Topical Issues of Applied Chemistry - Assignment Example

Chemistry List all of the possible quantum numbers for a 3s electron. Answer: By using Sodium; Na: 2:8 Visible parts of electromagnetic spectrum are capable of effecting electrons from the surfaces of metals. (Photoelectric emissions). The electrons emitted are called photoelectrons- energy required to just eject an electron from the surface of a neutral material without setting that electron in motion is called work function. Metals with loosely held electrons (group I elements- Sodium, Potassium) have very low work functions. 2. Light with a wavelength of 220nm has been emitted from an atom. From what energy level could the electron fall if its final energy state was n=2 Answer: When fast moving electrons hit target metal, the inner core electrons in the atoms of the target metal get 'excited' and move from the first orbit (n=1) to say the second orbit (n=2) or third orbit (n=3). The electrons have moved from lower energy level to higher energy level. Hence from the question the electron falls from n=3 energy level 3. 10.0g-ice cube at 00C is added to 50.0g of water at 25.00C. Find the final temperature of the mixture. Answer: Ice = mass x latent heat of fusion of ice (h) = 10gx320=3200joules h=320joules /gram Water = MCT = 10x4.2x25=1050 Total heat supplied = 1050=3200=4250joules Therefore 60g x 4.2 x T = 4250 T= 4250/252 = 16.870C 4. Pure hydrogen peroxide (H2O2) is a bit thick in consistency and its boiling point is 1520C. The atoms in hydrogen peroxide are in the order HOOH in terms of intermolecular forces, why does hydrogen peroxide have different physical properties than water Answer: H2)2 structure is H-O-O-H H2O structure is The two behave like isomers (have same molecular formula but different structure) For isomers:- H2O2 - Has more bonds hence more intermolecular forces making it have higher boiling point since more energy is needed to break the bonds. 5. Which of the following has the highest boiling point; Hcl, Ar, F2. Explain in terms of intermolecular forces. Answer: HCL= 2.8.7 Ar=2.8.8 F2= 2.7 The forces of attraction between molecules increase with increase in size of the molecules. In Argon there is weak force of attraction between the atoms hence the low boiling point For Hcl, the chlorine gas alone has a boiling point of -350C. Therefore chlorine has a higher boiling point than fluorine, which is of the same group because of increase in size of molecule in chlorine. When chlorine reacts with hydrogen to from Hcl, a covalent bond is created. This bond is stronger than the forces of attraction between molecules and therefore require more energy to break hence higher boiling point. It should be noted that these are gases and gases have low boiling point. Hcl can form Hcl acid, which is a liquid with high boiling point. Therefore Hcl is has the highest boiling point followed by Argon and F2 has the lowest. 6. Which noble gas has the largest intermolecular forces and why Answer: Noble gases are elements in group VIII of the periodic table. They don't form molecule but exist as free atoms. e.g. Helium (He) 2 Neon (Ne) 2.8 Argon(Ar) 2.8.8 Krypton (Kr) 2.8.8.8 Xenon (Xe) 2.8.8.8.8 They all have eight electrons in their outermost energy level (full) hence have negligible tendency to gain or lose electrons. Therefore stable and non-reactive. Atomic radius increases down the group due to increase in number of energy levels. And weak forces of attraction between atoms. As the atomic size increase down the group there is increase in strength of attraction between atoms. Therefore Xenon has the largest intermolecular forces because it has a large atomic radius. In Xenon, the outermost electrons are relatively far from the positive nucleus, it can therefore take part in some reactions by loosing electrons. 7. Compare the phase diagram for water and carbon dioxide. Why would dry ice (solid Carbon dioxide) be unsuitable to use for a hockey rink Answer: Phase diagram of water Ice Liquid Vapor Phase diagram for Carbon dioxide Solid CO2 gaseous CO2 Hockey players on the rink will produce heat as a result of sliding friction. Dry ice is therefore dry ice is not suitable since when heated it sublimes (changes directly to gas) leaving no residual behind which is needed for sliding purposes by the players. On the other hand, when water is used, the friction makes the ice to melt to form liquid water. The heat is not enough to make the water vaporize. Therefore the liquid remains on the ice and when there is no more friction, the liquid changes into ice. This is what a hockey rink need for a superb sliding. 8. Using the following reaction: H2C=CH2+F2+H3C-CH3, H=-550kj Given that the carbon-carbon bond energy is 350kj/mol, the carbon=carbon bond is 615kj/mol, and the F=F bond energy is 155kj, find the carbon-fluorine bond energy. Answer: C-C bond energy =350kj/mol C=C " =615 " F-F " =155 " C-H " = 412 " C-F " = The total bond energies should be equal to -550kj 4(C-H) +1(C=C)+1(F-F)+6(C-H)+1(C-C)= -550kj When CH2=CH2 combines with F2 the product is CH2FCH2F In chemical reactions bonds are broken and new ones formed. In order to break bond energy must be supplied (endothermic) when atoms are formed; energy is released to the surrounding (exothermic). The overall energy change H= Exothermic +Endothermic From the equation, the product is. 4(C-H) + 1(C-C)+2(C-F) = 1(F-F) + 4(C-H)=1(C+C) = 1648 + 350+2(C-F) = 155+1648+615 1998 +2(C-F) = 2418 2(C-F)=2418-1998 2(C-F)=420 (C-F) =420/2 =210kj/mol 9. In this class several periodical trends were discussed. However, if one understands one of these trends the remaining