May/June 2017

Gas X shows these properties: 1 colourless 2 does not affect either red or blue litmus paper 3 does not change limewater 4 flammable What is gas X?

Identification of ions and gases

Which substance, when in the molten state, is able to conduct electricity?

Ion and ionic bonds

A compound is made up of $70\%$ iron by mass and $30\%$ oxygen by mass. What is the empirical formula of this compound? [$A_r$: O, $16$; Fe, $56$]

Formulae

Hydrated copper(II) nitrate is represented by the formula $\text{Cu(NO}_3)_2 \cdot x\text{H}_2\text{O}$. Its mass is made up of $36.5\%$ water of crystallisation. Determine the value of $x$. [$A_r$: H, $1$; N, $14$; O, $16$; Cu, $64$]

The mole and the Avogadro constant

Dilute sulfuric acid is electrolysed using inert electrodes. Which of the following statements are correct? 1 Hydrogen is given off at the negative electrode. 2 Oxygen is given off at the positive electrode. 3 Sulfur dioxide is given off at the positive electrode. 4 The acid becomes more concentrated.

Electrolysis

Concentrated aqueous calcium iodide is electrolysed in much the same way as concentrated aqueous sodium chloride. What would be produced at each electrode?

Electrolysis

Aluminium is produced by electrolysing molten aluminium oxide. Which row identifies the electrode where aluminium is produced and gives the correct equation for how it is formed?

Electrolysis

The energy profile diagram for the forward direction of a reversible reaction is shown. For the reverse reaction, which row correctly gives the sign of the activation energy and the kind of enthalpy change?

Exothermic and endothermic reactions

The conversion of hydrogen and oxygen into liquid water can happen in three steps. 1. $2\text{H}_2(g) + \text{O}_2(g) \rightarrow 4\text{H}(g) + 2\text{O}(g)$ 2. $4\text{H}(g) + 2\text{O}(g) \rightarrow 2\text{H}_2\text{O}(g)$ 3. $2\text{H}_2\text{O}(g) \rightarrow 2\text{H}_2\text{O}(l)$ Which of these steps are exothermic?

Exothermic and endothermic reactions

This equation represents sulfur trioxide being formed in the contact process. $2\text{SO}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{SO}_3(g) \quad \Delta H = -196\,\text{kJ mol}^{-1}$ What would lower the yield of sulfur trioxide?

Reversible reactions and equilibrium

Magnesium carbonate and dilute hydrochloric acid react to produce magnesium chloride, carbon dioxide and water. $\text{MgCO}_3(s) + 2\text{HCl}(aq) \rightarrow \text{MgCl}_2(aq) + \text{CO}_2(g) + \text{H}_2\text{O}(l)$ To determine the rate of reaction, magnesium carbonate and dilute hydrochloric acid are mixed in a conical flask. The mass of the flask and its contents is recorded every twenty seconds. Which graph shows correctly how the mass of the flask and contents changes with time?

Rate of reaction

A gas is produced during a reaction. Which two pieces of apparatus would allow the rate of this reaction to be measured?

Rate of reaction

When the reaction begins, a $1.00\,\text{dm}^3$ solution contains $0.300\,\text{mol}$ of ethanol. By $100\,\text{s}$ the concentration of the ethanol has fallen to $0.296\,\text{mol dm}^{-3}$. What is the rate of reaction during the first $100\,\text{s}$?

Rate of reaction

Which statement concerning sulfuric acid is correct? Sulfuric acid is employed

The characteristic properties of acids and bases

Which row gives the sequence of increasing pH (from lowest to highest) for strong acids, strong bases, weak acids and weak bases at the same concentration?

The characteristic properties of acids and bases

The table gives the proton numbers for four elements. Which option is correct?

Atomic structure and the Periodic Table

The diagram illustrates part of the Periodic Table. Which statement about the elements W, X and Y is correct?

