Question

Formic acid has the chemical formula HCOOH. It is a colorless liquid that has a density of 1.220 \(\mathrm{g} / \mathrm{mL}\) . (a) The carbon atom in formic acid is bound to one \(\mathrm{H}\) and both \(\mathrm{O}^{\prime}\) 's. Draw the Lewis structure for formic acid, showing resonance if present. (b) Formic acid can react with NaOH in aqueous solution to produce the formate ion, HCOO- . Write the balanced chemical equation for this reaction. (c) Draw the Lewis structure of the formate ion, showing resonance if present. (d) How many milliliters of a 0.100 M solution of NaOH would it take to completely react with 0.785 \(\mathrm{mL}\) of formic acid?

Short answer

The Lewis structure for formic acid (HCOOH) is H-C(=O)-OH, and there is no resonance. The balanced chemical equation for the reaction between formic acid and NaOH is HCOOH + NaOH → HCOO- + H2O + Na+. The Lewis structures of the resonance forms for the formate ion (HCOO-) are: (1) O=C-O-H, and (2) H-O-C=O. To completely react with 0.785 mL of formic acid, it requires 208 mL of the 0.100 M NaOH solution.

Step-by-step solution

Draw the Lewis Structure of Formic Acid (HCOOH)

To draw the Lewis structure, we count the total number of valence electrons for the compound: H: 1 valence electron C: 4 valence electrons O: 2 * 6 valence electrons = 12 valence electrons Adding them together gives us 18 total valence electrons. Now, arrange the atoms as they are connected (C is connected to the H atom and both O atoms). Place a pair of electrons between each bonded pair of atoms and then distribute the remaining electrons according to the octet rule: O || H - C - O - H We can see the carbon atom has an octet of electrons (8), and both oxygen atoms have an octet. The hydrogen atoms only require 2 electrons to satisfy the duet rule. There is no resonance in the formic acid molecule.

Write the Balanced Chemical Equation for Formic Acid and NaOH Reaction

Formic acid (HCOOH) reacts with sodium hydroxide (NaOH) in an acid-base reaction, which will produce the formate ion (HCOO-) and a water molecule (H2O). The balanced chemical equation is: HCOOH + NaOH → HCOO- + H2O + Na+

Draw the Lewis Structure of the Formate Ion (HCOO-)

To draw the Lewis structure for the formate ion, we count the total number of valence electrons: H: 1 valence electron C: 4 valence electrons O: 2 * 6 valence electrons = 12 valence electrons Additional electron from the negative charge: 1 This gives us a total of 18 valence electrons. Connect the atoms, place a pair of electrons between each bonded pair of atoms, and distribute the remaining electrons according to the octet rule. We have resonance in the formate ion, meaning the double bond can exist between the carbon atom and either oxygen atom: Resonance Structure 1: O- | C - O - H Resonance Structure 2: O | H - O - C In both resonance structures, each atom has an octet (or duet for hydrogen).

Calculate the Required Volume of NaOH Solution

We are given the volume and density of formic acid and the molarity of the NaOH solution. The reaction between formic acid and NaOH is a 1:1 ratio, meaning 1 mole formic acid reacts with 1 mole NaOH. First, convert the volume and density of formic acid to moles: Density of formic acid: \(\rho = 1.220\,g/mL\) Volume of formic acid: \(V_{FA} = 0.785\,mL\) Mass formic acid: \(m_{FA} = \rho \times V_{FA} = 1.220\,g/mL \times 0.785\,mL = 0.958\,g\) Molar mass of formic acid (HCOOH): \(M_{FA} = 1.0\,g/mol + 12.0\,g/mol + 16.0\,g/mol \times 2 = 46.0\,g/mol\) Moles of formic acid: \(n_{FA} = m_{FA} / M_{FA} = 0.958\,g / 46.0\,g/mol = 0.0208\,mol\) Now, we calculate the volume of the NaOH solution required to react with the formic acid using the molarity of the NaOH solution: Molarity of NaOH solution: \(C_{NaOH} = 0.100\,M\) Volume of NaOH solution: \(V_{NaOH} = n_{FA} / C_{NaOH} = 0.0208\,mol / 0.100\,M = 0.208\,L = 208\,mL\) To completely react with 0.785 mL of formic acid, it requires 208 mL of the 0.100 M NaOH solution.

Key concepts

Understanding the Lewis Structure

A Lewis structure is a visual representation of the valence electrons in atoms and molecules. These structures aid in understanding how atoms are arranged and how they share electrons to form chemical bonds. To illustrate this concept, consider formic acid (HCOOH), a simple organic acid. When drawing its Lewis structure, you'll want to count the total valence electrons, which come to 18 for HCOOH. Remember, hydrogen wants two electrons (duet rule) while other non-metals strive for eight electrons to satisfy the octet rule.

In the Lewis structure of formic acid, you’ll see that the carbon atom is in the center, bound to both oxygen atoms and one hydrogen atom. The carbon achieves an electron octet, the oxygens each have eight electrons, and the hydrogen atoms follow the duet rule. By representing the molecule in such a manner, one can clearly see that all atoms achieve their desired electron configuration without the need for resonance structures, as each can maintain a stable arrangement with no need to delocalize electrons.

Balancing Chemical Equations

The balancing of chemical equations is essential for understanding the stoichiometry of a reaction—how much of each reactant is consumed and how much product is formed. In the reaction between formic acid and sodium hydroxide (NaOH), the chemical equation must reflect a conservation of mass and charge. The balanced equation is:
\[ \text{HCOOH} + \text{NaOH} \rightarrow \text{HCOO}^- + \text{H}_2\text{O} + \text{Na}^+ \]
In this equation, one molecule of formic acid reacts with one molecule of NaOH to produce one formate ion, one water molecule, and one sodium ion. This balance ensures that there are equal numbers of each type of atom on both sides of the reaction, adhering to the principle that matter is neither created nor destroyed during a chemical reaction.

The Role of Resonance Structures

Resonance structures are alternate ways of drawing the Lewis structure for a molecule where the atomic skeleton is the same, but the placement of electrons differs. These structures are especially important for delocalized electrons that can be distributed over two or more atoms, which is often seen in ions and certain molecules.

For the formate ion (HCOO-), which is produced in the reaction of formic acid with NaOH, there are two resonance structures that demonstrate the delocalization of electrons. Both oxygens have the potential to carry the negative charge by forming a double bond with the carbon atom. The resonance structures highlight how the extra electron can be shared between the two oxygen atoms, which in reality contributes to the stability of the ion. In essence, the true structure is a hybrid of these resonance structures, reflecting a molecule where charge and bonding are spread out more evenly than in a single Lewis structure.

Solving Problems with Stoichiometry

Stoichiometry is the quantitative aspect of chemistry that involves calculating the amounts of reactants and products in a chemical reaction. For the reaction between formic acid and NaOH, stoichiometry helps determine how much of one reactant is needed to completely react with a given amount of the other. Since the reaction is a 1:1 molar ratio, the stoichiometry is straightforward: each mole of formic acid requires one mole of NaOH to react completely.

By applying stoichiometry, we can calculate the volume of NaOH needed by using its molarity and the known quantity of formic acid. Once we convert the volume of formic acid to moles, we can then use the molarity of NaOH to find the corresponding volume of NaOH solution. Understanding the molarity concept and using the formula \(\text{volume} = \frac{\text{moles}}{\text{molarity}}\), allows us to find that 208 mL of 0.100 M NaOH is needed to react with 0.785 mL of formic acid, showcasing how stoichiometry is applied to effectively solve quantitative problems in chemistry.