CHEM 115 Lecture Notes - Lecture 2: Graduated Cylinder, Atomic Mass, Unified Atomic Mass Unit

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17 Jun 2017

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Use the marks on the graduated cylinder to determine the amount of liquid. Use all the digits you are certain of, and estimate to one more digit. Step 2: determine the difference between markings on the larger graduated cylinder. An increment is each horizontal mark on the cylinder. Step 3: how to determine the number of significant figures. The markings on this graduated cylinder are in increments of 1. Therefore, you can be sure of your reading up to the ones place. You should then estimate to one more decimal place beyond what you are certain of. So, in this case, your answer should be reported to the tenths place. For the larger cylinder, the bottom of the meniscus lies halfway between 1 and 2. Step 1: think about the number of decimal places that you can accurately measure with each graduated cylinder.

Related Questions

Suppose that you have a vial of an unknown liquid. You are trying to determine its identity by studying how its volume changes with temperature. You fill a Pyrex graduated cylinder to 100.00 mL with the liquid when the liquid and the cylinder are at 0 C. You then raise the temperature to 50 C, allowing the graduated cylinder and liquid to come to equilibrium at each temperature. The final reading of the graduated cylinder of the water is 102.46 mL.

Using the subscript l for the liquid and g for the glass, determine an equation for the apparent volume of the liquid. Take V_o to be the initial volume of the liquid when the liquid is at 0.000 C.

Use the fact that DV = V_o b DT

b_g = 9x10^-6 C^-1

Based on your previous result, should there be a linear relationship between temperature and volume? If so, what would the slope m of the line be in terms of the initial volume of the liquid and the coefficients of expansion for the glass and liquid? Use this equation for the slope to find an expression for the coefficient of expansion of the liquid, b_l.

pre lab question:

1. Assume for the moment that air consists of 80.00% nitrogen (N₂) and 20.00% oxygen (O₂) by volume. Use these figures and typical values for temperature and pressure (1.000 atm and 25.00Â°C) to calculate the density of air in g/L.

2. Explain how you will determine the mass of CO₂ gas in your flask.

3. This experiment will require you to know the volume of the air/gas present in your flask. How will you measure this volume?

4. If you are use a graduated cylinder with markings in increments of 0.2 mL to measure liquids, you should interpolate and record volume readings to the nearest what?

Experiment 1: Calculating Rate of Reaction

In this experiment you will calculate the rate of reaction of potassium iodide and hydrogen peroxide. The order of the reaction will also be determined.

Materials:

20 mL 3% Hydrogen peroxide, H₂O₂
15 mL Iodine-Potassium Iodide Solution, IKI (1% Iodine, 2% Potassium Iodide)
100 mL Beaker
10 mL Graduated cylinder
100 mL Graduated cylinder
250 mL Beaker
(2) 250 mL Erlenmeyer flasks
1-Hole Rubber stopper
2-Hole Rubber stopper
(2) 3 in. Rigid tubing pieces
(1) 6 in. Rigid tubing
6 Pipettes

Stopwatch
Permanent marker
Waste beaker (any volume)
*Access to graphing software
*Access to a computer
*24 in. Flexible tubing
*Water
*10 mL Distilled water

* You must provide

*You must cut this piece of tubing into two, 12 inch pieces. (if you have not already done so).

Procedure

Preparation of Apparatus

Set up apparatus as shown in Figure 2. To do this, begin by labeling the Erlenmeyer Flasks as 1 and 2. The reaction will take place in Flask 1.

Fill Flask 2 approximately three quarters of the way full with water.

Press the 2-hole rubber stopper into the top of Flask 2. Place one three in. piece and one six in. piece of rigid tubing into each hole of the rubber stopper. This should create an airtight system.

Place the one-hole stopper on Flask 1, and fit the remaining 3 in. piece of rigid tubing in the stopper hole.

Connect Flask 1 and Flask 2 with the two, 12 in flexible tubing pieces. One piece should connect Flask 1 to Flask 2, and the second piece should connect Flask 2 to the graduated cylinder. The tubing which connects Flask 2 to the graduated cylinder should be positioned low enough to be immersed in the water in Flask 2.

Figure 2: Apparatus set-up. Note this is a sample set-up and is not drawn to scale. Your specific equipment may vary slightly.

