Hi there,

 

I need ampicillin solution at 100mg/ ul I was wondering how i go about making this up? How many Grams per ml.

 

Thanks heaps!

Put 100 mg of ampicillin, and fill the container to 1 uL. More than that, looks like homework question. Do you know how to convert units?

Even if this is homework, the result of 100mg of ampicillin in 1ug of liquid sounds like wet ampicillin. Anyway, what you are looking to do is called dimensional analysis. For demonstration, I will convert 3 g/mL into kilograms per cubic decimeter (liter). To start off write your original units and note that it is a fraction with different units in the numerator and denominator.

 

3 grams / 1 mililiter

 

Then, I multiply by a conversion factor. When you multiply fractions, the same units in opposite positions on their fractions cancel out. So, there are 1000 grams in a kilogram, so I write:

 

3 grams / 1 mililiter x 1 kilogram / 1000 grams = 3 kilograms / 1000 mililiters

 

Notice that grams is in the numerator of the first term and in the denominator of the second? Once they cancel out, I'm left with 3 kilograms / 1000 mililiters. Now I convert mililiters into cubic decimeters, which I know to be liters. There are 1000 mililiters in a liter. To make mililiters cancel out, I put the mililiters in the numerator and the cubic decimeters in the denominator:

 

3 kilograms / 1000 mililiters x 1000 mililiters / 1 cubic decimeter = 3 kilograms / 1 cubic decimeter

 

Not only have the mililiters cancelled out, but there was a 1000 on both the top and bottom that cancels out.

 

The answer is written as 3 kg/dm^3

Actually I am not that sure whether it will get wet very much.

Thanks very much for your responses! Greatly appreciated