Chemical bonding - student copy

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YISHUN INNOVA JUNIOR COLLEGE 2021 JC2 H2 CHEMISTRY CHEMICAL BONDING (FOUNDATION) NYJC/2020/I/3 1 In which pair do the species have different shapes from each other? A BeCl 2 and CO 2 B BH 4 and NH 4 + C OF 2 and SCl 2 D PH 3 and SO 3 NYJC/2020/I/4 2 Liquids X and Y do not react with one another. They have identical boiling points. When a particular volume of X is shaken with a similar volume of Y , they form a liquid mixture Z . The average intermolecular forces in liquid Z are stronger than the average of the forces in X and the forces in Y . Which deductions from this information are correct? 1 The mixing of X and Y is exothermic. 2 The vapour pressure of liquid Z will be less than that of either liquid X or liquid Y at the same temperature. 3 The boiling point of liquid Z will be lower than that of either liquid X or liquid Y at the same pressure. A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only SAJC/2020/I/5 3 Which species contain a dative (co-ordinate) bond?
1 CO 2 CO 3 2− 3 N 2 H 4 4 N 2 O 4 A 2, 3 and 4 B 1 and 2 only C 1 and 4 only D 3 and 4 only SAJC/2020/I/18 4 Which bond angles are present in sulfonamide? 1 105° 2 107° 3 109.5° 4 120° A 2, 3 and 4 B 2 and 3 only
C 1 and 3 only D 1 only TJC/2020/I/7 5 Which of the following cannot be explained by hydrogen bonding? A The difference in the boiling points between water and ammonia. B The difference in volatility between pentan-2-ol and octan-2-ol. C The difference in boiling point between 2-nitrophenol and 4-nitrophenol. D The difference in the relative molecular mass of ethanoic acid molecules in benzene and in water. NYJC/2020/I/4 6 Element E has a high melting point of 1287 °C and conducts electricity. The chloride of E has a melting point of 399 o C, does not conduct electricity in solid or liquid state, and is soluble in benzene. Which of the following could be element E ? A Beryllium B Carbon C Copper D Lithium ACJC/2020/II/1c 7 (c) A diagonal relationship is said to exist between certain pairs of diagonally adjacent elements in the second and third Periods. The elements and their compounds in these pairs are observed to share similar properties. An example of such a pair is beryllium and aluminium. (i) Draw the dot-and-cross diagram for A l C l 3 and state the C l A l C l bond angle.
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Dot-and-cross diagram of A l C l 3 [1] Bond angle: ………………………………. [1] (ii) Unlike A l C l 3 which dimerises to form A l 2 C l 6 , BeC l 2 polymerises and exists as long chains in the solid state. Draw a section of one chain with three BeC l 2 monomers, showing clearly the bonding within the chain. [1] (iii) With a small amount of water, BeC l 2 hydrolyses in the same manner as A l C l 3 . Write an equation for the hydrolysis of BeC l 2 . DHS/2020/II/3d 8 (d) The bond angle in CO 2 is 180 º. The bond angle in SO 2 is approximately 120 º. Explain the difference in the two bond angles given above. [1] EJC/2020/II/1a-c 9 (a) Nitrogen can form a few hydrides such as NH 3 and N 2 H 4 . The boiling points of these two hydrides are given in Table 1.1. Table 1.1 compound boiling point / ºC NH 3 33 N 2 H 4 114 Provide two explanations for why N 2 H 4 has a higher boiling point than NH 3. [2]
(b) When NH 3 is reacted with BF 3 in the gaseous phase, a white solid of NH 3 BF 3 is formed. (i) Draw a dot-and-cross diagram to show the bonding within NH 3 BF 3 and state the shape about the nitrogen atom. [2] (ii) State the type of reaction that NH 3 has undergone with BF 3 , and explain why it is possible. [2] (c) Both NH 3 and PH 3 have trigonal pyramidal shape, but the bond angles in NH 3 are 107º while those in PH 3 are 94º. By considering the electronegativities of the central atoms, suggest why this is so. [2] HCI/2020/II/5b 10 (b) Sidewalks in many cities are paved with Noxer blocks, which are cement mortar coated with TiO 2 to a thickness of 5 to 7 mm. The photocatalytic properties of TiO 2 enables it to remove pollutants from the air, particularly nitrogen dioxide, NO 2 , and nitrogen monoxide, NO, both of which are radicals. (i) Draw a dot-and-cross diagram to show the bonding in NO 2 . [1] (ii) The bond angle in NO2 is experimentally