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# Category Archives: Chemistry

## pH diets, health, and homeostasis

### Students need to be aware of pseudoscience diets. Some of these claim that by eating more acidic or basic foods you can change your body’s pH level, and thus treat disease.

### Not only is this entire idea incorrect, if a person does change their pH beyond even a tiny bit then they will almost immediately die. Changing one’s body pH is almost impossible, but when it happens it is fatal,

### What are acids and bases? Acids are bases are complimentary types of chemicals. Acids perform one kind of chemical reaction; bases perform the opposite action. Learn more here about acids and bases.

### Here’s the critical point: When it comes to living, what matters is whether acids and bases are working in a safe balance. Cells only work correctly in a very narrow range of conditions.

### Too much or too little of any molecule, and they begin to malfunction or die. Homeostasis is the body’s way of keeping chemicals in a safe, dynamic balance.

### Alkaline Diet, SkepDic

### Alkaline Diet, RationalWiki

### pH Mythology: Separating pHacts from pHiction

### Alkaline Water Surges Despite Lack of Evidence

### Alkaline food, McGill University

### Chemistry lesson for The Food Babe… and everyone else #19: Alkaline Diets Do Not Cure Disease, McGill University

## Physics Hanukkah Fun

### During the holiday season many science teachers have a fun day on “The physics of Christmas.” What about “the physics of Hanukkah?” (*) Here’s an idea, would love feedback.

### During this holiday Jews light a Chanukah menorah מנורת חנוכה, also called a Ḥanukiyah חַנֻכִּיָּה.

### The wick is above the oil, drawing fluid up the wick through capillary action.

## Capillary action & molecule forces

### Oil is drawn up through a wick by a mechanism called capillary action, or wicking. This is a tale of two competing forces:

### There is an adhesive force between the molecules of oil and the cotton molecules.

### There is an intermolecular/cohesive force between the oil molecules.

### Cohesion = ability of like molecules to stick together

### Adhesion = ability of dissimilar molecules to stick together

### When the former force > latter force then oil molecules are slowly pulled into the wick.

### Sean Snider, writing on Quora, explains:

### A fluid such as heating oil will tend to flow upwards against gravity due to capillary motion. The individual atoms in the oil will interact with the fiber atoms to cause adhesion. The oil atoms will bump into the fiber atoms and move upwards due to intermolecular forces. The difference in charge between the two types of atoms causes them to repel in all directions, including up.

### The oil atoms will keep moving up unless the forces between them cause them to clump together so that intermolecular forces weaken and their collective mass is too much to repel the force of gravity.

### Typically the density of the fiber itself prevents the oil particles from clumping enough to reach this threshold, so they continue to move upward. This allows the oil to reach the top of the wick and burn. Instead of the fiber burning quickly, the oil burns. Some of the fiber also burns, but much less quickly.

### Student activities

### Wick lab/game! sciensation.org

### Capillary action and diffusion lab

### Lights, Camera, (Capillary) Action! Scientific American

### Once lit, the heat from the flame would likely warm up the small olive oil vessel below. Those vessels are often transparent.

## Convection & temperature differentials

### That heat would cause a temperature differential, with warmer oil at the top and cooler oil at the bottom. This would cause convection and/or turbulence in the fluid, which might be visible if we study it with a high speed, high-resolution smartphone camera.

### (Convection, turbulence, and related topics are usually left out of high school physics curriculum, this might be a fun way to introduce it.)

### Experiment: Add drop of coloring into oil. Light the wick. Visually observe convection currents.

## Dreidel physics

### A dreidel (Yiddish: דרײדל) or sevivon (Hebrew: סביבון) is a four-sided spinning top, played by children during the Jewish holiday of Hanukkah.

### It is a Jewish variant on the teetotum, a gambling toy found in many European cultures.

### Let’s take a look at Extreme High-Speed Dreidel Physics by Alexander R. Klotz:

### … a dreidel is an example of a spinning top, a source of extremely difficult homework problems in undergraduate classical mechanics related to torque and angular momentum and rigid body motion and whatnot. I was chatting with a theorist I know who mentioned that it would be fun to calculate some of these spinning-top phenomena for the dreidel’s specific geometry (essentially a square prism with a hyperboloid or paraboloid base), and I suggested trying to compare it to high-speed footage [1000 frames per second] ….

