Dilution

[Katherine Wu 1H]

When a solution is diluted what is the main concept that one must be aware of?
The answer is that the moles of solute remain the same but I'm confused as to why this is something that we have to keep in mind. Why doesn't the moles of solute change?

[Harry Zhang 1B]

Imagining you have a cup of water with five red beans in it. The solute is the red beans and the solvent is the water. To dilute this solution, we add water to the cup, however, the number of red beans remain unchanged and therefore the number of moles of solute remains unchanged; in this case, it's always going to stay at 5/avogadro's number(moles of red beans). Although red bean is different from what we normally expect as chemical compounds, the concept is the same.

[Jainam Shah 4I]

A concept that is essential to understanding dilution is molarity. Molarity is the number of of moles per liter or in other words the concentration. With regards to dilution, you must know two definitions: solvent and solute. The solvent is a liquid that dissolves a solid, liquid, or gaseous substance. The solute is a substance that is dissolved by the solvent. Now during dilution the number of moles do not change, because we are not changing the amount of solute. For example, let's say you are diluting an aqueous solution of sodium chloride. In that dilution you would not be adding or removing any sodium chloride, but you would be adding something like water as a solvent. In dilution, the volume of the solvent is simply increased and there is no net change in the solute. We know molarity is moles per liter, thus when dilution occurs the amount of solvent is increased. The denominator of the molarity equation increases, thus reducing the molarity or concentration.

Hope this helps!

[Alan Wu]

When dilution occurs, you are only adding water (or solvent) to the solution. Whatever the solute is remains unchanged in amount. Only solvent has been added. Therefore, the moles of solute remains the same prior to and after dilution. This means that M1V1 = M2V2, and by knowing 3 of those values, you can find the last one easily. Basically, molarity is inversely proportional to volume because they multiply always to become the same number (moles). Also just think that if you add more solvent to increase the volume of solution, the molarity would decrease because the solution becomes more diluted.

[tonyhu]

Even though some mols of substance is diluted in another container, those specific mols do not change as mols measure an actual amount and not a concentration.

[KaleenaJezycki_1I]

Dilution is adding a solvent to a solute to make a solution. Think of it like putting sugar in your tea. The sugar is the solute and you decide to put one packet of sugar in your tea; no more sugar will be made-- you only put one packet of sugar. However you can add as much tea as you want in to the cup and after a while the sugar will be harder and harder to taste because it is being more diluted. Regardless of the amount of tea you add, there will only ever be one packet of sugar in your tea (your solution). Therefore the amount of solute (sugar) is a definite number.

[Michelle Xie 2B]

The amount of solute doesn't change, only the solvent. So when you are calculating dilutions, you only need to account for the added solvent since you already know the amount of solute already.

[Haley Dveirin 1E]

Hi this may be a dumb question but I can't figure out how to post a new topic/question? So far all of the questions I have asked I posted as replies to another persons question because I couldn't find any button that says "post a new topic" but I could find the "post a reply" button.

[JohnWalkiewicz2J]

@Haley Dveirin 4B
Haha its ok I think I literally just figured it out! If you are reading this right now, scroll up, there should be a link name "Chem 14A" to the top left of your screen. Once you click it, you should see a bunch of topics (Sig Figures, Properties of Light, etc) find one you want to ask a question about, click on it, then there should be a button named "New Topic" in red on the top left of your screen. You should be able to post a new topic if you click it. Hope this helps!! ;))

[Manav Govil 1B]

Dilutions are real interesting.

The moles of the solute do not change because you are not adding or subtracting moles from the solute when you are diluting. When you dilute, you are basically adding or subtracting the solvent (in most cases water). This does change the molarity of the solute (moles/L), but not the moles itself. A simple way to remember to calculate dilutions is M1V1 = M2V2. You can see that only the molarity and volume are changing, but not the moles.

I really do hope this helps.