Arrangement of elements

Lead(II) sulfate can be prepared by reacting dilute sulfuric acid with what substance?

Preparation of salts

Which pair identifies two uses of argon?

Noble gases

Which two substances are taken out from the base of a blast furnace?

Extraction of metals

Which row shows the correct catalyst for the process named?

Rate of reaction

Some metals and the compounds found in their ores are shown here. Which type of reaction takes place when each of these metals is extracted from its ore?

Extraction of metals

Which of these statements about pure hexane, $\text{C}_6\text{H}_{14}$, is correct?

Alkanes

Following the failure of a river bridge, a new car was submerged in the river water for several months. After it was retrieved, the car parts made from steel, an alloy of iron, were found to have corroded. The parts made of aluminium had not corroded. Which statement accounts for these differences in corrosion?

Corrosion of metals

A farmer applied ammonium nitrate, a nitrogenous fertiliser, to a field. On the following day, he applied calcium hydroxide to that same field. As a result, nitrogen was lost from the ammonium nitrate. Which chemical reaction took place?

The characteristic properties of acids and bases

Which row gives the correct comparison between carbon dioxide and methane?

Simple molecules and covalent bonds

Some internal combustion engines run on fossil fuels. Which pollutants are released by an internal combustion engine when it burns fossil fuels?

Air quality and climate

An ester is formed when the carboxylic acid $\text{HCO}_2\text{H}$ reacts with the alcohol $\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}$. State the name and structure of the ester formed.

Naming organic compounds

The repeat unit of a polymer is displayed. Which monomer could form this polymer?

Polymers

Each compound W, X, Y and Z is either an unbranched alkane or an unbranched alkene. W: $\text{C}_9\text{H}_{18}$ X: $\text{C}_9\text{H}_{20}$ Y: $\text{C}_{10}\text{H}_{20}$ Z: $\text{C}_{10}\text{H}_{22}$ Which two compounds take part in an addition reaction with bromine?

Alkenes

Each alkane is completely burnt when one mole is used. Which alkane gives seven moles of products?

Alkanes

Which of the following statements about macromolecules is correct?

Polymers

An organic compound, X, has molecular formula $\text{C}_4\text{H}_8\text{O}_2$ and changes damp, blue litmus paper to red. What structural formula does X have?

Carboxylic acids

Which statement concerning the particles $^{19}_{9}\text{F}^-$, $^{20}_{10}\text{Ne}$ and $^{23}_{11}\text{Na}^+$ is correct?

Atomic structure and the Periodic Table

Which polymer is composed of only three different elements?

Polymers

A zinc chloride solution in water is examined by adding reagents. Which observation would be correct?

Identification of ions and gases

Among the molecules shown, how many have only a single covalent bond? $\text{Cl}_2$ \quad $\text{H}_2$ \quad $\text{HCl}$ \quad $\text{N}_2$ \quad $\text{O}_2$

Simple molecules and covalent bonds

Which substance has a giant covalent structure and includes atoms from more than one element?

Giant covalent structures

Which statement best accounts for the fact that chlorine, $\text{Cl}_2$, at $40\,^{\circ}\text{C}$ diffuses more slowly than neon, $\text{Ne}$, at $20\,^{\circ}\text{C}$?

Diffusion

Metals are able to conduct electricity. The motion of which particles causes this electrical conductivity?

Metallic bonding

The diagram shows four pieces of apparatus used to measure the volume of a gas or a liquid. Which piece of apparatus must always be filled to the same level?

Acid–base titrations

Nitrogen monoxide reacts with oxygen to produce nitrogen dioxide. $2\text{NO}(\text{g}) + \text{O}_2(\text{g}) \rightarrow 2\text{NO}_2(\text{g})$ What is the greatest volume of nitrogen dioxide that can be made when 1 dm$^3$ of nitrogen monoxide reacts with 2 dm$^3$ of oxygen?

The mole and the Avogadro constant

Dilute sulfuric acid is electrolysed using inert electrodes. Which of the following statements are correct?

