Problem 80 - Chemistry: The Central Science

Question

Assume that you encounter the following sentences in your reading. What is the chemical formula for each substance mentioned? (a) Sodium hydrogen carbonate is used as a deodorant. (b) Calcium hypochlorite is used in some bleaching solutions. (c) Hydrogen cyanide is a very poisonous gas. (d) Magnesium hydroxide is used as a cathartic. (e) Tin(II) fluoride has been used as a fluoride additive in toothpastes. (f) When cadmium sulfide is treated with sulfuric acid, fumes of hydrogen sulfide are given off.

Step-by-Step Solution

Answer

The chemical formulas for each substance mentioned are: (a) Sodium hydrogen carbonate: \(NaHCO_3\) (b) Calcium hypochlorite: \(Ca(ClO)_2\) (c) Hydrogen cyanide: \(HCN\) (d) Magnesium hydroxide: \(Mg(OH)_2\) (e) Tin(II) fluoride: \(SnF_2\) (f) Cadmium sulfide: \(CdS\)

Step 1: 1. Sodium hydrogen carbonate

Sodium is represented by the symbol "Na" and has a valency of +1. Hydrogen carbonate is also known as bicarbonate, which is a polyatomic anion with the formula HCO3^-. So, we have Na^(+1) and HCO3^-.

Step 2: 2. Calcium hypochlorite

Calcium is represented by the symbol "Ca" and has a valency of +2. Hypochlorite is a polyatomic anion with the formula ClO^-. It has a valency of -1. We have Ca^(+2) and ClO^(-1).

Step 3: 3. Hydrogen cyanide

Hydrogen is represented by the symbol "H" and has a valency of +1. Cyanide is a polyatomic anion with the formula CN^-. It has a valency of -1. We have H^(+1) and CN^(-1).

Step 4: 4. Magnesium hydroxide

Magnesium is represented by the symbol "Mg" and has a valency of +2. Hydroxide is a polyatomic anion with the formula OH^-. It has a valency of -1. We have Mg^(+2) and OH^(-1).

Step 5: 5. Tin(II) fluoride

Tin is represented by the symbol "Sn" and has a valency of +2 for Tin(II). Fluoride is an anion with the formula F^-. It has a valency of -1. We have Sn^(+2) and F^(-1).

Step 6: 6. Cadmium sulfide

Cadmium is represented by the symbol "Cd" and has a valency of +2. Sulfide is an anion with the formula S^2-. It has a valency of -2. We have Cd^(+2) and S^(-2). Now that we have identified the elements and their corresponding valencies, we'll write the chemical formula for each substance mentioned in the exercise.

Step 7: 1. Sodium hydrogen carbonate formula

Combining Na^(+1) and HCO3^(-1), we have the balanced chemical formula: NaHCO3.

Step 8: 2. Calcium hypochlorite formula

Combining Ca^(+2) and ClO^(-1), we need two ClO^- to balance the charge, giving us the chemical formula: Ca(ClO)2.

Step 9: 3. Hydrogen cyanide formula

Combining H^(+1) and CN^(-1), we have the balanced chemical formula: HCN.

Step 10: 4. Magnesium hydroxide formula

Combining Mg^(+2) and OH^(-1), we need two OH^- ions to balance the charge, giving us the chemical formula: Mg(OH)2.

Step 11: 5. Tin(II) fluoride formula

Combining Sn^(+2) and F^(-1), we need two F^- ions to balance the charge, giving us the chemical formula: SnF2.

Step 12: 6. Cadmium sulfide formula

Combining Cd^(+2) and S^(-2), we have the balanced chemical formula: CdS. So, the chemical formulas for each substance mentioned are: (a) Sodium hydrogen carbonate: NaHCO3 (b) Calcium hypochlorite: Ca(ClO)2 (c) Hydrogen cyanide: HCN (d) Magnesium hydroxide: Mg(OH)2 (e) Tin(II) fluoride: SnF2 (f) Cadmium sulfide: CdS

Key Concepts

Valency in Chemistry

Understanding valency is crucial when constructing chemical formulas. Valency represents the combining power of an element and dictates how many electrons an atom is willing to gain, lose, or share to achieve a full outer shell. In simple terms, it's the number of chemical bonds an element can form with other elements.

For example, sodium (Na) has a valency of +1, which means it can form one bond by donating one electron to another element. In contrast, magnesium (Mg) has a valency of +2, indicating it can form two bonds by donating two electrons. This becomes especially important when combining elements to create compounds. The ultimate goal is to align elements such that their valencies cancel each other out, resulting in a neutral compound.

The step by step solution to the problem starts with identifying the valency of each element in the given compounds. Real-life examples like Sodium hydrogen carbonate (NaHCO3) or Magnesium hydroxide (Mg(OH)2) become straightforward once their valencies are understood. Remember, the subscript numbers in chemical formulas often come from the valency of the respective elements or ions.

Polyatomic Ions

Polyatomic ions are ions composed of more than one atom, behaving as a single charged unit. They play a significant role in the composition of various compounds. A key to mastering chemical formulas is to remember the common polyatomic ions and their charges.

For instance, the hydrogen carbonate ion (HCO3-) is a polyatomic ion composed of hydrogen, carbon, and three oxygen atoms, carrying a charge of -1. Similarly, hypochlorite (ClO-) is another polyatomic ion with a net charge of -1. Recognizing these ions helps accurately piece together compounds such as Sodium hydrogen carbonate and Calcium hypochlorite. Understanding the structure and charge of polyatomic ions is also essential when balancing chemical equations due to their multiple-atom nature.

The solution procedure described leverages the knowledge of these ions to form correct chemical compounds. For clarity, whenever polyatomic ions like HCO3- and ClO- are involved, they should be treated as a single entity respecting their charge in the creation of compounds, as seen in Ca(ClO)2.

Writing Chemical Equations

Writing chemical equations is like solving a puzzle where the pieces are elements and compounds. It's all about balancing the atoms and charges to reflect the conservation of mass and charge. Each equation must have the same number of each type of atom on both sides of the reaction.

When writing chemical formulas, as done in the step-by-step solutions, the goal is to combine atoms or polyatomic ions to produce electrically neutral compounds. For example, to derive the formula for Calcium hypochlorite, we observe that the calcium ion (Ca2+) requires two hypochlorite ions (ClO-) to balance its charge, resulting in Ca(ClO)2.

To aid with learning, using models or visual representations can greatly improve one's ability to write chemical equations. This provides a tangible way to see how the elements come together and how their valencies work in harmony to form stable compounds. Mastery of this process enables one to predict the products of chemical reactions and to write balanced chemical equations, a fundamental skill in chemistry.