Question 6

  • Bond angle

    Boron Hydride Trigonal Planar E. P. G. Trigonal Planar Molecular C Ophardt. c Geometry 2003

    95.84 рт о 104.450 н

Question 33

  • Erlenmeyer flask

    الاوس/ و0س ـم ا 'WOOS الأن

  • Volumetric flask

    C:\\8E425445\\852EE352-60A8-43EB-A33B-8042A84EBC3A\_files\\image162.png

Question 40

  • Strong + Strong --> Weak + Weak

    Conjugate acid-base pair CH3COOH + H20 H30 + CH3COO Weak acid Weak base Strong acid Strong base Conjugate acid-base pair

Question 42

  • The order of Boiling point: HF > HI > HBr > HCl

    Now, it must intuitively be certain that more the number of electrons then more the amount of London dispersion forces. This is true; the more the electrons the atom has, the stronger the amount of London dispersion forces and hence greater the attraction. The greater the attraction, the more energy you have to put to break the bonds apart. If you see the trend above, Iodine has more electrons than Bromine hence has a greater attraction force between its atoms hence has a greater boiling point. Similar for the case of Bromine and Chlorine. Hence, you can place the order of their boiling points as: Hence, HI > HBr > HCI

    However, you notice an anomaly; HF should have a boiling point below that of HCI, then how come it has the highest boiling point? After all, Fluorine has lesser electrons than Chlorine and hence should have lesser London dispersion forces between them. This is true but there is another reason behind that: Hydrogen Bonding. Picture fluorine; it sits right above the other halogens. It belongs to Period 2 which does not have many shells to itself. Since it has so less electrons, it must be very small. In fact, it is. Fluorine is so small yet it has a really high charge density. Why does it have a high charge density? Its outer electrons are not as shielded by the inner electrons and it has 7 outer electrons. (read more on: Shielding effect t) These seven electrons face tremendous attraction from its nucleus hence it 'shrinks'. This causes the fluorine atom to shrink hence its charge density increases. As such, it can attract other electrons to itself when it is covalently bonded to another element. This property is called electronegativity. Now, this effect is very strong in case of smaller atoms like Fluorine. When fluorine is bonded with Hydrogen, it attracts certain portion of the bonded electrons to itself. This effect is strong enough that it stays like that permanently but since the electrons are always moving, it must mean that the electrons love to spend more 'time' with fluorine than hydrogen. When this happens, a permanent dipole is created since the electrons are not evenly distributed. As such, two charges are created in the two ends: ö+ and 5—

    Electron Density Distribution

    As you know, charges attract each other. Since the fluorine atom is so electronegative, this charge difference must be very great. Since the difference is so great, this attraction effect is very strong. As such, these molecules of HF start to 'clump' together (since they attract each other) in what is known as hydrogen bonding. Hydrogen bonding is the attraction between highly electronegative atoms with hydrogen bonded covalently. This attraction is stronger than London dispersion forces hence the presence of a hydrogen bond significantly raises the boiling point of the compound. Hence, HF has the highest boiling point amongst the four compounds.

Question 65

  • Calorimetry

    qcal AT water bomb calorimeter adiabatic walls system

Question 71

x o-bonds It-bonds

1 0 bond H H H H N-Z-N 1 0 bond 2 11 bonds 1 0 bond 1 11 bond

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