CHEMISTRY 20 Formative Assessment Intermolecular Forces RECORD ALL RESPONSES IN THIS QUESTION BOOK STUDENTS ARE TO KEEP QUESTION BOOK AND ANSWER KEY AS PART OF THEIR STUDY MATERIALS
1. The high surface tension of water is due to the small size of water molecules high kinetic energy of water molecules covalent bonds in water molecules hydrogen bonding in water molecules 2. The density of ice is less than the density of water because ice is lighter than water the same mass occupies a larger volume the molecules in ice are more closely packed none of the above 3. Consider the following list of bonds and attractive forces. 1. dipole - dipole 2. ionic 3. covalent 4. London 5. hydrogen bonding When the above list is ordered from strongest to weakest, on a single bond/attraction basis only, the sequence is E. 12345 54321 34125 23514 43152 4. When two atoms experience a greater attraction towards each other, the bond becomes weaker and energy is released weaker and energy is absorbed stronger and energy is released stronger and energy is absorbed Chemistry 20 Assessment: Intermolecular Forces Page 1
5. Use the graph showing the boiling points of different hydrogen compound to answer the question. Boiling Point ( C) The Boiling Points of Hydrogen Compounds for the Halogens 20 0 20 40 60 80 100 120 HF HCl HBr HI Using energy concepts, the best explanation for the high boiling point of HF is that the forces of attraction between HF molecules are 110425 smaller so a greater endothermic change is needed greater so a greater endothermic change is needed smaller so a greater exothermic change is needed greater so a greater exothermic change is needed 6. A student wanted to find the relationship between molecular polarity and strength of the intermolecular bonds. The choices of chemicals were to be selected from the following list. Lot 1: C 2 H 6, C 2 H 5 OH, and C 2 H 5 Cl Lot 2: CH 4, C 2 H 6, and C 3 H 8 Lot 3: SiH 4, PH 3, and H 2 S Lot 4: LiF, NaF, and KF The best choice of chemicals to use is Lot 1 Lot 2 Lot 3 Lot 4 7. Argon is a noble gas that freezes to a solid at -189 What type of bonding will form between atoms of argon in the solid state? London force hydrogen bonding dipole-dipole intramolecular Chemistry 20 Assessment: Intermolecular Forces Page 2
8. Which one of the compounds listed below has only London (dispersion) forces between molecules? C 4 H 9 OH K 2 Cr 2 O 7 PH 3 CH 3 F 9. Water (H 2 O) boils at 100 C and hydrogen sulfide (H 2 S) boils at -61 Which statement explains this difference in boiling point? The total number of electrons is greater in H 2 S than in H 2 O. There are stronger dipole-dipole attractions between H 2 O molecules. There are greater London dispersion forces between H 2 O molecules. The molar mass of H 2 S is greater than the molar mass of H 2 O. 10. Consider the following diagram of a portion of a DNA strand. What type of bond or attractive force is indicated by X? ionic covalent london force hydrogen bonding Chemistry 20 Assessment: Intermolecular Forces Page 3
11. A student was given data concerning the boiling points of hydrogen compounds in the fourth period of the periodic table. Compound GeH 4 AsH 3 H 2 Se HBr Boiling Point ( C) 89 55 42 67 The best hypothesis the student could make to explain the drop in boiling points between H 2 Se and HBr is that fewer intermolecular bonds can form with HBr compared to H 2 Se because of its shape HBr has too many lone pairs of electrons to make strong intermolecular bonds the H 2 Se intramolecular bonds are more polar than for HBr hydrogen bonding occurs with H 2 Se but not with HBr 12. Natural gas may be separated into CH 4, C 2 H 6, C 3 H 8, and C 4 H 10 by cooling in large cooling towers. This is possible because as the size of the molecule gets larger, the boiling point increases due to stronger intermolecular forces increases due to stronger intramolecular forces decreases due to stronger intermolecular forces decreases due to stronger intramolecular forces 13. In order to determine whether a set of liquids were polar or non-polar, a student suggested the following procedures. 1. Pour a small amount of oil into each liquid. 2. Measure the boiling points of each liquid. 3. Collect data determining the miscibility of each liquid with water. 4. Observe the effect of holding a charged rod near a thin stream of each liquid. The procedure which would yield useful data are 1, 2, and 3 1, 2, and 4 1, 3, and 4 2, 3, and 4 Chemistry 20 Assessment: Intermolecular Forces Page 4
