Common Polyatomic Ions Chemistry Quiz

HSO4- is the chemical formula for the hydrogensulphate ion, also known as bisulphate. This ion is derived from sulfuric acid (H2SO4) by the loss of one proton (H+), resulting in a negatively charged ion. It contains both sulfur and oxygen, and its structure features one hydrogen atom bonded to the sulfate group (SO4). This distinguishes it from the sulfate ion (SO4^2-), which lacks the hydrogen. Thus, HSO4- is specifically recognized as hydrogensulphate or bisulphate.

Ions with a valency of 2 can combine with two monovalent ions or equivalent amounts of other ions. Sulphate (SO4²-), Carbonate (CO3²-), and Chromate (CrO4²-) all carry a -2 charge, indicating their ability to bond with two positive charges. This characteristic is essential for forming stable compounds, as these ions are often involved in various chemical reactions and play significant roles in biological and environmental processes. In contrast, Nitrate (NO3-) has a valency of 1, as it carries only a -1 charge.

The hydrogencarbonate ion, commonly referred to as bicarbonate, is a polyatomic ion with the formula HCO3-. It plays a crucial role in maintaining pH balance in biological systems and is an important component of the carbonic acid-bicarbonate buffer system in the blood. The terms "hydrogencarbonate" and "bicarbonate" are often used interchangeably in both scientific literature and everyday language, confirming that the statement is accurate.

The ion with the formula SO4²- is known as the sulfate ion. It consists of one sulfur atom covalently bonded to four oxygen atoms, carrying a net charge of -2. Sulfate is commonly found in various chemical compounds, including salts and minerals, and plays a significant role in biological systems and industrial processes. The other options listed—hydrogensulfate, carbonate, and chromate—have different chemical formulas and structures, making sulfate the unique match for SO4²-.

Phosphate is a polyatomic ion consisting of one phosphorus atom bonded to four oxygen atoms. Its chemical formula, PO4³-, indicates that the ion carries a negative charge of three. This charge arises because the phosphorus atom shares its electrons with oxygen atoms, leading to a stable configuration. Phosphate plays a crucial role in biological systems, particularly in energy transfer through ATP and in forming DNA and RNA. Understanding its formula helps in grasping its significance in both chemistry and biology.

NH4+ (ammonium) and H3O+ (hydronium) are polyatomic ions that carry a positive charge due to the presence of extra protons. NH4+ has four hydrogen atoms bonded to a nitrogen atom, giving it a net positive charge. H3O+ is formed when water (H2O) gains an additional hydrogen ion (H+), resulting in a positively charged hydronium ion. In contrast, OH- (hydroxide) and NO3- (nitrate) are negatively charged ions, as they have an excess of electrons compared to protons. Thus, only NH4+ and H3O+ are positively charged among the options provided.

The valency of the dichromate ion (Cr2O7²-) is determined by the total charge of the ion and the oxidation states of the chromium and oxygen atoms. In dichromate, each chromium has an oxidation state of +6, and each oxygen has an oxidation state of -2. With 2 chromium atoms and 7 oxygen atoms, the overall charge can be calculated as follows: (2 × +6) + (7 × -2) = +12 - 14 = -2. Therefore, the valency, which indicates the combining capacity of the ion, is 2.

The carbonate ion (CO3²-) has a valency of 2 because it can combine with two positive charges to form stable compounds. This is due to its ability to accept two protons (H⁺) or bond with two cations, reflecting its overall charge of -2. The presence of three oxygen atoms bonded to a central carbon atom allows for resonance structures, which further stabilizes the ion and confirms its valency. Thus, the carbonate ion's capacity to interact with other ions supports its classification as having a valency of 2.

Ammonium is a positively charged ion formed when ammonia (NH3) accepts a proton (H+). Its chemical formula is represented as NH4+, indicating that it consists of one nitrogen atom (N) and four hydrogen atoms (H), along with a positive charge. This distinguishes it from other species listed, such as nitrate (NO3-), hydroxide (OH-), and hydronium (H3O+), which have different compositions and charges. Ammonium plays a significant role in various biological and chemical processes, making its identification important in chemistry.

The nitrate ion (NO3-) has a valency of 1 because it carries a single negative charge. Valency refers to the combining capacity of an ion, which is determined by the number of electrons it can gain, lose, or share to achieve a stable electron configuration. In the case of NO3-, it can bond with one positively charged ion, such as a metal ion, to form a stable compound. Thus, its valency is represented as 1, indicating its ability to form one bond in chemical reactions.

Chromate is a polyatomic ion that consists of chromium and oxygen. Its chemical formula is CrO4²-, indicating that it contains one chromium (Cr) atom and four oxygen (O) atoms, with a net charge of -2. This distinguishes it from other related ions, such as dichromate (Cr2O7²-), which has a different structure and charge. Chromate is commonly found in various chemical applications, including pigments and corrosion inhibitors.

Phosphate ions (PO4^3-) have a valency of 3 because they can form three bonds with other elements or compounds. This is due to the presence of one phosphorus atom bonded to four oxygen atoms, where one of the oxygen atoms carries a negative charge, resulting in a total charge of -3. This allows phosphate to participate in various chemical reactions and form stable compounds by combining with cations that have a positive charge, thus exhibiting its trivalent nature.

Hydronium is formed when a water molecule (H2O) accepts an extra proton (H+), resulting in the chemical formula H3O+. This ion is commonly encountered in acid-base chemistry, where it represents the presence of acidity in solutions. The positive charge indicates that it has one more proton than the neutral water molecule, making it a crucial species in many chemical reactions, particularly in aqueous environments.

Dichromate is a polyatomic ion composed of chromium and oxygen. Its chemical formula is Cr2O7²-, indicating that it contains two chromium atoms and seven oxygen atoms, with an overall charge of -2. This ion is commonly found in various chemical compounds and reactions, particularly in redox processes and as an oxidizing agent. The presence of two chromium atoms in the formula distinguishes it from other related ions, such as chromate (CrO4²-), which has a different structure and properties.

The sulphate ion (SO₄²⁻) has a valency of 2 because it carries a charge of -2. This charge results from the loss of two electrons, allowing the ion to bond with positively charged ions, such as metals, to form stable compounds. The structure of the sulphate ion includes one sulfur atom surrounded by four oxygen atoms, with the overall negative charge distributed across the molecule, confirming its valency of 2.

Permanganate is a polyatomic ion commonly represented by the formula MnO4-. It consists of one manganese (Mn) atom surrounded by four oxygen (O) atoms, and carries a negative one charge. This ion is known for its strong oxidizing properties and is often used in various chemical reactions, including titrations and as a disinfectant. The other options provided, such as CrO4²- and Cr2O7²-, represent different ions and do not correspond to permanganate.

HCO3- is known as hydrogencarbonate or bicarbonate. This ion consists of one carbon atom, three oxygen atoms, and one hydrogen atom, which gives it a negative charge of one. It plays a crucial role in maintaining pH balance in biological systems and is commonly found in various chemical reactions, particularly in buffering systems. In contrast, carbonate (CO3^2-) has a different composition and charge, while nitrate (NO3-) and hydroxide (OH-) are entirely different ions with distinct structures and functions.

The valency of the hydroxide ion (OH-) is 1 because it can combine with one positive charge from a cation to form a neutral compound. The hydroxide ion has a single negative charge, indicating that it can accept one hydrogen ion (H+) to achieve neutrality. This characteristic allows it to participate in various chemical reactions, particularly in acid-base chemistry, where it acts as a base by accepting protons. Thus, its valency is defined as 1.