Breadth in chemistry paper 1 2016

Question 1

What is the formula of ammonium sulfide ?

Answer 1

(NH4)2S

Question 2

Calcium nitrate, Ca(NO3)2 decomposes when heated.
Ca(NO3)2 (s) → CaO(s) + 2NO2 (g) +1/2 O2 (g)
A student decomposes 0.00500 mol of Ca(NO3)2 and collects the gas that is produced
Calculate the volume of gas that the student should expect to collect, measured temperature and pressure

Answer 2

2.5 x 0.005 = 0.0125
0.0125 x 24 = 0.3
300 cm3

Question 3

What is the oxidation. no. of nitrogen in Mg(NO3)2 ?

Answer 3

-2 x 3 = -6 x 2 = -10
Mg = +2
2-12 = 10/2 = -5
+5

Question 4

How many orbitals are occupied in a silicon atom?

Answer 4

8

Question 5

What is the shape and bond angle in a molecule of NCl3?

Answer 5

Pyramidal

107

Question 6

What is the shape around the carbon atoms in graphene ?

Answer 6

Trigonal Planar

Question 7

Which ionisation configuration represents the element with the largest first ionisation energy?

Answer 7

1s2 2s2 2p6

Question 8

Successive ionisation energies of 4 elements in period 3 are shown.
Which letter could represent magnesium?

Answer 8

B

Question 9

A student adds aqueous sodium carbonate to one test tube and aqueous silver nitrate to a second test tube. `The student adds dilute sulfuric acid to each test tube?

Answer 9

Effervescence and Precipitate

Question 10

The enthalpy change for combustion. 
4C +5H2 →C4H10
C= -394
H2=-286
C4H10 = -2877

Answer 10

4x -394 =- 1576
3x -286 = -1430
1576-1430-2877 =129
-129 
combustion is negative

Question 11

When heating with NaOH(aq), 1 -iodobutane is hydrolysed at a much faster rate than 1-chlorobutane?

Answer 11

The C-I bond requires less energy to break than the C-Cl bond

Question 12

State the similarities and differences between the atomic structure of isotopes of the same element ?

Answer 12

S- same no. of protons and electrons

D- different no. of neutrons

Question 13

Calculate the relative atomic mass of the copper used to make the coins? Give ur answer to 2dp (2)

Answer 13

(63 × 69.17) + (65 × 30.83)
100
OR 63.6166 OR 63.617
= 63.62 (to 2 DP)

Question 14

One coin has a mass of 5.00g and contains 84% of copper, by mass. Calculate the no. of copper atoms in one coin. Give your answer in standard form and to 3 sf. (2)

Answer 14

n(Cu) = 5.00 × 0.840
63.62 =
4.2
63.62 = 0.066(0) (mol)
Cu atoms = 0.0660 × 6.02 × 1023
 = 3.97 × 1022

Question 15

Nickel nitrate, Ni(NO3)2 can be prepared by reacting nickel oxide with dilute nitrite acid. Write the equation for this reaction. (1)

Answer 15

NiO + 2HNO3  Ni(NO3)2 + H2O

Question 16

A hydrated salt, compound A, is analysed and has the following percentage composition by mass
Cr, 19.51%; Cl, 39.96 %; H, 4.51%; O, 36.02%
Calculate the formula of compound A, showing clearly the water of crystallisation. (3)

Answer 16

Cr, 19.51/52.0 = 0.375
; Cl, 39.96/35.5 = 1.126
; H, 4.51/1.0 = 4.51
; O, 36.02/16.0 = 2.25

Cr, 1; Cl, 3; H, 12; O, 6
Formula with water of crystallisation
CrCl3•6H2O

Question 17

The maximum error in each mass measurement using the balance is +-0.005g. Calculate the percentage error in the mass of water removed.

Answer 17

2 × 0.005/0.58 × 100 = 1.72%

Question 18

suggest 1 modification that the student could make to their method to reduce the percentage error in the mass of water removed (1)

Answer 18

Use balance weighing to 3/more decimal places
OR
Use a larger mass/amount

Question 19

The student is not sure that all the water of crystallisation has been removed ? How could the student modify the experiment to be confident that all the water of crystallisation has been removed?

