Understanding Atomic Structure and Chemical Reactions in
School
Zewail University of Science and Technology**We aren't endorsed by this school
Course
CHEM 102
Subject
Chemistry
Date
Dec 11, 2024
Pages
22
Uploaded by hend_montaseb
Question 1 Partially correct Mark 3.60 out of 6.00 ¥ Hag question Atomic structure a) Which of the following ions would be least deflected by an electromagnetic field in a mass spectrometer? (1 mark) 43 Sc* 42 Ca* 435c** 42 Ca?*x Mark 0.00 out of 10.00 The correct answer is: 43 Sc* b) Which of these atoms has the largest number of neutrons? (1 mark) “He 3H SHev ALi Mark 10.00 out of 10.00 The correct answer is: He €) Which of these contains the greatest number of atoms? (1 mark) 137 mg of iodine (1) 1.54x10"* kg of sodium (Na)v* 1.70x10"* kg of carbon dioxide (CO,) 81.0 mg of water (H,0) Mark 10.00 out of 10.00 The correct answer is: 1.54x10 kg of sodium (Na)
d) An atom of element X has two more protons and two more neutrons than an atom of P135l Give the symbol, including mass number and atomic number, for this atom of X. (1 mark) Symbol:{ a ‘v Mass number:‘ 855 ‘x Atomic number:| 17 |v e) Bromine exists as two isotopes 7?Br and 8'Br in the ratio 1:1. When a sample is analysed in a mass spectrometer three peaks were observed. The m/z values of each of the peaks are 158, 160 and 162. What is the ratio between the peaks? (1 mark) 1:2:11v 2:1:2 L 111 Mark 10.00 out of 10.00 The correct answer is: 1:2:1 f) You can assume that bromine exists as two isotopes, and that hydrogen and carbon exist as one isotope each. How many molecular ion peaks will be shown in the mass spectrum of C4 HgBr4 where there is a +1 charge? (1 mark) Number of peaks: l 3 ‘x
Question 2 Partially correct Mark 4.00 out of 6.00 Y EHag question Moles, gases and solutions a) What is the pressure of 3 moles of gas in a 520 dm? container at a standard temperature? The gas constant is 8.314) mol™' K. (1 mark) 14 300 kPa 1199 Pa 14.3 kPav’ 413 Pa Mark 10.00 out of 10.00 The correct answer is: 14.3 kPa Magnesium phosphate reacts with aqueous sulfuric acid to produce phosphoric acid and magnesium sulfate as shown in the equation. The reaction is only partially balanced. Mga(POy); + 3H,504 — H3POy + MgSOy b) Balance the chemical reaction by adding the correct coefficients to the products. | 2 H;Pofl[ 3 L« MgSO, (1 mark) ) Work out the relative molecular mass (M,) of magnesium phosphate. Give your answer to 3 significant figures. (1 mark) M, (Mg3(POy),) = l 263 v d) A student carried out this reaction and produced 6.82g of magnesium sulfate. Calculate the moles of magnesium sulfate produced, given M, (MgS0y) = 120.4. Give your answer to 3 significant figures. (1 mark) Moles of MgSO, =| 0.0566 + moles
e) Asecond student repeated the experiment and used 0.0316 moles of magnesium phosphate. Determine the moles of phosphoric acid produced in this reaction. Give your answer to 3 significant figures. (1 mark) Moles of H3PO, = [ 0.095 ‘x moles ) Athird student carried out the experiment and made 0.0316 moles of phosphoric acid in a total volume of 42.0 cm?. Calculate the concentration, in mol dm3, of phosphoric acid in this solution. Give your answer to 3 significant figures. (1 mark) Concentration of H3P04=‘ 0.000 Jx mol dm-3
