Structure 1. Models of the particulate nature of matter

1.1 Introduction to the particulate nature of matter

1.2 The nuclear atom

1.3 Electron configurations

1.4 The mole

1.5 Ideal gases

Structure 2. Models of bonding and structure

2.1 The ionic model

2.2 The covalent model

2.3 The metallic model

2.4 From models to materials

Structure 3. Classification of matter

3.1 The periodic table

3.2 Functional groups: Organic compounds

Reactivity 1. What drives chemical reactions?

1.1 Measuring enthalpy changes

1.2 Energy cycles

1.3 Energy from fuels

Reactivity 2. How much, how fast and how far?

2.1 Amount of chemical change

2.2 Rate of chemical change

2.3 Extent of chemical change

Reactivity 3. What are the mechanisms of chemical change?

3.1 Proton transfer reactions

3.2 Electron transfer reactions

3.3 Electron sharing reactions (Radicals)

3.4 Electron-pair sharing reactions

IB Chemistry SL 2.3 Extent of chemical change Question Bank

[Maximum number: 1]

Urea, $\left(\mathrm{H}_{2} \mathrm{~N}\right)_{2} \mathrm{CO}$ , is excreted by mammals and can be used as a fertilizer.

(a)

Urea can also be made by the direct combination of ammonia and carbon dioxide gases.

2 \mathrm{NH}_{3}(\mathrm{~g})+\mathrm{CO}_{2}(\mathrm{~g}) \rightleftharpoons\left(\mathrm{H}_{2} \mathrm{~N}\right)_{2} \mathrm{CO}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{~g}) \quad \Delta H<0

Predict, with a reason, the effect on the equilibrium constant, $K_{\mathrm{c}}$ , when the temperature is increased.

[ 1 ]

[Maximum number: 3]

Nitrogen dioxide, $\mathrm{NO}_{2}$ , is a brown, toxic and corrosive gas. It can be made in a school laboratory by heating a group II metal nitrate or by the reaction of copper, Cu , with concentrated nitric acid, $\mathrm{HNO}_{3}$ .

(a)

A sample of 0.0100 moles of $\mathrm{NO}_{2}$ was placed in a $1 \mathrm{dm}^{3}$ sealed container and maintained at a constant temperature of $40^{\circ} \mathrm{C}$ .

[ 2 ]

(i)

The equilibrium concentration of $\mathrm{NO}_{2}$ was monitored using colorimetry. A student started the experiment and recorded the absorbance value immediately.

Suggest why this may not give a reliable result.

[ 1 ]

(ii)

Suggest how the problem identified in part (c)(ii) could be overcome.

[ 1 ]

(b)

The initial amount of $\mathrm{NO}_{2}$ was determined by titration. The oxide was first dissolved in water according to the following equation:

2 \mathrm{NO}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow \mathrm{HNO}_{3}(\mathrm{aq})+\mathrm{HNO}_{2}(\mathrm{aq})

The solution was made up to $250.0 \mathrm{~cm}^{3}$ and $25.0 \mathrm{~cm}^{3}$ portions of this solution were then titrated against a $0.0500 \mathrm{~mol} \mathrm{dm}^{-3}$ standard solution of sodium hydroxide, NaOH .

[ 1 ]

(i)

Deduce if the results in part (e)(iv) are consistent with the enthalpy of reaction data given in part (b).

[ 1 ]

[Maximum number: 3]

This question is about a mug made of a lead alloy.

The rate of lead dissolving in common beverages with various pH values was analysed.

Lead dissolving in beverages at various times and temperatures

(a)

(i)

Suggest why the relationship between time and lead concentration for Cola at $16^{\circ} \mathrm{C}$ is not linear.

[ 1 ]

(b)

(i)

Lead(II) chloride, $\mathrm{PbCl}_{2}$ , has very low solubility in water.

\mathrm{PbCl}_{2}(\mathrm{~s}) \rightleftharpoons \mathrm{Pb}^{2+}(\mathrm{aq})+2 \mathrm{Cl}^{-}(\mathrm{aq})

Explain why the presence of chloride ions in beverages affects lead concentrations.

[ 2 ]

[Maximum number: 6]

A class studied the equilibrium established when ethanoic acid and ethanol react together in the presence of a strong acid, using propanone as an inert solvent. The equation is given below.

