date:
prepwork part 1: melting point oer practice
1. which of the following compounds will have the highest melting point?
(a) srs (b) bas (c) bes (d) mgs
2. briefly explain your response to q1:

3. if a student chose answer choice (a) instead, what mistake did s/he make? how can s/he avoid this
in the future?

4. which of the following compounds will have the highest melting point?
(a) na₂p (b) nacl (c) gacl₃ (d) mg₃n₂
5. briefly explain your response to q4:

6. if a student chose answer choice (b) instead, what mistake did s/he make? how can s/he avoid this
in the future?

Question

date:
prepwork part 1: melting point oer practice
1. which of the following compounds will have the highest melting point?
   (a) srs  (b) bas  (c) bes  (d) mgs
2. briefly explain your response to q1:

3. if a student chose answer choice (a) instead, what mistake did s/he make? how can s/he avoid this
   in the future?

4. which of the following compounds will have the highest melting point?
   (a) na₂p  (b) nacl  (c) gacl₃  (d) mg₃n₂
5. briefly explain your response to q4:

6. if a student chose answer choice (b) instead, what mistake did s/he make? how can s/he avoid this
   in the future?

Accepted Answer

### Question 1
# Explanation:
## Step1: Identify Compound Type
All compounds (SrS, BaS, BeS, MgS) are ionic compounds. Ionic melting point depends on lattice energy: $ E = \frac{kQ_1Q_2}{r} $, where $ Q $ is ion charge, $ r $ is ion radius.
## Step2: Analyze Ion Charges and Radii
All have $ S^{2-} $, cations: $ Be^{2+}, Mg^{2+}, Sr^{2+}, Ba^{2+} $ (all $ +2 $ charge). Ionic radius: $ Be^{2+} < Mg^{2+} < Sr^{2+} < Ba^{2+} $ (smaller radius → smaller $ r $ in lattice energy formula).
## Step3: Relate to Lattice Energy
Smaller $ r $ (ion radius) → larger lattice energy (since $ r $ is in denominator). Larger lattice energy → higher melting point. $ Be^{2+} $ has smallest radius, so BeS has highest lattice energy.
# Answer:
C. BeS

### Question 2
# Brief Explanations:
All are ionic compounds with $ S^{2-} $ and $ +2 $ cations. Melting point depends on lattice energy ($ E \propto \frac{Q_1Q_2}{r} $). Cation charges are equal, so compare ionic radii: $ Be^{2+} < Mg^{2+} < Sr^{2+} < Ba^{2+} $. Smaller $ r $ (Be²⁺) gives larger $ E $, so BeS has highest melting point.
# Answer:
All compounds are ionic with $ S^{2-} $ and $ +2 $ cations. Lattice energy depends on ion radius (smaller radius → larger energy). $ Be^{2+} $ has the smallest radius, so BeS has the highest lattice energy and thus highest melting point.

### Question 3
# Brief Explanations:
The student likely ignored ion radius effect. Sr²⁺ has a larger radius than Be²⁺, Mg²⁺. Lattice energy for SrS is smaller than BeS (and MgS) because $ r $ (Sr²⁺) is larger. To avoid, recall lattice energy depends on both charge and ion radius (smaller radius → higher energy for same - charge cations).
# Answer:
Mistake: Ignored ion radius. Sr²⁺ is larger than Be²⁺/Mg²⁺, so SrS has smaller lattice energy than BeS. To avoid, consider both ion charge and radius when comparing lattice energy (smaller radius → higher lattice energy for same - charge cations).

### Question 4
# Explanation:
## Step1: Identify Compound Types and Ion Charges
- $ Na_2P $: $ Na^+ $, $ P^{3-} $ (charges: $ +1, -3 $)
- $ NaCl $: $ Na^+ $, $ Cl^- $ (charges: $ +1, -1 $)
- $ GaCl_3 $: Likely covalent (Ga is a post - transition metal, $ GaCl_3 $ is covalent), lower melting point than ionic.
- $ Mg_3N_2 $: $ Mg^{2+} $, $ N^{3-} $ (charges: $ +2, -3 $)
## Step2: Calculate Charge Products ($ Q_1Q_2 $)
- $ Na_2P $: $ ( + 1)( - 3)= - 3 $ (magnitude 3)
- $ NaCl $: $ ( + 1)( - 1)= - 1 $ (magnitude 1)
- $ Mg_3N_2 $: $ ( + 2)( - 3)= - 6 $ (magnitude 6)
## Step3: Relate to Lattice Energy
Lattice energy magnitude $ \propto Q_1Q_2 / r $. $ Mg_3N_2 $ has largest charge product (6) among ionic compounds (GaCl₃ is covalent, lower melting). So $ Mg_3N_2 $ has highest lattice energy.
# Answer:
D. $ Mg_3N_2 $

### Question 5
# Brief Explanations:
$ GaCl_3 $ is covalent (lower melting). For ionic compounds: $ Na_2P $ ( $ +1, - 3 $, product 3), $ NaCl $ ( $ +1, - 1 $, product 1), $ Mg_3N_2 $ ( $ +2, - 3 $, product 6). Lattice energy $ \propto $ charge product (and ion radius, but charge product difference is large here). $ Mg_3N_2 $ has largest charge product, so highest lattice energy and melting point.
# Answer:
$ GaCl_3 $ is covalent (low melting). Ionic compounds: $ Na_2P $ (charge product 3), $ NaCl $ (1), $ Mg_3N_2 $ (6). Lattice energy depends on charge product (and radius); $ Mg_3N_2 $ has largest charge product, so highest lattice energy and melting point.

### Question 6
# Brief Explanations:
The student chose $ NaCl $, likely ignored charge product. $ NaCl $ has charge product (1) much smaller than $ Mg_3N_2 $ (6). $ Mg_3N_2 $ has higher lattice energy due to larger charge product. To avoid, calculate ion charges (find $ Q_1Q_2 $ magnitude) and recognize covalent vs ionic (GaCl₃ is covalent). Compare charge products for ionic compounds.
# Answer:
Mistake: Ignored charge product and covalent/ionic distinction. $ NaCl $ has charge product (1) less than $ Mg_3N_2 $ (6), and $ GaCl_3 $ is covalent. To avoid, analyze ion charges (calculate $ Q_1Q_2 $) and identify covalent compounds, then compare ionic compounds' lattice energy via charge product (and radius if needed).

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QUESTION IMAGE

Question

Explanation:

Question 1

Step1: Identify Compound Type

Step2: Analyze Ion Charges and Radii

Step3: Relate to Lattice Energy

Answer:

Question 2