Moles & amount of substance

0.200 mol of HOOCCH₂CH₂COOH is reacted with 0.300 mol NaOH.

How many water molecules are formed?

A 1.204 × 10²³

B 1.806 × 10²³

C 2.408 × 10²³

D 3.612 × 10²³

This question is about different compounds that each contain O and H atoms covalently bonded together.

The alcohol 2,3‑dimethylhexan‑1‑ol has the molecular formula C₈H₁₈O.

Draw the skeletal formula of 2,3‑dimethylhexan‑1‑ol.

What is the number of H atoms in 8.45 g of 2,3‑dimethylhexan‑1‑ol?

Give your answer to 3 significant figures and in standard form.

Why does paracetamol not react with Na₂CO₃(aq)?

The student uses the reaction of nuromol tablets with Na₂CO₃(aq) to determine the mass of ibuprofen and the mass of paracetomol in one nuromol tablet.

The student’s method is outlined below.

• Weigh four nuromol tablets.

• Add the tablets to an excess of aqueous sodium carbonate.

• Collect the gas produced and measure its volume.

Results Mass of four nuromol tablets = 2.80 g Volume of gas collected at RTP = 48.0 cm³

Assume that ibuprofen is the only compound in nuromol tablets that reacts with Na₂CO₃(aq).

Determine the mass of ibuprofen and the mass of paracetomol, in mg, in one nuromol tablet.

Barium hydroxide, Ba(OH)₂, is an alkali. A student is supplied with a solution of Ba(OH)₂ with a concentration of 46.80 g dm^–3 at 25 °C.

The student dilutes 20.0 cm³ of this solution of Ba(OH)₂ with water and the solution is made up to 100.0 cm³ at 25 °C.

Calculate the pH of the diluted solution of Ba(OH)₂ at 25 °C.

Give your answer to 2 decimal places.

This question is about inorganic chemistry.

The flowchart shows reactions involving SO₃^2–(aq) ions.

What is the systematic name of a SO₃^2– ion?

Construct an ionic equation for the reaction of SO₃^2– with H⁺/Cr₂O₇^2–.

The structure of a neutral nickel(II) complex, A, is shown below.

What is the empirical formula of complex A ?

Complete the 3D diagram below to show a stereoisomer of complex A.

-Amino acids have the general formula RCH(NH₂)COOH.

The R group in an -amino acid contains C and H only.

This R group has a molar mass of 91 g mol^–1.

A polymer is formed from 500 molecules of this -amino acid.

Determine the molar mass of this polymer.

Give your answer to the nearest whole number.

molar mass of polymer =........ g mol^–1

This question is about different areas of chemistry.

Why do all average bond enthalpies have a positive value?

Determine the C–H bond enthalpy, in kJ mol^–1, using the information above.

C–H bond enthalpy =........ kJ mol^–1

Hydrogen gas is being considered as a household fuel to replace methane.

The enthalpy change of formation, _fH, for H₂O(l) is –285.8 kJ mol^–1.

Determine the energy released when 60.0 m³ of hydrogen is used as a household fuel at RTP.

Give your answer to 3 significant figures and in standard form.

Compound A is a chloride of a Period 3 element.

A student carries out the 2 steps below to find the formula of compound A.

Step 1 The student adds 5.00 10^–4 mol of compound A to water. A colourless solution is formed.

Step 2 The colourless solution reacts with exactly 60.0 cm³ of 2.50 10^–2 mol dm^–3 AgNO₃(aq) to form a white precipitate.

Write an ionic equation, with state symbols, for the reaction in Step 2.

Determine the formula of compound A.

Compound B, shown below, is an antiviral medicine.

What is the molecular formula of compound B ?

How many chiral carbon atoms are there in one molecule of compound B ?

How many hydrogen atoms are in 2.50 g of pharmacolite, CaHAsO₄•2H₂O (M_r = 216.0)?

