Calculation problem! Help!

Tinker_Bella

I've an exam tomorrow and i was looking over calculation notes and came across a calculation question that I'm finding difficult to work out. Can you help?

You are given 4ul of a 5ug/ul solution of human DNA in buffer. What volume of buffer should you add to the 4ul to give you a solution containing 2ug/ul?


Any help wil be grateful!

Thanks

GLaDOS

5 ul/ug is a ratio of 5:1, and you need a ratio of 2:1. in your 4 ul you have 20 ug (4ul x 5 ug/ul). 20:4 is your 5:1 ratio. By adding 6 ul of buffer to your existing 4 you bring the ratio up to 20:10, i.e. 2:1

Kevster

Is that right? - Is the answer not 10ul? The dilution factor to bring the solution from 5ug/ul to 2ug/ul is 2.5 (i.e. 5/2).

Therefore, you must add 2.5x4ul=10ul to your 4ul solution to change it's concentration to 2ug/ul.

Kevin

Capt'n Midnight

yes you want to end up with 10ul

but you have to remember that you already have 4ul , so you only need to add another 6ul

the devil as they say is in the detail

Kevster

haha... THAT part of this type of equation always 'got' me!

Kevin

Capt'n Midnight

Kevster wrote: »

haha... THAT part of this type of equation always 'got' me!

Kevin

My blind spot in physics was optics could never tell if it was a real or virtual image

GLaDOS

Thought I'd ****ed up for a second there

Kevster

...it was actually I who "****ed up" - haha