Gen Chem: Normality and solution question

[INH]

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A 1.6 gram sample of monoprotic acid neutralizes 100ml of .08M NaOH solution. What is the molar mass of the acid?

( I know this must be a normality problem, and I was originally thinking N1M1=N2M2.... )


How many gram of 2% [w/w] NaCl solution contain .50g of NaCl?
a. 600g
b. 13500g
c. 135g
d. 90g
e. 160g


thank you for the help! 🙂

 

[aznriptide859]

Not sure if these are right since I'm not the best at GC.

For #1, since NaOH (strong base) completely neutralizes an acid, then the # of moles of base used should equal # of moles of acid originally found.

So, moles = M2 * V2 = 0.08M * 0.1L = 0.008 mol (which I think equals mols of original acid)

Molar mass is just in units of g/mol, so MM = 1.6g/0.008mol = 200g/mol.

No idea on #2, sorry.

 

[SafetyDog]

You have the answer choices mixed up for the second question with the question before.

 

[INH]

These are really great explanations and I apologize for posting the wrong answer choices for the 2nd question! Additionally, I am still having difficulties understanding the ratio used in the second question. It kind of reminds me of a %ionized type of ratio. Would you mind explaining how to set it up? Much appreciated

 

[SafetyDog]

Sure. The second problem is worded really weird and I had a hard time with it at first too. So basically, whenever it's a x% [w/w] that means its x grams per 100 grams no matter what. Same goes for [w/v] which is weight per volume. This means it's x grams per 100 milliliters.

In this case, it means that you have 2 grams NaCl per 100 grams of the solution. So if you want 0.5 grams of NaCl, which is a fourth of 2, you would naturally divide the 100 by 4 to get your answer of 25 grams solution.

 

[INH]

Great, I knew there was a format to follow for these concentration problems -- Safety Dog this was super helpful