A 6.97 10²¹

B 2.09 10²²

C 2.79 10²²

D 3.48 10²²

Your answer

This question is about aromatic compounds containing the –COOH and –OH functional groups.

Salicylic acid, shown below, is used in the manufacture of some important medicines.

Salicylic acid

Complete the flowchart for reactions of salicylic acid, by adding the organic products in each

PAS, shown below, is an antibiotic used to treat several diseases including tuberculosis (TB).

A student predicts that PAS could polymerise to form a polymer containing both ester and amide linkages.

Draw a section of this polymer.

The section should contain one amide and one ester linkage, which should be displayed.

For the treatment of TB, the maximum daily dosage of PAS that should be prescribed is 300 mg per kg of body mass.

A child weighs 20.0 kg.

Calculate the number of PAS molecules in the maximum daily dosage of PAS for this child.

The three elements that, when in a molecule, can form hydrogen bonds with other suitable molecules.

An element that is a solid at RTP with a simple molecular lattice structure.

The two elements with atoms containing five unpaired electrons.

The element in Period 3 that exists in the solid state as a network of atoms bonded by strong covalent bonds.

The p-block element in Period 3 that forms a compound with fluorine with octahedral molecules.

The element that forms 1– ions most readily.

The element with an average atomic mass of 1.244 10^–22 g.

The mass of 4 molecules of a substance is 2.125 × 10^–22 g.

What is the possible formula of the substance?

A CH₄

B O₂

C SO₂

D I₂

Your answer

The graph shows the first ionisation energies for elements from helium, He, to boron, B, in the periodic table.

Complete the graph for C, N, O, F and Ne.

Explain why the first ionisation energies of He and Be are both higher than the first ionisation energy of Li.

Explanation for He:........

Explanation for Be:........

Explain why the first ionisation energy of Be is higher than the first ionisation energy of B.

This question is about organic acids.

Table 18.1 shows the R groups in four amino acids.

Most amino acids show optical isomerism.

Explain the term optical isomerism.

Draw 3-D diagrams to show the optical isomers of alanine.

How many optical isomers does threonine have?

Ibuprofen, shown below, is used as a painkiller.

What is the molecular formula of ibuprofen?

One ibuprofen tablet contains 400 mg of ibuprofen.

Calculate the number of ibuprofen molecules in one ibuprofen tablet.

Give your answer to 3 significant figures.

Tablets based on ibuprofen and lysine are now available from pharmacies.

These tablets are claimed to act faster than ibuprofen by being absorbed into the body more quickly than ibuprofen alone.

One type of these tablets contains a salt of ibuprofen and the amino acid lysine (R = –(CH₂)₄NH₂) in a 1:1 molar proportion.

Suggest why tablets based on a salt of ibuprofen should act faster in the body than ibuprofen.

What is the molecular formula of the steroid molecule below?

A student carries out an investigation to identify two metals, M and X, by two different methods.

In Stage 1, a redox reaction takes place between M and HC l (aq), forming hydrogen and a solution containing M in the +2 oxidation state.

Write an overall equation, with state symbols, for this reaction. Write half-equations for the oxidation and reduction processes.

Overall equation........

Oxidation half-equation........

Reduction half-equation........

In Stage 1, suggest two observations that would confirm that all of metal M has reacted.

In Stage 3, write the ionic equation for the reaction taking place in the titration.

Metal M can be identified following the steps below.

1. The amount, in mol, of excess HC l (aq) that remains after the reaction of M with HC l (aq).

2. The amount, in mol, of HC l (aq) that reacted with M.

3. The identity of metal M.

Analyse the results to identify metal M.

The student is provided with the carbonate of an unknown metal, X₂CO₃.

The student measures the mass loss when the X₂CO₃ is reacted with an excess hydrochloric acid. The equation is shown below.

X₂CO₃(s) + 2HCl (aq) → 2XCl (aq) + CO₂(g) + H₂O(l)

The reaction is carried out using this method:

Step 1 Add 100 cm³ HCl (aq) to a conical flask and weigh.

