The average pH of the ocean is 8.1, which means it is on the base side of the pH scale (remember, less than 7 is acidic, greater than 7 is basic). When scientists talk about ocean acidification, they are actually talking about ocean ‘de-basicifiction’—but that doesn’t sound as good 🙂
Ocean acidification
An unusual type of acid is carbon dioxide (CO2). It’s unusual because most acids have a hydrogen atom/ion on them somewhere that can dissociate when the acid is mixed with water. Here’s the process that carbon dioxide undergoes when mixed with water:
How carbonic acid effects shells in the ocean
Watch the following video. It is part a review of acid/bases and pH, and part an introduction to oceans turning a bit more acidic.
Remember: pH 7 is neutral, greater than 7 is basic, lower than 7 is acidic.
In the simplest definition, acids are substances that when dissolved in water release hydrogen ions (H+), and bases are substances that release hydroxide ions (OH-).
In chemistry class, you will dig deeper into acids and bases, and develop a more complete definition of acids and bases, but these two definitions will do for this class.
The pH scale was developed as a means of classifying the concentration of H+ ions and OH- ions in a solution.
The pH scale
7 is neutral (same number of H+ as OH-)
lower numbers are acidic with more H+ than OH- ions
You can also find most of this information on page 238 and 239 in your textbook.
You may be most used to the word concentration used in terms of paying attention to something. For example, you may concentrate on your study the night before a test. What are you doing when you concentrate? You are trying to focus all your attention on that one thing.
To concentrate can been seen as to focus all of your attention in a small area. Taking that definition into science, to concentrate is to put a lot of stuff (we call this the solute) into a smaller portion of the stuff you are mixing into (the solvent).
To calculate the concentration, simply divide the amount of solute by the total amount of the solution:
Concentrations as a percent
We frequently express concentrations as a percent. Percent means ‘per hundred.’ If you calculate your grade, say you got 40/50, into a percent, what you are really saying is ‘if the test were worth 100 points, I would have earned 80 points.’ The equation is, therefore:
Then you ‘cross-multiply and divide to get the answer of 80%.
To calculate the concentration as a percent, the equation starts with:
So, we generally rearrange this formula (by multiplying both sides by 100) and use the following to solve any solution percent concentration.
The equation for percent concentration, therefore, is
Calculating concentrations as percents
Video
The following video shows how to calculate mass percents. Don’t worry about the when she talks about PPM (stands for Parts Per Million), but the rest of the video is helpful.
Moles: Counting molecules, atoms, and ions
Chemicals are made up of such small particles that we cannot count them individually. Lets look at some examples to help you understand this huge counting number.
Dozen
Can you imagine going to the grocery store and asking to buy one egg? Eggs are small enough that they sell them in dozens (sometimes half-dozen, two-dozen, and two and one half-dozen).
Score
Score is a word that means 20. It’s not used much these days, but has an memorable role in US history, used by President Lincoln in the Gettysburg Address.
Gross
Small parts or materials sold to businesses are often sold by the gross. A gross is a dozen dozens. A jeweler might by a gross of gold studs, or a school might by a gross of pencils.
One other counting word based on the dozen is the great gross, which is a dozen gross.
The mole
You’ll learn much more about this in chemistry, but the mole is just a very large number. To get a sense of how large this number is, if you could count all the grains of sand on the earth, this would only be about 1 ten-thousandth of a mole. That means it would take 10,000 earths to have one mole of sand grains.
A twelve-ounce can of soda has about 20 moles of water! Hopefully that gives you an idea how small molecules, ions, and ions are.
Concentrations in moles/liter
One of the common measurements for concentration is the mole per liter. You can read about this on Page 239 in your textbook. To calculate the concentration in moles/liter, it’s a simple division calculation:
Video: Solving for molarity
The following video provides a good overview. At about 4:45 into the video, it gets into chemical formulas that you won’t need to do in this class (again, you’ll get to this in chemistry).
Online molarity simulation
If you would like to experiment with solutions, this PhET simulation is a great tool that allows you to adjust the amount of water, solutes, evaporation, and see the results with a meter.
Substances are made of up small particles (atoms, molecules, ions) that can mix together and may or may not take up the same space after mixing.
These particles have kinetic/thermal energy, and thus are always moving and/or vibrating.
Solutions contain two parts.
A solvent is the majority part
One or more solutes are the minority parts
Electrical conductivity and solutions
Watch the following video then answer the questions.
Quiz
Review
Many of you may have been surprised that pure water does not conduct electricity…but pure water does not conduct electricity. The reason we think about water as being dangerous around electricity is that almost no water is pure! All the water we interact with is a solution of some type; even our drinking water has fluoride and chlorine as solutes in it (fluoride for healthy teeth, and chlorine–in various chemical formulas–to prevent growth of microorganisms).
The copper aluminum metal was able to conduct electricity when it was dry because each grain of aluminum was touching another, and a continuous path of metal existed between the two probes. But when it was mixed in the water, the continuous path was broken because the aluminum fell to the bottom.
Molecules and ions
So, why does salt in solution conduct electricity, and sugar and silicon dioxide do not. The answer is in how these substances behave when dissolved in water. Watch the following video to look at the shapes of some substances.
If you want to create your own 3D models of compounds, visit Moview.org. Enter a name of a chemical in the search box in the upper left corner, and they will likely have a model of it.
Definitions
Molecules
Substances whose atoms are connected by sharing atoms and have a net charge of zero (just like with forces in opposite directions can cancel each other out, positives and negatives can cancel each other out) are called molecules. (Much more about this when you take chemistry, but this will do for now.)
Ions and ionic substances
Other substances have either a positive or negative charge. These can either be atoms combined similar to molecules, but still with a non-zero net charge, or single atoms with an ‘extra’ electron, or ‘missing’ an electrons. These substances are called ions. Neutral particles that combine both of these are called ionic substances. Salt is an example of an ionic compound.
Quiz
Next page: Solutions Part 3: Calculating concentration of solutions
This week and next we will be studying solutions, as well as acids and bases. The science department considers this essential knowledge for your success in Biology next year, so please do your best to learn it. Remember, we are minimizing the content we are covering to help you through our current COVID-19 difficulties, but we are providing you with information that we hope you pay attention to.
Mixing materials
Watch the following video, then answer the questionnaire after it.
Definitions
When making a solution, two parts are mixed together. These two parts are given the following names:
The solute is the substance there is less of.
The solvent is the substance there is more of.
Examples
In a the ocean, water is the solvent, and salts are the solutes.
In a soda, water is the solvent and sugar and flavorings are the solutes.
In white gold, gold is the solute and platinum or palladium are the solutes.
In air, nitrogen is the solvent, and oxygen, water vapor, and carbon dioxide are the solutes (and, unfortunately, often smoke or other pollution).
Mixing food coloring in water
Watch the following video, then answer the questions after it.
