SOLVE THIS
the package information enclosed with the vial containing 5,000,000 units of penicillin G specifies that when 23 ml of solvent are mixed to dry powder the resultant concentration is 200,000 unit/ml.on the basis of this information ,how many ml of sterile water injection should be used to prepare a solution containing penicillin G potassium 500,000 unit/ml?
a-8
b-9.2
c-10
d-18.4
e-25
well the answer they give is A 8 ml but i dont think so.
the idea is when the amount of the substance remains the same but there is concentration or dilution we can use this formula Q1 X C1= Q2 X C2
200000 x 23= V2 X 500000
V2=9.2 ML
THIS IS MY WAY OF SOLVING IT ,MAY BE THERE IS SOME TRICK I CANT SEE IT SO IF ANYONE HAS ANY IDEA PLEASE PARTICIPATE,MY PROBLEM THERE IS 4 QUESTIONS LIKE THIS AND ALL ARE SOLVED IN ANOTHER WAY
well mat this is a question from pharmacyprep.com,some freind send it for me,as i see i copied the question as it is. i have two more if u wqant and they r really difficult ,so if u can help it would be great
I knew I recognized the question, I believe it was originally taken from Pharmaceutical Calculations for the Pharmacy Technician. The question in original context gives you a little more information, but whether it is part of the question or answer is unclear.
The whole point of this question is that the dry powder itself adds to the final volume of the solution. If you are not told this then your clue should be the fact that 5 million units divided by 23ml does not equate to a 200,000 unit/ml solution. What does that mean? It means that the volume of the resulting solution is not actually 23ml (that is just what we put in), the powder is adding to the final volume. Now take another look at the question and see if you can get the correct answer.
You can view the question and the answer in original context thanks to Google Books.
By all means post any other calculation questions (provided they are not from past PEBC exam papers) so everyone can benefit.
First step
5000000/200000 = 25 ml total volume of the solution
now u r adding 23 ml to make final solution so volume of the power penicillin is 25-23 = 2 ml
second step
5000000/500000 = 10 ml final solution of the second liquid
now volume of the power is 2 ml so 10-2 = 8 ml is the water that you should add
ok this is another question
the label of dry powder for oral suspension states that when 111 ml of water are added to the powder 150 ml of a suspension containing 250mg/5ml amicillin are prepared . How many ml should be used to prepare a suspension which would contain a dose of 8 mg/kg per 5 ml to be given to a child weighing 60 lbs.
a- 97
b- 110
c-133
d- 150
e- 172
I'm sure there are many way of answering this question, but here is how I would approach it. With all calculation questions read through them once and then read through them again determining:
- What is the question asking for?
- What information have you been provided?
- What information is not required?
Some calculation questions are quite straightforward but they will try and confuse you by making the question long, and wordy. Often information will be included that you might not need. So lets look at what we have here.
- What is the question asking for?
- What information have you been provided?
- What information is not required?
"a suspension which would contain a dose of 8 mg/kg per 5 ml to be given to a child weighing 60 lbs" from "dry powder for oral suspension that states that when 111 ml of water are added to the powder 150 ml of a suspension containing 250mg/5ml Ampicillin are prepared".
We know we are dosing a child who is 60 lb.
We know we need to prepare a suspension providing 8 mg/kg/5 ml.
We know that if we add 111 ml to our dry Ampicillin powder we get a solution with afinal volume of 150ml and a concentration 250 mg/ml.
All information provided here is relevant, but always bear in mind that calculation questions may provide you with lots of irrelevant background information.
So let's use what we have and get to what we need:
A dose of 8mg/kg. Our child is 60 lb and that equals 27.27 kg (1 kg =2.2 lb). Therefore we want a solution with a final concentration of 218 mg/5 ml (rounded to nearest decimal place).
We start with dry powder such that when we add 111 ml of solvent we get a final volume of 150 ml and a concentration of 250 mg/5 ml. How do we get from 111 ml to 150 ml? This is telling us something important...the dry powder is adding 39 ml (150 - 111 ml) to the final volume.
So we need a 218 mg /5 ml solution, this means we need the solution to be more dilute than the solution suggested by the label on the bottle and this means we need to add more than 111 ml. How do we find out how much solvent we need to add? Well to find the concentration of a solution we need to know how much drug we have in solution and the volume of the solution. How much drug is in the original powder?
150ml of 250 mg / 5ml = 250/5 * 150 = 7500 mg
How much solution does this need to be dissolved in to create a concentration of 218 mg /ml? Lets use a proportion to find out:
7500mg/x = 218 / 5
218 * x = 7500 * 5
x = 37500 / 218
x = 172 ml
So if our powder is dissolved in a solution with a final volume of 172 ml then we get our desired concentration. But wait....is that what we are asked for?....NO.....We are asked for "how many ml would be used" and what we have here is the final volume in ml of the solution. We know our powder adds 39 ml to the final volume and therefore we know to get a final volume of 172 ml we must have added:
172 - 39 ml = 133 ml (option c)
thank you mat,it wasnt easy to find it by myself.
but let me tell u how i could solve it thx to ur very important not about the volume of the suvstance we add..
as a rule when the amount of the substance remains the same use this formula it helps a lot
Q1X C1= Q2XC2
In our case we want V2 = 150x 250/218= 172ml
this is the volume of solution- 39=133ML
Absolutely, everyone has their own method and should stick to what works for them.
Hi Husseinmr,
I can tell you that 8ml is the correct answer and I can provide the reasoning behind it...but first of all....
This question looks famililiar so I know I have had to wrap my brain around this one in the past. Could you tell us where you have copied this question from. I ask this because the question as it is written here seems to be incomplete, is this exactly how the question is written? If there are any further details then let us know exactly how the question is written word for word.
The question as I have seen it in the past should indicate something about the final volume in the vial when 23ml of solvent and the dry powder in the vial are first mixed. This is your first clue ;) I would like everyone to think about this as it is a great question (when all the details are provided)
Let me know if there is more information and I will be happy to tell everyone how the answer is acheived.
Mat :)