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# salters A2 individual investigation NBS help. watch

1. okay so i standardising my NBS with ascorbic acid, and i need starch and 4% potassium iodide as an indicator? How do i make up 4% of potassium iodide solution?
Thanks Help would be much much appreciated! + rep ofc.
2. (Original post by xxcherry-popxx)
okay so i standardising my NBS with ascorbic acid, and i need starch and 4% potassium iodide as an indicator? How do i make up 4% of potassium iodide solution?
Thanks Help would be much much appreciated! + rep ofc.
I am assuming the 4% refer to concentration, ie 0.04M KI, then that depends on how much you want to produce, let say 1 dm^3, then that'd be 0.04 mol = mass of KI/RMM of KI, find out the mass of KI required, then just make up to 1 dm^3.

To make up less than 1 dm^3, you just tweak the ratio, ie use less mass of KI to still get the same concentration.
3. (Original post by shengoc)
I am assuming the 4% refer to concentration, ie 0.04M KI, then that depends on how much you want to produce, let say 1 dm^3, then that'd be 0.04 mol = mass of KI/RMM of KI, find out the mass of KI required, then just make up to 1 dm^3.

To make up less than 1 dm^3, you just tweak the ratio, ie use less mass of KI to still get the same concentration.
Thank-you!! using that method i got 6.64grams of KI does that sound right?
Also just checking doesnt concentration of 4% also mean 4grams of solid KI in every 100cm^3?
4. (Original post by xxcherry-popxx)
Thank-you!! using that method i got 6.64grams of KI does that sound right?
Also just checking doesnt concentration of 4% also mean 4grams of solid KI in every 100cm^3?
Hmm, this is why probably it is best for someone to check my suggested answer. I could be wrong about that really, but it is always best to check with your lab technician, people who actually prepare chemicals for you guys; they know best about these, trust me!

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