\mathrm{CH}_{3} \mathrm{COOH}+\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} \rightleftharpoons \mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5}+\mathrm{H}_{2} \mathrm{O}

One group made the following initial mixture:

(a)

Deduce the equilibrium constant expression for the reaction.

[ 1 ]

(b)

Outline how you could establish that the system had reached equilibrium at the end of one week.

[ 1 ]

(c)

Outline why changing the temperature has only a very small effect on the value of the equilibrium constant for this equilibrium.

[ 1 ]

(d)

Outline how adding some ethyl ethanoate to the initial mixture would affect the amount of ethanoic acid converted to product.

[ 2 ]

(e)

Suggest one other reason why using water as a solvent would make the experiment less successful.

[ 1 ]

[Maximum number: 1]

Water contaminated with mercury contains methylmercury ions, $\mathrm{CH}_{3} \mathrm{Hg}^{+}$ . These ions are absorbed by living organisms, then slowly metabolized and excreted.

Young fish were taken at regular intervals from a mercury contaminated lake and tested to determine mercury ion content.

Mercury ion content in muscle tissue of fish

(a)

(i)

Suggest why the mercury ion concentrations changed very little after 8 months.

[ 1 ]

[Maximum number: 1]

There is a link between world energy consumption and carbon dioxide production.

(a)

Climate induced changes in the ocean can be studied using measurements such as the Atmospheric Potential Oxygen (APO). Trends in APO concentration from two stations, one in each hemisphere, are shown below.

[ 1 ]

(i)

The equilibrium expression for $\mathrm{O}_{2}$ exchange between the atmosphere and ocean is $\mathrm{O}_{2}(\mathrm{~g}) \rightleftharpoons \mathrm{O}_{2}(\mathrm{aq})$ . Identify one factor which shifts the equilibrium to the right.

[ 1 ]

[Maximum number: 3]

Ethane-1,2-diol, $\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}$ , has a wide variety of uses including the removal of ice from aircraft and heat transfer in a solar cell.

(a)

Ethane-1,2-diol can be formed according to the following reaction.

2 \mathrm{CO}(\mathrm{~g})+3 \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons \mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}(\mathrm{~g})

[ 3 ]

(i)

Deduce the equilibrium constant expression, $K_{\mathrm{c}}$ , for this reaction.

[ 1 ]

(ii)

State how increasing the pressure of the reaction mixture at constant temperature will affect the position of equilibrium and the value of $K_{\mathrm{c}}$ .

Position of equilibrium:
$K_{\mathrm{c}}:$

[ 2 ]

[Maximum number: 1]

Hydrogen cyanide, HCN , is a very toxic compound.

(a)

Hydrogen cyanide reacts with hydrogen according to the equilibrium:

\mathrm{HCN}(\mathrm{~g})+2 \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons \mathrm{CH}_{3} \mathrm{NH}_{2}(\mathrm{~g})

[ 1 ]

(i)

Write the expression for the equilibrium constant, K.

[ 1 ]

[Maximum number: 3]

Ammonia is produced industrially using the reversible reaction:

\mathrm{N}_{2}(\mathrm{~g})+3 \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{NH}_{3}(\mathrm{~g})

(a)

The volume of the reaction container of the mixture at equilibrium is suddenly decreased.

Sketch the graph of the concentration of nitrogen versus time on the axes below until after the new equilibrium is established at a constant temperature.

[ 3 ]

[Maximum number: 2]

Nitrogen (IV) oxide, $\mathrm{NO}_{2}$ , is a brown gas found in photochemical smog and has a pollutant causing acid deposition.

(a)

Nitrogen (IV) oxide exists in equilibrium with dinitrogen tetroxide, $\mathrm{N}_{2} \mathrm{O}_{4}(\mathrm{~g})$ , which is colourless.

2 \mathrm{NO}_{2}(\mathrm{~g}) \rightleftharpoons \mathrm{N}_{2} \mathrm{O}_{4}(\mathrm{~g})

[ 2 ]

(i)

At $100^{\circ} \mathrm{C} \mathrm{K}_{\mathrm{c}}$ for this reaction is 0.0665 . Outline what this indicates about the extent of this reaction.

[ 1 ]

(ii)

Calculate the value of $K_{\mathrm{c}}$ at $100^{\circ} \mathrm{C}$ for the equilibrium:

\mathrm{N}_{2} \mathrm{O}_{4}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{NO}_{2}(\mathrm{~g})

[ 1 ]

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