Problem 84 - Chemistry: An Atoms-Focused Approach

Question

Sodium bicarbonate and calcium carbonate both act as antacids and are found in common stomach remedies. Which substance will neutralize more acid on a per mole basis? Does the same substance also neutralize more acid on a per gram basis?

Step-by-Step Solution

Answer

Answer: Calcium carbonate (CaCO3) neutralizes more acid on both a per mole basis and a per gram basis.

Step 1: Write down the balanced chemical equations for both substances with HCl (acid)

For sodium bicarbonate (NaHCO3): NaHCO3 (s) + HCl (aq) -> NaCl (aq) + H2O (l) + CO2 (g) For calcium carbonate (CaCO3): CaCO3 (s) + 2HCl (aq) -> CaCl2 (aq) + H2O (l) + CO2 (g)

Step 2: Compare moles of acid neutralized per mole of each substance

From the balanced chemical equation for sodium bicarbonate, it's evident that 1 mole of NaHCO3 neutralizes 1 mole of HCl. From the balanced chemical equation for calcium carbonate, 1 mole of CaCO3 neutralizes 2 moles of HCl. So, calcium carbonate (CaCO3) neutralizes more acid on a per mole basis.

Step 3: Calculate the molar masses of sodium bicarbonate and calcium carbonate

Molar mass of sodium bicarbonate (NaHCO3): = (1 × 22.99) + (1 × 1.01) + (1 × 12.01) + (3 × 16.00) = 22.99 + 1.01 + 12.01 + 48.00 = 84.01 g/mol Molar mass of calcium carbonate (CaCO3): = (1 × 40.08) + (1 × 12.01) + (3 × 16.00) = 40.08 + 12.01 + 48.00 = 100.09 g/mol

Step 4: Compare the neutralization capacities of each substance on a per gram basis

We already know that 1 mole of NaHCO3 neutralizes 1 mole of HCl, and 1 mole of CaCO3 neutralizes 2 moles of HCl. Neutralization capacity of 1 gram of sodium bicarbonate: 1 mole of NaHCO3 neutralizes 1 mole of HCl So, 1 g of NaHCO3 neutralizes (1/84.01) moles of HCl Neutralization capacity of 1 gram of calcium carbonate: 1 mole of CaCO3 neutralizes 2 moles of HCl So, 1 g of CaCO3 neutralizes (2/100.09) moles of HCl Now, we have to compare (1/84.01) and (2/100.09). (1/84.01) = 0.0119 (2/100.09) = 0.0200 Since 0.0200 > 0.0119, 1 g of calcium carbonate (CaCO3) neutralizes more acid than 1 g of sodium bicarbonate (NaHCO3). In conclusion, calcium carbonate (CaCO3) neutralizes more acid on both a per mole basis and a per gram basis.

Key Concepts

Neutralization Capacity

Neutralization capacity refers to the ability of a substance to neutralize a given amount of acid. In the context of antacids like sodium bicarbonate and calcium carbonate, this is particularly important as they interact with stomach acid (hydrochloric acid, HCl) to relieve indigestion and heartburn. By using chemical equations, we can determine how many moles of hydrochloric acid each antacid can neutralize.

For sodium bicarbonate (\(\text{NaHCO}_3\)), the reaction with HCl is as follows: \(\text{NaHCO}_3 (s) + \text{HCl} (aq) \rightarrow \text{NaCl} (aq) + \text{H}_2\text{O} (l) + \text{CO}_2 (g)\). According to this balanced equation, one mole of sodium bicarbonate neutralizes one mole of HCl.

In contrast, the reaction for calcium carbonate (\(\text{CaCO}_3\)) is: \(\text{CaCO}_3 (s) + 2\text{HCl} (aq) \rightarrow \text{CaCl}_2 (aq) + \text{H}_2\text{O} (l) + \text{CO}_2 (g)\). Here, one mole of calcium carbonate neutralizes two moles of HCl, making it more effective on a per mole basis.

This means that calcium carbonate has a higher neutralization capacity than sodium bicarbonate when considering a mole-to-mole comparison. This is crucial for determining the efficiency of antacids in medical or commercial applications.

Molar Mass Calculation

Molar mass is an important concept in chemistry that helps us relate the mass of a substance to the amount in moles. By calculating molar masses, we can convert between mass and moles, which can then be used to determine the neutralization capacity on a per gram basis.

To calculate the molar mass of sodium bicarbonate (\(\text{NaHCO}_3\)), we add the molar masses of each constituent element based on the periodic table:

• Sodium (Na): 22.99 g/mol
• Hydrogen (H): 1.01 g/mol
• Carbon (C): 12.01 g/mol
• Oxygen (O): 16.00 g/mol (x3 as there are three atoms of oxygen)

The total comes to 84.01 g/mol.

Similarly, for calcium carbonate (\(\text{CaCO}_3\)), the molar masses are:

• Calcium (Ca): 40.08 g/mol
• Carbon (C): 12.01 g/mol
• Oxygen (O): 16.00 g/mol (x3)

This gives a total molar mass of 100.09 g/mol.

Understanding molar mass is essential to comparing substances on a per gram basis, as it allows us to take into consideration the actual weight of each compound used in reactions.

Chemical Equations

Chemical equations are symbols used to depict the substances involved in a chemical reaction. They provide essential insights into the reaction, indicating which substances are reactants, which are products, and their respective quantities or moles needed to satisfy the reaction.

In this exercise, writing balanced chemical equations for sodium bicarbonate and calcium carbonate with HCl was crucial for understanding neutralization.

A balanced chemical equation for sodium bicarbonate is:\(\text{NaHCO}_3 (s) + \text{HCl} (aq) \rightarrow \text{NaCl} (aq) + \text{H}_2\text{O} (l) + \text{CO}_2 (g)\), indicating a one-to-one mole ratio of \(\text{NaHCO}_3\) to \(\text{HCl}\).

For calcium carbonate, the equation is:\(\text{CaCO}_3 (s) + 2\text{HCl} (aq) \rightarrow \text{CaCl}_2 (aq) + \text{H}_2\text{O} (l) + \text{CO}_2 (g)\), showing that one mole of \(\text{CaCO}_3\) reacts with two moles of \(\text{HCl}\).

This difference in mole ratios is key to determining their abilities to neutralize acid, influencing their selection based on purpose (e.g., faster relief vs. dosage size). Understanding these chemical equations helps us predict and calculate reaction outcomes effectively.