CHEM 1210 Study Guide - Midterm Guide: Volumetric Flask, Calcium Sulfate, Sodium Sulfate

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28 Sep 2018

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Ohio State University

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Chemistry

Course

CHEM 1210

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All

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CHEM 1210 Full Course Notes

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Document Summary

In both cases the water slowly begins to evaporate. One mole of nacl(s) and one mole agcl(s) are added to different beakers of water. After waiting overnight all of the nacl has dissolved and some of agcl(s) sits at the bottom of the beaker. At the particle- level, what do these aqueous solutions of. Which of these is correctly characterized: ca(no3)2 strong electrolyte. Poor solubility: hno3 weak electrolyte. Poor solubility: kch3oo weak electrolyte. A particle- level representation is given for a strong base with a low concentration of oh- (aq) and a ph of 9. Water molecules have been omitted. All of these (i, ii, and iii) are correct: none of these are correct. 50 ml nitric acid in a 1. 00 l volumetric flask and then filling to the line with water. Calculate the molarity of the final solution. A 50 ml of 0. 1 m hno3 and a 50 ml of 0. 2 m naoh are combined.

Related Questions

Introduction: The first section of your lab report will be the introduction. In this paragraph or paragraphs, you are to provide information to the reader so that he or she can understand the purpose of the experiment.

Purpose: This should be a concise statement about the labâs objective.Background: Include a brief summary of the topic you are investigating. Include any information that would be necessary to understand the stated purpose.Findings: State the major result for your experiment.

Procedure: This is the second section in your lab report. This section includes information that the reader would need to repeat your experimental procedure. Do not include any observations or results in this section.

Some questions that you should ask yourself to complete this section include the following. What chemicals did you use? What equipment? How much of each chemical did you use? How long did you perform a step within the procedure?

Observations and Results: This is the third section of your report. In this section, you will communicate what you observed during the experiment. The results section is typically dominated by calculations, tables, and figures. In your tables, label the axes of any graphs

Discussion: This is the fourth section of your report. In this section, you will explain, analyze, and interpret your observations and results. Additionally, you will draw conclusions based on your existing knowledge. This is also where you demonstrate your understanding of the experiment by construing the significance or meaning of the results.

Conclusion: This is the last section of your report and is separate from the discussion section. Within a few sentences, provide a concluding statement about the results of your laboratory. In a scientific publication, this section summarizes the significant aspects and results and identifies implications for future study.

Part 1: Create Standard Curve

For your standard curve, you need to make up 100 ml of each of the following concentrations of salt.

100 parts per million (ppm)500 ppm1,000 ppm5,000 ppm10,000 ppm

Note: 1 ppm = 1 mg / 1 L.

Step 1: Obtain five 250 mL beakers and label them 1â5.

Use the Equipment selection from the toolbar.Select 250 mL beaker from the dropdown menu.Right-click on beaker and select Label.Label the first beaker 1, and write 100 ppm in the Annotated Note area of the dialog box.Repeat with four more beakers, labeling them with numbers 2â5 and the appropriate concentration in ppm.

Step 2: Add 100 mL of water to each beaker.

Right-click on the beaker and select Water.Select Volume Level of 100 mL.Select Room Temperature water.Click OK.

Step 3: Add the appropriate amount of NaCl to each beaker.

Right-click on beaker; select Chemicals.Select Sodium Chloride (NaCl), the last one in the list.Change units to mg. Be sure to do this or your experiment will not turn out correctly.Add the appropriate amount of NaCl to each beaker (see the table below).To mix, right-click on the beaker and select Stirring Rod.

Beaker Number

NaCl Concentration (ppm)

Amount of NaCl to add (mg)

100

500

1,000

100

5,000

500

10,000

1,000

Step 4: Measure the conductivity of standard NaCl solutions.

Select the conductivity meter from the Equipment menu. Right-click on the conductivity meter and select Conductivity Meter Mode and then ATC mode.Place the conductivity meter in the first beaker.Select both the conductivity meter and the beaker by drawing your cursor over both objects. You have selected both items when you have a single dotted-line box around both. Go to Arrange on the toolbar and select Combine. (Alternatively, right-click and select Combine.) This action actually places the conductivity meter in the beaker.Record the value on the conductivity meter.Measure the conductivity of Beakers 2â5 and record your results.

Part 2: Determine Conductivity of Unknown NaCl Solutions

Step 1: Obtain three 250 mL beakers and label them 1Uâ3U.

Use the Equipment selection from the Toolbar.Select 250 mL beaker from the dropdown menu.Right-click on the beaker and select Label.Label the first beaker 1U.Repeat with two more beakers, labeling them 2U and 3U.

