O Level Chemistry 5070 Paper 21, May/June 2024

is a catalyst in the Haber process

has a giant covalent structure

changes from a blue solid to a white solid when heated

removes tastes and odours during the treatment of the domestic water supply

has the empirical formula $\mathrm{C}{\mathrm{H}}_2\mathrm{O}$.

Construct the symbol equation for this reaction.

Calcium carbide is ionic. Deduce the formula of the carbide ion.

Fig. 2.1 shows the displayed formula of ethyne. $$\mathrm{H}-\mathrm{C}\equiv \mathrm{C}-\mathrm{H}$$ Fig. 2.1 Ethyne is an unsaturated hydrocarbon. Explain why ethyne is a hydrocarbon.

Suggest why ethyne is unsaturated.

Aqueous bromine reacts with ethyne. Predict the colour change that happens during this reaction.

Draw a dot-and-cross diagram to show the electronic configuration in a molecule of ethyne. Show only the outer shell electrons.

The equation for the complete combustion of ethyne is shown. $$2{\mathrm{C}}_2{\mathrm{H}}_2+5{\mathrm{O}}_2\to 4\mathrm{C}{\mathrm{O}}_2+2{\mathrm{H}}_2\mathrm{O}$$ This reaction is exothermic. Explain, using ideas about bond breaking and bond making, why this reaction is exothermic.

Complete the reaction pathway diagram in Fig. 2.2 for the complete combustion of ethyne. Label the: • reactants • products • enthalpy change of the reaction, $\mathrm{\Delta }H$ • activation energy, $E_{\mathrm{a}}$.

A $25.0\mathrm{c}{\mathrm{m}}^3$ sample of $0.133\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{/}\mathrm{d}{\mathrm{m}}^3\mathrm{N}{\mathrm{H}}_4\mathrm{N}{\mathrm{O}}_2$ is completely decomposed. Calculate the volume of nitrogen formed, measured at room temperature and pressure. Give your answer to two significant figures. volume of nitrogen = .................................................. $\mathrm{d}{\mathrm{m}}^3$

Describe and explain the effect of increasing the temperature on the rate of this reaction.

Describe and explain the effect of decreasing the concentration of ammonium nitrite on the rate of this reaction.

One way to measure the pH of aqueous ammonium nitrite is to use a pH meter. Describe one other way to measure the pH of aqueous ammonium nitrite.

Explain why potassium iodide has a high melting point.

Describe how potassium atoms and iodine molecules react to form potassium ions and iodide ions. Use ideas about electron transfer.

Predict the products at each electrode during the electrolysis of concentrated aqueous potassium iodide. at anode .................................................................................................................................... at cathode .................................................................................................................................

Aqueous potassium iodide reacts with aqueous acidified potassium manganate(VII). Suggest the colour changes that happen during this reaction.

The ionic equation for the reaction between aqueous potassium iodide and aqueous chlorine is shown. $$2{\mathrm{I}}^{-}(\mathrm{a}\mathrm{q})+\mathrm{C}{\mathrm{l}}_2(\mathrm{a}\mathrm{q})\to {\mathrm{I}}_2(\mathrm{a}\mathrm{q})+2\mathrm{C}{\mathrm{l}}^{-}(\mathrm{a}\mathrm{q})$$ Explain, in terms of electrons, why this reaction involves both oxidation and reduction.

The temperature of the closed system is increased and the pressure is kept constant. Predict how the position of equilibrium of this reaction is affected. Explain your answer.

The pressure of the closed system is decreased and the temperature is kept constant. Predict how the position of equilibrium of this reaction is affected. Explain your answer.

Calculate the maximum mass of zinc oxide that can be made from $25.5\mathrm{g}$ of zinc sulfite. mass of zinc oxide = ...................................................... $\mathrm{g}$

Zinc oxide reacts with both aqueous sodium hydroxide and dilute hydrochloric acid, but sulfur dioxide only reacts with aqueous sodium hydroxide. Explain why.

Solid zinc sulfite reacts with dilute nitric acid to give sulfur dioxide gas, an aqueous zinc salt and a colourless liquid. Construct the symbol equation for this reaction. Include state symbols.

Describe one adverse effect of increased global warming.

Describe how carbon dioxide causes global warming.

Photosynthesis removes carbon dioxide from the atmosphere. Write the word equation for photosynthesis.

Describe the conditions needed for photosynthesis.

Explain one strategy to reduce global warming caused by carbon dioxide.

A sample of chlorine has a volume of $240\mathrm{c}{\mathrm{m}}^3$ at room temperature and pressure. The pressure of the sample is increased at room temperature. Describe and explain, in terms of kinetic particle theory, what happens to the volume of the sample.

When heated at atmospheric pressure, iodine changes directly into a gas without becoming a liquid. Describe the changes in particle separation, arrangement and motion during this change. separation ................................................................................................................................. ................................................................................................................................................... arrangement ............................................................................................................................. ................................................................................................................................................... motion ....................................................................................................................................... ...................................................................................................................................................

At the same temperature and pressure, the rate of diffusion of chlorine gas is greater than that of iodine gas. Explain why.

The symbol of an iodide ion is shown. $${}_{\phantom{0}53}^{126}{\mathrm{I}}^{-}$$ Complete Table 7.1 about this iodide ion. Table 7.1

Compound A is one of the structural isomers of alcohols with molecular formula ${\mathrm{C}}_3{\mathrm{H}}_8\mathrm{O}$. State the name of compound A.

Draw the displayed formula of the other structural isomer of ${\mathrm{C}}_3{\mathrm{H}}_8\mathrm{O}$ that is an alcohol.

Draw the displayed formula of ester B.

Draw the structural formula of propanoic acid.

State the name and formula of compound D. name ......................................................................................................................................... formula ......................................................................................................................................

State the name of gas E and of gas F. E ............................................................................................................................................... F ...............................................................................................................................................

State the name of ester G.

Describe the differences between addition and condensation polymerisation.

PET is a condensation polymer. Name the type of linkage that bonds the repeat units to one another in PET.

A polymer contains 47.1% carbon, 6.5% hydrogen and 46.4% chlorine by mass. Calculate the empirical formula of this polymer. empirical formula .........................................................

Plastics are made from polymers. Describe two environmental challenges caused by plastics. 1 ................................................................................................................................................ 2 ................................................................................................................................................