1. Principles Of Chemistry Flashcards
What is an atom?
What is a molecule?
An atom is a basic unit of matter.
A molecule is made up of two or more atoms, either of the same element or of two or more different elements held together by covalent chemical bonds.
What is a faraday?
A faraday is 96500 coulombs (1 mole of electrons)
describe and explain experiments to investigate the small size of particles and their movement including:
dilution of coloured solutions
diffusion experiments
Dilution: a substance is put in a solvent to reduce its concentration
Diffusion: The movement of particles from an area of high concentration to an area of low concentration
Experiment 1, Diffusion
Hydrochloric acid is placed at one end of a tube, ammonia solution at the other.
Where they meet a ring of ammonium chloride appears.
The diagram shows it is closer to the ammonia solution.
From this we can tell that ammonia must have travelled faster, as it got further in the time. Lighter particles travel faster- so we can tell that ammonia is a lighter gas.
Experiment 2, Dilution
Put a coloured substance in a solvent e.g food colouring in water.
You can see that over time the colour levels out but is weaker than the original colour- this is dilution.
Dilution at different temperatures: more heat; means more energy; means more movement; so the particles can move to different areas more quickly. So applying heat decreases the amount of time taken for the coloured substance to be fully diluted.
What are the differences between elements, compounds and mixtures?
Elements- every atom in an element has the same amount of protons.
Compound- atoms from different elements bonded together
Mixture- different elements not bonded.
describe experimental techniques for the separation of mixtures, including:
simple distillation fractional distillation filtration crystallisation paper chromatography
Filtration:
This consists of a barrier which one component f a mixture can pass through but the other is caught by.
e.g water goes through filter paper, rocks are caught by it.
Distillation:
One substance is evaporated off.
e.g salt water is heated to 100 degrees; water evaporates off (it rises and the goes down into the condenser where it is cooled back into water), the salt is left in the original flask. See diagram.
Fractional distillation:
The mixture is evaporated and rises up the tube.
Different substances have different boiling points and so will condense at different temperatures; as the mixture travels up the tube the temperature decreases, substances begin to condense at different places (due to the change in temperature) and are collected. This separates the mixture into its different parts.
Crystallisation:
A solution is warmed allowing the solvent to evaporate, the solution is now left to cool and will form crystals.
Chromatography:
chromatography paper is placed in a substance, the different components of the substance will travel at different speeds (due to the size of their particles.)
What does a Chromatogram show?
How do you calculate the Rf value?
explain how information from chromatograms can be used to identify the composition of a mixture.
Chromatography paper is placed in a solvent, the different compounds will travel at different speeds (due to the size of their particles.)
Rf values:
The Rf value is calculate by Distance moved by compound divided by Distance moved by solvent.
Chromatogram:
The shape on the chromatogram can be compared with that of known substances and where they match they are the same substance.
Define:
atomic number
mass number
isotopes
relative atomic mass (Ar)
Atomic number: number of protons (the same as number of electrons.)
Atomic mass: number of protons + neutrons.
Isotopes: Atoms of an element with different numbers of neutrons.
Relative atomic mass (Ar): the mass of one atom of an element.
What is a mole?
mole: the Avogadro number of particles (atoms, molecules, formulae, ions or electrons) in a substance.
A mole is Avogadro’s number simply because if you have 1 mole of an element its weight in grams will be its atomic mass.
Percentage yield =
Percentage yield = actual yield/ theoretical yield x 100
Concentration = ( in terms of mole and volume)
Concentration = moles/volume
describe the formation of ions by the gain or loss of electrons
Electrons are transferred from one atom to another (this is in an effort to either fill or empty the outer shell to become stable.)
An atom has no charge because the electrons and protons have equal and opposite charges. But an ion will have a charge: an electron has a charge of -1, so loosing an electron looses one negative charge, making the ion +1. So gaining one electron will make an atom a -1, gaining two will make it -2.
The atoms the gain or loose electrons to each other will have opposite charges: for example if a gives away 1 atom and b gains it, a is +1 and b is +2. These charges mean that the ions are attracted to each other (ionic bond), so they form an ionic compound.
Oxidation=?
Reduction=?
Oxidation is loss of electrons
Reduction is gain of electrons
What is ionic bonding?
Ionic bonding happens between two ions: they are attracted to each other due to their opposite charges, so we say the ions have electrostatic attraction. This attraction bonds them together into an ionic compound.
Why do ionic compounds have high melting and boiling points?
To melt or boil anything, heat is used to break bonds. The stronger the bonds, the more heat needed. Ionic compounds have strong bonds, so they don’t melt or boil unless there is a considerable amount of heat, this means the have high melting and boiling points.
What is covalent bonding?
covalent bonding: a strong attraction between the bonding pair of electrons and the nuclei of the atoms involved in the bond
