When doing these kinds of problems you have to be aware that substance A is your solute while your solution is the mass of the solute + the mass of the solvent. An example question of this is: What mass of water must be added to 425 grams of formaldehyde to prepare 40.0% (by mass) solution of formaldehyde?
To solve this problem you would set up the equation like this: .400= 425g./(425g + Xg) this then becomes 170+ .400X=425 this means that X would equal 638g H2O
Another example:
http://image.slidesharecdn.com/ch3-140221122959-phpapp01/95/ch-34-law-of-definite-proportions-11-12-8-638.jpg?cb=1392985833
Kayla, I really like how you didn't just explain the steps of this concept, but you also went the extra mile to provide an example problem and worked it out. This lesson proved to be a challenge with a lot of little things to remember and I hope you did well on the test!
ReplyDeleteHow the answer is 25% please explain . I beg u again please explain step by step (briefly).
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