Question

Manganese silicide has the empirical formula MnSi and melts at \(1280^{\circ} \mathrm{C}\) . It is insoluble in water but does dissolve in aqueous HF. (a) What type of compound do you expect MnSi to be: metallic, molecular, covalent- network, or ionic? (b) Write a likely balanced chemical equation for the reaction of MnSi with concentrated aqueous HF.

Short answer

The type of compound MnSi is likely to be a covalent-network compound based on its high melting point and solubility in aqueous HF. The balanced chemical equation for MnSi reacting with concentrated aqueous HF is: \(MnSi + 6 HF \rightarrow MnF_{2} + SiF_{4}\)

Step-by-step solution

Part a: Determine the type of compound MnSi

Given the information, MnSi has a high melting point at 1280 degrees Celsius, which suggests it is a compound with strong bonds. It is insoluble in water but soluble in aqueous HF. This indicates that MnSi is not an ionic compound, as ionic compounds are typically soluble in water. From the given information, we can infer that MnSi is most likely a covalent-network compound.

Part b: Write a balanced chemical equation for MnSi reacting with concentrated aqueous HF

To write the balanced chemical equation, we first need to identify the products of the reaction. Since MnSi is a covalent-network compound and it dissolves in aqueous HF, we can assume that the reaction will produce MnF2 and SiF4, which are formed from the reactions between the metal and nonmetal elements and HF. The unbalanced equation is: MnSi + HF → MnF2 + SiF4 Now, we need to balance this chemical equation. We can use the method of counting the number of atoms of each element on both sides of the equation. Mn: 1 on both sides Si: 1 on both sides F: 1 on the reactants' side and 6 on the products' side To balance the equation for fluorine, we can multiply HF by 6: MnSi + 6 HF → MnF2 + SiF4 This equation is now balanced: 1 Mn, 1 Si, and 6 F on both sides of the equation. The balanced chemical equation for MnSi reacting with concentrated aqueous HF is: \( MnSi + 6 HF \rightarrow MnF_{2} + SiF_{4} \)

Key concepts

Chemical Properties of Materials

Understanding the chemical properties of materials like manganese silicide (MnSi) is essential for predicting how they will behave in various environments. Chemical properties are determined by the types of bonds between atoms and the structure of a substance. Covalent-network compounds, as inferred for MnSi, are characterized by strong bonds between atoms that form a continuous network throughout the material. This gives rise to distinctive properties such as high melting points and general insolubility in water.

The solubility of MnSi in hydrofluoric acid (HF), however, is an exception that highlights another chemical property; its reactivity with specific chemicals. Dissolving in HF, MnSi behaves differently from ionic compounds which typically dissolve in polar solvents like water. The reaction with HF suggests that it undergoes a chemical transformation, breaking its strong covalent bonds, which is a remarkable characteristic defining its reactivity profile.

Balancing Chemical Equations

Balancing chemical equations is paramount in accurately representing chemical reactions. The law of conservation of mass dictates that atoms are neither created nor destroyed in a chemical reaction, which means each element must have the same number of atoms on both sides of the equation. To balance the equation for the reaction of MnSi with HF, we account for each element.

The initial step is to write the unbalanced equation, then by counting atoms of each element and using coefficients, we adjust until the equation is balanced. In our case, the balanced equation reflects that 6 fluorine atoms from HF react with MnSi to form one molecule each of MnF2 and SiF4. For students, mastering the skill of balancing equations involves learning to systematically approach the problem and practice with various types of chemical reactions.

Reaction with Hydrofluoric Acid

The reaction of covalent-network compounds with hydrofluoric acid (HF) is a specific type of chemical interaction where HF acts as a solvent and etchant, capable of disrupting the strong network of covalent bonds. HF is unique due to its ability to react with silicon-based materials, making it an essential reactant in processes like etching glass or semiconductors.

In the case of MnSi, when it reacts with HF, a double replacement reaction occurs, creating silicon tetrafluoride (SiF4) and manganese(II) fluoride (MnF2). This type of reaction is highly specific and can be predicted based on the known behavior of HF with covalent-network solids. Through such reactions, HF proves itself to be an important reagent in chemistry, useful in both industrial applications and experimental work.