Background Information s5

Background Information The chemical and physical properties of a substance can be categorized into two groups: intensive and extensive. "Extensive" properties are ones that depend upon on the amount of a substance. For example, mass and volume are all extensive properties -- the more of a substance you have, the larger the value of that property.

"Intensive" properties, however, do not depend upon the amount of a substance. Boiling point, melting point, and density are all examples of such properties. No matter how much water one is working with, its boiling point remains 100C. Because intensive properties are not dependent upon the volume of a sample, they can be used to identify unknown substances.

In this lab you will choose from a selection of unknown solids and liquids and measure some of their intensive properties. You will then compare your findings to known literature values of solids and liquids, which will be provided, and use this information to identify the samples from among the following compounds:

Table of Solid Compounds

(D = density in g/mL, Sol = solubility in g/100mL H₂O, MP = melting pointing degrees C, BP = boiling point in degrees C)

AgNO₃, Silver Nitrate (D=35, Sol=235, MP=212, BP=227)

C₁₅H₂₄O, BHT (D=1.05, Sol=0, MP=71, BP=265)

C₆H₈O₆, Ascorbic Acid (D=1.7, Sol=40, MP=168, BP=347)

CaCO₃, Calcium Carbonate (D=2.71, Sol=0, MP=1330, BP=4727)

CaSO₄, Calcium Sulfate (D=2.96, Sol=0.21, MP=1193, BP=1460) CoCl₂, Cobalt Chloride (D=3.36, Sol=56.2, MP=740, BP=1049)

Zn(NO₃)₂, Zinc Nitrate (D=2.0, Sol=120.26, MP=110, BP=131)

Table of Liquid Compounds

(D = density in g/mL, BP = boiling point in degrees C)

C₂H₄O₂, Acetic Acid (D=1.05, BP=117.9)

C₂H₃N, Acetonitrile (D=0.79, BP=81.6)

C₆H₁₂, Cyclohexane (D=0.78, BP=80.7)

C₅H₁₁N, Cyclopentylamine (D=0.86, BP=107.0)

C₂H₆O, Ethanol (D=0.79, BP=78.3)

Procedure 1

1. The Chemicals shelf contains six unknown solids labeled S1 through S6. Select an unknown solid and record its number. Perform the following tests on this solid.

2. Measure the solubility of the solid in water:

NOTE: Some of these solids release a lot of heat when dissolved in water. If you don't give the test tube time to cool down a little between additions of solid, you may even see the water boil a little. This does not change the results of this test. (a) Take a test tube from the Glassware shelf and place it on the workbench.

(b) Add 10 mL of water to the test tube.

(c) Add the solid in increments of 1 gram until the solid appears at the bottom of the test tube.

(d) Give a qualitative score for the solubility of the solid as follows:

* If the solid appears in the water after 1 gram is added, then the solid is not soluble.

* If you can add 5g or more of the solid and all of it dissolves, then the solid is very soluble.

* If the solubility is somewhere in between these two conditions, then the solid is slightly soluble.

3. Measure the density of the solid:

If the solid is even slightly soluble in water, then there is no way measure its density in this lab. However, if the solid substance is not soluble in water, you can measure its density using the "displacement of water" method as follows:

(a) Take a graduated cylinder from the Glassware shelf and place it on the workbench.

(b) Add 20 mL of water to the graduated cylinder.

(c) Take a balance from the Tools shelf and drop it on the graduated cylinder to measure its mass.

(d) Add 10g of the solid substance to the graduated cylinder and record the solid's total mass as well as the total volume in the graduated cylinder as shown in the Data window for the "liquid/solid volume".

(e) The density of the solid substance is its mass (the total mass minus the mass of the cylinder and water) divided by the solid's volume (the total volume minus the water volume).

4. Measure the melting point of the solid:

(a) Take a clean test tube from the Glassware shelf and place it on the workbench.

(b) Add 5g of the solid to the test tube.

(c) Take a thermometer from the Tools shelf and attach it to the test tube.

(d) Take a heating plate from the Tools shelf and place it on the workbench.

(e) Open the Properties window and click on the heating plate. In the Properties window turn the heating plate on and turn the dial to approximately 250W.

(f) Take the heating plate and drop it onto the test tube.

(g) Open the Data window to help you determine when the solid is melting. Once the solid begins to melt, the temperature remains constant. The Data window will show that both solid and liquid are present. Record the melting point. If the temperature reaches several hundred degrees C and the solid has still not melted, stop the test and record the melting point as greater than the highest temperature that was displayed on the thermometer.

