8510873
| Pregunta | Respuesta |
| What is the definition of a compound? | Compounds are substances in which atoms of two or more elements are chemically combined. |
| Why do atoms take part in chemical bonding? | Atoms take part in chemical bonding in order to achieve the electronic structure of a noble gas (full outer energy level). |
| When an atom loses an electron, what charge does the remaining ion have? | When an atom loses an electron, the remaining ion has a positive charge. |
| When an atom gains an electron, what charge does the remaining ion have? | When an atom gains an electron, the remaining ion has a negative charge. |
| What can we say about the electronic structure of ions? | Ions have the electronic structure of a noble gas (Group 0). |
| What do we call the elements in Group 1 | Elements in Group 1 are called the Alkali metals. |
| When Group 1 metals react with non-metal elements, what type of ion is formed? | When Group 1 metals react with non-metal elements, the Group 1 element forms an ion with a single positive charge. |
| What do we call the elements in Group 7? | The elements in Group 7 are called the Halogens. |
| When Group 7 elements react with alkali metals, what charge does the halide ion gain? | When Group 7 elements react with alkali metals, the halide ion has a negative charge. |
| What type of structure is formed by ionic compounds? | Ionic compounds form giant structures. |
| What type of bonding happens when atoms share pairs of electrons? | When atoms share pairs of electrons, this is called covalent bonding. |
| What do we call covalent molecules with only a small number of atoms e.g. H2, Cl2, O2, HCl, H20, NH3 and CH4? | Covalent molecules with only a small number of atoms are called simple molecules. |
| What can we say about the melting and boiling points of simple molecules? | Simple molecules have low melting and boiling points? |
| Why do simple molecules have low melting and boiling points? | Simple molecules have low melting and boiling points as they have weak forces between the molecules. (HIGHER TIER) |
| Why do simple molecules not conduct electricity? | Simple molecules do not conduct electricity because the molecules do not have an overall electric charge. |
| Why do ionic compounds have high melting and boiling points? | Ionic compounds have high melting and boiling points because there are strong electrostatic forces between oppositely charged ions. |
| Why do solid ionic compounds not conduct electricity? | Solid ionic compounds cannot conduct electricity because the ions are not free to move. |
| Why do ionic compounds conduct electricity when they are melted or dissolved in water? | Ionic compounds can conduct electricity when melted or dissolved in water because now the ions are free to move. |
| What type of molecules are diamond, graphite and silicon dioxide? | Diamond, graphite and silicon dioxide are giant covalent lattices (macromolecules). |
| Why do giant covalent structures have very high melting points? | Giant covalent structures have very high melting points as all the atoms are linked to other atoms by strong covalent bonds. |
| Damond and graphite are formed from which element? | Diamond and graphite are formed from the element carbon. |
| What is this molecule? | This molecule is diamond. Each carbon atom is forming four covalent bonds. |
| What is this molecule? | This molecule is graphite. Each carbon atom is forming three covalent bonds. |
| Why is diamond very hard? | Diamond is very hard because each carbon atom forms four covalent bonds. |
| Why is graphite soft and slippery? | Graphite is soft and slippery because it consists of layers. There are no covalent bonds BETWEEN the layers so they are free to slide. |
| Why is graphite a good conductor of heat and electricity? (HIGHER TIER) | In graphite, one electron from each carbon atom is delocalised (free to move). These allow graphite to conduct heat and electricity. |
| What is the structure of fullerenes? (HIGHER TIER) | Fullerenes consist of hexagonal rings of carbon atoms. They have uses such as lubricants and in nanotubes. |
| Why are metals good conductors of heat and electricity? (HIGHER TIER) | Metals are good conductors of heat and electricity because they have delocalised (free) electrons which can move. |
| Why can metals be bent and shaped? | Metals can be bent and shaped because the layers of atoms in metals are able to slide over each other. |
| What are alloys? | Alloys are usually made from two or more different metals (however a metal plus a nonmetal such as carbon would also be an alloy). |
| Why are alloys harder than pure metals? | Alloys are harder than pure metals because the different sized atoms distort the layers so it is difficult for them to slide over each other. |
| What are shape memory alloys? | Shape memory alloys can return to their original shape after being deformed (eg dental braces). |
| What conditions can we change to alter the properties of a polymer? | To alter the properties of a polymer, we can change the reaction temperature or use a different catalyst. |
| What is meant by a thermosoftening polymer? | Thermosoftening polymers consist of individual tangled polymer chains. When we heat them, these polymers melt and can be reshaped. |
| What is meant by a thermosetting polymer? | Thermosetting polymers consist of polymer chains with cross-links between them. They do not melt when they are heated. |
