Regents Chemistry Exam August 2022
Calcium oxide, CaO, also known as lime, is an important industrial chemical. Lime can be obtained by the heating of limestone, which is mainly calcium carbonate, CaCO3. An equation representing the reaction for the production of lime is shown below.
CaCO3(s) + heat → CaO(s) + CO2(g)
70. State the solubility of limestone in water. 
Let's take a look at Table F on the Reference Table. On the right side it says that CO3^2- is insoluble unless it is with a Group 1 ions or ammonium (NH4+). Calcium ion is in group 2 and therefore, CaCO3 is insoluble in water.
71. State evidence from the equation that the reaction to form lime is endothermic. 
In an endothermic reaction, heat is absorbed. In an exothermic reaction, heat is released. In the equation heat is on the reactant side which means it is being absorbed.
72. Identify the noble gas that has atoms in the ground state with the same electron configuration as the calcium ion, in the ground state, in the CaCO3. 
Calcium ion, is Ca^2+, which means it lost 2 electrons. Calcium has an atomic number of 20 according to the Periodic table and therefore has 20 protons and 20 electrons in its neutral form. Losing 2 electrons, means it has 20-2=18 electrons left. Argon (Ar) has an atomic number of 18 and 18 electrons.
Answer: Argon (Ar)
73. State the type of chemical bonding in a sample of CaO. 
The different types of bonding are ionic and covalent. Covalent is between two or more nonmetals (nonmetals are to the right of the staircase on the Periodic Table). Ionic bonding is between a metal with a nonmetal or a metal with polyatomic ion. Calcium is a metal (to the left of the staircase on the Periodic Table) and oxygen is a nonmetal.
Answer: Ionic bonding