The Correct Answer and Explanation is:
Here are the correct answers to the chemistry questions, followed by a detailed explanation.
- d) 5
- d) Na₂O
- a) Al⁺³
- c) Cobalt (III) nitrate
- c) K₂SO₄
- a) Synthesis
- c) CH₄ + 2 O₂ → CO₂ + 2 H₂O
Valence Electrons and Ion Formation
The number of valence electrons an element has determines its chemical reactivity. For question 7, Nitrogen is in Group 15 of the periodic table, which means it has five valence electrons, the electrons in its outermost energy shell. This is why it tends to gain three electrons to achieve a stable octet. For question 9, Aluminum, in Group 13, has three valence electrons. As a metal, it tends to lose these three electrons to achieve the stable electron configuration of the preceding noble gas. Losing three negatively charged electrons results in an ion with a positive three charge, correctly written as Al⁺³.
Ionic Compound Formulas and Nomenclature
Ionic compounds are formed between positively charged ions (cations) and negatively charged ions (anions) in a ratio that results in a neutral overall charge. For question 8, sodium (Na) from Group 1 forms a Na⁺ ion, while oxygen (O) from Group 16 forms an O²⁻ ion. To balance the charges, two Na⁺ ions are needed for every one O²⁻ ion, resulting in the formula Na₂O. Similarly, for question 11, potassium (K) forms a K⁺ ion and the polyatomic sulfate ion has a formula of SO₄²⁻. Two potassium ions are required to balance the charge of one sulfate ion, giving the formula K₂SO₄. For question 10, Co(NO₃)₃, the nitrate ion (NO₃) has a charge of -1. Since there are three nitrate ions, the total negative charge is -3. Therefore, the cobalt (Co) ion must have a +3 charge to create a neutral compound. Because cobalt is a transition metal that can have multiple charges, its charge is indicated with a Roman numeral, making the correct name Cobalt (III) nitrate.
Types of Chemical Reactions
Chemical reactions are classified based on how reactants are rearranged to form products. The reaction in question 12, Mg + 2F → MgF₂, shows two simpler substances, magnesium and fluorine, combining to form a single, more complex product, magnesium fluoride. This process is defined as a synthesis reaction. Question 13 asks for an example of a combustion reaction. A typical combustion reaction involves a hydrocarbon reacting with oxygen to produce carbon dioxide and water. The equation CH₄ + 2 O₂ → CO₂ + 2 H₂O perfectly fits this definition, as methane (CH₄) burns in the presence of oxygen (O₂) to produce carbon dioxide and water, releasing energy. The other options represent decomposition, double displacement, and single displacement reactions, respectively.
