MC test: S2.1 The ionic model

Which compound will have the lowest melting point?

A. MgO 

B. Al₂O₃

C. P₄O₁₀

D. Na₂O

c. P₄O₁₀

Na₂O, MgO and Al₂O₃ are all ionic, P₄O₁₀ is covalent.
(The actual values for Na₂O, MgO and Al₂O₃ are 1132, 2852 and 2072 ^oC respectively. P₄O₁₀ melts at 340 ^oC.)

• covalent bonds have the weakest force of attraction
  → less energy is required to break the force of bonding

Which is the correct formula for aluminium nitride?
A. Al₂(NO₃)₃

B. Al(NO₃)₃

C. Al₂N₃ 

D. AlN

D. AlN
Al forms the Al³⁺ ion and N forms the N³⁻ ion. NO₃⁻ is the nitrate ion not the nitride ion.

Which substance will not conduct electricity in its molten state?

A. sodium chloride 

B. magnesium iodide

C. lead bromide

D. carbon tetrachloride

D. carbon tetrachloride

• Carbon tetrachloride is a covalent liquid and contains no ions, all of the other compounds are ionic.

  → molten state = LOWKEY liquid

Which row contains the correct formulas for all the respective ions?
A. 2

B. 3 

C. 4

D. 1

B. 3 
Hydrogencarbonate: HCO₃⁻, phosphate: PO₄³⁻ and sulfate: SO₄²⁻. SO₃²⁻ is the sulfite ion (sometimes called the sulfate(IV) ion).

Gadolinium is a lanthanoid. The formula of gadolinium oxide is Gd₂O₃. What will be the formula of gadolinium hydroxide assuming the oxidation state of gadolinium does not change?
A. Gd₂(OH)₃

B. Gd(OH)₃ 

C. Gd(OH)₂

D. GdOH

B. Gd(OH)₃ 

• From the formula for the oxide, gadolinium must be bonding as the Gd³⁺ ion. Since the hydroxide ion is OH⁻, the formula must be Gd(OH)₃

A metal M forms a nitrate, carbonate and hydroxide and has the same oxidation state in each compound. Which row contains all three correct formulas?
A. 1

B. 4

C. 2

D. 3 

B. 4

The oxidation states of M are 1,2,1 respectively in row 1; 2,2,1 in row 2 and 2,2,2 in row 4. Row 3 contains the nonsensical formula M₂(NO₃)₃ and M₂(CO₃)₂ can be shortened to MCO₃.

Which are correct statements about sodium chloride?

I. In the crystal lattice each sodium ion has six chloride ions as its nearest neighbours.

II. It can be formed by burning sodium in chlorine gas.

III. During its formation a sodium atom loses an electron and a chlorine atom gains an electron.

A. II and III only

B. I, II and III

C. I and III only 

D. I and II only

B. I, II and III

• Na⁺Cl⁻, which can be formed by burning sodium in chlorine ( 2Na(s) + Cl₂(g) → 2NaCl(s) ), forms a face-centred cubic lattice in which each Na⁺ ion is surrounded by six Cl⁻ ions and each Cl⁻ ion is surrounded by six Na⁺ ions.

Which are the correct formulas for both ammonium phosphate and ammonium sulfate?
A. (NH₃)₂(PO₄)₃ and (NH₃)₂SO₄

B. (NH₄)₂(PO4)₃ and (NH₄)₂SO4

C. (NH₄)₃PO₄ and NH₄SO₄

D. (NH₄)₃PO₄ and (NH₄)₂SO₄

D. (NH₄)₃PO₄ and (NH₄)₂SO₄

• Ammonium is NH₄⁺,  phosphate is PO₄³⁻ and sulfate is SO₄²⁻ so (NH₄)₃PO₄ and (NH₄)₂SO₄ are correct.

Which compound contains only ionic bonding?
A. aluminium nitrate

B. sodium bromide 

C. potassium carbonate

D. ammonium chloride

B. sodium bromide 

• Although all four are ionic compounds the nitrate and carbonate negative ions (anions) also contain covalent bonds and the ammonium positive ion (cation) contains covalent bonds between the nitrogen and hydrogen atoms.

Which will conduct electricity?

A. salt solution

B. sugar solution 

C. alcohol

D. NaBr(s)

A. salt solution

• Sugar solution and alcohol do not contain ions. Sodium bromide is ionic but in the solid state the ions are not free to move. Na⁺ and Cl⁻ are free to move to electrodes in salt solution and chemical decomposition occurs.