Chemistry 2.

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What are substances that consist of simple molecules?
Gases, liquids or solids with relatively low melting and boiling points.
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What do substances that consist of simple molecules have between the molecules?
Weak intermolecular forces.
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Is it the intermolecular forces or the covalent bonds that are overcome when the substance melts or boils?
Intermolecular forces because they are weak in comparison with covalent bonds.
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Why do substances that consist of simple molecules not conduct electricity?
Because the molecules do not have an overall electric charge.
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What features do ionic compounds have?
Regular structures (giant ionic lattices) in which there are strong electrostatic forces in all directions between oppositely charged ions.
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Why do these compounds have high melting points and high boiling points?
Bof the large amounts of energy needed to break the many strong bonds.
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What happens to ionic compounds when they are melted or dissolved in water?
Tconduct electricity because the ions are free to move and carry the current.
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What can atoms that share electrons also do?
Form giant structures or macromolecules.
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Diamond, graphite and silicon dioxide are examples of what types of structures?
Giant covalent structures of atoms.
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Do they have high or low melting points and why?
Very high melting points because all the atoms in these structures are linked to other atoms by strong covalent bonds.
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Why is diamond very hard?
Because in diamond, each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure.
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Why is graphite soft and slippery?
Because in graphite, each carbon atom bonds to three others, forming layers. The layers are free to slide over each other because there are no covalent bonds between the layers.
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In graphite, how many electrons are delocalised from each carbon atom?
One.
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What do these delocalised electrons allow graphite to do?
Conduct heat and electricity.
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Why can metals conduct heat and electricity?
Because of the delocalised electrons in their structures.
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What does conduction depend on?
The ability of electrons to move throughout the metal.
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Why can metals be bent and shaped?
Because the layers of atoms in metals are able to slide over each other.
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Why are alloys harder than pure metals?
Alloys are usually made from two or more different metals. The different sized atoms of the metals distort the layers in the structure, making it more difficult for them to slide over each other.
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What do the properties of polymers depend on?
What they are made from and the conditions under which they are made. For example, low density (LD) and high density (HD) poly(ethene) are produced using different catalysts and reaction conditions.
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What do thermosoftening polymers consist of?
Individual, tangled polymer chains with cross-links between them so that they do not melt when they are heated.
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What does nano science refer to?
Nanoscience refers to structures that are 1–100 nm in size, of the order of a few hundred atoms.
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How can atoms be represented?
.
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What is the relative mass of protons?
1
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What is the relative mass of neutrons?
1
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What is the relative mass of electrons?
Very small (0.0005)
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What is the total number of protons and neutrons in an atom called?
The mass number.
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What is it called when atoms of the same element can have different numbers of neutrons?
Isotopes of that element.
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What is the relative formula mass of a compound?
It is the sum of the relative atomic masses of the atoms in the numbers shown in the formula.
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What is the relative formula mass of a substance, in grams, known as?
One mole of that substance.
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How can elements and compounds be detected and identified?
By using instrumental methods. Instrumental methods are accurate, sensitive and rapid and are particularly useful when the amount of a sample is very small.
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What can be used to identify additives in food?
Chemical analysis.
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How can artificial colours be detected and identified?
By paper chromatography.
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What does gas chromatography allow?
The seperation of a mixture of compounds.
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What can be used to help identify the substance in gas chromatography?
The time taken for a substance to travel through the column.
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What can the output from the gas chromatography column be linked to?
A mass spectrometer, which can be used to identify the substances leaving the end of the column.
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What can the mass spectrometer also give?
The relative molecular mass of each of the substances seperated in the column.
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How can the percentage of an element in a compound be calculated?
From the relative mass of the element in the formula and the relative formula mass of the compound.
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How can the empirical formula of a compound be calculated?
From the masses or percentages of the elements in a compound.
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Even though no atoms are gained or lost in a chemical reaction, why is it not always possible to obtain the calculated amount of a product?
Because the reaction may not go to completion because it is reversible, some of the product may be lost when it is separated from the reaction mixture or some of the reactants may react in ways different from the expected reaction.
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What is the yield known as?
The amount of product obtained. When compared with the maximum theoretical amount as a percentage, it is called the percentage yield.