Question 3 Partially correct Mark 3.00 out of 6.00 " Hlag Question Molecular & empirical formulae a) Empirical and molecular formulas provide information about the constituents of a compound. i) Anempirical formula is [ the ratio of different atoms of an element in a compound. * ‘« (1 mark) ii) A molecular formula is ‘ the number of each type of atom of an element in a compound. # ‘v (1 mark) b) An alcohol Z was analysed and shows that it contains 39.3% by mass of carbon and 8.2% by mass of hydrogen. The remainder was oxygen. i) Complete the table using the information about alcohol Z and your periodic table. (2 marks) Carbon Oxygen Hydrogen Percentage by o [ 525 ‘v 5 mass L Relative atomic [ 12 L’ ‘ 15 ‘x l 5 ‘x mass ii) Determine the empirical formula of Z. Empmcalformula=‘ C2H502 ‘x (U mark) iii) Determine the molecular formula given that the relative molecular mass of Z is 122. Molecular formula =[ ]x (1 mark)
Question 4 Electron arrangements Correct a) Which change requires the largest amount of energy? (1 mark) Mark 6.00 out of 6,00 N(g) = N'(g) + e ¥ Flag He* (g) = He*(g) + e'v question Li (g) — Li"(g) + & Mg" (8) — Mg*(g) + e Mark 10.00 out of 10.00 The correct answer is: He' (g) = He‘”(g) +e b) The Pauli Exclusion principle states that: (1 mark) Different sub-levels contain different numbers of orbitals The lowest energy sub-levels are occupied first Only two electrons occupy any orbitalv Electrons remain unpaired if possible Mark 10.00 out of 10.00 The correct answer is: Only two electrons occupy any orbital €) Which atom and ion have the following electronic configurations? (1 mark) Atom: 152 2s? 2p? lon: 1s2 252 2p5 Nand N*v Band B3* Aland AP* P and P> Mark 10.00 out of 10.00
d) e) Electrons enter the 4s sub-level before the 3d sub-level because: The 4s orbital is spherical There is only one 4s orbital and there are five 3d orbitals The 3d orbitals have a lower energy The 4s orbital has a lower energyv” Mark 10.00 out of 10.00 The correct answer is: The 4s orbital has a lower energy (1 mark) The total number of electrons that can be accommodated in 4p orbitals is: 14 10 2 6v Mark 10.00 out of 10.00 The correct answer is: 6 (1 mark)
f) Select the correct spin diagram for the electron arrangement of phosphorous. mark) 1s [ 2s | 2p* | 2p¥ | 2p* | 3s | 3p* | 3p¥ | 3p* | 4s A o |n 1 noft 1 T 1 1 1s | 2s | 2p* | 2pY | 2p* | 3s | 3p* | 3p¥ | 3p* B 1 2! T ! 2 il 1 T T 1s | 2s | 2p* | 2p¥ | 2p* | 3s | 3p* | 3p¥ | 3p* c i1 Tt 1 1 " 1 1 T 1 1s | 2s | 2p* | 2p¥ | 2p* | 3s | 3p* | 3pY | 3p? D 1 1 1 T T Tl T 1 T & Bv D A Mark 10.00 out of 10.00 The correct answer is: B
Question 5 Correct Mark 6.00 out of 6.00 ¥ Hag question lonization energies a) Which change requires the largest amount of energy? (1 mark) N (g) = N*(g) + e Mg* (g) — Mg*'(g) + & He' (g) = He?'(g) +ev Li@—~Li'g) +e Mark 10.00 out of 10.00 The correct answer is: He' (g) = HCP'(g) +e b) Which one of the following explains why boron has a lower first ionisation energy than beryllium? ) (1 mark) (1 mark) In boron the 2p electron occupies a higher energy level than a 2s electronv” In beryllium all the electrons are paired in full sub-shells A beryllium atom has fewer protons than a boron atom Aboron atom is smaller than a beryllium atom Mark 10.00 out of 10.00 The correct answer is: In boron the 2p electron occupies a higher energy level than a 2s electron Which of the following require less energy than the first ionisation energy of oxygen? 0'(g) — 0*'(g) + & S~ S'g +ev N(g) = N'(g) + & F(g) = F'(g) +e Mark 10.00 out of 10.00
