What if you broke off a piece of cement (or bread) so that it was only half the volume of the original piece? What would happen to the mass?

The mass is also half of the mass of the original piece

Explanation:

Recall that the volume of a substance is defined as mass/volume. The density of substances is a constant. Hence, if a break off a piece of cement or bread such that what remains is only half the volume of the original piece, the mass of the new piece must also reduce to half of the mass of the original piece so that the volume of the material will remain constant.

Hence the answer above.

answer : one can design an experiment using a liquid and an additive that can be added to the liquid and observe the chemical changes in the reaction species.

one would need a beaker which is filled with a known amount of the liquid in which thermometer is placed to measure the temperature changes; after addition of the additive to the liquid solution one can note down the temperature change and find whether the reaction is endothermic or exothermic in nature. by subtracting the initial temperature value with the final temperature one can find the temperature changes.

various combinations of liquid and additive can be used. liquid in this case can be a known quantity of water and additives can be epsom salt or without epsom salt the experiment can be conducted to notice the changes. water and ice, hydrogen peroxide and dry yeast, vinegar and baking soda,etc.