# What is the mass of potassium nitrate which crystallizes?

• lioric
In summary, the conversation discusses the process of cooling a saturated solution of potassium nitrate from 68 to 36 degrees Celsius and determining the mass of potassium nitrate that crystallizes. The solubility of potassium nitrate at different temperatures is given, and the calculation involves finding the difference in the amount of dissolved potassium nitrate at 68 and 36 degrees Celsius. The final answer is 4.64g of potassium nitrate crystallizing from the solution. The conversation also mentions a typo in the original working, where the correct answer is 5.44g of potassium nitrate crystallizing.
lioric

## Homework Statement

20g of saturated solution of potassium nitrate is cooled from 68 to 36 degree Celsius
What is the mass of potassium nitrate which crystallizes?
Potassium nitrate solubility per 100g of water
68 degree Celsius = 120g
38 degree Celsius = 60g

## Homework Equations

I tried without equations just cross multiplying

## The Attempt at a Solution

Since the question says 20g of solution which means it's mass of potassium nitrate + water
So since
120g = 100g water = 220g solution (120+100)

120g = 220g
X = 20g
X= 10.9g of potassium nitrate in unknown amount of water

20-10.9= 9.1g of water

Therefore 20g of solution is actually 10.9g of potassium nitrate in 9.1g of water at 68 degree Celsius

In 38 degree Celsius = 60g potassium nitrate per 100 g of water

So
60g = 100g
X = 9.1g

X = 5.46g potassium nitrate in 38 degree Celsius in 9.1g water

Amount of potassium nitrate crystallized
10.9-5.46=5.44

Is this calculation correct?

Last edited:
The calculation is. The numbers are not.

BvU said:
The calculation is. The numbers are not.

Numbers are not? Please do tell what I did wrong? Or at least tel me which part?

lioric said:
X= 10.9g of potassium nitrate
lioric said:
10.1-5.46=4.64g

Oh that's right it s a typo
Actually I was wondering why I got 4.5 while in my original working I got 5.4
I thought I made a calculation error
Thanks
And thank you for your time

BvU
And of course the dissolved nitrate/water ratio drops by a factor of 2, the amount of water stays the same, so the amount of dissolved nitrate halves too...

BvU said:
And of course the dissolved nitrate/water ratio drops by a factor of 2, the amount of water stays the same, so the amount of dissolved nitrate halves too...

Could explain that part a bit more

120 g/100g water goes to 60 g/100 g water, so y g/x g water goes to ##1\over 2## y g/x g water.

BvU said:
120 g/100g water goes to 60 g/100 g water, so y g/x g water goes to ##1\over 2## y g/x g water.
Wow
Thank you very much

## 1. What is the definition of mass?

Mass is a physical property that measures the amount of matter in an object.

## 2. How is the mass of an object measured?

The mass of an object is typically measured using a balance or scale, which compares the gravitational force on the object to a known standard.

## 3. What is potassium nitrate?

Potassium nitrate, also known as saltpeter, is a chemical compound with the formula KNO3. It is commonly used in fertilizers, fireworks, and food preservation.

## 4. How does potassium nitrate crystallize?

Potassium nitrate typically crystallizes when a saturated solution of the compound is allowed to cool and evaporate, causing the molecules to come together and form a solid crystal structure.

## 5. What is the importance of knowing the mass of potassium nitrate that crystallizes?

Knowing the mass of potassium nitrate that crystallizes is important for understanding the chemical properties of the compound and for accurately measuring and predicting its effects in various applications, such as in agriculture or pyrotechnics.

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