Step 2 Add X₂CO₃ to the conical flask and immediately reweigh.

Step 3 After 5 minutes, reweigh the conical flask and contents.

Calculate the amount, in mol, of CO₂ released in the reaction.

After analysing the results, the student was told that their molar mass of X₂CO₃ was incorrect.

The student evaluated the experiment for possible reasons for the incorrect result.

The student wondered whether the reaction was complete when the mass was recorded after 5 minutes (Step 3).

How could the student modify the experimental procedure to be confident that the reaction was complete?

The student finds out that carbon dioxide is slightly soluble in water.

State and explain how the solubility of CO₂ would affect the calculated molar mass of X₂CO₃.

One molecule of a gas has a mass of 2.658 × 10⁻²³ g.

What is a possible formula of the gas?

A CH₄

B O₂

C SO₂

D SO₃

Your answer

This question is about unsaturated aldehydes and alcohols.

Outline the reaction mechanism for the formation of one of the organic products.

Include curly arrows and relevant dipoles.

Explain why one of the organic products forms in a much greater quantity than the other organic product.

Describe how the observations from a chemical test would distinguish between geraniol and citronellal.

What is the molecular formula of geraniol?

Explain why geraniol and citronellal are structural isomers of each other.

Explain the term stereoisomerism.

These short questions are from different areas of chemistry.

Explain why a CF₄ molecule has polar bonds but does not have an overall dipole.

Explain why a small proportion of molecules in water have a relative molecular mass of 20.

What is the partial pressure of O₂ (in Pa) in a gas mixture containing 21% O₂ by volume and with a total pressure of 1.0 × 10⁵ Pa?

What mass of carbon dioxide (in g) is formed by the complete combustion of 42.0 m³ (measured at RTP) of propane?

What is the number of oxygen atoms in 4.26 g of P₂O₅?

This question is about elements and compounds in Group 14 (Group 4) of the periodic table.

There are four oxides of lead: PbO, PbO₂, Pb₂O₃ and Pb₃O₄.

A student carries out an experiment to identify an unknown lead oxide, which is one of the four oxides of lead shown above.

The student plans to reduce the unknown lead oxide to lead by heating the lead oxide in a stream of methane gas, CH₄. The apparatus is shown below.

Student’s method

• Weigh an empty dish. Add the lead oxide to the dish and reweigh.

• Set up the apparatus and pass methane gas through the tube as shown. Heat the dish for 10 minutes.

• Pass cold air through the tube to cool the dish and contents.

• Weigh the dish and contents.

Write the equation for the reduction of Pb₂O₃ with CH₄.

The student uses safety glasses and a lab coat.

State, with a reason, one other important safety precaution the student should take when carrying out this experiment.

The student was not sure that all the oxygen had been removed from the lead oxide.

Suggest two modifications that the student could make to their method to be confident that all the oxygen had been removed. Explain your reasoning.

The student makes suitable modifications to the method and repeats the experiment to obtain the accurate results shown below.

Calculate the empirical formula of the lead oxide.

SiO₂ and CO₂ are oxides of other Group 14 (Group 4) elements.

Solid SiO₂ melts at 2156 °C. Solid CO₂ melts at −56 °C.

Suggest the type of lattice structure in solid SiO₂ and in solid CO₂ and explain the difference in melting points in terms of the types of force within each lattice structure.

Structure in SiO₂(s)........

Structure in CO₂(s)........

Explanation........

What is the number of hydrogen atoms in 0.125 mol of C₂H₅OH?

A 7.525 × 10²²

B 4.515 × 10²³

C 3.7625 × 10²³

D 3.612 × 10²⁴

Your answer

0.1 mol of HOOCCH₂COOH are reacted with 0.1 mol of aqueous NaOH.

How many molecules of water are formed?

A 6.02 × 10²²

B 3.01 × 10²²

C 6.02 × 10²³

D 3.01 × 10²³