1. the relative molecular mass of a gas is 56 and its...

1. The relative molecular mass of a gas is 56 and its empirical formula is CH2. What is the molecular formula of the gas?

A. CH2

B. C2H4

C. C3H6

D. C4H8 (Total 1 mark)

2. A fixed mass of gas has a certain volume at a temperature of 50 °C. What temperature is required to double its volume while keeping the pressure constant?

A. 100 K

B. 323 K

C. 373 K

D. 646 K (Total 1 mark)

3. Which sample has the greatest mass?

A. 1 mol of SO2

B. 2 mol of N2O

C. 2 mol of Ar

D. 4 mol of NH3 (Total 1 mark)

IB Questionbank Chemistry 1

4. What is the coefficient of Fe3O4 when the following equation is balanced using the lowest whole numbers?

__ Al(s) + __ Fe3O4(s) → __ Al2O3(s) + __ Fe(s)

A. 2

B. 3

C. 4

D. 5 (Total 1 mark)

5. 300 cm3 of water is added to a solution of 200 cm3 of 0.5 mol dm–3 sodium chloride. What is the concentration of sodium chloride in the new solution?

A. 0.05 mol dm–3

B. 0.1 mol dm–3

C. 0.2 mol dm–3

D. 0.3 mol dm–3 (Total 1 mark)

6. What is the maximum mass, in g, of magnesium oxide that can be obtained from the reaction of oxygen with 2.4 g of magnesium?

A. 2.4

B. 3.0

C. 4.0

D. 5.6 (Total 1 mark)


7. Brass is a copper containing alloy with many uses. An analysis is carried out to determine the percentage of copper present in three identical samples of brass. The reactions involved in this analysis are shown below.

Step 1: Cu(s) + 2HNO3(aq) + 2H+(aq) → Cu2+(aq) + 2NO2(g) + 2H2O(l)

Step 2: 4I–(aq) + 2Cu2+(aq) → 2CuI(s) + I2(aq)

Step 3: I2(aq) + 2S2O32–(aq) → 2I–(aq) + S4O6

2–(aq)

(a) (i) Deduce the change in the oxidation numbers of copper and nitrogen in step 1.

Copper:

...........................................................................................................................

Nitrogen:

........................................................................................................................... (2)

(ii) Identify the oxidizing agent in step 1.

........................................................................................................................... (1)

(b) A student carried out this experiment three times, with three identical small brass nails, and obtained the following results.

Mass of brass = 0.456 g ± 0.001 g

Titre 1 2 3

Initial volume of 0.100 mol dm–3 S2O32– (± 0.05 cm3) 0.00 0.00 0.00

Final volume of 0.100 mol dm–3 S2O32– (± 0.05 cm3) 28.50 28.60 28.40

Volume added of 0.100 mol dm–3 S2O32– (± 0.10 cm3) 28.50 28.60 28.40

Average volume added of 0.100 mol dm–3 S2O32–(± 0.10

cm3) 28.50


(i) Calculate the average amount, in mol, of S2O32– added in step 3.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

........................................................................................................................... (2)

(ii) Calculate the amount, in mol, of copper present in the brass.

...........................................................................................................................

........................................................................................................................... (1)

(iii) Calculate the mass of copper in the brass.

...........................................................................................................................

........................................................................................................................... (1)

(iv) Calculate the percentage by mass of copper in the brass.

...........................................................................................................................

........................................................................................................................... (1)

(v) The manufacturers claim that the sample of brass contains 44.2 % copper by mass. Determine the percentage error in the result.

...........................................................................................................................

........................................................................................................................... (1)


(c) With reference to its metallic structure, describe how brass conducts electricity.

......................................................................................................................................

...................................................................................................................................... (1)

(Total 10 marks)

8. Smog is common in cities throughout the world. One component of smog is PAN (peroxyacylnitrate) which consists of 20.2 % C, 11.4 % N, 65.9 % O and 2.50 % H by mass. Determine the empirical formula of PAN, showing your working.

