[jdxboy88]

i am confused i tried doing mass x = Mass of solute / mass of solvent then multiplying it by 100 and i cant seem to get the answer right the teacher never gives us enough information. can someone help plz .

A chemistry lab experiment requires 22.5 g of silver nitrate. How many grams of a 15.5% by mass solution of silver nitrate should be used?

[Padfoot]

This is how I would approach:

The mass percent concentration is 15.5%.
This means 15.5g of solute per 100g of solution.

Using ratio:
15.5/100 = 22.5/x

Solve for x, which is your answer

[AWK]

i am confused i tried doing mass x = Mass of solute / mass of solvent then multiplying it by 100 and i cant seem to get the answer right the teacher never gives us enough information. can someone help plz .

A chemistry lab experiment requires 22.5 g of silver nitrate. How many grams of a 15.5% by mass solution of silver nitrate should be used?

Use definition of mass percentage! - number grams of solute in 100 g of solution

[jdxboy88]

hmm, i tried the way that padfoot said, but didn't work..thanks though. i just dont understand how to set up the problem and i get confused between how to set up the equation for which is the solute and solvent and stuff.

[Padfoot]

hmm, i tried the way that padfoot said, but didn't work..thanks though.

Is this what you did?
15.5/100 = 22.5/x
x=22.5/(15.5/100)=145g

I just dont understand how to set up the problem and i get confused between how to set up the equation for which is the solute and solvent and stuff.

The question deals with ratios.  There are 15.5g of solute (AgNO3) per 100g.  In the question we simply scale up 100g by the same proportion we did 15.5g.
This is what the eqn (15.5/100 = 22.5/x) does.

[jdxboy88]

yea man, i did exactly what u said, i dunno it didn't work , this teacher just dont give us enough information ...and i can never ask her questions cuz out of the 400ppl in the class everyone crowds her with questions already...

[enahs]

and i can never ask her questions cuz out of the 400ppl in the class everyone crowds her with questions already...

That is why the have an office and office hours; as well as being willing to meet at other times if it is more convenient for you and they do not have other commitments.

[jdxboy88]

oh well thats cool office hours are awsome especially when u have one class after another then work afterwards, basically i cant understand her with that wierd accent and she works WAY to fast, she goes at her own pace, me and my friends have problems and we all work together

[Padfoot]

400ppl in the class everyone crowds her with questions already...

Yeah that happens a lot in my lectures as well (well, it used to, not many people bother any more  )
If you feel you don't have time to visit teacher after hours (though I'm sure you could find time), why not email?  Or simply sit near front so you get to teacher first?

Getting back to your question, you're right and teacher is wrong.