observed to be 135 o . Apply the principles of the VSEPR theory to account for this observation. [2] NYJC/2020/II/1c 11 (c) Lead(II) ethanoate, Pb(CH 3 COO) 2 , also known as sugar of lead is a white crystalline solid which is soluble in water and has a sweet taste. Ancient Romans used sweeteners that contained lead(II) ethanoate to sweeten wine or preserve fruit. Lead(II) ethanoate is no longer used in the production of sweeteners because of its recognised toxicity. Draw simple diagrams to show how a water molecule can be attached to a lead(II) cation, and to an ethanoate anion. Label each diagram to show the type of interaction involved. [3]
TJC/2020/II/2a 12 (a) Boron and its compounds have many uses. Boron trichloride, BC l 3 can be used in the refining process of aluminium. Boric acid, H 3 BO 3 sometimes known as B(OH) 3 , is widely used in pharmaceutical and cosmetic industries. Boric acid and borate salts such as sodium tetraborate, NaB(OH) 4 , exist naturally in rocks, soil, plants and water. (i) With reference to the Valence Shell Electron Pair Repulsion Theory , explain the shape and bond angle with respect to the B atom in B(OH) 3 . [2] (ii) Draw the dot-and-cross diagrams for BC l 3 and [B(OH) 4 ] . Clearly indicate any co-ordinate (dative covalent) bonds present. [3] Table 2.1 gives the melting points for boron compounds. Table 2.1 Compound Melting point / °C Boron trichloride -107.3 Boric acid 170.9 Sodium tetraborate 741 (iii) With reference to structure and bonding, explain the difference in melting points of the three componds in Table 2.1. [2] TMJC/2020/II/1a-c 13 Oxygen is the third most abundant element in the universe and is responsible for the differences in structure of many inorganic compounds. (a) Table 1.1 shows information on some oxides W, X, Y and Z . Table 1.1 oxide melting point / C electrical conductivity when molten reaction in water W 1710 poor none X 2072 good none Y 1132 good exothermic Z 360 poor exothermic Based on the information in the Table 1.1, (i) Account for the melting point and electrical conductivity of W and X using structure and bonding. [2]
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(ii) State, with reasoning, the acid base nature of Y and Z relating to their structure. [2] Several vitamins and minerals contain oxygen as a major constituent. Compound A is a derivative of ascorbic acid found in Vitamin C. O O H OH O Compound A (b) Draw a labelled diagram to show all the orbital overlaps found between the C=C bond in compound A. [2] (c) Compound A may be used as a food additive due to its solubility in water. With the aid of a diagram, show why compound A is highly soluble in water. [1] ASRJC/2020/III/3a 14 Organic compounds are molecules that contain carbon atoms covalently bonded to hydrogen atoms. (a) The boiling points of some organic compounds are shown in Table 3.1. Table 3.1 compound formula M r boiling point / C ethylbenzene CH 2 CH 3 106.0 136 benzylamine CH 2 NH 2 107.0 185 phenylmethanol CH 2 OH 108.0 205 benzylchloride CH 2 C l 126.5 179 Suggest explanations for these differences. [3]
HCI/2020/III/1c 15 (c) Another area of interest is the study of how long coronaviruses can survive on surfaces. It was found that coronaviruses have a far shorter life span on copper metal than many other surfaces. Describe the structure and bonding present in copper metal. [2] HCI/2020/III/5b 16 (b) Alumina, A l 2 O 3 and silica, SiO 2 have very high melting points which make them good refractory materials to withstand the very high temperatures in industrial processes. Explain the high melting points of A l 2 O 3 and SiO 2 in terms of their structures and bondings. [3] YISHUN INNOVA JUNIOR COLLEGE 2021 JC2 H2 CHEMISTRY CHEMICAL BONDING (ADVANCED) ASRJC/2020/I/5 1 Molecular dimerisation can be described as the process in which two identical molecules combine to give a single product. Examples of dimers are: A l 2 C l 6 , N 2 O 4 and (CH 3 CO 2 H) 2 . Which of the following descriptions about the above dimers is incorrect ? A Hydrogen bonds hold the CH 3 CO 2 H molecules together in the dimer. B Each aluminium atom is surrounded by four chlorine atoms in A l 2 C l 6 . C All the nitrogen oxygen bonds in N 2 O 4 are of equal length. D A l 2 C l 6 is a planar molecule.
