Given percent composition, find mass per litre of solution

In summary, we have a 15% by mass solution with a density of 1.2 g/mL. The question is asking for the mass per liter concentration of the solution, with options (a) 180 g/L, (b) 150 g/L, (c) 125 g/L, and (d) cannot be determined from this information. To solve this, we can use the equation D=m/v and the knowledge that 1000 mL = 1 L. The correct answer is (a) 180 g/L, which is 15% of 1200 g/L (the mass of 1 L of solution). Mass concentration is the amount of a substance dissolved in a solvent to make a solution.
  • #1
brbrett
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Homework Statement


A 15% by mass solution has a density of 1.2 g/mL. What is the mass per liter concentration of this solution?
→ (a) 180 g/L (this is the answer, pretend you don't know)
(b) 150 g/L
(c) 125 g/L
(d) cannot be determined from this information

Homework Equations


Density
Possibly percent composition

The Attempt at a Solution


I don't know g/L.
D=m/v
I assume 15% of the solution is 15g (This is clearly not the case, or I wouldn't be here)
1.2=15/v
v=12.5mL
Convert mL to L
15g/0.0125mL
1200g/L <---Not even on the answer list, and sounds unreasonable anyway

Without straight telling me the answer, how does one approach a question such as this?
 
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  • #2
It's not the best problem in my opinion because the solution has a mass of 1200 g per liter, and if you subtract out the material that was dissolved, you have presumably what is water (when you are given a solution and the material is unspecified, water is usually implied), that must have a density that is at least 1020 grams per liter, and the volume might even be slightly less than a liter. (Sometimes the dissolved material will add volume. When it is removed, the volume could decrease.) 15% by mass of 1200 grams is 180 grams. I guess it is also fair to assume that the solution is not a water solution. Anyway, to help you with your calculations, there are 1000 ml (milliliters) in a liter. To do a percentage, you divide by 100. e.g. for 15%, its fractional value is 15/100=0.15.
 
Last edited:
  • #3
brbrett said:

Homework Statement


A 15% by mass solution has a density of 1.2 g/mL. What is the mass per liter concentration of this solution?
→ (a) 180 g/L (this is the answer, pretend you don't know)
(b) 150 g/L
(c) 125 g/L
(d) cannot be determined from this information

Homework Equations


Density
Possibly percent composition

The Attempt at a Solution


I don't know g/L.
The problem statement clearly says the density of the solution is 1.2 g/mL. Don't you know that 1000 mL = 1 L?
D=m/v
I assume 15% of the solution is 15g (This is clearly not the case, or I wouldn't be here)
1.2=15/v
v=12.5mL
Convert mL to L
15g/0.0125mL
1200g/L <---Not even on the answer list, and sounds unreasonable anyway
This is the mass per liter of solution. It is not the mass concentration, however.
Without straight telling me the answer, how does one approach a question such as this?
X% mass concentration of a solution means that:

the mass concentration per liter = the mass of 1 liter of solution * X / 100
 
  • #4
Now that I think about it, my work above was kinda silly :p
Plugging into the equation, I get 180g/L from 1200x(15/100), which is the correct answer (which is just 15% of that number).
What is mass concentration exactly? Is it simply the the part of the solution we are looking at, which implies the rest of the solution is water/other substances?
 
  • #5
brbrett said:
Now that I think about it, my work above was kinda silly :p
Plugging into the equation, I get 180g/L from 1200x(15/100), which is the correct answer (which is just 15% of that number).
What is mass concentration exactly? Is it simply the the part of the solution we are looking at, which implies the rest of the solution is water/other substances?
Mass concentration is the amount of a substance dissolved in some sort of solute to make a solution. The solute can be water or any other liquid.

Concentration can be defined in several different ways:

https://en.wikipedia.org/wiki/Concentration
 
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  • #6
The mass concentration they are looking for is the mass of solute per liter of solution.
 
  • #7
Got it. Unfortunately I only get to use Molarity in my current year of chemistry, so it's good that I now know what mass concentration is. Thanks for the help!
 

1. How do you calculate the mass per litre of a solution given the percent composition?

The mass per litre of a solution can be calculated by multiplying the percent composition (expressed as a decimal) by the density of the solution. The resulting value is the mass per litre of the solution.

2. What is the density of a solution?

The density of a solution is the mass of the solution divided by its volume. It is usually expressed in units of grams per milliliter (g/mL) or grams per cubic centimeter (g/cm3).

3. How is the percent composition of a solution determined?

The percent composition of a solution is determined by dividing the mass of the solute (the substance being dissolved) by the total mass of the solution (solute + solvent) and multiplying by 100. This value represents the percentage of the solution that is made up of the solute.

4. Can the mass per litre of a solution be converted to other units?

Yes, the mass per litre of a solution can be converted to other units by using conversion factors. For example, to convert from grams per milliliter to kilograms per litre, you would multiply the mass per litre by 0.001.

5. How does the mass per litre of a solution relate to its concentration?

The mass per litre of a solution is directly proportional to its concentration. This means that as the mass per litre increases, so does the concentration. Concentration is typically expressed in units of moles per litre (mol/L) or grams per litre (g/L).

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