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

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: a) Sodium hydrogen carbonate

First, identify the elements present in sodium hydrogen carbonate: - Sodium (Na) has a valency of +1. - Hydrogen (H) has a valency of +1. - Carbon (C) has a valency of +4. - Oxygen (O) has a valency of -2. To form the formula for sodium hydrogen carbonate, we combine Na, H, C, and O according to their valencies. The formula is: NaHCO₃.

Step 2: b) Calcium hypochlorite

First, identify the elements present in calcium hypochlorite: - Calcium (Ca) has a valency of +2. - Chlorine (Cl), in its hypochlorite form (ClO), has a valency of -1. To form the formula for calcium hypochlorite, we combine Ca and ClO according to their valencies. The formula is: Ca(ClO)₂.

Step 3: c) Hydrogen cyanide

First, identify the elements present in hydrogen cyanide: - Hydrogen (H) has a valency of +1. - Carbon (C) has a valency of +4. - Nitrogen (N) has a valency of -3. To form the formula for hydrogen cyanide, we combine H, C, and N according to their valencies. The formula is: HCN.

Step 4: d) Magnesium hydroxide

First, identify the elements present in magnesium hydroxide: - Magnesium (Mg) has a valency of +2. - Oxygen (O) has a valency of -2. - Hydrogen (H), in its hydroxide form (OH), has a valency of -1. To form the formula for magnesium hydroxide, we combine Mg and OH according to their valencies. The formula is: Mg(OH)₂.

Step 5: e) Tin(II) fluoride

First, identify the elements present in tin(II) fluoride: - Tin (Sn), in its (II) form, has a valency of +2. - Fluorine (F) has a valency of -1. To form the formula for tin(II) fluoride, we combine Sn and F according to their valencies. The formula is: SnF₂.

Step 6: f) Cadmium sulfide

First, identify the elements present in cadmium sulfide: - Cadmium (Cd) has a valency of +2. - Sulfide (S) has a valency of -2. To form the formula for cadmium sulfide, we combine Cd and S according to their valencies. The formula is: CdS.

Key Concepts

Valency

Valency is a fundamental concept in chemistry that describes the ability of an atom to combine with other atoms. It is determined primarily by the number of electrons in the outermost shell of an atom. These electrons are known as valence electrons. Valency is crucial in forming chemical compounds as it dictates how atoms bond with each other.
Here are a few key points about valency:

• Valency can be thought of as the number of electrons an atom needs to either gain, lose, or share in order to achieve a stable electron configuration.
• Elements belonging to the same group in the periodic table typically have the same valency.
• For metals, valency often corresponds to the number of electrons lost, while nonmetals typically gain or share electrons.

Understanding valency helps in predicting the formulas of compounds and in balancing chemical equations effectively.

Sodium hydrogen carbonate

Sodium hydrogen carbonate, commonly known as baking soda, is a versatile compound with the chemical formula \( \text{NaHCO}_3 \). It combines sodium (Na), hydrogen (H), carbon (C), and oxygen (O). Each element contributes to the overall properties and uses of the compound.

• Sodium (Na) has a valency of +1, indicating it can lose one electron to form stable compounds.
• Hydrogen (H) also has a valency of +1, often involved in forming bonds with oxygen.
• Carbon (C) has four valence electrons, participating in various bonding scenarios, especially in organic chemistry.
• Oxygen (O) has a valency of -2, enabling it to form double bonds or pair with other elements easily.

Baking soda is widely used not just in cooking and deodorizing, but also in health applications as an antacid.

Calcium hypochlorite

Calcium hypochlorite, with the chemical formula \( \text{Ca(ClO)}_2 \), is utilized primarily as a disinfectant and bleaching agent. It is composed of calcium (Ca) and hypochlorite (ClO) ions. The effectiveness of calcium hypochlorite is largely due to the following attributes:

• Calcium (Ca) has a valency of +2, which allows it to form strong ionic bonds with anions like hypochlorite.
• Hypochlorite (ClO) has a valency of -1, aiding in the oxidative properties essential for its disinfecting role.

In water solutions, calcium hypochlorite releases chlorine, which is a powerful agent against bacteria and viruses. This makes it valuable in maintaining the hygiene of swimming pools and drinking water.

Magnesium hydroxide

Magnesium hydroxide, known for its use as an antacid and laxative, has the chemical formula \( \text{Mg(OH)}_2 \). It consists of magnesium (Mg) and hydroxide (OH) ions, each playing a significant role in its chemical behavior.

• Magnesium (Mg), with a valency of +2, bonds with hydroxide ions to form slightly soluble compounds in water.
• Hydroxide (OH) has a valency of -1, characterized by its ability to neutralize acids.

This compound works by reducing acidity in the stomach, thus providing relief from indigestion and heartburn. Its role in medicine underscores the practical importance of understanding chemical formulas.

Tin(II) fluoride

Tin(II) fluoride, chemically represented as \( \text{SnF}_2 \), plays an active role in dental care, particularly in strengthening tooth enamel. This compound involves tin (Sn) and fluoride (F) ions.

• Tin (Sn), in the +2 oxidation state, signifies it can donate two electrons to form stable compounds.
• Fluorine (F) has a valency of -1, known for its high electronegativity and ability to form strong ionic bonds.

Tin(II) fluoride is effective in preventing cavities because fluoride ions assist in the remineralization of teeth. This reinforces the importance of chemical formulations in practical applications like oral hygiene.

Cadmium sulfide

Cadmium sulfide, denoted as \( \text{CdS} \), is noteworthy for its application in the production of pigments and in electronic components. The compound is comprised of cadmium (Cd) and sulfide (S) ions.

• Cadmium (Cd) has a valency of +2, allowing it to form a stable bond with sulfide ions.
• Sulfur (S) forms the sulfide ion with a valency of -2, offering sulfur's versatile ability to bond with various elements.

Cadmium sulfide's properties, such as its color and semiconductor capabilities, make it valuable in solar cells and photoconductors. However, due to toxicity concerns, its handling and applications are regulated to mitigate environmental and health risks.