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9. Consider the following sequence of reactions.

RCH3 → 1reaction RCH2Br → 2reaction RCH2OH → 3reaction RCOOH

RCH3 is an unknown alkane in which R represents an alkyl group.

(a) The alkane contains 81.7 % by mass of carbon. Determine its empirical formula, showing your working.

(3)


(b) Equal volumes of carbon dioxide and the unknown alkane are found to have the same mass, measured to an accuracy of two significant figures, at the same temperature and pressure. Deduce the molecular formula of the alkane.

(1)

(c) (i) State the reagent and conditions needed for reaction 1. (2)

(ii) State the reagent(s) and conditions needed for reaction 3. (2)

(d) Reaction 1 involves a free-radical mechanism. Describe the stepwise mechanism, by giving equations to represent the initiation, propagation and termination steps.

(4)

(e) The mechanism in reaction 2 is described as SN2.

(i) State the meaning of each of the symbols in SN2. (1)

(ii) Explain the mechanism of this reaction using curly arrows to show the movement of electron pairs, and draw the structure of the transition state.

(3) (Total 16 marks)


10. What is the correct Lewis structure for hypochlorous acid, a compound containing chlorine, hydrogen and oxygen?

A. :H:....O:

..

..Cl:

B. :....O:H:

..

..Cl:

C. H:....O:

..

..Cl:

D. H:....Cl:

..

..O

(Total 1 mark)

11. How do the bond angles in CH4, NH3 and H2O compare?

A. CH4 = NH3 = H2O

B. CH4 < NH3 < H2O

C. NH3 < CH4 < H2O

D. H2O < NH3 < CH4 (Total 1 mark)

12. Which species does not contain delocalized electrons?

A. CH3CH2O–

B. CH3CO2–

C. O3

D. NO3–

(Total 1 mark)


13. How many σ and π bonds are present in a molecule of propyne, CH3CCH?

σ π

A. 5 3

B. 6 2

C. 7 1

D. 8 0 (Total 1 mark)

14. What are the correct formulas of the following ions?

Ammonium Hydrogencarbonate Phosphate

A. NH4+ HCO3

2– PO4–

B. NH3+ HCO3

– PO43–

C. NH4+ HCO3

2– PO42–

D. NH4+ HCO3

– PO43–

(Total 1 mark)

15. Which molecule has an octahedral shape?

A. SF6

B. PCl5

C. XeF4

D. BF3 (Total 1 mark)


16. Which order is correct when the following compounds are arranged in order of increasing melting point?

A. CH4 < H2S < H2O

B. H2S < H2O < CH4

C. CH4 < H2O < H2S

D. H2S < CH4 < H2O (Total 1 mark)

17. The graph below shows the first four ionization energies of four elements A, B, C and D (the letters are not their chemical symbols). Which element is magnesium?

(Total 1 mark)


18. Describe and compare three features of the structure and bonding in the three allotropes of carbon: diamond, graphite and C60 fullerene.

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................................................................................................................................................ (Total 6 marks)

19. Describe the structure and bonding in SiO2.

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................................................................................................................................................ (Total 2 marks)


20. Describe the delocalization of pi (π) electrons and explain how this can account for the structure and stability of the carbonate ion, CO3

2–.

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................................................................................................................................................ (Total 3 marks)

21. Ammonia, NH3, is a weak base.

(i) Draw the Lewis structure of ammonia and state the shape of the molecule and its bond angles.

......................................................................................................................................

......................................................................................................................................

...................................................................................................................................... (3)


(ii) The conjugate acid of ammonia is the ammonium ion, NH4+. Draw the Lewis structure of

the ammonium ion and deduce its shape and bond angles.

......................................................................................................................................

......................................................................................................................................

...................................................................................................................................... (3)

(Total 6 marks)

22. (i) Define the term first ionization energy of an atom. (2)

(ii) Explain the general increasing trend in the first ionization energies of the period 3 elements, Na to Ar.