Answer 19

Heat to a constant mass

Question 20

A student prepares a solution of sodium sulphate Na2SO4, by adding 6.25 x10-2 sulphuric acid H2S04 from a burette to 25 of 0.124 NaOH in a conical flask. 2NaOH(aq) + H2SO4(aq) = Na2SO4(aq) + 2H2O(l)
Calculate the minimum volume of the H2SO4, that the student would need to completely react with the NaOH present.

Answer 20

n(NaOH) = 0.124 × 25.0/1000 = 3.1(0) × 10–3 (mol) 
n(H2SO4) = 3.10 × 10–3/2
 = 1.55 × 10–3 (mol) 
V(H2SO4) = 1.55 × 10–3x 1000
/6.25 × 10–2 
= 24.8 (cm

Question 21

2Al(s) + 3H2(SO4)3 (aq) +3H2(g)

Answer 21

Element oxidised: aluminium/Al 0 to +3
Element reduced: hydrogen/H/H+
+1 to 0

Question 22

Write the electron configuration of a bromide ion, in terms of subshell

Answer 22

1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6

Question 23

Write an ionic equation for this reaction and state why this reaction takes place in terms of reactivity of the halogens

Answer 23

Cl2 + 2Br- → 2Cl- + Br2
Cl2 is more reactive/ stronger oxidising agent
reactivity decreases down the group

Question 24

Precipitation reactions can be used to distinguish between halide ions.
State the reagent needed for these precipitation reactions. (1)

Answer 24

Silver nitrate OR AgNO3

Question 25

How would the appearance of the precipitate allow you to distinguish between chloride, bromide and iodide ions ?

Answer 25

Chloride: white (precipitate) Bromide: cream (precipitate) iodide: yellow (precipitate)

Question 26

Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) +2KNO3(aq) The student follows this methord outlined below. - Add 50 cm of 1.5 Pb(NO3)2 (aq) to a polystyrene cup - Measure out 50cm of a solution of KI, which is in excess ... initial temp - 19.5 maximum temp - 30 give your answer to the appropriate no. of significant figures. Assume that the density of all solutions and specific heat capacity, of the reaction mixture is the same as for water.

Answer 26

``` = 100.0 × 4.18 × 10.5 = 4389 (J) OR 4.389 (kJ) n(Pb(NO3)2) = 1.50 × 50 1000 = 0.075(0) (mol) 4389 0.0750 OR (–)58520 (J) 4.389/0.0750 OR (–)58.52 ```

Question 27

Write an ionic equation for the reaction that the student carries out. Include state symbols (1)

Answer 27

Pb2+(aq) + 2I– (aq) → PbI2(s)

Question 28

The 50 cm of KI used in teh experiment contains 10% more KI than is needed to react with 50 of 1.5 Pb(NO3)2(aq). Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) +2KNO3(aq) Calculate the concentration of KI that the student used.

Answer 28

= 2 × 0.0750 = 0.150 mol × 1000 50 = 3 (mol dm–3 0% greater gives 3 × 1.1 = 3.3(0)

Question 29

Sulfur trioxide SO3 is used for the industrial manufacturers of sulphuric acid. 2SO2(g) + O2 (g) → 2SO3 /\ H = -197 KJ Using Le Chatelier's principle, show that a low temperature and a high pressure should be used to obtain a maximum equilibrium yield of SO3. Explain why the actual conditions used in industry may be different from the conditions needed for a maximum equilibrium yield.

Answer 29

- Temperature: (Forward) the reaction is exothermic/∆H is negative OR (Forward) reaction gives out heat  - Pressure: Right-hand side has fewer (gaseous) moles OR 3 (gaseous) moles form 2 (gaseous) moles  - Equilibrium shift Correct equilibrium shift in terms of temperature  Correct equilibrium shift in terms of pressure  Industrial Conditions Low temperature gives a slow rate/slower reaction OR high temperatures needed to increase rate  (High) pressure provides a safety risk OR (High) pressure is expensive (to generate) /uses a lot of energy 

Question 30

Workout KC?

Answer 30

[SO3]2/[SO2]2 [O2] OR [SO3]2/2.002× 1.20 = 0.160 × 2.002 × 1.20 = 0.768

Question 31

What reagents and conditions are needed to convert compound B into a saturated hydrocarbon?

Answer 31

Hydrogen/H2 AND Ni (catalyst)