[Soulshine]

The formula for mass/mass% is (weight of solute/volume solution) x 100.
When I plugged in this number, I get a wrong answer.
25.0 ml urine specimen having a mass of 25.725 g was found to contain 1.929g of dissolved solute. What is the mass/mass percent concentration of the urine sample?
I did: (25.725/25.0) x 100 = answer is wrong. : /

Also, how do you find the initial mass, such as..What is the mass of solution that contains 2.50 of dissolved solute in a 10% blood plasma sample?

And lastly, I keep messing up the formula for the ideal gas law. For example, a certain quantity of neon gas is under 1.05 atm pressure at 303K in a 10.0L vessel. How many mole of neon are present?
Ok, so this is how I see it.
n = (PT/V) x R
(1.05 atm x 303k/ 10.0L) x 0.0821 L x atm/mol x K = wrong answer again. I get very confused trying arrange which goes where. PV = nRT...the book gave an example for finding R : R= PV/nT.
What if I need to find T? Will it be T = PV/n x R?
@_@

[Borek]

The formula for mass/mass% is (weight of solute/volume solution) x 100.

No, that'll be mass/volume percentage and you are asked for mass/mass percentage.

Also, how do you find the initial mass, such as..What is the mass of solution that contains 2.50 of dissolved solute in a 10% blood plasma sample?

2.50 of what? gram? pound? stone? Use w/w% definition, just solve it for mass of the mixture.

And lastly, I keep messing up the formula for the ideal gas law. For example, a certain quantity of neon gas is under 1.05 atm pressure at 303K in a 10.0L vessel. How many mole of neon are present?
Ok, so this is how I see it.
n = (PT/V) x R
(1.05 atm x 303k/ 10.0L) x 0.0821 L x atm/mol x K = wrong answer again. I get very confused trying arrange which goes where. PV = nRT...the book gave an example for finding R : R= PV/nT.
What if I need to find T? Will it be T = PV/n x R?

You can do the same operation to both sides of the equation. You can add or substract something from both sides of the equation, you can multiply or divide by something (although you can't divide by zero).

So, PV=nRT and you want to "move" R to the left hand side... Divide both sides by R. That gives

PV/R = nRT/R

R on the RHS cancels out. That's the general method.

[Soulshine]

Ok, but when I try to plug in the number - (25.725 g /25.0 ml) x 100 - it's wrong. I even tried adding the dissolved solute and then divided by 25 ml x 100, and it's still wrong. Ugh! I suck in math.

The second question, I forgot to add grams - 2.50 g. I finally got the answer right, at last.

The ideal gas law, I am still unsure.
Where is the RHS?
I'm sorry if I'm so slow; I am really slow when it comes to math.

[sjb]

For part 1 * What is the definition of % w/w ?

For part 3 * If pV = nRT, rearrange for n, and plug your knowns in

You can do the same operation to both sides of the equation. You can add or substract something from both sides of the equation, you can multiply or divide by something (although you can't divide by zero).

So, PV=nRT and you want to "move" R to the left hand side... Divide both sides by R. That gives

PV/R = nRT/R

R on the RHS cancels out. That's the general method.

[Borek]

Ok, but when I try to plug in the number - (25.725 g /25.0 ml) x 100 - it's wrong.

It must be wrong, as you are dividing mass by volume, while you should divide mass by mass. You are simply using wrong definition.

Where is the RHS?

RHS stands for Righ Hand Side of the equation.
LHS stands for Left Hand Side of the equation.

LHS = RHS

[razor26]

%m/m= (mass solute/mass solvent)100
%m/m=(1.929g/25.725g)100
divide and multiply and there you have it.,ignore the 25mL.,

[Soulshine]

For part 1 * What is the definition of % w/w ?

For part 3 * If pV = nRT, rearrange for n, and plug your knowns in

You can do the same operation to both sides of the equation. You can add or substract something from both sides of the equation, you can multiply or divide by something (although you can't divide by zero).

So, PV=nRT and you want to "move" R to the left hand side... Divide both sides by R. That gives

PV/R = nRT/R

R on the RHS cancels out. That's the general method.

I see it now! 
This is the equation - PV/n = RT, I then divided PV, which is now n= RT/PV, but UGH! wrong answer again. Hmmm...

I've reading this chapter over and over again, but I cannot seem how to find the answer. When it comes to calculation, I become frozen. I am really weak in math, and now, in chemistry ( only for calculation). Trying to answer 1 question would take me around 10 minutes or even more. I know this question is soo simple to answer, but ughh I'm so frustrated...

What mass of water at 100 degree Celsius can be vaporized by the addition of 45.0 kcal of heat?

[sjb]

I see it now! 
This is the equation - PV/n = RT, I then divided PV, which is now n= RT/PV, but UGH! wrong answer again. Hmmm...

Not quite. Almost, but not quite. If you divide the RHS by pV, then you do the same to the LHS; which gives pV/npV = pV/npV = 1/n.

Perhaps it may be easier to think in terms of numbers? 15/5 = 3. Now, how do you manipulate 15 and 3 to get 5?

What mass of water at 100 degree Celsius can be vaporized by the addition of 45.0 kcal of heat?

What is the definition of a phase change? Do you have any further information in this question?

S