Question

Give the name and symbol or formula of a Group \(7 \mathrm{~A}(17)\) element or compound that fits each description or use: (a) Used in etching glass (b) Compound used in household bleach (c) Weakest hydrohalic acid (d) Element that is a liquid at room temperature (e) Organic chloride used to make PVC

Short answer

(a) HF, (b) NaOCl, (c) HF, (d) Br, (e) C2H3Cl

Step-by-step solution

Identify Group 17 elements

Group 17 is also known as Group 7A in the periodic table. The elements in this group are called halogens and include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).

Step (a) - Etching glass

Etching glass typically involves the use of hydrofluoric acid (HF), which reacts with silicon dioxide in glass to form gaseous silicon tetrafluoride, creating the etching. Therefore, the chemical used is hydrofluoric acid (HF).

Step (b) - Household bleach

Household bleach usually contains sodium hypochlorite (NaOCl), a compound that releases chlorine to bleach clothes and disinfect surfaces.

Step (c) - Weakest hydrohalic acid

Among the hydrohalic acids (HF, HCl, HBr, HI), hydrofluoric acid (HF) is the weakest due to its high bond dissociation energy.

Step (d) - Liquid at room temperature

Bromine (Br) is the only Group 17 element that is a liquid at room temperature.

Step (e) - Organic chloride used to make PVC

Polyvinyl chloride (PVC) is made from the organic compound vinyl chloride (C2H3Cl).

Key concepts

halogens

Group 17 elements in the periodic table are known as halogens. This group includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Halogens are known for their high reactivity, especially with alkali and alkaline earth metals. This high reactivity is due to their seven valence electrons, meaning they need only one more to achieve a full outer shell.

Halogens are found in various states of matter at room temperature: Fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids.

These elements are used in many applications, from disinfectants to pharmaceuticals. Fluorine, for example, is used in toothpaste to help prevent dental cavities, while iodine is crucial for thyroid hormone production in the human body.

hydrofluoric acid

Hydrofluoric acid (HF) is a solution of hydrogen fluoride in water. Unlike other hydrohalic acids, HF is relatively weak due to the strong bond between hydrogen and fluorine. This means it does not dissociate completely in water.

Despite being weak, HF is highly reactive and can dissolve many materials, including glass. This property makes it useful in glass etching and cleaning. However, it is also highly dangerous, requiring careful handling as it can cause severe burns and damage to tissues.

sodium hypochlorite

Sodium hypochlorite (NaOCl) is commonly known as bleach. It is used extensively for sanitizing and disinfecting surfaces, as well as for whitening clothes.

Sodium hypochlorite works by releasing chlorine, which breaks down the molecules that create stains and kill bacteria and viruses. When NaOCl is dissolved in water, it forms a weak acid called hypochlorous acid (HOCl), which is effective in eliminating pathogens.

bromine

Bromine (Br) is a dark reddish-brown liquid at room temperature, making it unique among the halogens. It is highly volatile and its vapors are toxic and irritating to the eyes and throat.

Bromine is less reactive than chlorine and fluorine but more reactive than iodine. It is used in various applications, such as in flame retardants, water treatment, and certain types of medications.

vinyl chloride

Vinyl chloride (C2H3Cl) is a colorless gas with a mild, sweet odor. It is used primarily to produce polyvinyl chloride (PVC), which is a versatile plastic. PVC is used in a wide array of products, from pipes and cable insulation to clothing and furniture.

Vinyl chloride is highly flammable and poses health risks. Long-term exposure to vinyl chloride can lead to serious health issues, including liver damage and an increased risk of cancer. Thus, its handling and use are tightly regulated.