SHREWSBURYSCHOOL
SIXTH FORM ENTRANCE EXAMINATION 2009
CHEMISTRY
(1 hour)
Instructions to candidates:
- Answer THREE questions from SECTION A and THREE questions from SECTION B.
- Each question is worth 10 marks.
- Answer on lined paper.
- You may use a calculator.
- You are provided with a copy of the periodic table.
Section A. Answer 3 questions only from this section.
1. John Dalton was a famous chemist who died 200 years ago. He made a list of substances that he thought were elements and gave them symbols. Here is a copy of his table.
a) We know some substances (such as hydrogen, carbon, oxygen, silver, gold and copper) are elements. Write down the names of twoother substances that we know are elements. [1]
b) Dalton stated that all elements are made up of atoms that cannot be split up into simpler particles. We now know that atoms contain smaller particles. Describe, with the aid of a labelled diagram, the structure of an atom of lithium. Use of the Periodic table may be helpful. [3]
c) The element, lithium, has two different natural occurring atoms: lithium-6 and lithium-7. These are called isotopes. Define the term ‘isotope’. [2]
d)Lithium is a reactive Group 1 element. Lithium is an example of a substance with what type of bonding between its particles? [1]
e)Lithium reacts readily in the presence of oxygen to form lithium oxide (Li2O). Write a balanced symbol equation for this reaction. [1]
f)Lithium also reacts vigorously with cold water. Suggest one main observation you would see if you performed this experiment in a laboratory and write a word equation for the reaction that occurs. [2]
2. This question is about organic chemistry (the study of carbon containing compounds). This question focuses on two organic molecules, chloroethene and chloroethane.
Chloroethene Chloroethane
a) Name the raw material from which most organic compounds are obtained from. [1]
b)Write down the molecular formula of chloroethene and chloroethane. [1]
c)Chloroethene is a member of the alkene family, whereas chloroethane is an alkane. Describe the chemical test you would use to distinguish between this alkene and alkane. Give the expected result for both chloroethene and chloroethane. [2]
d)Chloroethene can be used to make the polymer, poly(chloroethene), which is used to make water pipes.
(i)What is the important feature of the structure of chloroethene which allows it to act as a monomer for this polymerisation reaction? [1]
(ii)Draw a section of poly(chloropropene) showing two repeating units of the polymer. [2]
e)Poly(chloroethene) is classified as a non-biodegradable polymer. What does the term ‘non-biodegradable’ mean? Name one suitable method of disposing of this polymer, other than landfill. [2]
f)Another useful polymer in the home is poly(tetrafluoroethene). This is more commonly known as Teflon and it is used as a non-stick coating on cookware. Draw the structure of the monomer of this polymer. [1]
3.This question is about chemical bonding. The table shows some information about some compounds.
Formula / Type of structure / Melting point in oCCaO (calcium oxide) / Giant / 2900
H2O (water) / Molecular / 0
NaF (sodium fluoride) / Giant / 933
NH3 (ammonia) / Molecular / -78
a) What is the trend between the melting point and the type of structure? Use the information in the table to help you. [2]
b)The structure of a water molecule compound can be represented like this:
Water
The atoms are held together by covalent bonds. Define the term covalent bonding. [1]
c)Ammonia is also a covalent molecule. Draw the dot and cross diagram to show the arrangement of electrons in a molecule of ammonia.
You need only show electrons in outer shells.[2]
d)The melting point of calcium oxide is 2900oC. Explain why the melting point of calcium oxide is so high. [2]
e)Calculate the relative formula mass of calcium oxide, CaO.
Use the Periodic Table to help you. [1]
f)Calcium oxide readily reacts with water to form a solution of calcium hydroxide, Ca(OH)2. Suggest an approximate value of the pH of this solution. [1]
g)Sodium fluoride, NaF, can be prepared by direct combination of its elements, sodium and fluorine. Write a balanced symbol equation for this reaction. [1]
4. This question involves a simple chemical reaction and the questions that follow are all to do with the quantities of substance involved in the reaction. Show full working.
Mg burning in air
The simplest method of making magnesium oxide is to directly react magnesium and oxygen together: 2Mg + O2 2MgO
Relative atomic mass (Ar) of magnesium = 24, and Ar of oxygen = 16.
a)Name one safety precaution you would need to take when carrying out this reaction (assume lab coats and goggles are already being worn). [1]
b)1.2 grams of magnesium were burned in excess oxygen.
(i)What does the word ‘excess’ mean?[1]
(ii)What mass of magnesium oxide would we expect to form?[2]
(iii)In the experiment, only 1.4 grams of magnesium oxide were formed. What is the percentage yield of this reaction? [1]
c)Another magnesium compound, magnesium nitride, Mg3N2 was formed when doing this experiment.
