How can I convince my mother to let me buy Potassium Nitrate

Now, I understand that this chemical can be very reactive and if used irresponsibly can result in damage to myself/others. I wish to order some from a website in 100 g units and have them shipped to our house. One problem, it requires a credit card. Being only 16 years old, this makes me completely reliant on my parents for this purchase. My intentions are to build a "smoke bomb" using electical tape, organic dye (powdered), cardboard tubing, Potassium Nitrate, and sugar.
Now, the smoke itself is non-toxic. The final product (potassium and sugar cooked together) is relatively stable, and is simple to combine. It is just that my mother is fixated on this one idea that im trying to make some sort of bomb out of this. No matter how much persuasion I use the argument always returns to me making a "bomb". Im not even sure if its possible to make a bomb out this to begin with. What I'm looking for is a factual yet endorsing argument I can use.
Any Ideas?

buy it from somewhere else.
KNO3 is found everywhere.

my first internet purchase was when i was 11 and I paid with money order. that was spring 1999.
surely money orders are still accepted?

my first "questionable purchase" was when I was 14. and it was questionable. after hitting dead end after dead end with retails only accepting debit/credit cards, I found a source on eBay that accepts money orders. I paid with a money order (transaction fee $1.25) and I got my stuff in 2 weeks shipped to a friend's house with parents whom didn't care what comes in the mail.

actually my first-ever online purchase was a questionable purchase. luckily the day i received it both parents were out of the house. otherwise there'd be come difficult explaining to do. but the purchase was 100% legal, if anyone wishes to dig thru 1000s of BATF legal documents. which back then was on paper and it would be painful and very laborious. today its all online and a fairly very painless process to find what you need.

Go to the store and buy a pre-paid Visa card and buy it yourself. :-)

You used to be able to buy potassium nitrate as saltpeter in many garden supply stores. While it is difficult to find saltpeter, you can still purchase potassium nitrate, which is used to make smoke bombs and certain other fireworks, as 'stump remover'. In the United States, you can find it at Lowes or Home Depot, among other places. Look for the Spectracide brand in those stores near the insecticides.

Note: based on comments to the above citation, Lowe's has KNO3 in their stump remover. Home Depot does not. See link provided.