I heard someone say today if you mix bi-carb soda and lemon juice together it works as a teeth whitener. should i try this?

Lemon = Acid: Citrus fruits (like lemons) contain citric acid which can dissolve your enamel. Baking soda is abrasive (like sandpaper) so that too will wear away your enamel. While you are trying to get your teeth whiter, you will be slowly destroying them. Purchase drugstore whitening products if your budget does not allow for professional application.