Step 2: Add 100 mL of Unknown Brine Solution 1 to Beaker 1U.

Right-click on Beaker 1U.Select the Chemicals menu.Select 100 ml of Unknown Brine Solution 1U.Click Okay.

Step 3: Repeat Step 2 with Unknown Brine Solutions 2 and 3.

Add 100 ml of Unknown Brine Solution 2 to a beaker labeled 2U.Add 100 ml of Unknown Brine Solution 3 to a beaker labeled 3U.

Step 4: Measure the conductivity of Unknown Brine Solution 1.

Select the conductivity meter from the Equipment menu. Right-click on the conductivity meter, and select Conductivity Meter Mode and then ATC mode.Place the conductivity meter in Beaker 1U.Select both the conductivity meter and the beaker by drawing your cursor over both objects. You have selected both items when you have a single dotted-line box around both. Go to Arrange on the toolbar and select Combine. (Alternatively, right-click and select Combine.) This action actually places the conductivity meter in the beaker.Record the value on the conductivity meter.

Step 5: Measure the conductivity of Unknown Brine Solutions 2 and 3.

Repeat Step 4 with Beakers 2U and 3U.Record the values on the conductivity meter.

Part 3: Make Standard Curve

Now, you need to make a graph with the data from your five known samples of NaCl (Tubes 1â5). You will use this graph (called a standard curve) to determine the concentration of the unknown samples of NaCl (Tubes 1Uâ3U).

Step 1: Using Excel or another graphing program, make a graph of NaCl concentration (ppm) versus conductivity (ÂµS).

When making graphs, you want to have the independent variable on the x-axis and the dependent variable on the y-axis.In this experiment, you know the concentration of NaCl in the first five samples, so concentration is the independent variable and is on the x-axis. You donât know the conductivityâit depends on the concentration. So, conductivity is your dependent variable and is on the y-axis.If you are using Excel, be sure to select a scatter graph. Your graph should be a straight line; if your graph is not a straight line, you may have plotted it incorrectly.Be sure to give your graph a title and label the axes. A good title might be "The Dependence of Conductivity on NaCl Concentration."A sample graph is shown below.

Step 2: Follow the steps below created your graph

Arrange your standard curve data (Tubes 1â5) in two columns. The first one should be NaCl Concentration (ppm), and the second one is Conductivity (ÂµS) as shown below.

Salt Concentration (ppm)

Conductivity (ÂµS)

2.022

2.107

2.213

3.029

100

4.002

Highlight and select all data, including the names of each column.Go to the Insert menu in Excel. Under Charts, select Scatter. Select Scatter with Smooth Lines and Markers. Your graph will pop up.Under Chart Tools, go to Layout.Select Axis Titles, Primary Horizontal Axis Title, Title Below Axis and type in Salt Concentration (ppm).Repeat for the Primary Vertical Axis Title, Rotated Title and type in Conductivity (ÂµS). If you canât find the Âµ symbol, just use uS for your units.Under Chart Tools, go to Gridlines.Under Primary Horizontal Axis, select Major and Minor Gridlines.Repeat for the Primary Vertical Axis..Your graph should be plotted on a line graph.

Part 4: Determine Concentrations of Unknown NaCl Solutions

Now you will use your graph to determine the concentration of the three unknown solutions (1Uâ3U).

Find the conductivity value on the y-axis and go over to the line at that value. Then find the corresponding value on the x-axis. For example, if Sample 1U had a conductivity of 3.25 uS, the concentration of NaCl would be about 60 ppm. Nark it on a line graph

Record the approximate NaCl concentration for each unknown (1Uâ3U).

STEP 3: Write Your Lab Report

Follow the directions above to write your lab report. Write your lab report in Microsoft Word.

In your lab report, include the following information.

In the results section, include all your data and a copy of your graph.

Answer the following questions in the discussion section.

What were the concentrations of the three unknown brine solutions (Samples 1U, 2U, and 3U)?Why do you have to adjust the conductivity meter to a standard temperature? (25 Â°C)Why did the conductivity readings increase as the concentration of NaCl increased?Youâve probably heard of hard water. What makes water hard? How could you use a conductivity meter to determine the hardness of water samples?Calculate the molarity of each of the standard NaCl solutions. Be sure to show your work!Remember the following.The molecular weight of NaCl is 58.44 g / mole.1 ppm = 1 mg / 1 L, so 100 ppm = 100 mg / L, and so forth.Molarity = moles / L.

