Final answer:
The mass of the mixture decreases after Zack mixes vinegar and baking soda due to the release of carbon dioxide gas. The pH of the mixture increases as the baking soda neutralizes the acid in the vinegar.
Step-by-step explanation:
When Zack mixes vinegar and baking soda, a chemical reaction occurs where the baking soda (sodium bicarbonate) reacts with the vinegar (acetic acid) to produce carbon dioxide gas, water, and sodium acetate. The bubbling observed is due to the production of carbon dioxide gas which escapes from the mixture, which would explain why the mass decreases from 125 grams to 103 grams after the reaction. According to the law of conservation of mass, the total mass should remain the same before and after the chemical reaction if it were to occur in a closed system. However, since the carbon dioxide is a gas, it leaves the mixture, thereby reducing the observed total mass.
The pH of the solution after mixing vinegar and baking soda will increase (become less acidic) due to the neutralization reaction between the acidic vinegar and the basic baking soda. Initially, vinegar is acidic due to the presence of acetic acid, but once neutralized by the baking soda, the resulting solution is closer to neutral pH.