d) Inwhich one of the following pairs is the first ionisation energy of element Y greater than that of element X? (1 mark) electronic configuration of | electronic configuration element X of element Y A. 1st 152 B. 1522s? 1s22s22p! [ 152252 2p? 152252 9p4 D. 1s2 252 2p 1s22522p0 357 D B AV C Mark 10.00 out of 10.00 The correct answer is: A e) Which one of the following lists the first ionisation energies (in k] mol™") of the elements Mg, Al, Si, P and S in this order? (1 mark) 577, 786, 1060, 1000, 1260 786, 1060, 1000, 1260, 1520 736, 577, 786, 1060, 1000v 1060, 1000, 1260, 1520, 418 Mark 10.00 out of 10.00
e) Which one of the following lists the first ionisation energies (in k| mol™") of the elements Mg, Al, Si, P and S in this order? (1 mark) 577,786, 1060, 1000, 1260 786, 1060, 1000, 1260, 1520 736, 577, 786, 1060, 1000v 1060, 1000, 1260, 1520, 418 Mark 10.00 out of 10.00 The correct answer is: 736, 577, 786, 1060, 1000 f) Which of the following is the electronic configuration of an element with a maximum oxidation state +5? (1 mark) 1s2 252 2p° 152 252 2p® 352 3p! 152252 2p% 352 3p3v 152 252 2p©3s2 3pb 3d7 4s? Mark 10.00 out of 10.00 The correct answer is: 1s? 252 2p®3s2 3p?
Question 6 Partially correct Mark 5.00 out of 6.00 ¥ EHag question Bonding a) Complete transfer of one or more electrons between atoms is part of forming: a mark) Covalent bonds lonic bondsv* Coordinate bonds Metallic bonds Mark 10.00 out of 10.00 The correct answer is: lonic bonds b) Metals lose electrons to form a lattice structure and become Cationsv Alkalis Anions Non-metals Mark 10.00 out of 10.00 The correct answer is: Cations (1 mark) €) Metals usually have high melting temperatures and boiling temperatures because there are: (1 mark) Strong attractions between the delocalized electrons Strong attractions between the ions and the delocalized electronsv Strong intermolecular forces Strong attractions between the ions Mark 10.00 out of 10.00
d) Which of these molecules has a coordinate bond? (1 mark) NH3 H,0 H30'v oH Mark 10.00 out of 10.00 The correct answer is: H30*
e) Identify the features labelled A - D, in the dot and cross diagram of the molecule below. (2 marks) “ < A =‘ Double covalent bond B=‘ Lone pair of electrons ~ # ‘v “ x C =‘ Single ionic bond « x D =‘ Hydrogen bond
Question 7 Intermolecular bonding i3 a) Which of the following molecules is polar? (1 mark) Mark 6.00 out. 0f 6.00 Ammonia, NHzv" ¥ flag Silicon tetrachloride, SiCly question Boron trifluoride, BF; Carbon dioxide, CO, Mark 10.00 out of 10.00 The correct answer is: Ammonia, NH3 b) What are the strongest forces between molecules of hydrogen fluoride, HF? (1 mark) Van der Waals forces Dipole-dipole forces lonic interactions Hydrogen bondsv Mark 10.00 out of 10.00 The correct answer is: Hydrogen bonds
€) Two organic compounds with similar relative molecular masses are shown below. 1Y Thd aea kesea Hu H H H H Ethanol Propane. i) State the strongest type of intermolecular force in each compound. (2 marks) Strongest intermolecular force in ethanol =| hydrogen bond < ‘v Strongest intermolecular force in propane =[ Van der Waals force 2 |v ii) Complete the statement. (2 marks) v because it has The compound with the highest boiling point is{ ethanol ¢ « Wwhich arethe| strongest & ‘v intermolecular force and take the most energy to break. hydrogen bonds s