Check out the article and videos here.

## Related dreidel topics to investigate

### rotation

### What keeps spinning tops upright? Ask a Mathematician/Physicist

### precession

### Precession, Wikipedia

### conservation of angular momentum

### Angular momentum

### gryroscopes – Gyroscopes

.

### Statistics

### Are dreidels fair? In other words, does the average dreidel have an equal chance of turning up any one of its four sides? Dreidel Fairness Study

### Ultra High Speed Physics.

### You’re not a mad scientist unless you ask questions like “Imagine a game of dreidel with a 60-billion-RPM top….” Focus: The Fastest Spinners. APS Physics

### (*) How is the holiday spelled? ELA connections

### Why write “Hanukkah” instead of “Chanukah” – surely one spelling is right and the other is wrong? The reason for the spelling confusion is the limitations of the English alphabet. Hanukkah is a Hebrew word (חנוכה)

### That first Hebrew letter of this word, ח , has a guttural sound. This sound used to exist in ancient English but doesn’t exist in modern English. The modern pronunciation of this letter is a voiceless uvular fricative (/χ/)

### As such there is no one correct-and-only way to transliterate this letter. Over the past 2 centuries four ways have developed:

### KH – **Khanukah** (used in old fashioned translations of Yiddish)

### CH – **Chanukah**

### H – **Hanukkah **(the extra ‘k’ is added just to make it 8 letters long.)

### H – **Ḥanukah** (notice the H with a dot under it.)

### Each of these transliterations is equally valid.

## Learning Standards

Convection & Temperature differential

**College Board Standards for College Success in Science**

ESM-PE.1.2.1 Describe and contrast the processes of convection, conduction and radiation, and give examples of natural phenomena that demonstrate these processes.

ESM-PE.1.2.1c Use representations and models (e.g., a burning candle or a pot of boiling water) to demonstrate how convection currents drive the motion of fluids. Identify areas of uneven heating, relative temperature and density of fluids, and direction of fluid movement.

**Next Generation Science Standards**

MS-PS1-4. Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.

**Massachusetts Science and Technology/Engineering Curriculum Framework**

7.MS-PS3-6 (MA). Use a model to explain how thermal energy is transferred out of hotter regions or objects and into colder ones by convection, conduction, and radiation.

**Transliteration**

Library of Congress (USA) ALA-LC Romanization Tables

## Gay-Lussac’s law (Amontons’ law)

### from the NASA Glenn Research Center website

### Gases have various properties that we can observe with our senses, including the gas pressure, temperature (T), mass, and the volume (V) that contains the gas.

### Careful, scientific observation has determined that these variables are related to one another and that the values of these properties determine the state of the gas.

### The relationship between temperature and volume, at a constant number of moles and pressure, is called Charles and Gay-Lussac’s Law in honor of the two French scientists who first investigated this relationship.

### Charles did the original work, which was verified by Gay-Lussac.

### They observed that if the pressure is held constant, the volume V is equal to a constant times the temperature T:

### V = constant * T

### For example, suppose we have a theoretical gas confined in a jar with a piston at the top. The initial state of the gas has a volume qual to 4.0 cubic meters, and the temperature is 300 Kelvin.

### With the pressure and number of moles held constant, the burner has been turned off and the gas is allowed to cool to 225 Kelvin. (In an actual experiment, a cryogenic ice-bath would be required to obtain these temperatures.)

### As the gas cools, the volume decreases to 3.0 cubic meters.

### The volume divided by the temperature remains a constant (4/300 = 3/225 ).

### Here is a computer animation of this process:

*Important! This is not a law of physics!*

### Rather, this is a generally useful rule, which is only valid when gas temperature and pressure is low enough for the atoms to usually be far apart from each other. As we begin to deal with more extreme cases, this rule doesn’t hold up.

.

