Question
A student adds excess large pieces of magnesium carbonate, MgCO3, to dilute hydrochloric acid, HCl, and measures the volume of carbon dioxide gas, CO2, given off.
(a) Add the missing state symbols to the chemical equation for the reaction.
MgCO3 ….. + 2HCl….. → MgCl 2(aq) + H2O ….. + CO2 ….. [1]
(b) Complete the dot-and-cross diagram to show the electron arrangement of the ions in magnesium chloride.
The inner shells have been drawn.
Give the charges on the ions.[3]
(c) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of carbon dioxide.
Show outer shell electrons only.[2]
(d) The graph shows how the volume of carbon dioxide gas changes with time.
(i) Describe how the graph shows that the rate of this reaction decreases as time increases.[1]
(ii) Explain, in terms of particles, why the rate of this reaction decreases as time increases.[2]
(iii) The student repeats the experiment using powdered MgCO3 instead of large pieces.
All other conditions stay the same.
On the grid, draw the line expected when powdered MgCO3 is used instead of large pieces. [2]
(e) Determine the volume of CO2 gas given off when excess MgCO3 is added to 25.0cm3 of 0.400mol/dm3 HCl at room temperature and pressure.
MgCO3 + 2HCl → MgCl2 + H2O + CO2
Use the following steps.
- Calculate the number of moles of HCl in 25.0cm3 of 0.400mol/dm3 of acid.
mol
- Determine the number of moles of CO2 gas given off.
mol
- Calculate the volume of CO2 gas given off in cm3.
cm3 [3] [Total: 14]
Answer/Explanation
Ans:
2(a) MgCO3(s) + 2HCl(aq) → MgCl2(q) + H2O(l) + CO2(g)
2(b) eight crosses in second shell of Mg
7 dots and 1 cross in third shell of both Cl
2+ charge on Mg and – charge on both Cl ions on correct answer line
2(c) C atom double bonded to 2 O atoms
4 non-bonding e– on each O and no non-bonding e– on C and both octets complete
2(d)(i) gradient (of line) decreases
2(d)(ii) concentration of particles (of acid) decreases
lower rate of collisions of particles
2(d)(iii) a new line steeper than printed line and starts at origin and levels off earlier than printed line
levels off at the same volume
2(e) M1 mol HCl = 0.400 × 25.0 / 1000 = 0.01(00)
M2 mol CO2 = M1 / 2 = 0.0100 / 2 = 0.005(00)
M3 volume CO2 = M2 × 24000 = 120 (cm3)
Question
Some elements are shown in the order they appear in the reactivity series. The most reactive element is at the top.
sodium
calcium
magnesium
aluminium
zinc
iron
hydrogen
copper
(a) Answer the questions using the list of elements. Each element may be used once, more than once or not at all.
Identify:
(i) a non-metal
(ii) a metal which is stored under oil
(iii) the main component of steel
(iv) a metal with three electrons in the outer shell of its atoms
(v) a metal found in brass
(vi) a metal that forms chlorides of the type \(XCl_2\) and \(XCl_3\).
(b) Name the main ores of:
(i) zinc ……………………………………………………………………………………………………………….
(ii) aluminium. ……………………………………………………………………………………………………..
(c) In an experiment, a sample of aluminium appeared less reactive than expected.
Explain why.
(d) Name two metals from the list which are extracted by reduction of their ores using carbon.
1 ……………………………………………………………………………………………………………………………….
2 ……………………………………………………………………………………………………………………………….
(e) When zinc granules are added to aqueous copper(II) sulfate, a reaction occurs. During the
reaction, a red-pink solid is formed and the solution becomes colourless.
(i) Name the red-pink solid.
(ii) Name the colourless solution.
(iii) Explain, in terms of particles, why the rate of this reaction increases when the temperature
is increased.
(iv) Suggest two other ways of increasing the rate of this reaction.
