Can someone tell what I'm doing wrong with this Pharmaceutics problem

[SauvignonBlanc]

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Question

How many fluid ounces of DDT (specific gravity 2.25) should be added to 70 grains of a substance to obtain 15% (w/w)


This is how I worked it:

1 grain = .0650g
1 fl oz. = 30ml

15g/100g = 70grains x 0.0650g == (4.55g x 100g) /15g = 30.33g

= 30.33g/2.25 = 13.48ml

= 13.48ml x 1 fl.oz/30ml = 0.449 fl. oz.

My answer is wrong, but I can't figure out why, can any one help?
Thank you.

Thanks

 

[sdn1977]

Question

How many fluid ounces of DDT (specific gravity 2.25) should be added to 70 grains of a substance to obtain 15% (w/w)


This is how I worked it:

1 grain = .0650g
1 fl oz. = 30ml

15g/100g = 70grains x 0.0650g == (4.55g x 100g) /15g = 30.33g

= 30.33g/2.25 = 13.48ml

= 13.48ml x 1 fl.oz/30ml = 0.449 fl. oz.

My answer is wrong, but I can't figure out why, can any one help?
Thank you.

Thanks

Is the answer 43.09ml?

I'm out of town & I don't have my Remington's to refer to (which is what I'd do in real life since I don't use these formulas very often) so I'm not exactly sure off the top of my head.

 

[TheChemist]

Here's what I did

70gr = 4.55g

M1V1 + M2V2 = M3V3

x(%100) + (4.55g-x)0% = 15%(x+4.55g)

solve for x

x=0.8029g

0.8029g x 1ml/2.25g = 0.357ml

0.357ml x 1floz/29.57ml = 0.012 floz

**note I'm using 1floz = 29.57ml
According to my school the naplex is using this conversion

I don't know if I'm right. I usually make a stupid mistake somewhere.

 

[norx]

How about posting the answer to confirm?

I worked it out almost the same way since I was studying for a calculations test we are having very soon. I got the same answer.

 

[dragonet]

Here's what I did

70gr = 4.55g

M1V2 + M2V2 = M3V3

x(%100) + (4.55g-x)0% = 15%(x+4.55g)

solve for x

x=0.8029g

0.8029g x 1ml/2.25g = 0.357ml

0.357ml x 1floz/29.57ml = 12.07floz

**note I'm using 1floz = 29.57ml
According to my school the naplex is using this conversion

I don't know if I'm right. I usually make a stupid mistake somewhere.

I got 0.01207 floz.

What is the correct answer supposed to be?

 

[sdn1977]

Wine lover.....get your head out of your bottle & come back & give us the answer!😡

 

[DrugDealer]

0.357ml x 1floz/29.57ml = 12.07floz

I think you multiplied 0.357 mL by 29.57 mL instead of dividing it here....

 

[DrugDealer]

I got 0.01207 floz.

I get that, too. Seems silly to put that value in ounces.

 

[taken2]

Yeah, I think the answer is 0.0120floz. Remember you should be using 29.57ml for 1floz instead of 30ml.

 

[TheChemist]

I think you multiplied 0.357 mL by 29.57 mL instead of dividing it here....

You're right. I was trying to do it fast on a napkin. It's always those stupid mistakes that get me on those exams. Well back to memorizing my drug list. I've got a quiz tomorrow.

 

[ZpackSux]

Dr. Pepper sez.. 23?

 

[SauvignonBlanc]

Wine lover.....get your head out of your bottle & come back & give us the answer!😡

I promise I'll be sober b'4 the next test:😉

Hi y'all

I see you all have been working hard on this; good job! I have also come up with another solution but I have no idea who is right or wrong, I'll be checking with my Professor today to see which of the answers on this board (yours/mine) is right, I will be sure to keep you posted:

How many fluid ounces of DDT (specific gravity 2.25) should be added to 70 grains of a substance to obtain 15% (w/w)


Note I'll be using 1gr = .0648g & 1fl oz = 29.57ml

15g/100g = 4.536g/x (x = solute + solvent)

= 453.6 = 15x = 30.24g

= 30.24g-4.536g = 25.704g/2.25(sp. g)= 11.4ml

(11.4ml/29.57ml)* 1fl. oz = 0.386 fl. oz

 

[norx]

15%/85% = 4.536g/X ml (by dimensional analysis)

Therefore, X = 25.704 ml / 2.25 (sp. gravity) = 11.424ml

So, 1 fl. oz./ Y fl. oz = 29.57 ml / 11.424 ml (by dimensional analysis)

Therefore, Y = 0.386 fluid ounces.