## Avogadro’s law

### Previously in Chemistry one has learned about Avogadro’s hypothesis:

### Equal volumes of any gas, at the same temperature and pressure, contain the same number of molecules.

### Reasoning

(from Modern Chemistry, Davis, HRW)

### In 1811, Avogadro found a way to explain Gay-Lussac’s simple ratios of combining volumes without violating Dalton’s idea of indivisible atoms. He did this by rejecting Dalton’s idea that reactant elements are always in monatomic form when they combine to form products. He reasoned that these molecules could contain more than one atom.

### Avogadro also put forth an idea known today as Avogadro’s law: equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

### It follows that at the same temperature and pressure, the volume of any given gas varies directly with the number of molecules.

### Avogadro’s law also indicates that gas volume is directly proportional to the amount of gas, at a given temperature and pressure.

### Note the equation for this relationship.

### V = kn

### Here, n is the amount of gas, in moles, and k is a constant.

### Avogadro’s reasoning applies to the combining volumes for the reaction of hydrogen and oxygen to form water vapor.

### Dalton had guessed that the formula of water was HO, because this formula seemed to be the most likely formula for such a common compound.

### But Avogadro’s reasoning established that water must contain twice as many H atoms as O atoms, consistent with the formula H2O.

### As shown below, the coefficients in a chemical reaction involving gases indicate the relative numbers of molecules, the relative numbers of moles, and the relative volumes.

### The simplest hypothetical formula for oxygen indicated 2 oxygen atoms, which turns out to be correct. The simplest possible molecule of water indicated 2 hydrogen atoms and 1 oxygen atom per molecule, which is also correct.

### Experiments eventually showed that all elements that are gases near room temperature, except the noble gases, normally exist as diatomic molecules.

## As an equation

### Avogadro’s Law – also known as Avogadro–Ampère law

### when temperature and pressure are held constant:

### volume of a gas is directly proportional to the # moles (or # particles) of gas

### n1 / V1 = n2 / V2

### or

### What does this imply?

### As # of moles of gas increases, the volume of the gas also increases.

### As # of moles of gas is decreased, the volume also decreases.

### Thus, # of molecules (or atoms) in a specific volume of ideal gas is independent of their size (or molar mass) of the gas.

*Important! This is not a law of physics!*

### Rather, this is a generally useful rule, which is only valid when gas temperature and pressure is low enough for the atoms to usually be far apart from each other. As we begin to deal with more extreme cases, this rule doesn’t hold up.

At what point does Avogadro’s law not apply?

## Example problems

### These problems are from The Chem Team, Kinetic Molecular Theory and Gas Laws

**Example #1:** 5.00 L of a gas is known to contain 0.965 mol. If the amount of gas is increased to 1.80 mol, what new volume will result (at an unchanged temperature and pressure)?

**Solution:**

## I’ll use V

_{1}n_{2}= V_{2}n_{1}## (5.00 L) (1.80 mol) = (x) (0.965 mol)

## x = 9.33 L (to three sig figs)

**Example #2:** A cylinder with a movable piston contains 2.00 g of helium, He, at room temperature. More helium was added to the cylinder and the volume was adjusted so that the gas pressure remained the same. How many grams of helium were added to the cylinder if the volume was changed from 2.00 L to 2.70 L? (The temperature was held constant.)

**Solution:**

### 1) Convert grams of He to moles:

### 2.00 g / 4.00 g/mol = 0.500 mol

### 2) Use Avogadro’s Law:

### V_{1} / n_{1} = V_{2} / n_{2}

2.00 L / 0.500 mol = 2.70 L / x

x = 0.675 mol

### 3) Compute grams of He added:

### 0.675 mol – 0.500 mol = 0.175 mol

0.175 mol x 4.00 g/mol = 0.7 grams of He added

**Example #3:** A balloon contains a certain mass of neon gas. The temperature is kept constant, and the same mass of argon gas is added to the balloon. What happens?

### (a) The balloon doubles in volume.

(b) The volume of the balloon expands by more than two times.

(c) The volume of the balloon expands by less than two times.

(d) The balloon stays the same size but the pressure increases.

(e) None of the above.