(2)

(iii) Explain why sodium conducts electricity but phosphorus does not. (2)

(Total 6 marks)

23. Draw the Lewis structures, state the shape and predict the bond angles for the following species.

(i) PCl3 (3)

(ii) NH2–

(3)


(iii) XeF4 (3)

(Total 9 marks)

24. Explain, using diagrams, why CO and NO2 are polar molecules but CO2 is a non-polar

molecule. (Total 5 marks)


1. D [1]

2. D [1]

3. B [1]

4. B [1]

5. C [1]

6. C [1]

7. (a) (i) Copper: 0 to +2 / increases by 2 / +2 / 2+; Allow zero/nought for 0.

Nitrogen: +5 to +4 / decreases by 1 / –1 / 1–; Penalize missing + sign or incorrect notation such as 2+, 2+ or II, once only. 2

(ii) nitric acid/HNO3 / NO3–/nitrate;

Allow nitrogen from nitric acid/nitrate but not just nitrogen. 1

(b) (i) 0.100 × 0.0285; 2.85 × 10–3 (mol); Award [2] for correct final answer. 2

(ii) 2.85 × 10–3 (mol); 1


(iii) (63.55 × 2.85 × 10–3) = 0.181 g; Allow 63.5. 1

(iv)

=×100

456.0181.0 39.7 % 1

(v)

=×

− 1002.44

7.392.44 10/10.2 %;

Allow 11.3 % i.e. percentage obtained in (iv) is used to divide instead of 44.2 %. 1

(c) Brass has: delocalized electrons / sea of mobile electrons / sea of electrons free to move; No mark for just “mobile electrons”. 1

[10]

8. C N O H 20.2 11.4 65.9 2.50 12.01 14.01 16.00 1.01 = 1.68 = 0.814 = 4.12 = 2.48 ;

814.068.1 = 2

814.0814.0 = 1

814.012.4 = 5

814.048.2 = 3 ;

C2NO5H3;

No penalty for use of 12, 1 and/or 14. Award [1 max] if the empirical formula is correct, but no working shown. 3

[3]

9. (a) nC = 01.127.81 = 6.80 and nH =

01.13.18 = 18.1;

ratio of 1: 2.67 /1: 2.7; C3H8; No penalty for using 12 and 1. 3

(b) C3H8; 1

(c) (i) Br2 /bromine; UV/ultraviolet light; Accept hf/hv/sunlight. 2

(ii) Cr2O72– /MnO4

– and acidified/ H+ /H3O+;


Accept names.

heat / reflux; 2

(d) Initiation: Br2 → 2Br•;

Propagation: Br• + RCH3 → HBr + RCH2•; RCH2• + Br2 → RCH2Br + Br•;

Termination: [1 max] Br• + Br• → Br2; RCH2• + Br• → RCH2Br; RCH2• + RCH2• → RCH2CH2R; Award [1] for any termination step. Accept radical with or without • throughout. Do not penalize the use of an incorrect alkane in the mechanism. 4 max

(e) (i) substitution and nucleophilic and bimolecular/two species in rate-determining step; Allow second order in place of bimolecular. 1

(ii)

curly arrow going from lone pair/negative charge on O in OH– to C;

Do not allow curly arrow originating on H in OH–

curly arrow showing Br leaving; Accept curly arrow either going from bond between C and Br to Br in bromoethane or in the transition state.

representation of transition state showing negative charge, square brackets and partial bonds; Do not penalize if HO and Br are not at 180° to each other. Do not award M3 if OH ---- C bond is represented unless already penalized in M1. Do not penalize the use of an incorrect alkyl chain in the mechanism. 3

[16]


10. C [1]

11. D [1]

12. A [1]

13. B [1]

14. D [1]

15. A [1]

16. A [1]

17. B [1]


18. Award [2 max] for three of the following features:

Bonding

Graphite and C60 fullerene: covalent bonds and van der Waals’/London/ dispersion forces; Diamond: covalent bonds (and van der Waals’/London/dispersion forces);

