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purpleclam363Lv1

29 Mar 2020

Hydrazine (H₂NNH₂), hydrogen peroxide (HOOH), and water (H₂O) all have exceptionally high surface tensions compared with other substances of comparable molecular weights. (a) Draw the Lewis structures for these three compounds. (b) What structural property do these substances have in common, and how might that account for the high surface tensions?

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Reid WolffLv2

27 May 2020

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Chemistry 162 Lab Activity

Introduction Water has an amazing ability to adhere (stick) toitself and to other substances. Hydrogen bonds form when hydrogenatoms covalently bonded to nitrogen (N), oxygen (O), or fluorine(F) in the form of covalent compounds such as ammonia (NH3), water(H2O) and hydrogen fluoride gas (HF). In these molecules, thehydrogen atoms do not pull as strongly on the shared electrons asthe N, O, or F atoms. Therefore, the molecules are polar; thehydrogen atoms become positively charged and are able to formhydrogen bonds to negative ions or negatively charged parts ofother molecules (such as the N, O, and F atoms that becomenegatively charged in these compounds). Hydrogen bonds are not truebonds like covalent bonds or ionic bonds. Hydrogen bonds areattractions of electrostatic force caused by the difference incharge between slightly positive hydrogen ions and other, slightlynegative ions. These attractions are much weaker than true ionic orcovalent bonds, but they are strong enough to result in someinteresting properties.

In the case of water, hydrogen bonds form between neighboringhydrogen and oxygen atoms of adjacent water molecules. Theattraction between individual water molecules creates a bond knownas a hydrogen bond (Fig. 1).
Fig. 1: Hydrogen bonds shown as the dotted lines between watermolecules.
Cohesion Molecules of pure substances are attracted to themselves.This sticking together of like substances is called cohesion.Depending on how attracted molecules of the same substance are toone another, the substance will be more or less cohesive. Hydrogenbonds cause water to be exceptionally attracted to each other.Therefore, water is very cohesive.
Adhesion Adhesion is similar to cohesion, but it involves unlike(i.e. different) substances sticking together. Water is veryadhesive; it sticks well to a variety of different substances.Water sticks to other things for the same reason it sticks toitself â because it is polar so it is attracted to substances thathave charges. In this lab activity, you will be asked to use thematerials and procedures provided to explore the properties ofwater that involve both cohesion and adhesion. Be sure to writedown your observations and results as you progress. sults as youprogress.

Fig. 1

Hydrogen bonds shown as the dotted

lines between water molecules.

Part 1:

Exploring Water

Procedure

How many drops of water can you fit on the surface of a pennywithout the water spilling over?

Predict how many drops of water will fit on a penny. Record yourprediction.

Use the plastic pipette to drop water on the surface of a penny.Drop car

efully and slowly to fit as

many drops as possible on the penny. Count each drop until thewater spills over the side of the

penny and record your results.

Compare your results to those of your classmates. Record therange and calculate the average

number

of drops that fit on a penny.

Add more drops to the penny, without letting the water spillover. Carefully observe and draw the

water on the penny.

Record

a hypothesis for the behavior of water that you observed, usingthe language of cohesion

and adhesion

in relation to the water and the penny.

Record your results and

thinking in your notebook.

Can you

disturb

the water on the penny without spilling it?

dd drops of water to the penny, until the water is almost readyto spill over.

Predict what will

happen when you insert a toothpick into the surface of the waterpiled on the

penny. Record your prediction.

Insert the

toothpick

and carefully observe the surface of the water.

Try inserting the

toothpick

in various ways. Observe the surface of the water.

Pay special attention to

the water surface where the skewer enters the water.

Record your observations and draw what you see.

Repeat

these

procedures using a paper clip and the metal clip part of abinder clip. Try to indent the

pile of water as much as p

ossible without spilling it.

Record your observations and dra

w what you see, paying careful

attention to the surface of the

water.

Record

a hypothesis for the behavior of water that you observed usingthe language of cohesion

and adhesion in relation to the

toothpick

, the paperclip, the binder clip, and the water.