ASRJC/2020/I/6 2 Which of the following observations can be explained by intermolecular hydrogen bonding? 1 Ammonia (NH 3 ) has a higher boiling point than methane (CH 4 ). 2 Water has a lower density at 0 °C than at 25 °C. 3 Formation of H 3 O + from water. A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only TJC/2020/I/3 3 Tetrathionic acid, H 2 S 4 O 6 , has been used as an antidote in cyanide poisoning. In tetrathionic acid, the oxidation number of hydrogen is +1 and oxygen is 2. What are the oxidation numbers of the four sulfur atoms? S 1 S 2 S 3 S 4 A +5 0 0 +5 B +6 0 +0 +6 C +2 +2 +5 +5 D +2 +2 +6 +6 HO OH 1 2 3 4
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TMJC/2020/I/3 4 Which feature is present in each of the ions CO 3 2 , SO 3 2 , NO 3 and HCO 2 ? A all bond angles are 120 o B three sigma bonds C one dative covalent bond D eight lone pairs of electrons VJC/2020/I/3 5 What is the number of σ and π bonds in the molecule, (CN) 2 CC(CN) 2 ? σ π A 5 9 B 9 5 C 9 9 D 13 5 VJC/2020/I/4 6 Which species have the same shape as XeF 2 ? A C l 2 O B NO 2 C I Br 2 D SO 3 2 ACJC/2020/II/2c 7 Vapour pressure is defined as the pressure exerted by a vapour in equilibrium with its liquid in a closed system. Table 2.2 shows the vapour pressure of HF and HC l measured at 25 °C. Table 2.2 compound vapour pressure / kPa HF 122 HC l 4660 Give a reason for the higher vapour pressure of HC l . [1]
DHS/2020/II/3e 8 A van Arkel triangle can be used to predict the type of bonding such as ionic, metallic or covalent, present in a compound based on the electronegativities of the elements involved. The van Arkel triangle is a graph which explains the bonding type in terms of the average electronegativity of their constituent elements and differences in electronegativity. The electronegativity values of some elements are shown in Table 3.1. Table 3.1 element electronegativity aluminium 1.6 silicon 1.9 carbon 2.5 oxygen 3.6 sulfur 2.6 For example, the coordinates of SiO 2 would be (2.75, 1.7). (e) (i) Plot the position of CO 2 on the van Arkel triangle below. Label your point clearly. [1]
(ii) Point C on the van Arkel triangle corresponds to ionic bonding. State the types of bonding that corresponds to points A and B . [1] (iii) Compare the bonding in aluminium oxide, A l 2 O 3 , and aluminium sulfide, A l 2 S 3 by circling the correct option. A l 2 O 3 is less ionic equally ionic more ionic [1] EJC/2020/II/1c 9 Both NH 3 and PH 3 have trigonal pyramidal shape, but the bond angles in NH 3 are 107º while those in PH 3 are 94º. By considering the electronegativities of the central atoms, suggest why this is so. [2] HCI/2020/III/1b 10 (b) The transmission of COVID-19 may be mitigated by the use of hand sanitisers, frequent washing of hands with soap and water, or wearing of N95 masks. (i) The structure of the phospholipid particles that make up the lipid membrane of the virus is shown below in Fig. 1.2. Fig. 1.2 The alcohol content in hand sanitisers destroy the lipid membrane by initially forming hydrogen bonds with it. On Fig. 1.2 above , illustrate a hydrogen bond formed between an ethanol molecule and a phospholipid particle. [2] (ii) The structure of a soap particle is shown below.
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Describe the chemical interactions between the soap particle and the lipid membrane, and hence suggest how soap and water together break up the membrane of the virus. [2] (iii) Contrary to common belief, N95 masks do not work like filters. Instead the fibers that make up the fabric of the mask are permanently charged on the surface. This allows the fiber to capture dust in the air or droplets that contain the coronavirus. The surface of the fibers may be positively or negatively charged depending on the manufacturing method. An example of a strand of positively charged fiber is shown in Fig. 1.3. Fig. 1.3 Assuming that dust particles behave like non-polar simple molecules, describe the chemical interactions that form between the fiber and dust particles. Explain how these interactions arise. [2] TMJC/2020/III/1c 11 (c) (i) Draw a dot-and-cross diagram of a molecule of SO 3 , and hence state its shape. [1] (ii) Suggest a possible structure of S 3 O 9 . [1]