there are no chemical bonds
Methods of separating mixtures
Filtration
Crystallisation
Chromatography
Distillation
Filtration
The technique of filtration is used to separate substances that are insoluble in a particular solvent from those that are soluble in the solvent.
• eg The sand that you collect on the filter paper can then be washed with distilled water to remove any salt solution left on it. The wet sand is finally dried in a warm oven to evaporate any water off and leave the pure, dry sand.
Crystallisation
To obtain a sample of pure salt (sodium chloride, NaCI) from the salt solution following filtration, you would need to separate the sodium chloride in the solution (called the filtrate) from the water. You can do this by evaporating the water from the sodium chloride solution.
The best way to do this is by heating it in an evaporating dish on a water bat. Using a water bath is a gentler way of heating than heating the evaporating dish directly on a tripod and gauze.
Heating should be stopped when the solution is at the point of crystallisation.
This is when small crystals first appear around the edge of the solution or when crystals appear in a drop of solution extracted from the dish with a glass rod. The rest of the water is then left to evaporate off the saturated solution at room temperature to get a good sample of sodium chloride crystals. A flat-bottomed crystallisation dish or Petri dish can be used for this final step, to give a large surface area for the water to evaporate from.
Distillation
sometimes you need to collect the solvent itself instead of just letting it evaporate off into the air. For examole, fresh water and sea water.
In simple distillation, a solution is heated and boiled to evaporate the solvent. The vapour given off then enters a condenser. Here the hot vapour is cooled and condensed back into a liquid for collection in a receiving vessel. Any dissolved solids will remain in the heated flask
Fractional distillation
Fractional distillation works because the different liquids have different boiling points. When the mixture is heated:
• vapours rise through a column which is hot at the bottom, and cooler at the top
• vapours condense when they reach a part of the column that is below the temperature of their boiling point
• each liquid is led away from the column
Substance with the lowest BP is collected first at the top of the column