Electrolysis

Caesium, $\text{Cs}$, belongs to the same group of the Periodic Table as sodium. What products are formed by the electrolysis of concentrated aqueous caesium chloride?

Electrolysis

The diagrams illustrate the apparatus used for the electrolysis of aqueous copper(II) sulfate. In experiment X, both electrodes are inert. In experiment Y, both electrodes are copper. At which electrodes does solid metal get deposited?

Electrolysis

A reversible reaction has its energy profile diagram displayed for the forward direction. For the reverse reaction, which row gives the correct sign of the activation energy and the kind of enthalpy change?

Exothermic and endothermic reactions

The production of liquid water from hydrogen and oxygen can take place in three steps. $1\quad 2\text{H}_2(\text{g}) + \text{O}_2(\text{g}) \rightarrow 4\text{H}(\text{g}) + 2\text{O}(\text{g})$ $2\quad 4\text{H}(\text{g}) + 2\text{O}(\text{g}) \rightarrow 2\text{H}_2\text{O}(\text{g})$ $3\quad 2\text{H}_2\text{O}(\text{g}) \rightarrow 2\text{H}_2\text{O}(\ell)$ Which stage or stages would be exothermic?

Exothermic and endothermic reactions

In four different experiments, 1, 2, 3 and 4, nitric acid was added to excess marble chips and the amount of carbon dioxide produced was measured by volume. The same volume of nitric acid was used in every experiment. Either its concentration, or its temperature, or both its concentration and temperature, were altered. The outcomes of the experiments are shown on the graph. Which statement is correct?

Rate of reaction

The equation below represents the formation of sulfur trioxide in the contact process. $2\text{SO}_2(\text{g}) + \text{O}_2(\text{g}) \rightleftharpoons 2\text{SO}_3(\text{g}) \qquad \Delta H = -196\,\text{kJ mol}^{-1}$ Which change would reduce the yield of sulfur trioxide?

Reversible reactions and equilibrium

Zinc undergoes reaction with dilute sulfuric acid. $\text{Zn} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2$ What conclusion can be drawn from this equation about the reaction?

Reactivity series

Look at the three reactions below. $1$ reaction of ammonium chloride with calcium hydroxide $2$ ethane combusting in air $3$ the reaction of ethanoic acid with ethanol Which statement is true for all three reactions?

Physical and chemical changes

The diagrams illustrate the structures of two forms of carbon. Which one of X and Y conducts electricity?

Giant covalent structures

Which statement concerning weak acids is correct?

The characteristic properties of acids and bases

Which gas, when dissolved in water, produces a solution with a pH above 7?

The characteristic properties of acids and bases

Element X makes an oxide with formula $X_2O_5$. X is most likely to be located in which group of the Periodic Table?

Arrangement of elements

Element M is a typical transition metal. Which property will it lack?

Transition elements

An atom of the element E produces a white oxide with formula $EO$. Which element is E?

Ion and ionic bonds

The table lists the proton numbers for four elements, Q, R, T and Z: Q = 9, R = 11, T = 17, Z = 19. Which statement is the correct one?

Atomic structure and the Periodic Table

The outcomes of experiments on four metals, W, X, Y and Z, and their ions are shown below: $Y(s) + Z^+(aq) \rightarrow Y^+(aq) + Z(s)$ $W(s) + X^+(aq) \rightarrow$ no reaction $Z(s) + X^+(aq) \rightarrow Z^+(aq) + X(s)$ How are the reactivities of the four metals ordered, from the most reactive to the least reactive?

Reactivity series

Within metals, positive ions are arranged in a ‘sea of electrons’. Metals can be bent and shaped because the ions can be made to slide past one another. The alloy brass is ......1...... malleable than both pure copper and pure zinc. Brass is ......2...... at conducting electricity. Which words correctly complete gaps 1 and 2?

