General Chemistry Lab Report 8 PDF

Preview

Summary

experiment 8...

Description

General Chemistry 1 SCC201.641B Afsana Abdul Rahim Lab Partners: Lamia Hauter Experiment 8: Classification of Bonding in Solids 11/11/2017 Professor Shashikanth Ponnala

Objectives: 

To observe the physical properties of solids containing ionic, polar covalent, nonpolar covalent, network covalent, and metallic bonds.



To classify unknown solids into the above bonding categories based on their physical properties.

Materials: 

Bunsen burner



Lighter



Test tubes



Test tube clamp



50 mL beaker



Spatula



Distilled water



50:50 acetone/ hexane mixture



Potassium Chloride (KCl)



Urea



Benzophenone (C13H10O)



Silicon (Si)



Zinc (Zn)



4 Unknown solid samples

Methods:

Four known materials, KCl, Benzophenone, Silicon, Urea and a piece of Zinc and four unknown substances, labeled A through D, were tested and observed for their physical properties; appearance, melting point, solubility, and conductivity using appropriate techniques and results recorded (Table 1 and Table 2). 1. Appearance The substances were observed with the naked eye. Observations were recorded on data sheet. 2. Melting Point A small amount of each substance was transferred into a separately marked test tube. The test tubes were then heated, one by one, in a back and forth motion, over the Bunsen burner flame. 3. Solubility A small amount of each substance was transferred into a separately marked test tube. Three milliliters of water were added to each test tube and stirred with a glass stirring rod. If the substance dissolved in water, the result was recorded. If the solid didn’t dissolve in water, test was repeating with using 3 mL of acetone/hexane, a new sample, and a fresh test tube. 4. Solution Conductivity A small amount (as much as the water could dissolve) of each substance was transferred into a separately marked 50 mL beaker with 20 mL of distilled water. The solution conductivity probe was washed with distilled water to wash away any impurities before and after each run. The test was performed on all the solutions and the results were recorded. 5. Solid state conductivity The conductivity probes were placed on two different areas of the metal sample. The presence of the reading on the screen, indicative of electricity conduction, was recorded.

Data and Calculations:

OBSERVATIONS Solubility(Y/N) Classification

Appearance

Name

Melting

Conductivity Water

Acetone

Soluble

hexane -

Yes

Soluble

-

No

Insoluble

Soluble

-

Insoluble

Insolubl

-

Point Ionic Polar

KCl

white color

melting

Crystal,

Medium

white color

melting

Crystal,

Low

white color

melting

Shiny, black

High

grey color

melting

Solid, fixed

Not

Not

Not

shape, grey

tested

tested

tested

Benzophenone

covalent Network

High

Urea

covalent Non-polar

Crystal,

Silicon

Covalent Metallic

Zinc

(Y/N)

e Yes

Table 1: Physical properties of the known samples.

Unknow n

Appearance

Melting

OBSERVATIONS Solubility(Y/N) Water Acetone Conductivit

Point

Hexane

y

Classification

High

Insolubl

Insoluble

(Y/N) -

Network covalent

grey color Crystal,

melting High

e Soluble

-

Yes

Ionic

C

white color Crystal,

melting Low

Insolubl

Soluble

-

Non-polar

D

white color Crystal,

melting Medium

e Soluble

Yes

covalent Polar covalent

A

Shiny, black

B

-

white color melting Table 2: Physical properties of the unknown samples. Discussion:

All matter is made of atoms. Atoms are held together by chemical bonds. Bonds are the forces holding atoms together to form molecules and compounds. An atom is a positively charged nucleus surrounded by clouds of electrons at distinct principal energy levels or shells. The number of electrons in the outermost shell are called valance electrons. An atom is most stable when it’s outermost shell is full, i.e., when it has eight electrons in its outer shell, it is then said to have a full octet. To achieve this octet, and atom can lose, gain or share and electron with another atom. This is called chemical bonding. To complete the octet, some atoms attract the electrons from another atom more strongly than the others. This tendency to gain electrons or to strip electrons away from other atoms is called electronegativity (Jespersen). When an atom loses an electron, and transfers it to another atom, the two atoms form an ionic compound. Ionic compounds are solids at room temperature, brittle, and have high boiling and melting points. When there is a sharing of electron(s) between two atoms, the bond formed is called a covalent bond. When one atom is more electronegative than the other, the electrons are denser around the nucleus of the atom with higher electronegativity and the bond formed is called a polar covalent bond. When the two atoms are of equal electronegativity, the electron density is evenly distributed between the two nuclei and the atoms form what is called a nonpolar covalent bond (Jespersen). “Polar compounds are dissolvable in polar solvents like water but not in non-polar solvents such as hexane, their do not conduct electricity, and have high melting and boiling points” (Miller, pg. 68). On the other hand, polar compounds are “gasses or liquids at room temperature, have low milting and boiling points, and are insoluble in polar solvents” (Miller, pg. 68). Network covalent solids are formed when “every atom is bonded to all adjacent atoms by covalent bonds” (Miller, pg. 68). This results in a big macromolecule that has high melting and boiling points, is unreactive, and non-dissolvable in any solvent. Metallic

bonding is simply bonds between two atoms of same pure metal. This does not fit into any of the above-mentioned categories. Metals are shiny, malleable, ductile, and conduct heat and electricity (Miller, pg. 68). In accordance with the information discussed above, the properties of four known and four unknown materials were tested and observed. Gain of practical understanding of the concepts discussed was along with the ability to correctly determine the chemical bonds formed by different substances. This experiment was conducted to observe and learn about the physical properties of solids with ionic, polar covalent, non-polar covalent, network covalent and metallic bonds. Ionic compound Potassium Chloride (KCl), non-polar compound (benzophenone), polar compound (Urea), network covalent compound (Silicon), and metallic zinc were tested and observed for their physical properties; appearance, melting point, solubility, and conductivity using appropriate techniques. The knowledge gained was then used to deduce and determine the nature of four unknowns, A through D. Unknown A was determined to be a network covalent compound, unknown B to be ionic compound, unknown C as non-polar covalent, and unknown D was determined to be a polar covalent compound. Experimental errors and precautions taken: 

The Conductivity probe was washed with distilled water to wash away any impurities before and after each run.



The conductivity of distilled water was measured as a negative control.



The glassware was washed with soap and water and then rinsed off with distilled water to minimize the contamination.



All chemical and agent names were checked by each lab partner before using to ensure correct materials being used.



Careful attention was paid in observing for melting points and conductivity.

Conclusion: Unknown A, a shiny, black grey colored powder, was found to have a high melting point, did not conduct electricity, and did not dissolve in either water or the acetone-hexane mixture. It was thus determined to be substance with network covalent bonds. Crystal, white colored sample B was determined to be an ionic compound as it dissolved in water, conducted electricity and had a high boiling point. Sample C, crystal, white color substance, had a low melting point, was soluble in the acetone-hexane mixture and did not conduct electricity. This, it was determined to be a non-polar covalent compound. Unknown D, a white crystalline substance, was deduced to be a polar covalent compound owing to its medium melting point, soluble nature in water and inability to conduct electricity. References: Jespersen, Neil. "Chemistry: Barron's College Review." Barron's Educational Series, Incorporated, 28 Apr. 1997. Web. 09 Sept. 2016. Miller, D. (2013). Measurement and Significant Figures. In SCC201 General Chemistry Laboratory Manual (pp. 23-24). Dubuque: Kendal Hunt. Print....