| In terms of intermolecular forces, why can thermosoftening polymers melt when heated? (HIGHER TIER) | Thermosoftening polymers have weak intermolecular forces between the chains. These are easily broken, so the polymer can melt easily |
| What is meant by nanoparticles? | Nanoparticles are between 1-100nm in size (very small). They consist of a few hundred atoms. |
| Why are nanoparticles useful? (a role may be described in the exam). | Nanoparticles are useful because they have a high surface area to volume ratio. |
| What is shown by the atomic number of an element? | The atomic number of an element tells us the number of protons in the nucleus of an atom. |
| What is shown by the mass number of an element? | The mass number tells us the total number of protons and neutrons in the nucleus of an atom. |
| How do we calculate the number of neutrons in the nucleus of an atom? | To calculate the number of neutrons in the nucleus of an atom, subtract the atomic number from the mass number. |
| What do we call atoms of the same element with different numbers of neutrons? | Atoms of the same element with different numbers of neutrons are called isotopes. |
| What is meant by the relative atomic mass (Ar) of an element? (HIGHER TIER) | The relative atomic mass (Ar) of an element is an average mass of the atoms of the isotopes compared with the 12C isotope. |
| What is meant by the relative formula mass (Mr) of a compound? | The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula. |
| What is one mole of a substance? | One mole of a substance is the relative formula mass in grams. |
| Elements and compounds can be detected and identified by instrumental methods. What does this mean and give an example. | An instrumental method involves using a machine. An example is gas chromatography. |
| What are the advantages of analysing a substance using an instrumental method? | Instrumental methods are accurate, sensitive and rapid. They are useful when the amount of a sample of very small. |
| How can we identify artificial colours in foods? | Artificial colours in foods can be identified using paper chromatography |
| Describe how gas chromatography works. | In gas chromatography, different substances carried by gas, travel through a column packed with solid material. Each substance travels through the column at a different speed so they are separated. |
| How can we tell from a gas chromatograph how many different compounds are present? | The number of peaks on a gas chromatograph shows the number of compounds. |
| How can we work out the retention time from a gas chromatograph? | The position of the peak indicates the retention time. |
| How can we work out the relative molecular mass of a substance from a mass spectrum? (HIGHER TIER) | The rightmost peak on a mass spectrum is called the molecular ion peak. This tells us the relative molecular mass of the substance. |
| Suggest why the yield of a reaction is often less than the maximum calculated amount. | The yield of a reaction is often less than the maximum calculated amount because • some of the compound may be lost when it is separated from the reaction mixture • There may be unexpected side-reactions • The reaction may not go to completion because it is irreversible |
| How do we calculate the percentage yield for a reaction. | percentage yield = (mass of product / theoretical maximum mass) x 100 |
| What does this symbol mean? | This symbol shows that the reaction is reversible |
| How can we calculate the rate of a reaction? | The rate of the reaction is calculated by either • dividing the amount of product formed by the time taken. • dividing the amount of reactant used by the time taken. |
| What is meant by the activation energy? | Activation energy is the minimum energy particles must collide with to react. |
| How does increasing the temperature of a reaction increase the rate of that reaction? | If we increase the temperature of a reaction, the particles collide more frequently and with more energy. This increases the rate of reaction. |
| How does increasing the pressure of reacting gases increase the rate of a reaction? | Increasing the pressure of reacting gases makes the particles collide more frequently which increases the rate of the reaction. |
| How does increasing the concentration of reactants in solution increase the rate of reaction? | Increasing the concentration of reactants in solution makes the particles collide more frequently which increases the rate of the reaction. |
| How does increasing the surface area of solid reactants increase the rate of reaction? | Increasing the surface area of solid reactants increases the frequency of collisions. This increases the rate of the reaction. |
| What is the effect of a catalyst on a chemical reaction? | Catalysts increase the rate of a chemical reaction. |
| How can using a catalyst save money when carrying out a chemical reaction? | Catalysts increase the rate of a reaction so we can use a lower temperature and save energy costs. |
| What is meant by an exothermic reaction? | An exothermic reaction releases energy to the surroundings. Generally exothermic reactions get hot. |
| What is meant by an endothermic reaction? | An endothermic reaction takes in energy from the surroundings. Generally endothermic reactions get cold. |
