Question

Antacid tablets contain a variety of bases such as NaHCO3, MgCO3, CaCO3, and Mg(OH)2. Only NaHCO3 has appreciable solubility in water. In parts 1 - 4, write a balances net ionic equation, including states of matter, for the reaction of each antacid with aqueous HCl. Then in part 5 choose the best statement to describe antacids.

Part 1

a) Write the net ionic equation for NaHCO3 + HCl

b)Write the net ionic equation for MgCO3 + HCl

c)Write the net ionic equation for CaCO3 + HCl

d)Write the net ionic equation for Mg(OH)2 + HCl

Part b

Choose the best answer to explain how insoluble substances can act as effective antacids. Choose one:

a)Even as a solid, the antacid will react with H+ to neutralize the acid The volume of the solid decreases the acid concentration,

b)causing the pH to rise.

c)A small portion of the solid dissolves and neutralizes the acid

Answer 1

Part-1: For better understanding let's first write Complete ionic equation and then write net ionic equation by canceling the common terms on both side.   

a) Complete ionic equation:

Na+(aq) + HCO3-(aq) + H+(aq) + Cl-(aq) ----> Na+(aq) + Cl-(aq) +  H2O + CO2

Net ionic equation:

HCO3-(aq) + H+(aq) ----> H2O(l) + CO2(g)

b)

Mg2+(aq) + CO3--(aq) + 2H+(aq) + 2Cl-(aq) ----> Mg2+(aq) + 2Cl-(aq) + H2O(l) + CO2(g)

Net ionic equation:

CO3--(aq) + 2H+(aq) ----> H2O(l) + CO2(g)

c)

Ca2+(aq) + CO3--(aq) + 2H+(aq) + 2Cl-(aq) ----> Ca2+(aq) + 2Cl-(aq) + H2O(l) + CO2(g)

Net ionic equation:

CO3--(aq) + 2H+(aq) ----> H2O(l) + CO2(g)

d) Mg(OH)2 + 2H+(aq) + 2Cl-(aq) ----> Mg2+(aq) + 2Cl-(aq) + 2H2O(l)

Net ionic equation:

2OH-(aq) + 2H+(aq) ------> 2H2O(l)

Part-b)

Even though the many anti-acids are insoluble or less soluble, however, a small amount of it goes into the solution and that reacts with water. So this solubility equilibrium is always on the right side and solid anti-acid continues to dissolve.

Thus answer is opiton c) A small portion of the solid dissolves and neutralizes the acid