**Solution:**

### We can perform a calculation using Avogadro’s Law:

V_{1} / n_{1} = V_{2} / n_{2}

Let’s assign V_{1} to be 1 L and V_{2} will be our unknown.

Let us assign 1 mole for the amount of neon gas and assign it to be n_{1}.

The mass of argon now added is exactly equal to the neon, but argon has a higher gram-atomic weight (molar mass) than neon. Therefore less than 1 mole of Ar will be added. Let us use 1.5 mol for the total moles in the balloon (which will be n_{2}) after the Ar is added. (I picked 1.5 because neon weighs about 20 g/mol and argon weighs about 40 g/mol.)

1 / 1 = x / 1.5

x = 1.5

answer choice (c).

**Example #4:** A flexible container at an initial volume of 5.120 L contains 8.500 mol of gas. More gas is then added to the container until it reaches a final volume of 18.10 L. Assuming the pressure and temperature of the gas remain constant, calculate the number of moles of gas added to the container.

**Solution:**

### V_{1} / n_{1} = V_{2} / n_{2}

5.120 L | 18.10 L | |

–––––––– | = | –––––– |

8.500 mol | x |

x = 30.05 mol <— total moles, not the moles added

30.05 – 8.500 = 21.55 mol (to four sig figs)

### Notice the specification in the problem to determine moles of gas added. The Avogadro Law calculation gives you the total moles required for that volume, NOT the moles of gas added. That’s why the subtraction is there.

### .

## Charles’s Law

### Charles’s Law – also known as Charles and Gay-Lussac’s Law.

### Describes how gases tend to expand when heated.

### When the pressure on a sample of a dry gas is held constant, the temperature and the volume will be in direct proportion.

### Volume proportional to temperature

### (Only true when measuring temperature on an absolute scale)

### This relationship can be written as:

### -> Gas expands as the temperature increases

### -> Gas contracts as the temperature decreases

### This relationship can be written as:

*Important! This is not a law of physics!* Rather, this is a generally useful rule, which is only valid when gas temperature and pressure is low enough for the atoms to usually be far apart from each other. As we begin to deal with more extreme cases, this rule doesn’t hold up.

Let’s see this in action!

## Origin

### Named after Jacques Alexandre César Charles (1746 – 1823) a French inventor, scientist, mathematician, and balloonist. Just so we’re all clear on this, he was kind of a mad scientist. And I say that with the utmost approval!

.Apps

## Learning standards

Massachusetts Science and Technology/Engineering Curriculum Framework

8.MS-PS1-4. Develop a model that describes and predicts changes in particle motion, relative spatial arrangement, temperature, and state of a pure substance when thermal energy is added or removed.

Next Generation Science Standards

MS-PS1-4. Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.

College Board Standards

Objective C.1.5 States of Matter

C-PE.1.5.2 Explain why gases expand to fill a container of any size, while liquids flow and spread out to fill the bottom of a container and solids hold their own shape. Justification includes a discussion of particle motion and the attractions between the particles.

C-PE.1.5.3 Investigate the behavior of gases. Investigation is performed in terms of volume (V ), pressure (P ), temperature (T ) and amount of gas (n) by using the ideal gas law both conceptually and mathematically.

Common Core Math

Analyze proportional relationships and use them to solve real-world and mathematical problems.

CCSS.MATH.CONTENT.7.RP.A.2

Recognize and represent proportional relationships between quantities.

CCSS.MATH.CONTENT.7.RP.A.2.A

Decide whether two quantities are in a proportional relationship, e.g., by testing for equivalent ratios in a table or graphing on a coordinate plane and observing whether the graph is a straight line through the origin.

CCSS.MATH.CONTENT.7.RP.A.2.B

Identify the constant of proportionality (unit rate) in tables, graphs, equations, diagrams, and verbal descriptions of proportional relationships.

## Boyle’s law (gas laws)

A general relationship between pressure and volume: Boyle’s Law

As the pressure on a gas increases, the volume of the gas decreases because the gas particles are forced closer together.

Conversely, as the pressure on a gas decreases, the gas volume increases because the gas particles can now move farther apart.