| How can we use anhydrous copper sulfate to test for the presence of water? | Anhydrous copper sulfate is copper sulphate without water. It is white. If we add water, we get hydrated copper sulfate which is blue. Hydrated means “contains water”. |
| What are the state symbols for • solid • liquid • gas • dissolved in water | Solid = s Liquid = l Gas = g Dissolved in water = aq |
| Describe how we can make a soluble salt by reacting a metal with an acid. | Add metal to the acid. Some metals are too unreactive (eg gold) and some metals are too reactive (eg group 1). The metal will effervesce (fizz) as the reaction releases hydrogen. When the metal stops reacting, all the acid has reacted. Now filter off the unreacted metal. Crystallise the salt produced by evaporation. |
| Describe how we can make a soluble salt by reacting an insoluble base with an acid. | Add the insoluble base to the acid. Keep adding until the insoluble base stops reacting (as the acid has all reacted). Now filter off the unreacted base. Crystallise the salt produced by evaporation. |
| Describe how we can make a soluble salt by reacting an alkali with an acid. | Add the alkali to the acid until the pH is 7 (neutral). This can be determined using indicator paper. Now crystallise the salt produced by evaporation (note: you do not need to filter). |
| When we mix two solutions together and produce a solid, what name do we give to the solid? | A solid produced by mixing two solutions together is called a precipitate. This is a precipitation reaction. |
| What is an alkali? | An alkali is a soluble metal hydroxide (eg sodium hydroxide). Alkalis have a pH value of 8-14. |
| Suggest a pH value for an acid. | Acids have a pH between 1 and 6. |
| What pH is a neutral solution? | A neutral solution has a pH of 7. |
| Which ion makes solutions acidic? | The hydrogen ion (H+) makes solutions acidic. |
| Which ion makes solutions alkaline? | The hydroxide ion (OH-) makes solutions alkaline. |
| What is the equation for neutralisation? |
The equation for neutralisation
is
Image:
Neutralisation (image/jpeg)
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| Which salts are produced from: • hydrochloric acid • sulfuric acid • nitric acid | • hydrochloric acid = chloride • sulfuric acid = sulfate • nitric acid = nitrate |
| How is ammonium nitrate produced and what is it used for? | Ammonium nitrate is produced by reacting ammonia solution with nitric acid. Ammonium nitrate is used as a fertiliser. |
| What is meant by electrolysis? | Passing an electric current through an ionic substance which is melted or dissolved in water, causing the substance to break down into elements. |
| In electrolysis, what is meant by the electrolyte. | In electrolysis, the electrolyte is the ionic compound which is broken down to its elements as electric current is passed. |
| During electrolysis, which ion moves to the negative electrode and why? | During electrolysis, the positive ion moves to the negative electrode. This is because opposite charges attract. |
| Suggest a reason why we electroplate a metal with a different metal. | Electroplating can be used to prevent corrosion. It can also be carried out to make a metal more attractive. |
| During electrolysis, what takes place at the negative electrode? | At the negative electrode, positive ions gain electrons. Gaining electrons is called reduction. |
| During electrolysis, what takes place at the positive electrode? | At the positive electrode, negative ions lose electrons. Losing electrons is called oxidation. |
| When electrolysing an ionic compound in solution, how do we work out what is produced at the negative electrode? | If the metal is more reactive than hydrogen, then hydrogen is produced at the negative electrode. If the metal is less reactive than hydrogen, the metal is produced at the negative electrode. |
| Write the half equation for the oxidation of chloride at the positive electrode. (HIGHER TIER) | |
| What is the role of cryolite during electrolysis of molten aluminium oxide? | Cryolite lowers the melting point which reduces the energy needed, saving money |
| During the electrolysis of molten aluminium oxide, what is produced at the negative electrode and what is produced at the positive electrode? | During electrolysis of aluminium oxide, aluminium is produced at the negative electrode and oxygen is produced at the positive electrode. |
| During electrolysis of molten aluminium oxide, why does the positive electrode need to be replaced regularly? | During electrolysis of molten aluminium oxide, graphite electrodes are used. Oxygen is produced at the positive electrode. The oxygen reacts with the carbon graphite, producing carbon dioxide. The positive electrode therefore needs replacing regularly. |
| During electrolysis of sodium chloride solution, what is produced at the negative electrode? | During electrolysis of sodium chloride solution, hydrogen gas is produced at the negative electrode. |
| During electrolysis of sodium chloride solution, what is produced at the positive electrode? | During electrolysis of sodium chloride solution, chlorine gas is produced at the positive electrode. This is used to make bleach and plastic. |
| During electrolysis of sodium chloride, what solution remains at the end? | During electrolysis of sodium chloride solution, sodium hydroxide solution remains at the end. This is used to make soap. |
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