Part A: Preparation of Reactants

Pour five mL of the IKI solution into a 10 mL graduated cylinder.

Add five mL of distilled water to the graduated cylinder to bring the total volume to 10 mL. This is the 0.5% - 1.0% (diluted) IKI solution.

Pour 15 mL of 3% H₂O₂ solution into a 100 mL beaker.

Add five mL of distilled water to this beaker and mix with a stir rod. This is the 2.25% (diluted) H₂O₂ solution.

Part B: Performing the Reaction

Remove the stopper from Flask 1 and place five mL of the 3% (undiluted) H2O2 solution and 10 mL of the undiluted IKI solution provided into the flask. Immediately replace the stopper on the flask.
Note: At this point, you should select an extra beaker (any volume) from your lab kit to use as an supplemental collection container beaker for Step 6. You do not need to use the beaker yet, but keep it in close proximity.

Swirl Flask 1 until you observe a steady dripping of water going into the 10 mL graduated cylinder. This could take 3 - 5 minutes. Check for leaks in the tubing or system if water does not start rising up the plastic tubing coming from Flask 2 and traveling towards the graduated cylinder within one minute.

Stop swirling Flask 1 when you notice the steady flow of water droplets. When you stop, the water drop -rate will significantly decrease (to around one drop every 5 - 20 seconds) and could take a few minutes to stabilize. If a steady flow of drops of water does not occur within a few minutes, swirl Flask 1 for 1 more minute and check again. Repeat this process until there is a steady flow of drops of water after you have stopped swirling Flask 1.

Quickly empty liquid that has collected in the 10 mL graduated cylinder and replace the empty cylinder back under the flexible tubing.

Allow the flow of drops to become steady again. This could take 1 - 3 mL of water.

Start timing once the drop rate is steady and the volume of water collected is at a whole number (such as three mL). Record the time in Table 1 each time 2 mL of is water displaced. Continue taking data until you have at least 10 data points (20 mL displaced).
Note: Use the extra beaker (located in Part B: Step 1) to collect additional fluid when the volume of displaced water exceeds 10 mL.

Return the collected water from your 10 mL graduated cylinder to Flask 2. Ensure the seal is air tight.

Empty, clean and dry Flask 1 and the graduated cylinder.

Repeat Steps 1 - 8 for the following trial conditions: 5 mL 3% (undiluted) H₂O₂ mixed with 10 mL of 0.5%-1.0% IKI solution (placed in Flask 1); and, 5 mL of 2.25% H₂O₂ mixed with 10 mL of 1.0%-2.0% IKI solution (placed in Flask 1). Record the data in Table 2 and Table 3, respectively.
Note: Clean the graduated cylinder and extra collection beaker before it is used to measure any additional reagents for Trial 2 or Trial 3; and, before it is used for collecting the water from the reaction in the apparatus.

Use a graphing software program to make a graph of each trial. The graph should demonstrate the relationship formed between time vs. mL of water displaced.

Find and record the slope and the inverse slope for each trial.

Table 1: 10 mL Undiluted (1.0 -2.0%) IKI and 5 mL 3% H₂O₂
mL water displaced	Time (seconds)
2
4
6
6
8
10
12
14
16
18
20
22
Slope:
Inverse Slope:

Table 2: 10 mL Diluted (0.5-1.0% IKI) and 5 mL 3% H₂O₂
mL water displaced	Time (seconds)
2
4
6
6
8
10
12
14
16
18
20
22
Slope:
Inverse Slope:

Table 3: 10 mL Undiluted (1.0 -2.0%) IKI and 5 mL 2.25% H₂O₂
mL water displaced	Time (seconds)
2
4
6
6
8
10
12
14
16
18
20
22
Slope:
Inverse Slope:

Calculations

Post-Lab Questions

1. Determine the order of the KI in this reaction.

2. Determine the order of the H2O2 in this reaction.

3. Calculate the rate law constant.

4. What is the overall rate law?

5. When finding the order of H2O2, why was Trial 1 and Trial 3 used?

6. When finding the order of KI, why was Trial 1 and Trial 2 used?

7. Research and identify some alternative catalysts that could be used to accelerate the decomposition of hydrogen peroxide. Evaluate these catalysts and determine which option is

CHEM 115 Lecture Notes - Lecture 2: Graduated Cylinder, Atomic Mass, Unified Atomic Mass Unit

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