9. The Periodic Table: chemical periodicity
A section of Chemistry, 9701
Listing 10 of 288 questions
Phosphorus and sulfur are two non-metallic elements on the right hand side of the Periodic Table. For each of these elements describe the observations you would make when it burns in air, and write a balanced equation for the reaction. phosphorus observation equation sulfur observation equation White phosphorus, P4, is produced commercially by heating calcium phosphate(rock with a mixture of silica, SiO2, and coke in an electric furnace at 1400 °C. Calcium silicate, CaSiO3, and carbon monoxide are the other products. Balance the following equation which represents the overall process. ___ Ca3(PO4)2 + ___ SiO2 + ___ C ___ P4 + ___ CaSiO3 + ___ CO When heated to 400 °C in the absence of air, white phosphorus is changed into the red form of the element. The following table lists some of the properties of the two forms, which are known as allotropes. allotrope electrical conductivity melting point / °C solubility in water solubility in benzene white none insoluble soluble red none insoluble insoluble Suggest the type of structure and bonding in each allotrope. allotrope type of structure type of bonding white red In both allotropes, phosphorus has a valency of 3. Suggest by means of diagrams how the phosphorus atoms might be joined together in each allotrope. white phosphorus red phosphorus
9701_s10_qp_41
THEORY
2010
Paper 4, Variant 1
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Describe how the behaviour of the oxides of tin and lead in their +4 oxidation states differ on heating. Explain the following by using data from the Data Booklet where appropriate, and writing equations for all reactions. A sample of liquid PbCl4 is placed in a flask and the flask is gently warmed. A gas is evolved and a white solid is produced. When the gas is bubbled through KI, purple fumes are produced. Repeating the same experiment using liquid SnCl4 instead of PbCl4 results in no evolution of gas, and no reaction with KI. The molecule dichlorocarbene, CCl2, can be produced under certain conditions. It is highly unstable, reacting with water to produce carbon monoxide and a strongly acidic solution. Suggest the electron arrangement in CCl2 and draw a dot-and-cross diagram showing this. Predict the shape of the molecule. Construct an equation for the reaction of CCl2 with water.
9701_s10_qp_41
THEORY
2010
Paper 4, Variant 1
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State and explain the variation in the oxidation numbers of the chlorides of the elements Na, Mg, Al and Si. Describe the reaction of phosphorus(chloride with water, and write an equation for the reaction. When microwave radiation is passed through phosphorus(chloride, PCl3, at low pressure, a new chloride of phosphorus, B, is formed. B contains 69.6% by mass of chlorine and 30.4% by mass of phosphorus, and its Mr is approximately 200. Calculate the empirical and molecular formulae of B. Assuming phosphorus and chlorine show their typical valencies, draw the displayed formula of B, showing all bonds and lone pairs. Calculate the oxidation number of phosphorus in B. One mole of B reacts with four moles of water. Suggest the structure of the phosphorus-containing product of this reaction.
9701_s11_qp_41
THEORY
2011
Paper 4, Variant 1
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Oxides are compounds which usually contain oxygen combined with one other element. Oxides are classifi ed as follows. acidic alkaline amphoteric basic Using these terms only, complete the table to describe the oxides of the elements of the third period of the Periodic Table sodium to sulfur. Na2O MgO Al 2O3 SiO2 P4O10 SO2 Cl 2O7 acidic Give the names of two elements from sodium to chlorine which form more than one oxide. and Sodium reacts with water. Describe, as fully as you can, what you would see when a piece of sodium is reacted with water. Write an equation for the reaction of sodium with water. Sulfur dioxide is present in small, but signifi cant, amounts in the Earth’s atmosphere. State one way by which sulfur dioxide enters the atmosphere. Give the formula of another sulfur compound which is formed in the atmosphere from sulfur dioxide. What are the environmental consequences of the compound you have identifi ed in ? Sulfur dioxide is used as a food preservative. What property of sulfur dioxide enables it to act in this way? Another sulfur compound which is present in the Earth’s atmosphere is carbonyl sulfi de, OCS. The sequence of atoms in the molecule is oxygen-carbon-sulfur and the molecule is not cyclic. Draw a ‘dot-and-cross’ diagram of the OCS molecule. Show outer electrons only. Suggest a value for the O – C – S bond angle.
9701_s12_qp_21
THEORY
2012
Paper 2, Variant 1
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The elements of the third period of the Periodic Table, sodium to sulfur, all form chlorides by direct combination. Sulfur forms a number of chlorides which are liquid at room temperature. Which other element of the third period forms a chloride which is liquid at room temperature? Name one element of the third period which burns in chlorine with a coloured fl ame. Aluminium chloride may be produced by passing a stream of chlorine over heated aluminium powder in a long hard-glass tube. State two observations you could make during this reaction. and Write a balanced equation, with state symbols, for this reaction of aluminium with chlorine. No chloride of argon has ever been produced. Suggest a reason for this. When chlorides of the elements of the third period are added to water, some simply dissolve while others can be seen to react with the water. Complete the table below, stating how the chlorides of Na, Al, and Si behave when mixed with water. In the fi rst column use only the terms ‘dissolve’ or ‘react’. element Does the chloride dissolve or react? approximate pH of the resulting solution Na Al Si What type of reaction takes place between a chloride and water? Sulfur forms the compound S4N4 with nitrogen. The structure of S4N4 is shown below. Assume all bonds shown are single bonds. S S S S N N N N a b Determine the number of lone pairs of electrons around a nitrogen atom and a sulfur atom in S4N4. nitrogen atom sulfur atom Which bond angle, a or b, in the S4N4 molecule will be smaller? Explain your answer.
9701_s12_qp_22
THEORY
2012
Paper 2, Variant 2
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Questions Discovered
288