14. Solutions
Types of Aqueous Solutions
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Here, we're told that the solubility of a substance is 56 grams per 100 ml of water at 20 degrees Celsius. So, basically, we can dissolve up to 56 grams within 100 ml of water at that temperature. Now here we're saying a solution of this substance is prepared by dissolving 80 grams in a 100 ml of water at 75 degrees Celsius. The solution is then slowly cool cooled slowly at 20 degrees Celsius without any solid forming. The solution is alright. So we're at a higher temperature, so heat has been applied to it, allowing our solution to dissolve more than the 56 grams it normally can. Here it's dissolving 80 grams. They're telling us that we're cooling it back down at 20 degrees Celsius and nothing recrystallizes. That means we have still 80 grams dissolved as we cool down to 20 degrees Celsius. So we're still dissolving more than amount, our maximum equilibrium amount, and because of that, because we've gone beyond our max, we are a supersaturated solution. So here, we'd say, c is the correct answer. We've gone beyond our 56 grams that we normally would dissolve at 20 degrees Celsius. Of course, it makes sense that we go beyond that 56 degrees that 56 grams at a higher temperature. What's most important is when I get that down to 20 degrees Celsius, am I still dissolving that extra amount? If I am, then I'm a supersaturated solution. So here, option c will be the best answer. D doesn't work because let's take it back down to 20 degrees Celsius and see if any recrystallization has occurred. That's when we know for sure we have a supersaturated solution. Here, these answers don't work either.
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