____________________________________________________________

This is how I normally do my weight to weight problems now, since I went over the entire chapter from my calculations textbook I can safely say it is correct.

 

[SauvignonBlanc]

I promise I'll be sober b'4 the next test:😉

Hi y'all

I see you all have been working hard on this; good job! I have also come up with another solution but I have no idea who is right or wrong, I'll be checking with my Professor today to see which of the answers on this board (yours/mine) is right, I will be sure to keep you posted:

How many fluid ounces of DDT (specific gravity 2.25) should be added to 70 grains of a substance to obtain 15% (w/w)


Note I'll be using 1gr = .0648g & 1fl oz = 29.57ml

15g/100g = 4.536g/x (x = solute + solvent)

= 453.6 = 15x = 30.24g

= 30.24g-4.536g = 25.704g/2.25(sp. g)= 11.4ml

(11.4ml/29.57ml)* 1fl. oz = 0.386 fl. oz

15%/85% = 4.536g/X ml (by dimensional analysis)

Therefore, X = 25.704 ml / 2.25 (sp. gravity) = 11.424ml

So, 1 fl. oz./ Y fl. oz = 29.57 ml / 11.424 ml (by dimensional analysis)

Therefore, Y = 0.386 fluid ounces.

____________________________________________________________

This is how I normally do my weight to weight problems now, since I went over the entire chapter from my calculations textbook I can safely say it is correct.

I did check with my Prof . and the answer is 0.386 fl. oz.

 

[npage148]

i got the same answer and the Chemist and Taken cept I did it a different way

I did
70gr= 4.536g

15/100=x/(4.536+x) and solved from there for x getting 800mg and then .39ml
it checkes too! 15/100=.800/(4.536+.800)


I really dont think SauvignonBlanc's answer is right. If we break out logic and think

15%= 15 grams per 100grams
her answer has
"30.24g-4.536g = 25.704g/2.25(sp. g)= 11.4ml" has like 24 grams in the solution so you would need like 160 grams of total mass not 70grains (4.536grams)

Im not really sure what your professor is thinking but you should double check with him again

 

[golf299]

Doing problems like that is a great way to waste a students time in pharmacy school.

 

[npage148]

So seriosuly, which answer is right? .386 ounces or .012 ounces

 

[SauvignonBlanc]

i got the same answer and the Chemist and Taken cept I did it a different way

I did
70gr= 4.536g

15/100=x/(4.536+x) and solved from there for x getting 800mg and then .39ml
it checkes too! 15/100=.800/(4.536+.800)


I really dont think SauvignonBlanc's answer is right. If we break out logic and think

15%= 15 grams per 100grams
her answer has
"30.24g-4.536g = 25.704g/2.25(sp. g)= 11.4ml" has like 24 grams in the solution so you would need like 160 grams of total mass not 70grains (4.536grams)

Im not really sure what your professor is thinking but you should double check with him again

So seriosuly, which answer is right? .386 ounces or .012 ounces

npage, the correct answer is 0.386.

Let me explain how I did it. 4.536 is 15% of the total solution

my equation is 15% = 4.536/(x+4.536) this can be written as 15g/100g = 4.536/(4.536+x)

= 15g(4.536g+x) = 453.6

68.04g +15x = 453.6

x = (453.6-68.04)/15 = 25.704g

25.704g/2.25(sp. g)= 11.4ml/29.57 = 0.386 fl.oz.

==========================================================

"15/100=x/(4.536+x) and solved from there for x getting 800mg and then .39ml"
it checkes too! 15/100=.800/(4.536+.800)

Look carefuly at your set up esp. the right side, what do you mean by "x/(x + 4.536)", what is x in this equation? that's where your error is coming from

 

[npage148]

Ok, i figured it out
you solved it so that the DDT is the solvent and the 70gr of the substance is the solute

I did it the other way around, with the 70gr being the slolvent and the DDT beiing the solute. What a badly worded problem

 

[TheChemist]

That was a poorly written problem.