Question 8 Partially correct Mark 5.00 out of 6.00 ¥ Eag Question Shapes of molecules a) Choose the shape of the phosphine molecule (1 mark) Octahedral Trigonal pyramidalv Trigonal bipyramidal Trigonal planar Mark 10.00 out of 10.00 The correct answer is: Trigonal pyramidal
b) Which of the following combinations best describes the shape of the ions/molecules below? (1 mark) *—0o A B [ 54 D 1 2 3 4 A NH; cor co, H,0 B. cor NH3 co, H,0 c NH; cor H,0 co, D. cor NH3 H,0 o, B A cv D Mark 10.00 out of 10.00 The correct answer is: C
€) Ammonia, NHs, forms a coordinate bond with H' ions to form the ammonium ion, NH,* i) What part of the ammonia molecule allows it to form coordinate bonds? (1 mark) The unpaired electron on the nitrogen atom The unpaired electron on a hydrogen atom The lone pair on the nitrogen atomv” The lone pair on a hydrogen atom Mark 10.00 out of 10.00 The correct answer is: The lone pair on the nitrogen atom i) State the shape of an ammonium ion, NH,* (1 mark) Tetrahedralv’ Trigonal planar Trigonal pyramidal square planar Mark 10.00 out of 10.00 The correct answer is: Tetrahedral iii) The ammonium ion has[ four % ‘-/ pairs of bonding electrons which arrange 3+ (% (2 marks) themselves as| close as possible/maximum repulsion
Question 9 Energetics feily et a) Dinitrogen oxide is formed when ammonia is oxidised according to the following equation. Mark 4.00 out o 12.00 2NHs(g) + 205(8) — NO() + 3H0() V Flag Use the standard enthalpies of formation in the table below to calculate a value for the Question standard enthalpy change of this reaction. (1 mark) NHs(g) Oa(8) N20(g) Hz0(8) AH'¢, k) mol! 46 0 +82 286 -868 kJ mol”! +868 kJ mol”! +684 k| mol % -684 k) mol”! Mark 0.00 out of 10.00 The correct answer is: -684 k| mol!
b) An equation for the complete combustion of ethanol is shown. CH3CH,0H(g) + 30(g) — 2CO,(g) + 3H20(g) C-H c-0 O-H c=0 =0 c-C Bond enthalpy / kJ 412 360 463 805 496 346 mol™! Calculate: i) The total enthalpy of the reactants =‘ 0.00405 ]x k) mol”! (1 mark) ii) The total enthalpy of the products ={ ‘ %k mol” (1 mark) iii) The overall enthalpy of the reaction =‘ ‘x k) mol! (1 mark) c) 0.3gof butanol heated 160g of water from 19.5°C to 30.4°C i) Calculate the moles of butanol that were combusted. Give your answer to 3 significant figures. Moles of butanol =‘ lx ii) Which equation is used for calculating the enthalpy change in this reaction? AH=cmATv AH=AT/mc AH=cAT/m mAH=cAT Mark 10.00 out of 10.00 The correct answer is: AH=cmAT
iii) Give the value of AT in this experiment. AT = [ 10.9 ‘v °C iv) Calculate the enthalpy, in kiloJoules (k) of combustion of 0.3g of butanol (C4H100) where the specific heat capacity of water, ¢, is 4.18 ] g K. Give your answer to 4 significant figures. AH =‘ ‘x k] v) Calculate the standard enthalpy of combustion, AH, for butanol. Give your answer as a whole number. AH, =‘ - ¢ 1« ‘ :x k) mol”! vi) This reaction is an example of a neutralisation reaction. a reduction reaction. an exothermic reaction. v an endothermic reaction. Mark 10.00 out of 10.00 The correct answer is: an exothermic reaction.