Metallic bonding

Which two substances are drawn off from the base of a blast furnace?

Extraction of metals

Aluminium is used in making aeroplanes. What property of aluminium also explains this use?

Properties of metals

Reagents are added to an aqueous solution of zinc chloride. Which observation is correct?

Identification of ions and gases

In what way can the reaction between nitrogen and hydrogen be described?

Reversible reactions and equilibrium

Small quantities of sulfur dioxide may be added to bottled fruit juice. What is this for?

Oxides

Substances dissolved in water may lead to eutrophication. How many of the ions shown bring about this effect? $Cl^-$, $CO_3^{2-}$, $Na^+$, $NO_3^-$, $PO_4^{3-}$

Water

Which list includes only gases that are always found in unpolluted air?

Air quality and climate

When one mole of each alkane is completely combusted, which alkane produces seven moles of products?

Alkanes

Ethanoic acid is produced when ethanol reacts with acidified potassium manganate(VII). What is this process called?

Alcohols

The displayed structure of compound X is $CH_3-CH_2-CH_2-CH_2-OH$. Which statement is incorrect?

Alcohols

Following which conversion does the product have more carbon atoms than the reactant?

Formulae, functional groups and terminology

Molecules 1-4 are straight-chain hydrocarbons. 1 $\text{C}_{10}\text{H}_{22}$ 2 $\text{C}_{10}\text{H}_{20}$ 3 $\text{C}_{9}\text{H}_{20}$ 4 $\text{C}_{8}\text{H}_{16}$ Which row correctly classifies these hydrocarbons as alkanes or alkenes?

Formulae, functional groups and terminology

Which polymer is made up of only three different elements?

Polymers

Which of the following statements about the particles $^{19}_{9}\text{F}^-$, $^{20}_{10}\text{Ne}$ and $^{23}_{11}\text{Na}^+$ is correct?

Ion and ionic bonds

Which of the following statements about macromolecules is correct?

Polymers

The table presents some properties of four substances. Which one is an ionic compound?

Ion and ionic bonds

Four samples are placed as spots on chromatography paper. It is known that one of these samples is pure compound Q. A separate spot of pure compound Q is also put onto the paper. The paper is then put into a solvent. The diagram shows the chromatogram obtained. Which statement is correct?

Chromatography

Among the molecules shown, how many contain just one covalent bond? $\text{Cl}_2$, $\text{H}_2$, $\text{HCl}$, $\text{N}_2$, $\text{O}_2$

Simple molecules and covalent bonds

Which of the following statements about sulfur and its compounds are correct?

Elements, compounds and mixtures

50.0 cm$^3$ of 0.10 mol dm$^{-3}$ silver nitrate, $\text{AgNO}_3$, is poured into 150.0 cm$^3$ of 0.05 mol dm$^{-3}$ sodium chloride, $\text{NaCl}$, in a beaker. Besides solid silver chloride, what else is in the beaker after the reaction?

Ion and ionic bonds

Select the oxides listed below to answer the questions. calcium oxide carbon dioxide copper(II) oxide silicon dioxide sodium oxide sulfur dioxide sulfur trioxide zinc oxide Any oxide may be used once, more than once, or not used at all.

Oxides

Atoms and ions are composed of three kinds of sub-atomic particle.

Isotopes

Alkalis neutralise acids.

Preparation of salts

Calcium chloride, CaCl$_2$, is classified as an ionic compound.

Electrolysis

Ethanol and butanol are each alcohols.

Alcohols

Photosynthesis is a chemical reaction that takes place in the leaves of green plants. Carbon dioxide and water are changed into glucose and oxygen. $6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$ This reaction absorbs energy and is catalysed by enzymes.

