[mjcapri]

Hi Guys,

I'm actually a construction student with no expertise in chemistry, so hopefully you will find this straightforward....

I've conducted some laboratory tests using a straightforward protocol. Basically, I added 5g of powdered concrete to 10ml distilled water (I'm in England so the measureas are metric, sorry!). I then used a Quantab strip to determine the chloride content of the solution. As you'll know, the figure that shows on the strip is cross referenced with the table on the container to provide the actual chloride content.

What I'm not sure of is whether or not this is the final figure I need, i.e. an indication of the chloride content of the original concrete sample. The lab technician thinks the figure needs to be multiplied, in this case by 3, to compensate for the fact that the powder was dissolved in 10ml of water. Is this the case?

From this figure I can then calculate the chloride content by weight of cement which I'm comfortable with.

Any help is much appreciated guys,

Thanks,

Mark.     

[fledarmus]

If this http://www.ldeo.columbia.edu/edu/k12/snapshotday/activities/Salinity_Quantab_final.pdf is an accurate picture of what you are using...

The results that you read off the bottle is a concentration of chloride ion in mg/L. What fraction of a liter is the 10 mL you were measuring? That fraction of the amount of chloride ions you were measuring will be the total amount of chloride in your 5 g sample:

x/10mL = (quantab measured value)mg/1000mL

where x = mg chloride in 5 g powdered concrete. Then you can put that relationship in whatever units you want.