Moles Lab

Part A:

Procedure:

1. Fill the cup about 3/4 full of water and find the mass.
2. Swallow one mouthful of water from the cup and find the new mass.
3. Subtract the mass in Step 2 from the mass in Step 1 to find the mass of water contained in one mouthful.
4. Calculate the molar mass of water by adding the molar masses of the 2 hydrogen atoms and the 1 oxygen atom present in the compound.
5. Divide the mass you calculated in Step 3 by the molar mass of water.
6. Multiply the mass calculated in Step 5 by one mole (6.02 x 10^23) to convert to molecules in one mouthful.

Conclusion: The purpose of this lab was to determine the number of water molecules in a mouthful of water. We found the mass of one mouthful of water by finding the difference between the mass of a cup full of water and the same cup after we'd swallowed one mouthful. By multiplying that value by the value of one mole, then dividing by the molar mass of water, we concluded that there are roughly 1.5825 x 10^24 molecules of water in one mouthful.

	Mass in Grams
Cup with all water	176.29 g
Cup with water remaining after swallowing mouthful	128.93 g

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Part B:

Purpose: Determine the amount of sugar cubes needed to contain 1.18 x 10^22 molecules of sugar.

Procedure:

1. Find the mass of one sugar cube.
2. Multiply the mass by one mole (6.02 x 10^23).
3. Calculate the molar mass of sugar by adding the molar mass of each element multiplied by the number of atoms of that specific element in the compound.
4. Divide the molar mass of sugar, by the number calculated in Step 2.
5. Multiply the value from Step 3 by the desired number of sugar molecules (1.18 x 10^22).

Conclusion: The purpose of this lab was to determine the amount of sugar cubes needed to contain 1.8 x 10^22 molecules of sugar. By dividing the mass of one mole of sugar by the amount of sugar in one cube multiplied by the value of one mole, we concluded that 1.8742 sugar cubes are needed to contain that many molecules of sugar.

	Mass in Grams
1 sugar cube	3.58 g

Unit 2 Blog (Gas Laws)

Grace Wynveen

Pressure and Volume Lab

In this lab we changed the volume of a set number of air particles by moving the piston on a syringe. The temperature stayed constant throughout the experiment, meaning the particle speed didn’t change. We found that as the volume increased, the pressure recorded by the pressure sensor decreased. This illustrates Boyle’s Law. The decrease in pressure occurs because as volume increases particles move further apart, causing a decrease in the number of collisions. This exerts less force on the inside of the container. As we decreased the volume, the pressure increased.

The picture above demonstrates the inverse relationship between pressure and volume. #1 and #2 each have 12 particles and 2 whooshies, showing that the number of particles and temperature stayed the same. To show an increase in volume, I drew the container bigger. To show an increase in pressure I drew less collision events because the number of collisions decreases when pressure decreases.

Pressure and Number of Particles Lab

In this lab we put different numbers of particles in a syringe and kept the volume and temperature constant. We did this by starting the syringe at different volumes and then moving the piston to allow each sample 10.0 mL of space. The greater the number of particles we fit into the 10.0 mL, the greater the pressure in the syringe. The increase in pressure is caused by a greater number of collisions that occur because the particles are packed more densely.

The picture above demonstrates the direct relationship between pressure and number of particles. The volume and temperature remains the same, so I drew the container the same size and included the same number of whooshies in #1 and #2. #1 has 8 particles and 3 collision events, whereas #2 has 16 particles and 6 collision events to illustrate both the number of particles and the pressure increasing.

Pressure and Temperature Lab

In this lab the volume and number of molecules of our gas sample stayed constant. We placed our gas sample in water at 4 different temperatures. As the temperature increased, the pressure of the gas sample increased. This increase occured because the gas particles collided with the glass container it was in. When the particles of water collided with the same glass, energy was transferred from the gas to the water. The gas had lost energy, which caused the particle speed to decrease. Because the particle speed decreased, the number of collisions with the wall of the container decreased. This shows a direct relationship between pressure and temperature, which is defined by Guy-Lussac’s Law.

The picture above demonstrates the direct relationship between pressure and temperature. I drew the containers for #1 and #2 the same size to indicate a constant volume and I included 11 particles in each container to show that the number of particles does not change. The increase in temperature is illustrated by another whooshie on each particle in #2. To show the pressure increasing, the number of collision events increases from 2 in #1 to to 4 in #2.