The Behavior of Substances in Water

Part 1:

Ammonia, NH₃, is a weak electrolyte. It forms ions in solution by reacting with water molecules to form the ammonium ion and hydroxide ion. Write the balanced chemical reaction for this process, including state symbols.
From everyday experience, you are probably aware that table sugar (sucrose), C₁₂H₂₂O₁₁, is soluble in water. When sucrose dissolves in water, it doesn’t form ions through any reaction with water. It just dissolves without forming ions, so it is a nonelectrolyte. Write the chemical equation for the dissolving of sucrose in water.
Both NH₃ and C₁₂H₂₂O₁₁ are soluble molecular compounds, yet they behave differently in an aqueous solution. Briefly explain why one is a weak electrolyte and the other is a nonelectrolyte.
Hydrochloric acid, HCl, is a molecular compound that is a strong electrolyte. Write the chemical reaction of HCl with water.
Compare the ammonia reaction with that of hydrochloric acid. Why are both of these substances considered electrolytes?
Explain why HCl is a strong electrolyte and ammonia is a weak electrolyte.
Classify each of the following substances as either ionic or molecular:

KCl
NH₃
CO₂
MgBr₂
HCl
Ca(OH)₂
PbS
HC₂H₃O₂

For those compounds above that, you classified as ionic, use the solubility rules to determine which are soluble.
The majority of ionic substances are solids at room temperature. Describe what you would observe if you placed a soluble ionic compound and an insoluble ionic compound in separate beakers of water.
Write the chemical equation(s), including state symbols, for what happens when each soluble ionic compound that you identified above is placed in water. Are these substances reacting with water when they are added to water?
How would you classify the soluble ionic compounds: strong electrolyte, weak electrolyte, or nonelectrolyte? Explain your answer.
Sodium chloride, NaCl, is a strong electrolyte, as is hydroiodic acid, HI. Write the chemical equations for what happens when these substances are added to water. m
Are NaCl and HI strong electrolytes because they have similar behavior in an aqueous solution? If not, describe, using words and equations, the different chemical process that takes place in each case.

Part 2:

You have two hypothetical molecular compounds, AX and AY. AX is a strong electrolyte and AY is a weak electrolyte. The compounds undergo the following chemical reactions when added to water.

AX (aq) + H₂O (l) → AH₂O⁺ (aq) + X⁻ (aq)

AY (aq) + H₂O (l) → AH₂O⁺ (aq) + Y⁻ (aq)

Explain how the relative amounts of AX ( aq ) and AY ( aq ) would compare if you had a beaker of water with AX and a beaker of water with AY.
How would the relative amounts of X⁻ ( aq) and Y⁻ ( aq) in the two beakers compare? Be sure to explain your answer.

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OBJECTIVE:

In this lab, you will produce several different voltaic cells, measure the total voltage, and determine the corresponding half-cells and total potentials. A copper electrode and a copper gluconate electrolyte solution will be used in every system, and four additional half-cells with different metals and salts will be run against it to compare the half-cells and total overall voltage. The salt bridge, consisting of filter paper and potassium chloride, connects the two cells.

PROCEDURE

Put on your goggles and lab apron.

Label five clean, dry 100 mL beakers as copper gluconate, tin sulfate, aluminum sulfate, iron sulfate, and zinc

sulfate.

Using a clean, dry 100 mL graduated cylinder (and pipette if needed), measure and pour 25.0 mL of each

solution into the corresponding beaker. Be sure to thoroughly rinse the graduated cylinder with dH2O before measuring out a new solution. Some of your bottles of solution may need shaken up before using to re- dissolve anything that has settled out. If shaking doesnât completely work, use a clean, dry glass stirring rod to help break up and dissolve. Mix thoroughly. Just be sure to clean the stir rod before moving it to a different solution bottle.

Lightly sand the provided metal strips of copper, tin, aluminum, iron, and zinc down with sand paper to remove the oxidized layer. When finished, wipe off any debris. Set the strips aside. Be sure you have sanded these well to ensure reaction.

Use scissors to cut the filter paper into five strips. Each strip should measure about 20 mm (2 cm) x 150 mm (15 cm).

Note: When your electrochemical cell apparatus is set-up, each strip should be long enough to connect the electrolyte solutions in the two adjacent beakers (half-cells). The strips may look short now, but after they soak, you will see that are the proper length. See pic below.

Using a clean, dry 100 mL graduated cylinder, measure and pour 25.0 mL of potassium chloride solution into a 100 mL beaker. Place the filter paper strips into the beaker. Allow the strips to soak for approximately 5 minutes. This process creates the salt bridge. Be sure all papers are in contact with KCl and get soaked.

