Relative formula mass

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 ?

This question is about the chemistry of compounds containing phosphorus.

Phosphorus forms several acids including H₃PO₄ and H₃PO₃.

H₃PO₄ is a tribasic acid. The equilibria for the dissociations are shown below.

During the equilibria, H₂PO₄^– behaves both as an acid and as a base.

Explain this statement, using the equilibria 1, 2 and 3, as required.

In a H₃PO₃ molecule, the O atoms are covalently bonded to the P atom. The H atoms are bonded to the O atoms.

Draw the structure of a H₃PO₃ molecule, showing all the bonds.

On your diagram, add the values for the O–P–O and P–O–H bond angles.

The systematic name of H₃PO₄ is phosphoric(V) acid.

What is the systematic name of H₃PO₃?

Phosphine, PH₃, is a poisonous gas.

Phosphine reacts with oxygen gas to form phosphorus(V) oxide and water.

Write the equation for this reaction.

Aqueous silver nitrate, AgNO₃, is reduced by PH₃. The unbalanced equation is shown below.

Balance the equation and use oxidation numbers to explain why this is a redox reaction.

Explanation........

When phosphorus(V) chloride, PCl₅, and ammonium chloride are heated together, the compound P₃N₃Cl₆ is formed, together with HCl gas.

P₃N₃Cl₆ has a cyclic structure, like the Kekulé structure of benzene.

Write an equation for the reaction of PCl₅ and ammonium chloride to form P₃N₃Cl₆.

Calculate the percentage by mass of P in P₃N₃Cl₆.

Give your answer to 2 decimal places.

Suggest one example of evidence that could show that P₃N₃Cl₆ has a Kekulé structure rather than a delocalised structure.

In a molecule of P₃N₃Cl₆ all the N and Cl atoms are bonded to P atoms.

Suggest a possible structure for a molecule of P₃N₃Cl₆.

The structure of the painkiller, paracetamol, is shown below.

A tablet contains 3.31 × 10^–3 mol of paracetamol.

What is the mass of paracetamol in the tablet?

A 493 mg

B 497 mg

C 500 mg

D 506 mg

This question is about compounds that contain the carboxylic acid functional group.

Carboxylic acids react with alkalis, metals and carbonates to form salts.

Write full equations for the following three reactions. Show structures for organic compounds.

• the reaction of propanoic acid with aqueous potassium hydroxide:

• the reaction of aqueous methanoic acid with magnesium:

• the reaction of the –amino acid, aspartic acid (R=CH₂COOH), with an excess of aqueous sodium carbonate, Na₂CO₃:

This part is about polymers derived from carboxylic acid monomers.

Poly(pent-3-enoic acid) is an addition polymer.

Draw the structure of pent-3-enoic acid and two repeat units of this polymer.

Butanedicarboxylic acid and 1,4-dihydroxy-2-methylbenzene react to form a condensation polymer.

Draw one repeat unit of this condensation polymer.

Three repeat units of a condensation polymer are shown below.

Draw the structure of the monomer required to form this polymer.

A polymer is formed from 400 molecules of 2-aminopropanoic acid.

Draw one repeat unit of this polymer.

What is the relative molecular mass, M_r, of the polymer?

Select an element from the first three periods that fits each of the following descriptions.

The element that forms a 1– ion with the same electron configuration as helium.

The element with the highest first ionisation energy.

The element in Period 3 which has the successive ionisation energies shown below.

The element which forms a compound with fluorine that has octahedral molecules.

An element which reacts with water to form an acidic solution.

The element X, which forms a compound with hydrogen, XH₃, with a molar mass of 34.0 g mol^–1.

An element which forms a compound with hydrogen in which the element has an oxidation number of –4.

The element which has a density of 1.33 × 10^–3 g cm^–3 at room temperature and pressure.

Table 1.1 shows some properties of Period 3 chlorides.

Explain the properties shown in Table 1.1 in terms of bonding and structure.

This question is about organic compounds containing nitrogen.

Sodium cyanide, NaCN, can be reacted with many organic compounds to increase the length of a carbon chain.

1-Chloropropane, CH₃CH₂CH₂Cl, reacts with ethanolic sodium cyanide by nucleophilic substitution.

Outline the mechanism for this reaction.

Include curly arrows, relevant dipoles and the structure of the organic product.

Compound G is used to synthesise compounds H and I as shown in the flowchart below.

Complete the flowchart showing the structure of compound G and the formulae of the reagents for Reaction 2 and Reaction 3.

Compound H reacts with dilute hydrochloric acid to form a salt.

Explain why compound H can react with dilute hydrochloric acid and suggest a structure for the salt formed.

Explanation........

Structure

Compound I is the monomer for the biodegradable polymer J.

Draw two repeat units of polymer J and suggest a reason why it is biodegradable.

The repeat unit of Nylon 6,6 is shown below.

Draw the structures of two monomers that can be used to form Nylon 6,6.

A sample of Nylon 6,6 has a relative molecular mass of 21500.

Estimate the number of repeat units in the sample.

Give your answer as a whole number.