Problem 104 - Chemistry An Atoms First Approach

Question

Glass is a mixture of several compounds, but a major constituent of most glass is calcium silicate, \(\mathrm{CaSiO}_{3}\). Glass can be etched by treatment with hydrofluoric acid; HF attacks the calcium silicate of the glass, producing gaseous and water-soluble products (which can be removed by washing the glass). For example, the volumetric glassware in chemistry laboratories is often graduated by using this process. Balance the following equation for the reaction of hydrofluoric acid with calcium silicate. $$\mathrm{CaSiO}_{3}(s)+\mathrm{HF}(a q) \longrightarrow \mathrm{CaF}_{2}(a q)+\mathrm{SiF}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(l)$$

Step-by-Step Solution

Answer

The balanced chemical equation for the reaction of hydrofluoric acid with calcium silicate is: $$\mathrm{CaSiO}_{3}(s)+6\mathrm{HF}(aq) \rightarrow \mathrm{CaF}_{2}(aq)+\mathrm{SiF}_{4}(g)+3\mathrm{H}_{2} \mathrm{O}(l)$$

Step 1: Identify the elements in the reaction and count their atoms initially

First, let's identify the elements involved in the reaction. We have Calcium (Ca), Silicon (Si), Oxygen (O), Hydrogen (H), and Fluorine (F). Now, count the number of atoms for each element on both sides of the equation: Reactants: - Ca: 1 - Si: 1 - O: 3 - H: 1 - F: 1 Products: - Ca: 1 - Si: 1 - O: 1 - H: 2 - F: 6

Step 2: Balance the equation one element at a time

To balance the equation, we will start adjusting the coefficients for the compounds containing the least common elements and work our way through to the most common elements (usually H and O). 1. Balance F: Since there are 6 F atoms in the products and only 1 F atom in the reactants, add a coefficient of 6 to the HF reactant: $$\mathrm{CaSiO}_{3}(s)+6\mathrm{HF}(a q) \longrightarrow \mathrm{CaF}_{2}(a q)+\mathrm{SiF}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(l)$$ Now there are 6 H atoms and 6 F atoms in the reactants. 2. Balance O: There are 3 O atoms in the reactants and only 1 O atom in the products. Add a coefficient of 3 to the H2O product to balance the O atoms: $$\mathrm{CaSiO}_{3}(s)+6\mathrm{HF}(a q) \longrightarrow \mathrm{CaF}_{2}(a q)+\mathrm{SiF}_{4}(g)+3\mathrm{H}_{2} \mathrm{O}(l)$$ Now there are 6 H atoms and 3 O atoms in both the reactants and products. 3. Check the balance for Ca and Si: There is no need to adjust the coefficients for Ca and Si, as there is already 1 Ca and 1 Si atom on both sides of the equation. At this point, the equation is balanced. The balanced chemical equation for the reaction of hydrofluoric acid with calcium silicate is: $$\mathrm{CaSiO}_{3}(s)+6\mathrm{HF}(aq) \rightarrow \mathrm{CaF}_{2}(aq)+\mathrm{SiF}_{4}(g)+3\mathrm{H}_{2} \mathrm{O}(l)$$

Key Concepts

Glass Etching

Glass etching is a fascinating process that allows for intricate designs to be created on glass surfaces. This technique is primarily used for artistic purposes and in industrial applications, such as marking and measuring glassware in laboratories. The etching process involves the controlled removal of the surface layer of the glass, creating a frosted or patterned appearance.
When hydrofluoric acid (HF) is applied to glass, it reacts with the compounds within, specifically the calcium silicate (\( \text{CaSiO}_3 \)) that is a primary component in many types of glass.

• HF is a highly reactive and hazardous substance, making it ideal for etching by transforming compounds into gaseous or soluble products that are easily washed away.
• The result is a glass that has been "etched" with the desired design or measurement.
• As seen in laboratory settings, this allows precise measurement markers to be etched onto glassware.

Understanding the chemical reactions involved in glass etching, like the balance of chemical equations, helps ensure safety and precision in these processes.

Calcium Silicate

Calcium silicate, \( \text{CaSiO}_3 \), plays a crucial role in the structure of glass. It serves as one of the primary components responsible for the integrity and durability of the glass material.

• Glass composition varies, but calcium silicate is commonly found in construction-grade and laboratory-grade glasses.
• As a compound, calcium silicate combines calcium (Ca), silicon (Si), and oxygen (O), forming a stable and strong crystalline structure.
• In glass etching, calcium silicate reacts with hydrofluoric acid (HF), which attacks the compound and facilitates etching by breaking down its structure.

Balancing the reaction equation between hydrofluoric acid and calcium silicate is crucial. This equation ensures that the chemical transformation is understood and controlled, which is vital for both practical applications and safety purposes.

Hydrofluoric Acid Reaction

A hydrofluoric acid reaction, especially with glass, is a key process in the etching and modification of glass surfaces. HF is unique because it can dissolve glass, which is typically resistant to most acids. This ability makes it invaluable in both artistic and scientific fields.
Here’s what you need to know about this reaction:

• The reaction between HF and calcium silicate yields calcium fluoride (\( \text{CaF}_2 \)), silicon tetrafluoride (\( \text{SiF}_4 \)), and water (\( \text{H}_2 \text{O} \)).
• Balancing the chemical equation helps to illustrate the conservation of mass and ensure that reactions are performed efficiently.
• Safety is paramount when handling HF due to its high reactivity and potential health hazards upon contact with skin or inhalation.

Thus, understanding the implications and reactions of hydrofluoric acid, particularly in the context of glass etching, is essential for safe and effective application.