trends can be easily predicted. Which trend can be used to predict the other trends Briefly describe how each of the other trends can be predicted Answer: Elements in the same period have the same number of occupied energy levels. Elements in the same group exhibit similar properties. Those across a period show a gradual change from metallic to non-metallic properties e.g. period 3 elements are Sodium, Magnesium, Aluminium, Silicon, Phosphorus, Sulphur, Chlorine and Argon. The period starts with reactive alkaline metal and ends with a relatively inert non-metallic noble gas. Silicon, which is at the middle, exhibits both metallic and non-metallic properties. The trends, which can be used to predict the others, is the physical state and appearance. They include: - melting point, boiling point, electrical/thermal conductivity, reaction with oxygen, water and acids. The physical state and appearance is defined by the electronic arrangement that define the ionic and atomic radius of an element. In all of the above, if one knows the ionic or atomic radius of an element then he can predict other periodical trends of that element. 10. The electron affinity for sulphur is more exothermic than that for oxygen. Explain. Answer: The two belong to group VI of the periodic table. They lack two electrons in their outermost energy level. O = 2.6 S = 2.8.6 Electron affinity is the ability to attract electrons. The positive nucleus is responsible for this attraction. Oxygen has 8 protons (positively charged) and Sulphur has 16 protons (positively charged) in the nucleus. The net nuclear charge for sulphur is more and therefore capable of attracting electrons than Oxygen. Since electrons are being forced into an atom, energy is given out which will be more in Sulphur than in Oxygen due to increased force of attraction. 11. Which of the following is the largest species PO2- Ln3+ Bi3- Po=Polonium Ln=Indium Bi=Bismuth Indium reacts by loosing 3 electrons to become an ion3+. Therefore the electrons lefts are held tightly by now the increased +ve charged nucleus, it also looses one energy level when it looses the three electrons hence among the three it's the smallest ion. As an atom, it has one energy level less. Polonium and Bismuth are in the same period. Hence have the same number of energy levels. Po reacts by gaining 2 electrons while Bismuth gains three electrons. The atomic radius decreases across the period due to increase in nuclear charge, which attracts outer electrons. Hence Bi atom is larger than Polonium atom. The electrons attracted enter the same energy level but since there is less protons in Bi, attracting three extra electrons, Bi ion is larger than Po ion. Therefore, the largest species is Bismuth Polonium is second largest and Indium the smallest. 12. Describe the hybridization of each carbon in the following molecule. CO2 What is the formal charge on each carbon Carbon has four valency electrons in its outermost energy level, which it can loose, or share when reacting. Oxygen atom lacks 2 electrons in its outermost energy level to become stable. Hence carbon being a non-metal and oxygen being a non-metal reacts by sharing electrons. The Carbon combines with two atoms of Oxygen to form the hybrid of CO2 The charge for Carbon is: The charge for any compound is zero The charge for oxygen is atom is usually -2 Therefore CO2 =0 C+(2(-2) =0 C+(-4) =0 C=4 Hence Carbon charge is +4 13. Predict the molecular shape -Give bonding angles -Describe (what specific orbital or hybrid orbital overlap. -Is the molecular polar or non-polar a) SiO2 Si = 2.8.4 O = 2.6 Linear shape, with bond angle O-Si-O being 1800 The two are non-metal hence covalent bond The outermost orbital overlap It's non-polar because the charges are neutralized b) All3 Al = 2.8.7 I = 2.8.18.18.7 Al -has 3 electrons in outermost energy level. Iodine lacks one hence:- Planar shape, one of I-Al-I bond angle is 1200 and the other 105o The bond is covalent It's non-polar since the charges are neutralized The outermost orbital does not overlap The bond angle is c) SbF5 Sb= Antimony has 5 electrons in outermost energy level. Fluorine has 7 electrons in outermost energy level Tetrahedral shape, the F-Sb-F bond angle is 109o Both are non-metals. Sb will donates its 5 electrons to fluorine hence the bond is ionic non polar The outermost orbital does not overlap d) CO32- Planar shape, one of O-C-O bond angle is 1200 and the other 105o Carbon has 4 electrons to share, which it shares with 2 oxygen atoms. The third one doesn't have electrons to fill its outer orbital. Hence the CO3 ion lacks 2 electrons therefore reacts by gaining those two electrons The ion is polar i.e. negatively charged. The outermost orbital overlap e) F3S-SF3 S = 2.8.6 F= 2.7 Fluorine has one electron to share with sulphur while sulphur has two to share. Therefore two sulphur atoms will share with four atoms of fluorine. The other two extra fluorine atoms share with the same sulphur. Is the same as F2S -SF2 molecule Hexagon shape, bond angles F-S-F being 900 The bond is covalent and non-polar The outermost orbital overlap f) H3C-CCl3 Hexagon shape, bond angle Cl-C-Cl and H-C-H being 900 There is covalent single bond between carbon atoms and chlorine atoms and covalent single bonds between carbon and hydrogen. Hence the bond is non-polar Outermost orbital overlaps g) H2C=CH2 Planar shape, (its completely flat), the H-C=C and H-C-H bond angles are 120oand 1050 respectively. There is covalent double bond between carbon atoms and single covalent bonds between carbon and hydrogen. Hence the bond is non-polar Outermost orbital overlaps Read More