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The rate of a chemical reaction can be found by measuring the amount of a reactant used or the amount of product formed over time:
Rate of reaction = amount of reactant used/time or amount of product formed/time
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When can chemical reactions only occur?
When reacting particles collide with each other and with sufficient energy.
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What is the activation energy?
The minimum amount of energy particles must have to react.
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What happens when the temperature is increased?
The speed of the reacting particles is increased so that they collide more frequently and energetically which increases the rate of reaction.
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What happens when you increase the pressure of reacting gases?
The frequency of collisions increases and so increases the rate of reaction.
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What happens when you increase the concentration of reactants in solutions?
The frequency of collisions increases and so increases the rate of reaction.
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What happens when you increase the surface area of solid reactants?
The frequency of collisions increases and so increases the rate of reaction.
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What do catalysts do?
Catalysts change the rate of chemical reactions but are not used up during the reaction. Different reactions need different catalysts.
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What happens when chemical reactions occur?
Energy is transferred to or from the surroundings.
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What is an exothermic reaction?
An exothermic reaction is one that transfers energy to the surroundings.
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What is an endothermic reaction?
An endothermic reaction is one that takes in energy from the surroundings.
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What happens if a reversible reaction is exothermic in one direction?
It is endothermic in the opposite direction. The same amount of energy is transferred in each case.
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What are the state symbols in equations?
(s), (l), (g) and (aq)
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Soluble salts can be made from acids by reacting them with:
metals – not all metals are suitable; some are too reactive and others are not reactive enough.
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Soluble salts can be made from acids by reacting them with:
insoluble bases – the base is added to the acid until no more will react and the excess solid is filtered off.
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Soluble salts can be made from acids by reacting them with:
alkalis – an indicator can be used to show when the acid and alkali have completely reacted to produce a salt solution.
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When salt solutions are crystallised what do they produce?
Solid salts.
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How can insoluble salts be made?
Insoluble salts can be made by mixing appropriate solutions of ions so that a precipitate is formed.
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What can precipitation be used for?
Precipitation can be used to remove unwanted ions from solutions, for example in treating water for drinking or in treating effluent.
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What are metal oxides and hydroxides known as?
Bases. Soluble hydroxides are called alkalis
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What does the particular salt produced in any reaction between an acid and a base or alkali depend on?
the acid used (hydrochloric acid produces chlorides, nitric acid produces nitrates, sulfuric acid produces sulfates) and the metal in the base or alkali.
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What does ammonia dissolve in water to produce?
An alkaline solution.
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What is it used to produce?
Ammonium salts which are important as fertilisers.
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Hydrogen ions make solutions...?
Acidic.
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Hydroxide ions make solutions...?
Alkaline.
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What happens in neutralisation reactions?
Hydrogen ions react with hydroxide ions to produce water. This reaction can be represented by the equation: H+(aq) + OH–(aq) H2O(l)
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When an ionic substance is melted or dissolved in water, what happens to the ions?
The ions are free to move about within the liquid or solution.
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What happens when you pass an electric current through ionic substances that are molten (eg. lead bromide) ?
The solution breaks the ionic substances down into elements. This process is called electrolysis and the substance that is broken down is called the electrolyte.
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What happens during electrolysis?
Positively charged ions move to the negative electrode, and negatively charged ions move to the positive electrode.
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What happens at the different electrodes?
At the negative electrode, positively charged ions gain electrons (reduction) and at the positive electrode, negatively charged ions lose electrons (oxidation).
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What happens if there is a mixture of ions?
The products formed depend on the reactivity of the elements involved.
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What is manufactured by the electrolysis of a molten mixture of aluminium oxide and cryolite?
Aluminium which forms at the negative electrode and oxygen at the positive electrode.
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What is the positive electrode made of?
Carbon, which reacts with the oxygen to produce carbon dioxide.
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What does the electrolysis of sodium chloride solution produce?
Hydrogen and chlorine and sodium hydroxide solution. These are important reagents for the chemical industry, eg sodium hydroxide for the production of soap and chlorine for the production of bleach and plastics.
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Other cards in this set

Card 2

Front

What do substances that consist of simple molecules have between the molecules?

Back

Weak intermolecular forces.

Card 3

Front

Is it the intermolecular forces or the covalent bonds that are overcome when the substance melts or boils?

Back

Preview of the front of card 3

Card 4

Front

Why do substances that consist of simple molecules not conduct electricity?

Back

Preview of the front of card 4

Card 5

Front

What features do ionic compounds have?

Back

Preview of the front of card 5
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