Building a DNA Profile Relate these terms: agarose, digest, DNA, DNA

fingerprint/profile, restriction enzymes, PCR & gel

electrophoresis.

second option, baking soda mixed into vinegar, because the production of bubbles indicates that a new substance formed.

Explanation:

1) Indeed the evolution of bubbles when two different substances are mixed together is a good indication that a new substance has been formed. That is because the bubbles are a gas product of the chemical reaction between the reactants.

2) Since, baking soda (NaHCO₃) and vinegar (acetic acid, CH₃COOH) are aqueous solutions, you do not have bubles evolving when they are not mixed. Once, they are mixed, the acetate ion (CH₃COO⁻) will combine with the sodium ion (Na⁺) forming sodium acetate (CH₃COONa) and CO₂ which is the gas (bubbles).

3) Regarding the other options:

i) ice mixed into warm oil: the melting of the ice is just a change of phase, and that is all what you can tell about this interaction. Certainly not a chemical change. In fact, that change can be easily reversed by cooling the mixture.

ii) sugar mixed into hot water: the disappearance of the solid sugar does not indicate that the chemical identity of the sugar changed; it just dissolved; a solution was formed. If you heat the solution, the water will evaporate and you will be able to see the sugar crystals.

4) sand mixed into water: this is a classical example of a heterogeneous mixture, where both substances remain clearly being the same. The addition of mass is not an indicator of a reaction. Mass conservation is a principle that is valid for both physical and chemical changes.