Can you help me understand reagent dilutions?

Question

I am trying to figure out exactly what it is that I don't understand about these dilutions. I know it isn't difficult so I'm hoping somebody can just word it our for me in a way that clicks. Or if anyone knows of a very clear website. The point is that I've read the texts and stuff, and their way doesn't work, I just need to see it from a different angle I think. Also, this question isn't about any specific homework or anything, these are just examples that illustrate my difficulties.

Essentially I think my main confusion comes down to the following few areas:

1) If I add 500mL of reagent 1 and 500mL of reagent 2, what is my ratio? 1:1 (which I think is right)? 1:2?

2) How do you do account for m/v dilutions? 10g of solute to 100mL solvent for 10% solution? Also, we presume 1g = 1mL under all situations?

3) In v/v for example, is 10% SDS solution 10mL + 90mL, or is it 10mL + 100mL? (It seems like people always do this differently)

As you can see I'm missing some fundamental concept, link, call it what you will. Hopefully somebody can word it for me and it will just click. Thanks in advance to all, as this problem is at the point of being nothing short of keeping me up at night!!

Answer 1

This whole matter of expressing dilutions is very confusing and certainly open to a lot of different interpretations. This is because different dilution systems were introduced for varying industries. Abbreviations are used to try and clarify the situation. But I still think that there is a lot of misunderstanding. I therefore have sympathy and understanding for your problem. I always use the expression: 10g solute in 100g solvent for clarity and to avoid confusion. This method is used extensively in most technical literature. This is the problem you are having with the SDS solution. Strictly speaking for a V/V solution I would interpret this to mean 10ml SDS  dissolved in 100ml solvent. Others will probably violently disagree.This does present some practical problems because at ambient temperature SDS is a solid, so measuring out 10ml would be problematic. The abbreviation V/V is normally used for liquids in liquids.

To answer your other problems:

1 This is a 1:1 dilution

2 For the diluted solutions used in most chemical laboratories, it is generally safe to take 1ml = 1 gram like water. Fortunately the most common solutions in the laboratory are molar solutions, M solutions, where density plays no role.A 1M solution is 1 mole of solute diluted to 1000ml or 1 litre or 1dm³ of solution. So any volumetric subdivision of the litre will automatically give the same subdivision of the molar mass.

Answer 2

1) When you add equal parts to each other then the final ratio is always 1:1.

2)  your example is a simple percentage.  10 / 100 = .10 or 10%

3)  Are you referring to Sodium Dodecyl Sulfate (SDS)?