Distinguishing Ionic and Covalent Compounds

When ionically bonded substances dissolve in water, = the ions separate from each other enabling electric current to flow through the solution. An ionic compound can usually be identified by its high melting point. As a result of this high melting point, ionic compounds are crystall= ine solids at room temperature.

A covalent compound is made of molecules. Weak intermolecular forces hold molecules of covalent materials together. The weak forces are responsible f= or their relatively low melting points. Covalent compounds are usually liquids= or gases at room temperature. With a few important exceptions, covalent compou= nds do not conduct electricity when dissolved in water, when they dissolve in w= ater at all.

In this laboratory activity you will:

a. use a conductivity tester to determine which substances produce ions in aqueous solution;

b. examine various compounds to determine their state;

c. research the literature to determine the melting points of these compounds;

d. predict whether the compounds are more likely to be ionic or covalent.

OBJECTIVES

• Measure conductivity of solutions= .

• Observe the states of compounds.<= o:p>

• Research the melting temperatures= of compounds.

• Relate properties to bond type.

HYPOTHESIS:
MATERIALS<= span style=3D'font-size:16.5pt;font-family:Arial'>

Conductivity tester

9 V battery

thin-stem pipet

apron

goggles

Handbook of Chemistry and Physics

96-well microplate <= i>

96-well template

KCl- potassium chloride

NH₄₌Cl – Ammonium chloride

CH₃₌COCH₃ – Acetone

C_2<=
/span>H_5<=
/span>OH – Ethyl alcohol

C_3<=
/span>H_5<=
/span>(OH)₃ – Glycerine

HCl – Hydrochloric Acid

KI- Potasium iodide<= o:p>

CH₃₌OH – Methyl alcohol

NaCl – Sodium chloride

H_2<=
/span>SO₄₌ – Sulfuric Acid

HOH – Dihydrogen monoxide- Distilled water

C₁₂H₂₂O₁₁-Sucrose

PROCEDURE

Part 1: Testing Solutions for Conductivity<= /o:p>

CAUTION: Many of the chemicals you will use are toxic. Both hydrochloric acid (HCl) and sulfuric acid (H₂SO_4<=
/sub>) are very corrosive. Avoid contact with skin and eyes. Follow proper chemical hygiene procedures. Wash your hands thoroughly after completing this laboratory activity.

1. Place 10 drops of solution 1 in well A1 of your = microplate. Note the name and formula of the solute o= n the observation table. Place 10 drops of solution 2 in well A2 of your microplate. Note the name and formula of the solute o= n the observation table. Continue i= n like manner until each solution available to you has been dispensed into your microplate. (Do not contaminate the pipet).

2. Insert the electrodes of the tester into a well = that contains a solution. The electrodes must not touch each other.

3. Note the relative conductivity of the solution by looking at the brightness of the LED.

4. Record your observation on the observation table= . Use the following code:

SCALE	RED LED<= /span>	GREEN LED	CONDUCTIVITY
0=	OFF	OFF	LOW OR NONE
1=	DIM	OFF	LOW
2=	MEDIUM	OFF	MEDIUM
3=	BRIGHT	DIM	HIGH
4=	VERY BRIGHT	MEDIUM	VERY HIGH

5. Test all the solutions. Wash the leads with dist= illed water after each test.

Record the results.

Part 2: Observing the Physical State

1. Inspect the flasks containing each of the undissolved substances.

2. In the corresponding box of observation table, r= ecord for each compound “s” if the compound is a crystalline solid, “l” if the material is liquid, and “g” if the subst= ance is a gas.

Part 3: Finding the Melting Point

1. Use a reference source, such as the Handbook = of Chemistry and Physics, to find the melting temperatures of all the substances used in this activity.

2. In the corresponding box of your observation tab= le record the melting temperature (in degrees Celsius) for each compound.<= /span>

DATA AND OBSERVATIONS

Refer to the instructions in step 4 of Part 1, s= tep 2 of Part 2, and step 2 of Part 3 to record your observations and information about each substance in the following table. Also, indicate your predictions about bond type.<= o:p>

SUBSTANCE	CONDUCITIVITY	STATE	MELTING PT (^oC)	PREDICTED BOND TYPE
KCl- potassium chloride
NH₄Cl – Ammonium chloride<= span style=3D'font-size:16.0pt'>
CH₃COCH₃ – Acetone
C₂H₅OH – Ethyl alcohol
C₃H₅(OH)₃ – Glycerine
HCl – Hydrochloric Acid
KI- Potasium iodid= e
CH₃OH – Methyl alcohol
NaCl – Sodium chloride
H₂SO₄ – Sulfuric Acid
HOH – Distilled water<= /p>
C₁₂H₂₂O₁₁-Sucrose

ANALYSIS

1. BASED ON YOUR OBSERVATIONS, LIST THE SUBSTANCES THAT ARE IONICALLY BONDED.<= o:p>

2. BASED ON YOUR OBSERVATIONS, LIST THE SUBSTANCES THAT ARE COVALENTLY BONDED.=

CONCLUSIONS

1. WHAT PROPERTIES ARE USEFUL TO ESTABLISH THE BOND PATTERN THAT EXISTS IN A COMPOUND?

2. WRITE A GENERALIZED STATEMENT THAT RELATES ION FORMATION IN WATER, ELECTRICAL CONDUCTIVITY OF SOLUTIONS, AND BONDING.

EXTENSION AND APPLICATION

THE COMPOUND HYDROGEN CHLORIDE (HCl) IS COVALENTLY = BONDED AND YET CONDUCTS ELECTRICITY WHEN DISSOLVED IN WATER. BASED ON THE EQUATION

HCl(g) =3D H₂O(l) --> H₃O⁺(aq) + Cl^-(aq)<= o:p>

EXPLAIN WHY SOME COVALENT COMPOUNDS CONDUCT ELECTRICITY.

12 well template<= /p>

1 KCl- potassium ch= loride

2 NH₄Cl – Ammonium chloride=

3 CH₃COCH₃ – Acetone

4 C₂H_=
5OH – Ethyl alcohol

5 C₃H_=
5(OH)₃ – Glycerine=

6 HCl – Hydro= chloric Acid

7 KI- Potasium iodide

8 CH₃OH – Methyl alcohol

9 NaCl – Sodi= um chloride

10 H₂SO₄ – Sulfuric Acid

11 HOH – Dihydrogen monoxide- Distilled water

12 C₁₂H₂₂O₁₁-Sucrose