14. The density of water is higher than the density of alcohol (C 2 H 5 OH) even though the molar mass of alcohol is about 2.5 times that of water. From this information, one could predict that water is bent alcohol is more polar than water alcohol has no hydrogen bonding water has stronger intermolecular forces of attraction 15. Intermolecular forces of attraction occur when a cation is attracted to an anion an electron in an atom is attracted to its own nucleus two electrons are unevenly shared between two atoms the electrons in one molecule are attracted to the nucleus in another molecule 16. Use the table showing the boiling points of various alcohols to answer the question. Compound CH 3 OH C 2 H 5 OH C 3 H 7 OH C 4 H 9 OH C 5 H 11 OH Boiling Point ( C) 65 78 97 117 137 Based on the data, one could conclude that polarity of the molecule increases as the size of the molecule gets larger intermolecular forces increase strength as the molecule gets larger boiling point increases as the molecule becomes more polar hydrogen bonding gets stronger as the molecule gets larger Chemistry 20 Assessment: Intermolecular Forces Page 5
17. Chlorofluorocarbons (CFCs) include a variety of compounds some of which are shown. When CFCs were originally made, they were used extensively in refrigerators and air conditioners because they easily evaporate. However, when it was discovered that they destroyed the ozone layer, their use was discontinued and alternatives were sought. Based on this information, any environmentally safe alternative should have similar characteristics such as being non-polar with strong intermolecular forces non-polar with weak intermolecular forces polar with strong intermolecular forces polar with weak intermolecular forces 18. Diamonds are extremely hard and have high melting points because hydrogen bonding is very strong each molecule has a polar and a non-polar part to it the ions in the crystal lattice are very strongly attracted to each other they contain very few intermolecular forces of attraction and many covalent bonds 19. Which of the following chemicals is likely to exhibit evidence of London forces, dipole-dipole forces and hydrogen bonding? CH 3 OH H 2 CH 4 H 2 S 20. Scientists have developed theories to explain intermolecular forces. The name for the weak attraction between molecules, believed to be caused by the random movement of electrons in an atom or molecule producing temporary partial charges is dipole-dipole force hydrogen bonding London force network bonding Chemistry 20 Assessment: Intermolecular Forces Page 6
21. The relatively strong forces between molecules containing F H, O H, and N H bonds are attributed to dipole-dipole force hydrogen bonding ionic bonding London force 22. In order to explain the bending of a liquid stream by a charged rod, chemists use the theoretical concept of covalent bonds hydrogen bonds London dispersion forces polar molecules 23. Hydrogen bonds are weaker than i but are stronger than ii. The above statement is completed by: i ii covalent bonds ionic bonds london forces covalent bonds covalent bonds dipole-dipole force ionic bonds covalent bonds 24. What is broken when liquid water is decomposed into hydrogen and oxygen gases? intermolecular forces intramolecular bonds both intermolecular forces and intramolecular bonds neither intermolecular forces nor intramolecular bonds Chemistry 20 Assessment: Intermolecular Forces Page 7
25. Researchers at the University of Alberta are using state of the art technology to study London Forces is certain substances. The subject of their research is most likely involving interactions between water molecules. interactions between atoms of neon. bonding of atoms in molecules of sodium chloride. bonding of atoms in molecules of hydrogen chloride gas. 26. Water exists as a liquid at room temperature, whereas hydrogen chloride exists as a gas. Which of the following statements is false? Intermolecular forces can be important in affecting the nature of a substance. Hydrogen bonding occurs in water. Intermolecular forces between water molecules keep it in the liquid state at room temperature. Both water and hydrogen chloride experience hydrogen bonding. You have completed the assessment. Chemistry 20 Assessment: Intermolecular Forces Page 8
