Principles of Chemistry Flashcards
(112 cards)
Name the processes responsible for the following phase changes: solid ⇄ gas
Sublimation (s to g)
Deposition (g to s)
What is diffusion?
It is the overall movement of particles from an area of high concentration to an area of low concentration.
E.g. a gas will diffuse through all the space it can find.
E.g. if you spray some perfume in one corner of the room, soon you will be able to feel the smell at the other end of the room.
What is a solubility curve?
It is a curve that shows how the solubility of a substance (in grams per 100 g of water) changes with temperature
Outline the main assumptions of the kinetic theory of matter.
a) Matter is made up of atoms, molecules and ions of different sizes.
b) At the same temperature, small particles move faster than large particles
c) As temperature rises, the particles have more kinetic energy and move faster
d) Solids are made up of ordered arrangement of closely packed particles
e) Liquids do not have particles arranged regularly. Particles can move around.
f) In gases, the particles are far apart. They move fast. Their motion is random.
Explain what is meant by centrifuging
It is a method for separating out particles of different densities in a substance. It can be used to separate suspended solids (very small particles of solid) from the liquid they are suspended in. It is used when the particles are so small that they can’t be separated via filtration. In a centrifuge, the sample is spun at high rates. This forces the solid particles to settle down at the bottom of the tube. The liquid can be decanted.
What is an atom?
An atom is the smallest particle of a chemical element that can exist.
What is an element?
An element is a substance made up of only one type of atom.
How are the elements listed and approximately how many are there?
They are listed in the periodic table; there are approximately 100.
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; the constituent materials keep their own chemical properties, but the mixture may have different chemical properties (e.g. melting point) as a whole.
What are the methods through which mixtures can be separated
(there are five)? Do these involve chemical reactions?
- Filtration,
- evaporation/crystallisation,
- simple distillation,
- fractional distillation
- chromatography;
- they do not involve chemical reactions
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 (it drips and is collected into a separate beaker).
Describe and explain evaporation/crystallisation.
Evaporation is a technique for separation of a solid dissolved in a solvent from a solvent (e.g. salt from H2O). The solution is heated until all the solvent evaporates; the solids stays in the vessel. Crystallisation is similar, but we only remove some of the solvent by evaporation to form a saturated solution (the one where no more solid can be dissolved). 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 method of separating liquids in a mixture based on their different boiling points. The process involves using a fractionating column containing glass beads, which helps to separate the compounds. The column is hot at the bottom and cold at the top, and the liquids condense at different heights, allowing for separation. This technique is commonly used in industry, where mixtures are repeatedly condensed and vaporized.
Describe and explain filtration
Filtration is used to separate an insoluble solid suspended in a liquid. The insoluble solid (called a residue) gets caught in the filter paper, because the particles are too big to fit through the holes in the paper. The filtrate is the substance (liquid) that comes through the filter paper.
Apparatus: filter paper + funnel.
Describe and explain chromatography
Chromatography is used to separate a 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).
Describe the paper chromatography experiment
- a) A start line is drawn near the bottom of the paper. The mixture is spotted on the line.
- b) A beaker is filled with small amount of solvent (it cannot touch or go above the start line when paper is placed in a beaker)
- c) Paper is hung on a rod and placed in a beaker.
- d) Solvent travels up the paper, thus separating the components.
- e) Before solvent level reaches the end, the paper is taken out and the finish line is marked. The paper is dried.
- f) The procedure works when the components dissolve differently in the solvent. More soluble components travel further up the paper. Less soluble components have a stronger attraction for the paper and travel less slowly with the solvent, therefore less further up the paper.
- g) Paper is called the stationary phase - it doesn’t move. Solvent is the mobile phase.
Distance moved by the spot (solute component) / distance moved by solvent
It has a higher affinity for the solvent than for the paper.
What is a separating funnel?
A separatory 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.
Describe the plum-pudding model
The atom is a ball of positive charge with negative electrons embedded in it