Exothermic and endothermic reactions

Copper can react with concentrated nitric acid. $\text{Cu}(s) + 4\text{HNO}_3(aq) \rightarrow \text{Cu(NO}_3)_2(aq) + 2\text{NO}_2(g) + 2\text{H}_2\text{O}(l)$

Preparation of salts

Pick from the chlorides below to answer the questions. ammonium chloride calcium chloride carbon tetrachloride copper(II) chloride hydrogen chloride magnesium chloride zinc chloride Each chloride may be used once, used more than once, or not used at all. Which chloride is this?

Elements, compounds and mixtures

The table gives some data on the homologous series of unbranched alcohols.

Alcohols

The table presents information about six particles.

Isotopes

Acids are neutralised by insoluble bases.

Preparation of salts

Sodium oxide, $\text{Na}_2\text{O}$, is classified as an ionic compound.

Electrolysis

Both ethanoic acid and butanoic acid belong to the carboxylic acids.

Carboxylic acids

Respiration is the process that occurs in living cells to release energy. The overall reaction includes the oxidation of glucose. $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O}$ This reaction is exothermic and is catalysed by enzymes.

Exothermic and endothermic reactions

Copper is made to react with hot concentrated aqueous sulfuric acid. $\text{Cu}(s) + 2\text{H}_2\text{SO}_4(aq) \rightarrow \text{CuSO}_4(aq) + \text{SO}_2(g) + 2\text{H}_2\text{O}(l)$

Redox

Nitrogen dioxide, $\text{NO}_2$, combines with itself to form dinitrogen tetroxide, $\text{N}_2\text{O}_4$, in an exothermic reaction. This reaction is studied at $140^\circ\text{C}$ inside a sealed container. A dynamic equilibrium mixture is then obtained. $2\text{NO}_2(g) \rightleftharpoons \text{N}_2\text{O}_4(g)$ $\text{NO}_2(g)$ is a dark brown gas. $\text{N}_2\text{O}_4(g)$ is a colourless gas.

Reversible reactions and equilibrium

At room temperature, methane, ethane and propane are all gases.

Diffusion

In this experiment, a student changes magnesium into magnesium oxide, MgO. A 0.36 g portion of magnesium is heated strongly for several minutes with the apparatus shown.

Experimental design

Since sand does not dissolve in water, whereas sodium chloride does dissolve in water, a beaker containing $10.0\text{ g}$ of a sand and sodium chloride mixture is provided.

Separation and purification

A sample of ethanoic acid, $\text{CH}_3\text{COOH}$, may be made using the apparatus illustrated.

Carboxylic acids

A learner is given a bottle of tiny pieces of scrap iron. She must determine how pure the iron sample is. A small amount of the iron is put into a container that has already been weighed, and the container is then weighed again.

Experimental design

A student is given compound M, which has one cation and one anion. He carries out the following tests to identify the two ions.

Identification of ions and gases

A student is examining how soluble potassium chlorate(V) and sodium chloride are, using the apparatus shown.

Solids, liquids and gases

A student puts a known mass of magnesium ribbon into $100\,\text{cm}^3$ of dilute hydrochloric acid, which is in excess, in the apparatus illustrated. Hydrogen gas is produced.

Identification of ions and gases

Using the apparatus shown, a student separates propanoic acid (b.p. $141\,^{\circ}\text{C}$) from butanoic acid (b.p. $164\,^{\circ}\text{C}$).

Separation and purification

Copper(II) sulfate crystals include water of crystallisation, which can be driven off by heating.

Experimental design

A learner is asked to work out the percentage purity of an impure magnesium carbonate sample.

Acid–base titrations

The following aqueous solutions of four different metal sulfates are supplied: • chromium(III) sulfate • copper(II) sulfate • iron(II) sulfate • iron(III) sulfate

Identification of ions and gases

A student is making sodium sulfate crystals by titration. First, the student places $25.0\,\text{cm}^3$ of $1.00\,\text{mol dm}^{-3}$ sodium hydroxide into a conical flask, then adds dilute sulfuric acid from a burette. Following each addition of sulfuric acid, the student measures and notes the pH of the mixture with a pH meter.

Acid–base titrations