Procedure 2

1. The Chemicals shelf contains five unknown liquids labeled L1 through L5. (Click the arrow to scroll across the Chemicals shelf). Select an unknown liquid and record its number. Perform the following procedures on this unknown liquid.

2. Measure the density of the liquid:

(a) Take a graduated cylinder from the Glassware shelf and place it on the workbench.

(b) Take a balance from the Tools shelf and drop it on the graduated cylinder. Record its mass.

(c) Add 10 mL of the liquid to the graduated cylinder. Record the total mass and the volume of the liquid as shown in the Data window.

(d) Calculate the mass of the liquid (the difference between the total mass of the graduated cylinder plus the liquid and the mass of the empty graduated cylinder).

(e) Calculate the density of the liquid by dividing its mass by its volume (Density is recorded in g/mL).

3. Measure the boiling point of the liquid:

(a) Take a clean test tube from the Glassware shelf and place it on the workbench.

(b) Add 5 mL of the liquid to the test tube.

(c) Take a thermometer from the Tools shelf and drop it on the test tube.

(d) Take a heating plate from the Tools shelf and place it on the workbench. Open the Properties window and click on the heating plate. In the Properties window turn on the heating plate and turn the dial to 250W.

(e) Take the heating plate and drop it onto the test tube.

(f) Once the liquid begins boiling, its temperature will be constant and you will see vapors rising out of the test tube. The data window will show the moles of the liquid decreasing. Record this temperature as the boiling point.

Assignment 1 (from procedure 1)

1. Record the number of the unknown solid you selected.

2. Record the three intensive properties of the solid substance - solubility in water, density and melting point.

3. Identify the unknown solid from the chart of solid substances in the Background section of the lab manual. My answer in red: Also wanted to ask how much solid is made when added to the water is it's taken out of the 20 mL or if it's the 20 mL AND the 10 mL of what the substance is.

Solid 1 - Takes 6 g to form a solid - slightly soluble Calculations for density - Cylinder with 20 mL of H2O - 107.470 g Cylinder with 20 mL of H2O and 10 g of S1 -117.470 g Volume of H20 - 20 mL Volume of H2O and S1 - 23.92 mL Melting Point - Higher than 271 degrees Celsius which is the highest the thermometer will go.

Solid 2 - Takes 4 grams to form a solid - slightly soluble Calculations for density - Cylinder with 20 mL of H2O - 107.470 g Cylinder with 20 mL of H2O and 10 g of S2 - 117.470 g Volume of H2O - 20 mL Volume of H2O and S2 - 27.06 mL Melting Point - 168.5 degrees Celsius

Solid 3 - Takes 8 g to form nothing- VERY SOLUBLE Calculations for density - Cylinder with 20 mL of H2O - 107.470 g Cylinder with 20 mL of H2O and 10 g of S3 - 117.470 g Volume of H2O - 20 mL Volume of H2O and S3 - 26.25 mL Melting Point - 110 degrees Celsius

Solid 4 Takes 1 g to make a solid - NOT SOLUBLE Calculations for density - Cylinder with 20 mL of H2O - 107.470 g Cylinder with 20 mL of H2O and 10 g of S4 - 117.470 g Volume of H2O - 20 mL Volume of H2O and S4 - 29.52 mL Melting Point - 71 degrees Celsius

Solid 5 - Takes 8 g to form nothing - VERY SOLUBLE Calculations for density - Cylinder with 20 mL of H2O - 107.470 g Cylinder with 20 mL of H2O and 10 g of S5 - 117.470 g Volume of H2O - 20 mL Volume of H2O and S5 - 22.87 mL Melting Point - 212 degrees Celsius

Solid 6 - Takes 1 g to form a solid - NOT SOLUBLE! Calculations for density - Cylinder with 20 mL of H2O - 107.470 g Cylinder with 20 mL of H2O and 10 g of S6 - 117.470 g Volume of H2O - 20 mL Volume of H2O and S6 - 23.69 mL Melting Point - Higher than 271 degrees Celsius which is the highest the thermometer will go. Assignment 1 (from procedure 2)

1. Record the number of the unknown liquid you selected.

2. Record the 2 intensive properties of the liquid substance - density and boiling point.

3. Identify the unknown liquid from the chart of liquid substances in the Background section of the lab manual.

My answer in red:

Liquid 1 - Calculations for Density - Empty Cylinder - 87.470 g Cylinder with 10 mL of L1 - 96.070 mL Liquid Volume of all - 10 mL Melting Point - 107.00 degrees Celsius

Liquid 2 Calculations for Density - Empty Cylinder - 87.470 g Cylinder with 10 mL of L2 - 95.370 mL Liquid Volume of all - 10 mL Melting Point - 78.30 degrees Celsius