Practice Test 12

A student mixes baking soda and vinegar in an open beaker. Reaction: $\mathrm{NaHCO_3(s) + HC_2H_3O_2(aq) \rightarrow CO_2(g) + H_2O(l) + NaC_2H_3O_2(aq)}$. Masses measured:

• Before: beaker + contents = 120 g
• After bubbling stops: beaker + contents = 116 g Which statement best explains the 4 g decrease?

A strip of magnesium is burned in air in an open crucible. Reaction: $\mathrm{2Mg(s) + O_2(g) \rightarrow 2MgO(s)}$. Mass of magnesium before heating: 6 g. Mass of the white magnesium oxide after heating: 10 g. Which statement best explains the mass increase?