Question

Ammonium chloride, \(\mathrm{NH}_{4} \mathrm{Cl},\) is a very soluble salt in water. (a) Draw the Lewis structures of the ammonium and chloride ions. (b) Is there an \(\mathrm{N}-\) Cl bond in solid ammonium chloride? (c) If you dissolve 14 gof ammonium chloride in 500.0 \(\mathrm{mL}\) of water, what is the molar concentration of the solution? (d) How many grams of silver nitrate do you need to add to the solution in part (c) to precipitate all of the chloride as silver chloride?

Short answer

(a) Lewis structures: Ammonium ion: ``` H | H - N+ - H | H ``` Chloride ion: ``` Cl - ``` (b) There is no direct N-Cl bond in solid ammonium chloride. It forms a crystalline lattice structure via ionic bonds between NH4+ and Cl- ions. (c) The molar concentration of the ammonium chloride solution is 0.52336 M. (d) 44.48 grams of silver nitrate are required to precipitate all the chloride as silver chloride.

Step-by-step solution

a) Lewis Structures

To draw the Lewis structures for the ammonium ion and chloride ion, we need to analyze their valence electrons and bonding preferences. For the ammonium ion (NH4+), nitrogen has five valence electrons, and hydrogen has one. In the ammonium ion, nitrogen shares its electrons with four hydrogen atoms, forming covalent bonds. After forming the bonds, nitrogen loses one electron, resulting in a positive charge for the ion. Lewis structure of the ammonium ion: ``` H | H - N+ - H | H ``` For the chloride ion (Cl-), chlorine has seven valence electrons. In the chloride ion, chlorine gains one electron, resulting in a negative charge for the ion. Lewis structure of the chloride ion: ``` Cl - ```

b) N-Cl Bond

In solid ammonium chloride, ionic bonds form between the ammonium ions (NH4+) and chloride ions (Cl-) to produce a crystalline lattice structure. There is no direct N-Cl covalent bond in solid ammonium chloride.

c) Molar Concentration

To find the molar concentration of the ammonium chloride solution, we need to follow these steps: 1. Determine the molar mass of ammonium chloride (NH4Cl): N(1) + H(4) + Cl(1) = 14.01 g/mol + 4.04 g/mol + 35.45 g/mol = 53.50 g/mol 2. Calculate the moles of NH4Cl dissolved in the water: moles = mass (g) / molar mass (g/mol) = 14g / 53.50 g/mol = 0.26168 mol 3. Convert the volume of the solvent (water) to liters: 500 mL = 0.500 L 4. Calculate the molar concentration of NH4Cl: concentration = moles / volume (L) = 0.26168 mol / 0.500 L = 0.52336 M The molar concentration of the ammonium chloride solution is 0.52336 M.

d) Precipitation of Silver Chloride

To determine how many grams of silver nitrate (AgNO3) are required to precipitate all the chloride as silver chloride (AgCl), we can use the stoichiometry of the reaction and the molar mass of AgNO3. The balanced chemical equation for this reaction is: ``` AgNO3 (aq) + NH4Cl (aq) -> AgCl (s) + NH4NO3 (aq) ``` From the equation, the stoichiometric ratio of AgNO3 to NH4Cl is 1:1. 1. Calculate the moles of NH4Cl: 0.26168 mol (from part c) 2. Calculate the moles of AgNO3 needed: 0.26168 mol (same stoichiometric amount as NH4Cl) 3. Determine the molar mass of AgNO3: Ag(1) + N(1) + O(3) = 107.87 g/mol + 14.01 g/mol + 48 g/mol = 169.88 g/mol 4. Calculate the mass of AgNO3 required: mass (g) = moles * molar mass (g/mol) = 0.26168 mol * 169.88 g/mol = 44.48 g Therefore, 44.48 grams of silver nitrate are required to precipitate all the chloride as silver chloride.

Key concepts

Lewis Structures

Understanding Lewis structures is vital for grasping how atoms bond and form compounds. In the case of ammonium chloride (NH_{4}Cl), we have an ammonium ion (NH_{4}^+) and a chloride ion (Cl^-). The Lewis structure for the ammonium ion shows nitrogen at the center with four hydrogen atoms bonded to it. Since nitrogen forms four covalent bonds, it shares its electrons with the hydrogen atoms, leading to a positive charge because it has given up an electron. Meanwhile, the chloride ion has a single negative charge, reflected by adding an extra electron to its valence shell. A clear depiction of these structures helps students visualize the electron sharing and charge distribution, essential concepts in chemical bonding.

When drawing these structures, remember that Hydrogen is always on the outside with its single electron forming a bond and that formal charges are crucial to indicate any electrons that have been gained or lost during bond formation.

Ionic Bonding

The concept of ionic bonding is exemplified in the formation of solid ammonium chloride. Ionic bonding occurs between positively and negatively charged ions. In ammonium chloride, positively charged ammonium ions (NH_{4}^+) and negatively charged chloride ions (Cl^-) attract each other to create a stable ionic compound. Contrary to what some may believe, there is no direct nitrogen-to-chlorine (N-Cl) covalent bond; rather, the compound is held together by the electrostatic forces between ions. This distinction between ionic and covalent bonding is a fundamental concept in chemistry that influences the properties and behaviors of substances.

Molar Concentration

Solving for molar concentration is a basic operation in chemistry that conveys how much of a substance is present in a given volume of solution. It's often expressed in moles per liter (M). To find the molar concentration of a substance like ammonium chloride in water, first, calculate the molar mass of NH_{4}Cl, then determine how many moles are dissolved in the water, and finally relate this to the volume of solution in liters. Understanding this concept allows students to interpret the ratio of solute to solvent, and it is crucial for preparing solutions for reactions and for analytical purposes. It's important to note that the solution's volume must always be in liters for standard molarity calculations.

Stoichiometry

The principle of stoichiometry involves the quantitative relationship between reactants and products in a chemical reaction. By understanding stoichiometry, one can predict the amounts of substances consumed and produced in reactions. In our example, to find how much silver nitrate (AgNO_{3}) is needed to completely react with the ammonium chloride in the solution, we use the balanced chemical equation and the concept of stoichiometry. Since the reaction ratio between AgNO_{3} and NH_{4}Cl is 1:1, stoichiometry tells us that we need an equal amount of moles of AgNO_{3} to fully precipitate the chloride as silver chloride (AgCl). Remember that stoichiometric calculations involve using molar masses and balanced equations to accurately find the mass of reactants or products.