Hey hey hey all you super smart and talented peoples :D I really need some tutoring right now! My teacher has been sick this past week so we had a sub and she could not teach chemistry to save her life! So can anyone help me with Solution Concentration?

Question

thomaster · Answer

I'll try :) what's the problem?

anonymous · Answer

OMG THANKS A BUNCH :D ok so the problem is: What is the percent by volume of isopropyl alcohol that contains 24mL of isopropyl alcohol in 1.1 L of water?

thomaster · Answer

Okay, it's very simple.
The 1.1 liter = 100% (the total volume)
the 24 mL is the percentage that you need to calculate.

1.1 liter converted to mL is 1100 mL

1100 mL = 100%
24 mL     = ???%

You can solve this with crosstable, don't know if you know how a crosstable works.
You take the number left or right of the number that you need to calculate. You multiply that number by the number diagonally above and then divide it by the number right or left.
|dw:1366598202537:dw|
So in this case that's (24 * 100%) / 1100 = 2.18% and that's the answer.

anonymous · Answer

How do I know which is the solute and which is the solvent?

thomaster · Answer

The solute is dissolved in the solvent.
So the water is the solvent and the solute is the alcohol

anonymous · Answer

Thank you :)

thomaster · Answer

no problem :D

anonymous · Answer

Can I ask you one more question? It has to do with calculating molarity

thomaster · Answer

sure

anonymous · Answer

Oh thank you thank you thank you!!! You are a lifesaver :) ok so the question is: Calculate the molarity of 1.60 L of a solution containing 1.55g of dissolved KBr. I have been trying to figure this out but I dont know where to start....

thomaster · Answer

You start with calculating how many moles 1.55g KBr is. To do this you need to find the molecular weight of KBr. Kbr (potassiumbromide) consists of K (potassium) and Br (bromide) Find the weight of these 2 in a periodic table ( http://www.ptable.com) and sum them up. Weight of K + weight of Br = weight of KBr. Now you know the molecular weight of KBr. This weight is displayed in amu (atomic mass unit) which is the same as grams per mol. So you know how many grams of KBr equals 1 mol. Then you can calculate how many moles equals 1.55 gram KBr. You know how many moles of KBr you have. This amount of moles is dissolved in 1.6L solution. The molarity is displayed in mol per liter. You know how many moles you have and you know how many liters you have, so you can calculate how many moles per liter you have.