How to do calculations involving solubility?

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la95
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The question I have in my chemistry booklet is:

A student was finding the solubility of sodium chloride in water.
He heated a saturated solution of sodium chloride to dryness, using an evaporating basin.
The following table of results was obtained.

Mass of evaporating basin + sodium chloride solution = 140.57g
Mass of evaporating basin = 72.00 g
So mass of sodium chloride solution = 68.57 g

Mass of evaporating basin + dry sodium chloride = 90.57g
Mass of evaporating basin = 72.00 g
So mass of dry sodium chloride = 18.57 g

1) State the mass of water in the sodium chloride solution.
2) Calculate the solubility of sodium chloride in water in g/100g if water.


I assume that for 1), I must simply subtract 90.57 from 140.57? However, I have no idea how to work out 2). Any input is appreciated!
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username878045
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(Original post by la95)
The question I have in my chemistry booklet is:

A student was finding the solubility of sodium chloride in water.
He heated a saturated solution of sodium chloride to dryness, using an evaporating basin.
The following table of results was obtained.

Mass of evaporating basin + sodium chloride solution = 140.57g
Mass of evaporating basin = 72.00 g
So mass of sodium chloride solution = 68.57 g

Mass of evaporating basin + dry sodium chloride = 90.57g
Mass of evaporating basin = 72.00 g
So mass of dry sodium chloride = 18.57 g

1) State the mass of water in the sodium chloride solution.
2) Calculate the solubility of sodium chloride in water in g/100g if water.


I assume that for 1), I must simply subtract 90.57 from 140.57? However, I have no idea how to work out 2). Any input is appreciated!
Well, the solubility in g/100g is simply found by dividing the grams of NaCl in the water you had, by the mass of water. However, you need to make sure that the water is expressed in units of 100g, which would be the mass of water in grams divided by 100 (in this case 0.5).
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la95
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(Original post by PythianLegume)
Well, the solubility in g/100g is simply found by dividing the grams of NaCl in the water you had, by the mass of water. However, you need to make sure that the water is expressed in units of 100g, which would be the mass of water in grams divided by 100 (in this case 0.5).
Thank you so much for your help! I just wanted to ask for clarification on something (you'll have to bear with me - calculations, even the simplest ones, often go over my head). Why would dividing the mass of water in grams by 100 produce a unit of 100g? I feel silly asking, but I struggle to make such connections!
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username878045
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(Original post by la95)
Thank you so much for your help! I just wanted to ask for clarification on something (you'll have to bear with me - calculations, even the simplest ones, often go over my head). Why would dividing the mass of water in grams by 100 produce a unit of 100g? I feel silly asking, but I struggle to make such connections!
Well think about if it was kg - kg is the same as writing 1000g. To convert from g to kg, you have to divide by 1000. Does that help?
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la95
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(Original post by PythianLegume)
Well think about if it was kg - kg is the same as writing 1000g. To convert from g to kg, you have to divide by 1000. Does that help?
Ah, I see! Thank you - I feel a bit silly now! :P
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la95
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I'm really struggling with these solubility questions! Does anyone have any idea about this one?

2. A solution of magnesium sulfate is heated to increase solubility and is then cooled. Crystals of hydrated magnesium sulfate are then filtered off and dried. The solubility of hydrated magnesium sulfate at two temperatures is given below.


At 20 degrees C, solubility in g per 100g of water = 36
At 90 degrees C, solubility in g per 100g of water = 123


In a batch process, a saturated solution of magnesium sulfate at 90 degrees C contained 200kg of water. Use the table to calculate the mass of solid hydrated magnesium sulfate crystals produced when the solution was cooled to 20 degrees C.
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Borek
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How much gram of magnesium sulfate will precipitate out of every 100g of water?

Once you have that, see if if you can calculate how many grams of the sulfate will precipitate out of 100g of the solution.
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la95
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(Original post by Borek)
How much gram of magnesium sulfate will precipitate out of every 100g of water?

Once you have that, see if if you can calculate how many grams of the sulfate will precipitate out of 100g of the solution.
I really have no idea how to do either of those things! I'm useless when it comes to anything remotely mathematical. :shy2::sigh:
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Borek
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There were 123 g dissolved, now there are 36 g dissolved, how many precipitated out?
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la95
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(Original post by Borek)
There were 123 g dissolved, now there are 36 g dissolved, how many precipitated out?
Ah I see! Thank you.
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