IGCSE Chemistry : Principles of chemistry

Pregunta	Respuesta
Experiment to investigate dilution?	Put a coloured substance in a solvent e.g food colouring in water. Over time the colour levels out but it is weaker than the original colour.
Experiment to investigate diffusion?	Hydrochloric acid placed t one end of a tube, ammonia solution at the other. Where they meet a ring of ammonium chloride appears. From this we can tell that ammonia must have travelled faster, as it got further in time.
What is an atom and a molecule?	An atom is made up of a nucleus (protons and neutrons) and shells with electrons on. A molecule is two or more atoms bonded together.
What is filtration?	A barrier which one component can pass through but the other is caught by.
What is distillation?	One substance is evaporated off, e.g if salt water is heated to 100 degrees water evaporates off and the salt is left in the original flask.
What is 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 change in temperature) and are collected. This separates the mixture.
What is an isotope?	Atoms of an element with different numbers of neutrons.
What is a mole?	A mole is an amount, you can have a mole of carbon.
Describe the formation of ions by the gain or loss of electrons?	Electrons are transferred from one atom to another (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.
What is the name given to loosing electrons, and name given to gaining electrons.	Oxidation is the loss of electrons, Reduction is the gain of them.
What is ionic bonding?	Ionic bonding happens between two ions, they are attracted to each other due to their opposite charges. This attraction bonds them together into an ionic compound.
Key features of an ionic compound?	They have a high melting and boiling point because of the strong electrostatic force between the oppositely charged ions.
Difference between ionic charge and melting point and boiling point in ionic compound?	The bigger the difference in charge the stronger the attraction. The stronger the attraction, the harder it is to break the bonds which means that the melting point and boiling points will be higher.
What is an ionic crystal?	An ionic crystal is a lattice of electrons in the shape of a cube, the ions are alternate positive and negative and their opposite charges hold the structure together.
What is a covalent bond?	A covalent bond is a bond formed between atoms by sharing a pair of electrons (one from each atom).
Key features of a covalent bond?	Poor conductors of heat and electricity
Problem with a simple molecule?	Only has a few atoms and therefore has a low melting point.
Why do substances with simple molecular structures have low melting and boiling points.	A substance with a simple molecular structure is one that contains only a few atoms in a molecule. The intermolecular forces are weak, so it doesn't take much energy - or heat to break them which means they will melt and boil under low heats.
Explain the high melting and boiling points of substances with giant covalent structures.	A giant covalent structure is one with many atoms bonded together. To melt or boil them you are not separating intermolecular bonds but INTRA molecular bonds. These bonds are strong covalent bonds which take a lot of energy to break, meaning they have a high melting and boiling point.
How the uses of diamond and graphite depend on their structures.	In graphite the atoms form layers, these layers can slide over each other, so can be used as lubricant. Diamond is extremely hard because it has many bonds in it, this means it is great for cutting as it can cut anything.
A metal as a giant structure?	In a metal, atoms come together into a lattice, the electrons become detached from their atoms or de localized making the atoms positive ions.
What makes a metal conductive and malleable?	Metals have de localized electrons, electrons carry electricity, so because there are free electrons charge can pass easily through them. Structure of a metal is the rows of atoms of one another, in pure metals all the atoms will be the same size, the layers can slide over one another easily making them easy to bend.
Why don't covalent compounds conduct electricity?	In covalent compounds there are no electrons free to move, this means there can be no transfer of electricity through a covalent compound.
Why do ionic compounds conduct electricity only when molten or in solution?	When ionic compounds are molten or in solution, the positive and negative ions separate this means that there are ions free to flow, so they can conduct electricity.
Understand that electrolysis involves the formation of new substances.	In electrolysis ionic compounds conduct electricity. Positively charged ions move to one end, negatively to the other, these are then turned into atoms (by losing their charge) and so new substances are formed.

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IGCSE Chemistry : Principles of chemistry

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