dilution problem

[Guest guest]

lorivepcc,

You are going the right way, but don't forget that you will need to subtract

the 360 G from your answer to solve the problem. (360*2.25) / 1.5 = 540 =>

540 - 360 = 180 G

You can also solve the problem by comparing the " parts " to each other

- from your alligation you have determined that you need 0.75 parts of

2.5% HC (which you need to determine the amount in Grams) and 1.5 parts of 0.25%

HC (which is equal to 360 G)

=> 0.75 / 1.5 = x / 360 G (note: 0.75 / 1.5 = 1/2 or 0.5)

=> 0.5 * 360 G= x

=> x = 180 G

Hope this helped.

Respectfully,

Anne P LaVance, BS, CPhT

Instructor

Pharmacy Technician Program

Delgado Community College

New Orleans, LA

TEXTPERT ;-)

[Guest guest]

Hi Lori-

It looks like you're heading in the right direction. Now just solve

for X.

0.75/2.25= X/360

X = 120gm of the 2.5% cream

1.5/2.25= X/360

X = 240gm of the 0.25% cream

The formula structures get tweaked when the messages are posted. For

those who would like to see an example the " allegation lay out "

please click on the files option on in the yellow box to your left

and then scroll way down until you come to Tutorials, allegation I

and II.

Sincerely,

Dora

Group Mod

> How many grams of 2.5% hydrocortisone cream should be mixed with

360g

> of 0.25% cream to make a 1% hydrocortisone cream?

>

>

> This is what I have so far:

>

> 2.5% 0.75

> ------

> 2.25

> 1%

>

> 0.25% 1.5

> -----

> 2.25

>

> I'm not sure if this is right. (1.5/2.25)* X = 360g and solve for

X.

> I need help. Thanks in advance.

[Guest guest]

TO all-

My apologies for the incorrect answer. I misread it as a total of

360gm of 1% cream---not 360gm of 0.25% cream plus Xgm of the 2.5%

I hate making careless mistakes like that!

For my penance I will perfom 20 alligations, 10 ratio/proportions,

and 2 temperature conversions.

Study hint for PTCB candidates: Make sure you read the exam questions

*correctly*

Sincerely,

Dora

Group Mod

[Guest guest]

Dear Dora,

You and I both HATE making erors! But I have to confess YOU HAVE

NEVER BEFORE MADE ANY KIND OF AN ERROR IN THE FOUR YEARS I HAVE HAD

THIS SITE AND IN THE LAST YEAR THaT YOU HAVE BEEN THE OFFICIAL

MODERATOR!

I APPRECIATE ALL OF YOUR INPUT.

Respectfully,

Love ya

Jeanetta

PS. You now have absolution!

> TO all-

> My apologies for the incorrect answer. I misread it as a total of

> 360gm of 1% cream---not 360gm of 0.25% cream plus Xgm of the 2.5%

> I hate making careless mistakes like that!

> For my penance I will perfom 20 alligations, 10 ratio/proportions,

> and 2 temperature conversions.

>

> Study hint for PTCB candidates: Make sure you read the exam

questions

> *correctly*

>

> Sincerely,

> Dora

> Group Mod

[Guest guest]

Jeanetta,

I went to your tutorial on dilution and concentration, and I like the

way you explain it, but one this specific problem I thought this

method would be easier.

Tell me if you agree on this one:

The doctor has ordered 60ml of a 12% solution of a specific drug (Rx).

However, on the shelf you have only 30% (Availability or Av).

What can you do? or use instead?

Answer -

if we know an old volume we can get the new volume from it.

the formula is (ov)*(o%)=(nv)*(n%)

(xml)*(30%)= (60ml)*(12%)

x=24 ml.

then 60-24=36 ml of water.

Am I right?

thanks.

[Guest guest]

There is no  problem using the formula that you have here.

But allow me to state what would you do if the RPh said dillute the

30% with an 8% that will expire in 60 days to use it up?

In that case an alligation may be a better way to go. For that reason Iike using

the alligation method for these dilution problems when ever I can use them.

For the beginning student this answer is 24 ml o f30% Solution and 36 ml of H2O.

Jeanetta Mastron CPhT BS

From: spokane94 <spokane94@...>

Subject: dilution problem

Date: Monday, September 22, 2008, 8:07 AM

Jeanetta,

I went to your tutorial on dilution and concentration, and I like the

way you explain it, but one this specific problem I thought this

method would be easier.

Tell me if you agree on this one:

The doctor has ordered 60ml of a 12% solution of a specific drug (Rx).

However, on the shelf you have only 30% (Availability or Av).

What can you do? or use instead?

Answer -

if we know an old volume we can get the new volume from it.

the formula is (ov)*(o%)=(nv)*(n%)

(xml)*(30%)= (60ml)*(12%)

x=24 ml.

then 60-24=36 ml of water.

Am I right?

thanks.

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