1 …………………………………………………………………………………………………………………………
2 …………………………………………………………………………………………………………………………
Answer/Explanation
Answer:
(a) (i) hydrogen
(ii) sodium
(iii) iron
(iv) aluminium
(v) zinc or copper
(vi) iron
(b) (i) zinc blende
(ii) bauxite
(c) protective oxide layer
(d) Any 2 from 3
• zinc
• iron
• copper
(e) (i) copper
(ii) zinc sulfate
(iii)
M1 particles have more energy
M2 More collisions (between particles) occur per second / per unit time
M3 A greater percentage / proportion / fraction of collisions (of particles) are successful / have energy above activation
energy / have energy equal to activation energy
(iv) Any 2 from 3:
• use a catalyst
• use smaller granules
• increase concentration
Question
The Periodic Table is a method of classifying elements.
(a) Identify the element which is in Group VI and Period 4.
(b) Calcium is in Group II and chlorine is in Group VII of the Periodic Table.
Explain, in terms of number of outer shell electrons and electron transfer, how calcium atoms
and chlorine atoms form ions. Give the formulae of the ions formed.
(c) Group V chlorides are covalent molecules. The boiling points of some Group V chlorides are
shown.
(i) Suggest the approximate boiling point of \(PCl_3\).
(ii) Explain the trend in boiling points in terms of attractive forces between particles.
(iii) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of
\(PCl_3\).
Show outer electrons only.
(d) PCl 3 reacts with chlorine, Cl2, to form PCl 5. This reaction is exothermic and reaches an
equilibrium.
\(PCl_3(g) + Cl_2(g) \leftrightarrow PCl_5(g)\)
(i) Describe two features of an equilibrium.
(ii) State the effect, if any, on the position of this equilibrium when the following changes are
made.
Explain your answers.
temperature is increased ……………………………………………………………………………………….
pressure is increased ……………………………………………………………………………………………
(iii) Explain, in terms of particles, what happens to the rate of the forward reaction when the
reaction mixture is heated.
(e) \(PCl_5\) reacts with lithium fluoride, LiF, to form \(LiPF_6\).
\(PCl_5 + 6LiF → LiPF_6 + 5LiCl\)
Calculate the mass of LiF needed to form 3.04g of \(LiPF_6\) using the following steps.
● Calculate the number of moles of LiPF6 formed.
[Mr : \(LiPF_6\), 152]
number of moles = …………………………
● Deduce the number of moles of LiF needed.
number of moles = …………………………
● Calculate the mass of LiF needed.
mass = ………………………… g
(f) Lithium fluoride has ionic bonding.
(i) What is an ionic bond?
(ii) Give two physical properties of ionic compounds.
Answer/Explanation
Answer:
(a) selenium / Se
(b) Ca has 2 and Cl has outer electrons 7 (1)
Ca (atoms) lose electrons (1)
Cl (atoms) gain electrons (1)
\(Ca^{2+}\) (ions) (1)
\(Cl^–\) (ions) (1)
(c) (i) any number in the range 72 – 129°C
(ii) 3 P- Cl dot cross bonds (1)
2 (only) non-bonding electrons to make an octet on P (1)
6 (only) non-bonding electrons to make an octet on each Cl (1)
(d) (i)
constant concentrations (1)
rate of forward reaction
= rate of reverse reaction (1)
(ii) increased temperature:
(equilibrium) shifts to LHS (1)
(forward) reaction is exothermic (1)
increased pressure:
(equilibrium) shifts to RHS (1)
fewer moles (of gas) on RHS (1)
(iii) rate increases and particles have more energy (1)
more collisions (between particles) occur per second / per unit time
more (of the) particles / collisions have energy greater than activation energy
or
more (of the) particles / collisions have sufficient energy to react
or
a greater percentage / proportion / fraction of collisions (of particles) are successful
(e) mol of LiPF6 = 3.04 / 152 = 0.02(00) (1)
mol of LiF = 0.02(00) × 6 = 0.12(0) (1)
mass of LiF = 3.12 g (1)
(f) (i) oppositely charged ions
(ions) are attracted
(ii) any two from:
physical constants: high boiling point / melting point
conductivity: conduct (electricity) when aqueous or conduct (electricity) when molten
solubility: soluble in water