Delocalized electrons

Graphite and C60 fullerene: delocalized electrons; Diamond: no delocalized electrons;

Structure

Diamond: network/giant structure / macromolecular / three-dimensional structure and Graphite: layered structure / two-dimensional structure / planar; C60 fullerene: consists of molecules / spheres made of atoms arranged in hexagons/pentagons;

Bond angles

Graphite: 120° and Diamond: 109°; C60 fullerene: bond angles between 109–120°; Allow Graphite: sp2 and Diamond: sp3. Allow C60 fullerene: sp2 and sp3.

Number of atoms each carbon is bonded to

Graphite and C60 fullerene: each C atom attached to 3 others; Diamond: each C atom attached to 4 atoms / tetrahedral arrangement of C (atoms); 6 max

[6]

19. network/giant structure / macromolecular; each Si atom bonded covalently to 4 oxygen atoms and each O atom bonded covalently to 2 Si atoms / single covalent bonds; 2 Award [1 max] for answers such as network-covalent, giant-covalent or macromolecular-covalent. Both M1 and M2 can be scored by a suitable diagram.

[2]


20. delocalization/spread of pi/π electrons over more than two nuclei; equal bond order/strength/length / spreading charge (equally) over all three oxygens; gives carbonate ion a greater stability/lower potential energy; 3 M3 can be scored independently. Accept suitable labelled diagrams for M1 and M2 e.g.

OR

Do not penalize missing brackets on resonance structure but 2– charge must

be shown. Allow –2 for charge on resonance structure.

[3]

21. (i)

Accept any combination of dots/crosses and lines to represent electron pairs.

(trigonal/triangular) pyramid; Allow 3D representation using wedges and dotted bonds of trigonal pyramidal molecule. 107°; 3

Accept any angle between 105º and 108.5º. No ECF for shape based on incorrect Lewis structure.


(ii)

Charge needed for mark.

tetrahedral; Allow a 3D representation using wedges and dotted bonds of tetrahedral molecule.

109.5°/109°/109° 28'; 3 No ECF for shape based on incorrect Lewis structure.

[5]

22. (i) energy/enthalpy change/required/needed to remove/knock out an electron (to form +1 /uni-positive/ M+1 ion); in the gaseous state; Award [1] for M(g) → M+(g) + e–. Award [2] for M(g) → M+(g) + e– with reference to energy/enthalpy change. 2

(ii) increasing number of protons/atomic number/Z/nuclear charge; atomic radii/size decreases / same shell/energy level / similar shielding/ screening (from inner electrons); No mark for shielding/screening or shielding/screening increases. 2

(iii) Na: delocalized electrons / mobile sea of electrons / sea of electrons free to move; No mark for just “mobile electrons”.

P: atoms covalently bonded / no free/mobile/delocalized electrons; 2 [6]

23. (i)

trigonal pyramid; in the range of 100–108°; 3


(ii)

Must include minus sign for the mark. bent/V–shaped; in the range of 100–106°; 3

(iii)

square planar; 90°; Penalize once only if electron pairs are missed off outer atoms. 3

[9]

24. CO:

Award [1] for showing the net dipole moment, or explaining it in words (unsymmetrical distribution of charge).

NO2:

Award [1] for correct representation of the bent shape and [1] for showing the net dipole moment, or explaining it in words (unsymmetrical distribution of charge).

CO2:

Award [1] for correct representation of the linear shape and [1] for showing the two equal but opposite dipoles or explaining it in words (symmetrical distribution of charge).

For all three molecules, allow either arrow or arrow with bar for representation of dipole moment. Allow correct partial charges instead of the representation of the vector dipole moment. Ignore incorrect bonds. Lone pairs not needed. 5

[5]


1. the relative molecular mass of a gas is 56 and its...

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