Example: Weather balloons get larger as they rise through the atmosphere to regions of lower pressure because the volume of the gas has increased; that is, the atmospheric gas exerts less pressure on the surface of the balloon, so the interior gas expands until the internal and external pressures are equal.

from Libretexts, Chemistry, 5.3: The Simple Gas Laws: Boyle’s Law, Charles’s Law and Avogadro’s Law, CC BY-NC-SA 3.0.

This means that, at constant temperature, the pressure (P) of a gas is inversely proportional to the volume (V).

PV = c

*Important! This is not a law of physics!* Rather, this is a generally useful rule, which is only valid when gas temperature and pressure is low enough for the atoms to usually be far apart from each other. As we begin to deal with more extreme cases, this rule doesn’t hold up.

Let’s see the relationship in action, here:

from http://www.grc.nasa.gov/WWW/K-12/airplane/boyle.html

## How was this general rule discovered?

Early scientists explored the relationships among the pressure of a gas (P) and its temperature (T), volume (V), and amount (n) by holding two of the four variables constant (amount and temperature, for example), varying a third (such as pressure), and measuring the effect of the change on the fourth (in this case, volume).

The history of their discoveries provides several excellent examples of the scientific method.

The Irish chemist Robert Boyle (1627–1691) carried out some of the earliest experiments that determined the quantitative relationship between the pressure and the volume of a gas. Boyle used a J-shaped tube partially filled with mercury.

In these experiments, a small amount of a gas or air is trapped above the mercury column, and its volume is measured at atmospheric pressure and constant temperature. More mercury is then poured into the open arm to increase the pressure on the gas sample.

The pressure on the gas is atmospheric pressure plus the difference in the heights of the mercury columns, and the resulting volume is measured. This process is repeated until either there is no more room in the open arm or the volume of the gas is too small to be measured accurately.

Details: Boyle’s Experiment Using a J-Shaped Tube to Determine the Relationship between Gas Pressure and Volume.

(a) Initially the gas is at a pressure of 1 atm = 760 mmHg (the mercury is at the same height in both the arm containing the sample and the arm open to the atmosphere); its volume is V.

(b) If enough mercury is added to the right side to give a difference in height of 760 mmHg between the two arms, the pressure of the gas is 760 mmHg (atmospheric pressure) + 760 mmHg = 1520 mmHg and the volume is V/2.

(c) If an additional 760 mmHg is added to the column on the right, the total pressure on the gas increases to 2280 mmHg, and the volume of the gas decreases to V/3

(This section from from Libretexts, Chemistry, 5.3: The Simple Gas Laws: Boyle’s Law, Charles’s Law and Avogadro’s Law, CC BY-NC-SA 3.0)

## Learning standards

Massachusetts Science and Technology/Engineering Curriculum Framework

8.MS-PS1-4. Develop a model that describes and predicts changes in particle motion, relative spatial arrangement, temperature, and state of a pure substance when thermal energy is added or removed.

Next Generation Science Standards

MS-PS1-4. Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.

College Board Standards

Objective C.1.5 States of Matter

C-PE.1.5.2 Explain why gases expand to fill a container of any size, while liquids flow and spread out to fill the bottom of a container and solids hold their own shape. Justification includes a discussion of particle motion and the attractions between the particles.

C-PE.1.5.3 Investigate the behavior of gases. Investigation is performed in terms of volume (V ), pressure (P ), temperature (T ) and amount of gas (n) by using the ideal gas law both conceptually and mathematically.

Common Core Math

Analyze proportional relationships and use them to solve real-world and mathematical problems.

CCSS.MATH.CONTENT.7.RP.A.2

Recognize and represent proportional relationships between quantities.

CCSS.MATH.CONTENT.7.RP.A.2.A

Decide whether two quantities are in a proportional relationship, e.g., by testing for equivalent ratios in a table or graphing on a coordinate plane and observing whether the graph is a straight line through the origin.

CCSS.MATH.CONTENT.7.RP.A.2.B

Identify the constant of proportionality (unit rate) in tables, graphs, equations, diagrams, and verbal descriptions of proportional relationships.