AS & A Level Chemistry 3.5 Shapes of molecules : Exam Style Questions Paper 1

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Question

Which molecules have no overall dipole moment?

1 boron trifluoride
2 methane
3 phosphorus pentafluoride

▶️Answer/Explanation

Ans:A

Question: 

A stable ion \(N_{5}^{~+}\) has been produced by research chemists. Which structure is most likely to show the electron arrangement of this ion?

▶️Answer/Explanation

Ans:B

Question: 

Which molecule does not have any 90° or 180° bond angles?

A \(C_{2}H_{6}\)          B \(CO_{2}\)          C \(PF_{5}\)      D \(SF_{6}\)

▶️Answer/Explanation

A

Question

The characteristic smell of garlic is due to alliin.

What are the approximate bond angles x, y and z in a molecule of alliin?

▶️Answer/Explanation

Ans:C

Question

Which series shows molecules in order of increasing bond angle?
A $\mathrm{CH}_4 \rightarrow \mathrm{BF}_3 \rightarrow \mathrm{NH}_3$
B $\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{CO}_2 \rightarrow \mathrm{BF}_3$
C $\mathrm{NH}_3 \rightarrow \mathrm{CH}_4 \rightarrow \mathrm{CO}_2$
D $\mathrm{NH}_3 \rightarrow \mathrm{CH}_4 \rightarrow \mathrm{H}_2 \mathrm{O}$

▶️Answer/Explanation

Ans:C

Question

 For which molecule is the dipole moment zero?
A \(CH_3Cl\)            B \(CH_2Cl_2\)              C \(CHCl_3\)                 D \(CCl_4\)

Answer/Explanation

Ans: D

Question

 When ammonia, \(NH_3\), is dissolved in water, a small concentration of ammonium ions, \(NH_4^+\), is formed.
Which row is correct?

Answer/Explanation

Ans: D

 Question

Phosphorus forms two chlorides. Phosphorus(III) chloride, PCl3 , is a covalent liquid.

Phosphorus(V) chloride is an ionic solid. One of the ions present is [PCl4]+.

What is the shape of the PCl3 molecule and the [PCl4]+ion?

Answer/Explanation

Answer:     B

Question

Which molecules contain at least one bond angle of 120 °?

1 C2H4
2 PF5
3 NCl3

Answer/Explanation

Answer:     B

Question

The eight species that follow all have covalent bonds.

In which pair do the species have different shapes from each other?

A    BeCl2 and CO2
B    CH4 and NH4+
C    NH3 and BF3
D    SCl2 and H2O

Answer/Explanation

Answer:

C

Question

Histidine is an amino acid.

What are the approximate bond angles 1, 2, and 3?

Answer/Explanation

Answer:

B

Question

Which molecule or ion contains the smallest bond angle?

A C2H4               B CH3COCH3                  C NH4+                     D NH3

Answer/Explanation

Answer      D

Question

Which molecules and ions have a bond angle of 120°?

1 BF3
2 CH3–
3 NH3

Answer/Explanation

Answer     D

Question

What are the shapes of the molecules of water and boron trifluoride?

Answer/Explanation

Answer:

D

Question

Histamine is produced in the body to help fight infection. Its shape allows it to fit into receptors which expand blood vessels.

What are the bond angles x, y and z in histamine, from the smallest to the largest?

Answer/Explanation

Answer:     A

Question

Urea is a product of animal metabolism. It can also be used as a fertiliser.

The diagram shows angle x in this molecule.
Which statements about the structure of urea are correct?

1 Angle x is approximately 120°.
2 The molecule has two π bonds.
3 The molecule has only three lone pairs of electrons.

The responses A to D should be selected on the basis of

Answer/Explanation

Ans:D

 

Question

\(AlCl_{ 3}\) vapour forms molecules with formula\( Al _{2}Cl _{6 }\)as it is cooled.
What happens to the bond angles during the change from\( AlCl _{3} to Al_{ 2}Cl _{6}\)?

 A Some decrease, some remain the same.

B Some increase, some remain the same.

C They all decrease.

D They all increase.

Answer/Explanation

Ans:C

Question

Valence shell electron pair repulsion theory should be used to answer this question.
Which species are trigonal planar?

1    \(BH_3\)
2    \(CH_3^+\)
3    \(PH_3\)
The responses A to D should be selected on the basis of

No other combination of statements is used as a correct response.

Answer/Explanation

Ans: B

Question

In which pair do the molecules have the same shape as each other?

  1. H2O and CO2
  2. H2O and SCl2
  3. NH3 and BH3
  4. SCl2 and BeCl2
Answer/Explanation

Ans:

B

Question

Sodium borohydride, NaBH4, and boron trifluoride, BF3, are compounds of boron.
    What are the shapes around boron in the borohydride ion and in boron trifluoride?

Answer/Explanation

Ans:

D

Question

 Two conversions are outlined below.

NH4+ → NH3

C2H4 → C2H6

What similar feature do these two conversions have?

  1. a lone pair of electrons in the product
  2. change in oxidation state of an element
  3. decrease in bond angle of the species involved
  4. disappearance of a π bond
Answer/Explanation

Ans:

C

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