pharmaceutical calculation.. please help?!

[shorty1991]

Hello, im a pharmacy student, and am always getting stuck on this same type of question, i just cant work out what to do, would anyone please offer some help. thankyou.

You have two solutions of glucose one 40%w/v and one 4%w/v. You are asked to provide 500ml of a glucose solution containing 20%w/v glucose by mixing the two solutions. What volume of the 40% solution would be required?
Give your answer in ml to the nearest ml.

[Nik]

Give your answer in ml to the nearest ml.

First things first: If you want help on a calculation question, this is not the best way to go about it.
Secondly, if you are continually getting stuck on this type of question then why not show us your methods, so we can let you know what you are doing wrong ?
Third and final thing: No need to post multiple times. Once is enough.

[johnep]

It is simple proportion, should have learned at elementary school.
johnep

[Asterix]

Johnep, that really isn't helpful. Saying its a simple proportion is not going to do his confidence any good. Try and help rather than stay demotivating things.

[Asterix]

Hello, im a pharmacy student, and am always getting stuck on this same type of question, i just cant work out what to do, would anyone please offer some help. thankyou.

You have two solutions of glucose one 40%w/v and one 4%w/v. You are asked to provide 500ml of a glucose solution containing 20%w/v glucose by mixing the two solutions. What volume of the 40% solution would be required?
Give your answer in ml to the nearest ml.

So let's start of with what 40% w/v and 4%w/v mean. They are also both concentration terms. C1V1=C2V2

You are trying to find V2 in the above equation. Tell me which values you would substitute in.

[Itchy Feet]

Ok Shorty

firstly you need to understand that this calculation is not as difficult as it looks, you need to have a structured approach to the answer. I can sympathise, because when I first faced these kinds of questions I used to draw a blank too. You need to remember your concentration equations, and you'll require a little bit of rearrangement of an equation too. I used find listing the information given in the form v= and c= would give me a clue as to which kinds of equations to use.

To take this question I would suggest you have a c1=40%, c2=4%, c3=20%, you also have a v1=?, v2=?, v3=500ml but you also know that v1+v2=500ml

Now you'll find that the question becomes a lot easier to handle.

Let me know if you are still having trouble

[Nik]

So let's start of with what 40% w/v and 4%w/v mean. They are also both concentration terms. C1V1=C2V2

You are trying to find V2 in the above equation. Tell me which values you would substitute in.

Asterix is doing a Johnep:

Thinking about doing the hospital based Trainee Pharmacy Tech job/course

Does the original poster want to get involved ? Or do they just want someone to give them the answer ?

[johnep]

Is it a first for Asterix to give an answer rather than asking a question?
johnep

[Asterix]

Yes I am changing my ways for you JOHN!

[Nik]

Of course this will only work if you know the answer Asterix ?