Record your results and

thinking in your notebook.would you please answer the questionfor me . Thanks

1.Structural isomer refers to organic compound that have the same molecular formula but different structure (bonding pattern is different). This problem is designed to guide you to explore structure isomer.

(a)Go ahead and write Lewis structure for butane (C₄H₁₀). You may draw four C atoms connect straight as like in train.

(b)In the above structure, four C atoms are connected straight in a line. If you move one C atom to the side (like 3 C atoms in a line, one connected to the middle C atom), after you supply all the H atoms to make all the C atoms saturated with 4-bonds each. Will the molecular formula for your structure drawn be different from butane?

( c) Structures you obtained in (a) and (b) are an example of structural isomers. What kind of name we can give to structure in (b) so we can differentiate it from structure in (a)?

2.Alkane is the basic building block of organic compound. We often write alkane chain as a group R. On this basic chain, we can add different functional group, like âOH for alcohol, -COOH for carboxylic acid.

(a)Methanol refers to CH₃OH. Ethanol refers to CH₃CH₂OH. Draw the Lewis structure for these two compounds.

(b) If you have a straight alkane chain, where does âOH group can be attached? How do you name it so you can know where âOH group is attached?

3. Give the Lewis structure for CH₃COOH. Give its systematic name and common name.

4. Ester refers to two alkane chains connected through a single O atom. Write the Lewis structure for this simplest kind of ester: CH₃OCH₃. Find its name and some common use.

5. Benzene molecular formula is C₆H₆. The six carbon atoms are connected to form a ring (hexagon). Draw the Lewis structure for C₆H₆. Do you think the six bond lengths between C-C atoms should be same or not according to your drawn Lewis structure?

The following table presents the solubilities of several gases in water at 25 °C under a total pressure of gas and water vapor of 1 atm. (a) What volume of CH₄(g) under standard conditions of temperature and pressure is contained in 4.0 L of a saturated solution at 25 °C? (b) Explain the variation in solubility among the hydrocarbons listed (the first three compounds), based on their molecular structures and intermolecular forces. (c) Compare the solubilities of O₂, N₂, and NO, and account for the variations based on molecular structures and intermolecular forces. (d) Account for the much larger values observed for H₂S and SO₂ as compared with the other gases listed. (e) Find several pairs of substances with the same or nearly the same molecular masses (for example, C₂H₄ and N₂), and use intermolecular interactions to explain the differences in their solubilities.

The corresponding volume is

b) All three molecules are nonpolar and form very weak interactions with the water molecules. The solubility of ethane is higher that the solubility of methane as ethane is more massive molecule and forms stronger dispersion forces with the water molecule. Ethene is the most soluble gas as the C atoms in ethene are planar, sp² hybridized, and there are π electrons in the orbitals perpendicular to the carbon atoms. π electrons are less tightly held by the nucleus than σ electrons, allowing the dipole of water molecule to disturb the electron density more easily, leading to stronger dipole-induced dipole interactions.

c) The molecular weight is similar for three gases. O₂ and N₂ are nonpolar gases, but more water molecules surround O₂ as it is larger molecule. The O–O bond (double bond) is longer than N–N bond (triple bond). The water attracts nonpolar gases through the weak dipole-induced dipole interactions. NO is the most soluble gas as it has polar bond and the overall molecule is polar as it is linear structure. Water dissolves it via stronger dipole-dipole interactions.

d) H₂S is capable to form weak hydrogen bonds with the water molecules, and these interactions are much stronger than dipole-dipole and dispersion forces. SO₂ is even more soluble in water as it reacts with the water forming H₂SO₃. The very high values for the solubility of gas are the sign that the gas chemically reacts with the solvent.

d) N₂ and CH₄. Solubility of N₂ is lower as N₂ is smaller molecule than CH₄ and less hydrated.

NO and C₂H₆ have similar water solubility. NO is more soluble than ethane and form dipole-dipole interactions, but the dispersion forces of ethane and water are stronger than dispersion forces between NO and water as ethane is larger, more polarizable molecule. The sum of all intermolecular interactions is similar for these two gases, leading to the similar water solubility.

NO and O₂. NO is more soluble as it is polar molecule and form stronger intermolecular forces with polar solvent molecules compared to nonpolar O₂ molecule.