Practice Paper 2 (HL IB Chemistry)

Mercury forms two oxides, mercury(I) oxide and mercury(II) oxide, which decompose into their elements when heated above 500°C. 

After heating a 4.513 g sample of an oxide of mercury, 4.180 g of mercury was left. Determine the empirical formula of this oxide.

Formulate two equations, including state symbols, to show the decomposition of the two oxides of mercury.

Another sample of the same mass of mercury oxide in part (a) was heated and gave a lower mass of mercury. Suggest why less mercury could have been obtained.

Suggest why repeating the decomposition of the sample of mercury oxide in part (a) may give a higher mass of mercury than was obtained in part (a).

Organic compounds are classified into families called a homologous series.

State three features of members belonging to the same homologous series.

Table 1 shows the boiling points of the first five members of the alkane family.

 Table 1

On the axes below in Figure 1, draw a graph of boiling point against the number of carbon atoms in the alkanes. Estimate the boiling point of the next member of the homologous series, hexane, C₆H₁₄, and show on your graph how you arrived at your estimated boiling point. 

Figure 1

Estimated boiling point of hexane : ________ ^oC

State the general formula for an alkyne and give the molecular formula and name of the fifth member of the alkyne family.

The boiling point of ethyne, C₂H₂, is -84 ^oC.

State with, with a reason, whether the boiling point of ethyne would be expected to be higher or lower than the boiling point of ethane, C₂H₆.

Using your knowledge of atomic structure, complete the table below for the particles found in an atom. 

The actual mass of protons, neutrons and electrons is given.

Calculate the mass, in g, of a nitrogen molecule.

Oxygen consists of three stable isotopes, oxygen-16, oxygen-17, and oxygen-18.

State the particles present in each isotope and outline what differences would be expected in the chemical reactivity of the three isotopes.

Suggest why some elements have several isotopes and others, like fluorine, have only one known isotope (known as monoisotopic elements).

A group of students planned how to investigate the effect of changing the concentration of H₂SO₄ on the initial rate of reaction with magnesium: 

Mg (s) + H₂SO₄ (aq) MgSO₄ (aq) + H₂ (g) 

They decided to measure how long the reaction took to complete when similar masses of magnesium were added to acid. 

Two methods were suggested:

Method 1 - Use small pieces of magnesium ribbon, an excess of acid and record the time taken for the magnesium ribbon to disappear

Method 2 - Use large strips of magnesium ribbon, an excess of magnesium and record the time taken for bubbles to stop forming 

Deduce, giving a reason, which of method 1 and method 2 would be the least affected if the masses of magnesium ribbon used varied slightly between each experiment.

Neither method in part a) actually allows the initial rate to be calculated. Outline a method that would allow the calculation of initial rate.

The reaction is to be conducted across a few weeks.

State a factor that has a significant effect on reaction rate, which could vary between experiments across the weeks and therefore needs to be controlled.

One group collected the following data using 1.50 mol dm^-3 acid:

Trial	Time/ s ( 0.01 s)
1	91.56
2	98.33
3	72.08
4	89.41

Malonic acid is a naturally occurring acid found in fruits and vegetables and is shown in Figure 1.

Figure 1 

The first dissociation of malonic acid is:

C₃H₄O₄ (aq) + H₂O (l) ⇌ C₃H₃O₄^- (aq) + H₃O⁺ (aq)

Identify one conjugate acid-base pair from the equation.

The equilibrium constant for the first dissociation of malonic acid is 1.48 x 10^-3.

State, with a reason, the strength of malonic acid.

The anion C₃H₃O₄^- may be classified as amphiprotic. Explain the meaning of amphiprotic and write equations, using C₃H₃O₄^-_, to illustrate your answer.

The periodic table displays the chemical elements, arranged in order of increasing atomic number. It is made up of groups and periods of elements.

State and explain the general trend in first ionisation energy across a period of the periodic table.

The general trend in first ionisation energies stated in part (a) is seen across period 2 of the periodic table. However, boron and one other period 2 element deviate from this trend.

Identify this element and explain why it deviates from the general trend.

State why nitrogen is classed as a p block element and give its full electron configuration.

Identify the period 3 element that has the lowest melting point.

Explain your answer with reference to bonding and structure.

Nitrogen oxides produced by combustion are largely nitrogen monoxide or nitrogen dioxide.

Draw Lewis diagrams for nitrogen monoxide and nitrogen dioxide and use the diagrams to explain the meaning of the term free radical.

Platinum and rhodium are found in catalytic converters and facilitate the conversion of Carbon monoxide and nitrogen monoxides to nitrogen and carbon dioxide.

Write an equation for the reaction and state the changes in oxidation state for each carbon and nitrogen.

Use your answer to part (c) and the bond enthalpy data given in Table 1 to determine the enthalpy change for the reaction between carbon monoxide and nitrogen monoxide.

Table 1

Distinguish between the terms reaction quotient, Q, and equilibrium constant, K_c.

Write an expression for the reaction quotient, Q, for this reaction.

2SO₂ (g) + O₂ (g)  2SO₃ (g)

The equilibrium constant, K_c, for the reaction is 0.282 at temperature T whilst the reaction quotient is calculated to be 0.5.

Deduce the direction of the initial reaction.

Alkanes are generally unreactive and do not react with acids, bases, or with oxidising or reducing agents. However, they will react with halogens under suitable conditions, to form halogenoalkanes.

Methane reacts with chlorine in this way to form chloromethane.

The reaction described in part (a) consists of three steps. In the first step, the Cl-Cl bond is broken to form two chlorine free radicals.

Give the equations for each step of the reaction between methane and chlorine as described in part (a).

Label each equation with the name of the correct step. You only need to provide one equation for the final step.

Benzene, C₆H₆, typically undergoes electrophilic substitution

Benzene is a highly unsaturated molecule.

An aromatic organic compound with molecular formula C₇H₈ reacts with bromine in the presence of UV light to produce a compound with molecular formula C₇H₇