Chemistry 20 Intermolecular Forces Formative Test Blueprint Highlight each question number that was incorrect on your test (Note that a question may apply to more than one concept). The concept(s) with the most questions highlighted is/are the one(s) that need to be reviewed thoroughly. This is part of your responsibility as a student in this course. Questions Concept Outcome 3, 4, 15, 18, 24 7, 8, 9, 12, 16, 17, 20, 25 Intermolecular vs. intramolecular London force Explain intermolecular forces, London (dispersion) forces, dipole-dipole forces and hydrogen bonding. Explain intermolecular forces, London (dispersion) forces, dipole-dipole forces and hydrogen bonding. relate properties of substances (e.g., melting and boiling points, enthalpies of fusion and vaporization) to the predicted intermolecular bonding in the substances 6, 11, 13, 22 Dipole-dipole Explain intermolecular forces, London (dispersion) forces, dipole-dipole forces and hydrogen bonding. determine the polarity of a molecule based on simple structural shapes and unequal charge distribution 1, 2, 5, 10, 14, 19, 21, 23, 26 Hydrogen bond Explain intermolecular forces, London (dispersion) forces, dipole-dipole forces and hydrogen bonding. Chemistry 20 Lesson 1-10 Page 1 2012 T. de Bruin
Chemistry 20 Intermolecular Forces formative test answer key Question Answer Explanation 1 D Surface tension is a property of the surface of a liquid that allows it to resist an external force. This property is caused by cohesion (sticking together) of similar molecules, and is responsible for many of the behaviors of liquids.it is revealed, for example, in the floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects (e.g. water striders) to run on the water surface. 2 B Hydrogen bonding between water molecules in solid water forces the water molecules into a tetrahedral structure that occupies more space than hydrogen bonding between water molecules in the liquid phase. 3 D In general, the greater the difference in electronegativity, the stronger the bond. Since ionic and covalent bonding involves the valence electrons, intramolecular bonding is stronger than intermolecular bonding. Ionic bonding has a greater elecgtronegativity difference that covalent making it stronger than covalent. Evidence for this is that all ionic compounds are solid at room temperature and have very high melting points. 4 C The greater then attraction between two atoms, the stronger the bond. Bond formation always involves energy release. 5 B Hydrogen bonding between HF molecules is much stronger than the dipole-dipole between molecules in the other compounds. This results in a much high boiling point for HF 6 A If you are looking at molecular polarity vs. strength, you need to have similar sized molecules otherwise differences in London force become a problem. 7 A Argon is a monoatomic atom and thus can only have London Force. 8 C You must pick the Nonpolar molecule. 9 B Water has hydrogen bonding (a special form of dipole-dipole) whereas hydrogen sulphide does not. 10 D DNA strands are held together by hydrogen bonding. 11 A A v-shaped polar molecule has more intermolecular attractions than a linear molecule. 12 A All the molecules are nonploar and thus only have London Force. As the molecules get larger, the total London Force increases, increasing the boiling point of the compound. 13 C Oil is Nonpolar and will not mix with a polar liquid, such as water. A charged rod will attract or repel a thin stream of a polar liquid. 14 D The stronger intermolecular forces between the water molecules and its small size allow water molecules to pack together more efficiently, resulting in a higher density. 15 D Intermolecular means between two separate molecules. 16 B All of the compounds have hydrogen bonding, so that is not important in the comparison. What should be realized is that boiling point increases with increasing molecular size. 17 B All the molecules are small and nonpolar and thus have only weak London force. 18 D Diamond is covalent network of carbon atoms. It is nonpolar, has no hydrogen bonding and no ions present. Every carbon atom is bonded to four other carbon atoms. 19 A Hydrogen bonding is a very specific case intermolecular bond, so just look for the molecule that contains an O-H, N-H or H-F bond. 20 C London Force is due to temporary instantaneous dipoles. 21 B These bonds are the requirements of hydrogen bonding 22 D A charged rod will affect a polar substance. 23 C A hydrogen bond is the strongest of the intermolecular bonds. All intermolecular bonding is weaker than intramolecular bonding. 24 B Intramolecular bonds hold atoms together. 25 B London Forces are studied using nonpolar substances. 26 D Water has hydrogen bonding whereas hydrogen chloride does not. Chemistry 20 Lesson 1-10 Page 2 2012 T. de Bruin