Thermometer Discussion

When a thermometer is placed in a warmer environment, the liquid inside it expands and rises. We know this because as the air in the outside environment, which is a gas and is in a constant state of motion, collides with the glass tube of the thermometer it transfers energy to the liquid as it also collides with the glass. This increase in energy causes an increase in particle speed, which in turn causes the particles to move further apart, increasing the volume so that the liquid rises in the thermometer. Thermometers are not affected by pressure because the air is removed from them, making them vacuums.

*The before picture is right after moving the thermometer into the warmer environment.

The picture above demonstrates what happens at a molecular level when a thermometer is placed in a warmer environment. In the before and after picture the volume of the thermometer remains constant because I drew the containers the same size. There are 2 whooshies on the air particles in each drawing to show a constant temperature in the air outside. The air particles are colliding with the thermometer to show a transfer of energy. The temperature inside the thermometer increases. That’s illustrated by the increase in whooshies from the first to the second picture. The increase in temperature causes the liquid to expand, which is shown by drawing the particles farther apart and rising up the thermometer. There are no air particles inside the thermometer because thermometers contain no air.

Lab Write-Up Procedure for Density of a Gas Lab

Background Information:
Before beginning the experiment, I knew that density is the measure of how many particles a substance has for every amount of volume and that substances with less density go above more dense substances. I also knew that density can be calculated by dividing an object's mass by its volume and that mass cannot be created or destroyed. I was also aware that when making measurements and calculating, the rules of significant figures must be applied. That means measurements should always be estimated one digit past what you can read and that any measurement that landed on a marker still needs an estimated digit, 0. When adding or subtracting measurements, your significant figures can only go to as many places as the least accurate measurement. When multiplying or dividing, you can only have as many significant figures as your least number does.

Materials: test tube, support ring, stand, trough, bottle, tubing, 1/2 Alka Seltzer tablet, water, graduated cylinder, beaker, electronic balance, glass plate, clamp, marker

Purpose: The purpose of the lab is to find the volume of the gas formed by measuring how much water it displaced, then to find the mass of the gas by subtracting the mass of the water in the test tube after the reaction from the original mass of the water and Alka Seltzer separately, then to use those numbers and the density formula to calculate the density of the gas.

Procedure:
1) Fill the trough 1/2 full of water.
2) Fill the bottle with water until it's overflowing, cover securely with the glass plate, set upside down in the trough of water with the tubing sticking out from under it, and secure with the support ring.
3) Fill the test tube less than 1/2 full of water.
4) Place the test tube in a beaker along with the Alka Seltzer, not letting the tablet make contact with the water.
5) Find and record the mass of the beaker with the contents in it, being sure to set the electronic balance to zero before doing so.
6) Secure the test tube to the stand using the clamp.
7) Place the Alka Seltzer tablet in the water and cover with the corked tubing immediately. Allow the Alka Seltzer tablet to react with the water until there are no more bubbles traveling through the tubing. You may need to gently shake the test tube if the tablet is not fully dissolved.
8) Remove the tubing from the bottle so the bottle is resting flat on the bottom of the tub and mark the water line on the bottle.
9) Empty the bottle and fill it to the water line with water, so that the water is occupying the place where the gas was. Using the graduated cylinder, measure and record the volume of the water.
10) Place the test tube back in the beaker. Find and record the mass the same way you did the first time.

Data Tables:

	Test One
mass before reaction	187.07 g
mass after reaction	187.06 g
volume of gas	134.0 mL

Questions and Computations:

1. Use the mass and volume of the gas to determine the density.

2.  Determine your percentage error for the density of CO2 gas if the accepted value at room temperature is 2.0 x 10^-3 g/mL.

3. Draw a particle diagram of the CO2 gas produced in reaction that is consistent with your value of density.

Analysis and Reflection:

My results showed that the carbon dioxide formed was not very dense. There was not much change in mass after the reaction occurred, meaning the mass that was converted to a gas was minimal. 

Sources of error that I may have encountered are that the stopper wasn't placed on the test tube soon enough after the tablet was placed in the water, meaning that some of the gas produced was not captured and therefore not included in the volume measured. Next time the stopper could be added even sooner to ensure a closed system. The bottle could have lost some water while being placed in the trough, which would make the mass measurement greater than it was supposed to be. That could be avoided by handling the bottle carefully. The water line may not have been level at the time that I drew the mark on the bottle, which would result in an inaccurate measurement of volume. To fix that you could use a level to make sure the top of the bottle is level.

Another group that I compared my results with got a density of 0.24 g/mL. The difference in our results may be due to the possible errors I listed above.