Place the metal copper strip in the copper gluconate beaker, allowing it to lean against the side of the beaker.

Repeat Step 7 for each of the metal strips and the corresponding beakers (see pic below).

Place one of the potassium chloride soaked filter papers between the copper gluconate solution and the tin

sulfate solution so that the filter paper is immersed in both solutions simultaneously. The KCl strip must be touching both solutions (itâs OK for the strip to cling to the wall of each beaker, so long as it is touching both solutions)! Pick up the strip by the middle, and drain excess solution by touching the ends to a paper towel. Position the paper strip salt bridge so that it makes contact with both solutions, but is not touching the electrodes.

Assemble the 7-Function Multi-Meter by firmly pressing the positive (red) Test Lead into the V?mA (center) jack. Press the negative (black) Test Lead into the COM (bottom) jack. Rotate the red, center dial until it is pointing towards the DCV 2000 m position (Hint: this position is similar to the northwest position on a compassâsee pic below). 2000 m is equal to 2 volts. That means your read out is now in mV, so you will have to divide the readout by 1,000 when recording your data in V. For example, in the picture below, my readout of 980 mV would be 0.980 V. Turn the multi-meter on.

Touch the red multi-meter probe to the top of the copper strip, and the black multi-meter probe to the top of the tin strip. This works best when you press lightly down on the top edge of the metal strip with the side of the probe, as this creates more constant contact and less fluctuation movement. See pic below. If you happen to have a set of alligator clips to connect the probes to the metal, that would work even better.

Note: The red probe should be placed on copper for all of the half-cell apparatuses. The black probe should be placed on the remaining metals.

Note: Alternatively, you can bend the metal strips to rest over the edge of the beaker, and to give a flat surface that makes it easier to rest the probes:

Record the voltage differential created between the two half-cell in Table 1 (see below). Watch the voltage for a few seconds and then take a reading. Some readings stabilize quickly, others will drift for as long as you want to watch. (Swirling the solution with the electrode can also change the reading.) Typically, waiting a few seconds after connecting the cell yields the most reliable reading.

Take a picture of your voltaic cell. This will be a little tricky since you have to hold the probes, but try to get someone to help. Otherwise, do the best you can. The digital readout on the multimeter must be visible for each sample, and both half cells must be visible and clearly labeled. Your face must be visible in the picture also, as well as a label with your name/student ID, the lab title, and the date. Unless all fourâyour face, name/ID, the lab title, and the date are clear, you will not receive credit. Save this picture, and combine all four voltaic cells (Sn, Al, Fe, Zn) into a single PDF document in order to submit it in the Lab 14 Assignment.

Discard the salt bridge, and repeat Steps 9 -13 three more times using the aluminum sulfate solution, iron sulfate solution, and the zinc sulfate solution. Each solution should be paired with the copper gluconate solution, placing the red probe of the volt meter on the copper each time. A new salt-bridge should be used for each electrochemical cell. Record your data in Table 1 (see below).

Wash your glassware (and plasticware) with warm water and soap. To minimize spotting and mineral contamination, it is best to do a final rinse with dH2O. Dry your glassware (or leave set to dry) and put it away. All chemical solutions used in this lab can now be safely washed down the sink, and solid metals can be thrown away or recycled. Clean up your lab and put away your materials.

RESULTS

Make a data table in either Word or Excel that shows the multi-meter voltage measurements (V), experimental half-cell potential using copper electrode as the standard, the theoretical half-cell voltage, percent error, the half-cell and net cell reactions, and free energy (?G). Your table should look something like the one on page 6 of this document. Also see the description below the sample table for help in determining all of these values. Make sure that the calculation sections shown below are included within your Table 1 document as well.

Save your Table 1 as a PDF file to be submitted with the Lab 14 Assignment. Be sure your document includes your name/student ID, lab title, and date. Unless all threeâyour name/student ID, the lab title, and the date are on the document and legible, you will not receive credit. All columns and values must be clearly labeled.

You should have = 1 PDF of a pic of you and your 4 electrochemical cells being measured (Step 13) + (Steps 16-17). All pictures, tables, and labels must be clear and properly labeled or they will not receive credit.

Question:

You probably observed the cell voltage change slightly while you were observing it. Explain what is occurring at the electrode that causes the observed voltage to change?

CHEM 1210 Study Guide - Midterm Guide: Volumetric Flask, Calcium Sulfate, Sodium Sulfate

CHEM 1210 Full Course Notes

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