(i)Write a balanced symbol equation for the formation of this product.[2]
(ii)What is the charge on the nitride, N, ion?[1]
d)In another reaction, 1.2 grams of calcium were burned in excess oxygen and formed calcium oxide, CaO. What mass of calcium oxide would you expect to form? [2]
Section B. Answer 3 questions only from this section.
5.This question is about fuels. Sulfur compounds are found in fuels from crude oil. Pollution is caused when these sulfur compounds are burned. The EU has made it a requirement that the amount of sulfur allowed in road fuels will be limited to 10 ppm from 2009.
a) (i)Identify the sulfur compound formed when petrol burns.[1]
(ii)This sulfur compound formed in (i) is bad for the environment. Explain why. [2]
b)What is the name of the separation process in which petrol is obtained from crude oil? [1]
c)(i)Petrol consists of a some hydrocarbons with the formula, C5H12. Draw structural formulae of two different compounds with this formula. [2]
d)Ethanol (C2H5OH) is being used as a additive to petrol to conserve fossil fuels in some countries like Brazil and Italy. Write a balanced symbol equation for the complete combustion of ethanol. [2]
e)Incomplete combustion of hydrocarbon fuels results in the formation of a poisonous gas. Identify this gas. [1]
f)Combustion is an exothermic reaction. Give another example of a type of exothermic reaction. [1]
6.The question is about metals and their reactions.
Iron is a transition metal that is extracted from iron(III)oxide, Fe2O3, using carbon in a blast furnace. Copper is also a transition metal that can be extracted by this method.
a)Name two other elements that are transition metals.
Use of your Periodic Table may be helpful.[1]
b)State the number of protons, neutrons and electrons in an atom of iron. [2]
c)Write a balanced symbol equation for the reaction that takes place between iron(III) oxideand carbon in the blast furnace. [2]
d)The iron formed in this process is known as cast iron, which is a brittle and corrodes very easily. Most of this iron is converted into pure iron then mixed with other elements to form an alloy.
Show, with the aid of a diagram, the main differences in the structure of a pure metal and an alloy and how this affects the malleability of the material. [2]
e)Alumumium is extracted by electrolysis. Impure copper obtained from a similar method using a blast furnace can be purified by electrolysis. The purified copper is used in electrical wiring in houses.
What are the main physical properties of copper that make it suitable for this purpose [2]
f) Aluminium can not be extracted by this method. Suggest a suitable reason why. [1]
7. This question is about acids.
Asborbic acid (Vitamin C) is an essential nutrient for humans. There are many other naturally occurring molecules like citric acid (in citrus fruits) and tartaric acid (in grapes and bananas).
a)Asborbic acid, C6H8O6, dissolves in water to form an acidic solution. If a small amount of magnesium powder is added to the water, the following reaction occurs:
C6H8O6 (aq) + Mg (s) Mg(C6H6O6)2 (aq) + H2 (g)
(i)Suggest two observations you would expect to see when the reaction place? [2]
(ii)In the above equation, (aq) means in aqueous solution. What do the (s) and (g) mean? [1]
(iii)What is the charge on the asborbate ion, C6H6O6?[1]
(iv)Describe how would you obtain large crystals of magnesium asborbate from its aqueous solution. [2]
b)Tartaric acid, C4H6O6, is present in wine. What is the empricial formula of tartaric acid? [1]
c)Salts can be produced when the H+ ion of an acid is replaced by a metal ion or an ammonium, NH4+, ion. These salts usually have high melting and boiling points. Describe the trend in solubility and electrical conductivity of these salts. [3]
8.This question is about the rates of chemical reactions.
Bisodol is an indigestion relief tablet that it used to relieve heartburn and contains three active ingredients:
Calcium carbonate (CaCO3) / 0.522 gMagnesium carbonate (MgCO3) / 0.068 g
Sodium hydrogen carbonate (NaHCO3) / 0.064 g
All these ingredients help to neutralise the excess acidity in the stomach.
a)Magnesium carbonate, MgCO3 has a structure consisting of two different ions. What are the formulae of these ions? [1]
b)Stomach acid consists mainly of hydrochloric acid. Write a balanced symbol equation of the reaction between magnesium carbonate and hydrochloric acid. [2]
c)The reaction in (b) releases a gas, which is water soluble. Draw a labelled diagram of the apparatus you could you use to collect this gas. [2]
d)Sometimes it is better to break the tablet into smaller pieces before taking it to relieve heartburn quicker. Explain why. [2]
e)The rate of reaction between magnesium carbonate and hydrochloric acid increases with temperature. Explain why. [2]
f)Increasing concentration of hydrochloric acid can also increase the rate of this reaction. Explain why. [1]