Mixing solutions - wrong answer?

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In summary, the conversation discusses two problems involving conversions and concentration calculations. The first problem involves preparing a specific amount of sulfuric acid, while the second problem involves calculating the concentration of a compound in a pond. The solution to the first problem is disputed, with the answer suggesting 16ml while the calculation results in 5.56ml. For the second problem, the calculation is correct numerically, but there is a discrepancy in the units used for concentration. The conversation concludes with a clarification on the correct units to use for v/v concentration calculations.
  • #1
pivoxa15
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Homework Statement


Here is two similar questions but which I got a different answer to the back of the book

1. You are to prepare 50ml of 2M sulfuric acid, which is to be added to a sample of white wine to make the sulfur dioxide preservative in the wine available in solution, so that its concentration can be determined. What volume of concentrated (18M) acid will you prepare?

2. A factory discharged 15ML of a liquid waste containing 12ppm (v/v) of a highly toxix compound into a pond. Before it was added, this pond already contained 920ML of wastewater in which this compound was present at a concentration of 0.23ppm (v/v). What was the new concentration of this compound in this pond?


Homework Equations


conversions


The Attempt at a Solution


Q1.
2 moles/litre, 50ml => 0.1moles

18moles/litre. Need 0.1moles so 0.1/18=0.0056L=5.56ml but answers suggest 16ml


Q2.
ppm (v/v) => 1g/10^6g = 1g/1000kg

1L=1kg assuming solvent is water

15ML @ 12ppm => 15*10^6 kg @ 12g/1000kg => 15*10^3 * 12g grams of solute or 180kg of solute

920ML @ 0.23ppm => 920*10^6 kg @ 0.23g/1000kg => 920*10^3 * 0.23g or 211.6kg of solute

Hence total solute is 391.6kg. Total solution is 935ML. So a new total concentration of 391.6kg/(935*10^6kg) * 10^6g = 0.42g/10^6g or 0.42ppm. But the answers suggest 0.49ppm.

Who is wrong?
 
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  • #2
1. You are OK.

2. You are OK and wrong at the same time. Your result is correct numerically, but note that question is about v/v concetration - so you should calculate using L, not g.


concentration lectures
 
  • #3
v/v => ml of solute per 100ml of solution. Luck in solution of water, 1ml = 1g. I used 1g in my calculations. So all I had to do was to switch g to ml. The magnitude of the numbers wouldn't change. Thanks for picking that up for me. I will be more careful next time.
 

1. How does mixing solutions incorrectly affect the outcome?

Mixing solutions incorrectly can lead to inaccurate results, as the wrong proportions of substances can alter the chemical reactions and overall composition of the mixture. This can also affect the physical properties of the solution, such as its color, density, and pH.

2. Can mistakes in mixing solutions be dangerous?

Yes, mistakes in mixing solutions can be dangerous. Depending on the substances involved, incorrect mixing can result in explosions, fires, toxic fumes, and other hazardous situations. It is important to follow proper safety protocols when handling and mixing solutions.

3. What are some common mistakes made when mixing solutions?

Some common mistakes made when mixing solutions include using the wrong measurements or proportions, not following the correct order of mixing, and not properly diluting concentrated solutions. Not properly labeling or identifying solutions can also lead to mistakes.

4. How can I avoid making mistakes when mixing solutions?

To avoid making mistakes when mixing solutions, it is important to carefully read and follow instructions, use accurate measuring tools, and double-check calculations. It is also helpful to wear appropriate protective gear and work in a well-ventilated area.

5. What should I do if I realize I have mixed solutions incorrectly?

If you realize you have mixed solutions incorrectly, it is important to stop the experiment and dispose of the solution safely. If the incorrect mixture has already been used in an experiment, it may be necessary to repeat the experiment using the correct mixture.

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