Empirical formulae

Figure 4 shows the structure of molecules of three compounds, A, B and C.

Explain which compound, A, B or C, is an alkene.

What is the empirical formula of compound B ?

The test to distinguish between compounds B and C involves shaking separate samples of each compound with an orange solution.

The label on the orange solution is shown in Figure 5.

State the meaning of the hazard symbol shown.

Name the orange solution used to distinguish between compounds B and C.

What is the final appearance of the mixture when compound B is shaken with a few drops of the orange solution?

The molecular formula of compound A is C₄H₁₀O.

A sample of compound A undergoes complete combustion to form carbon dioxide and water.

Explain why this reaction is an oxidation reaction.

Calculate the mass of water formed from the complete combustion of 74 g of compound A, C₄H₁₀O.

(relative formula masses: C₄H₁₀O = 74, H₂O = 18)

Crude oil is a mixture of hydrocarbons.

The majority of hydrocarbons in crude oil belong to one homologous series.

Give the name of this series.

When hydrocarbons undergo combustion, water is produced.

Draw a dot and cross diagram of a molecule of water.

One compound in crude oil contains 0.96 g of carbon atoms combined with 0.32 g of hydrogen atoms.

Calculate the empirical formula of this compound.

(relative atomic masses: C = 12, H = 1.0)

*(d) Crude oil is separated into useful products called fractions using fractional distillation.

Figure 14 shows a fractional distillation column and the fractions kerosene and fuel oil.

Kerosene and fuel oil have different uses depending on their properties.

Describe the properties and uses of kerosene and fuel oil. Include in your answer

• the difference in boiling point

• the difference in viscosity

• the difference in ease of ignition

• their uses and how fuel oil can be converted into kerosene.

Crude oil is a mixture of hydrocarbons.

The majority of hydrocarbons in crude oil belong to one homologous series.

Give the name of this series.

When hydrocarbons undergo combustion, water is produced.

Draw a dot and cross diagram of a molecule of water.

One compound in crude oil contains 0.96 g of carbon atoms combined with 0.32 g of hydrogen atoms.

Calculate the empirical formula of this compound.

(relative atomic masses: C = 12, H = 1.0)

Figure 8 shows some information about an atom of chlorine.

35 C l 17

Figure 8

State the number of protons, neutrons and electrons in this atom.

Chlorine reacts with silicon to form silicon chloride.

A sample of silicon chloride contains 1.4 g of silicon atoms and 7.1 g of chlorine atoms.

Calculate the empirical formula of this sample of silicon chloride.

(relative atomic masses: Si = 28, C l = 35.5)

empirical formula =_........

The modern periodic table is organised into groups and periods.

State in which group and in which period of the periodic table silicon is found.

You should use the periodic table to help you answer this question.

Describe two differences between Mendeleev’s periodic table and the modern periodic table.

Damp iron wool reacts with oxygen in the air. A student uses the apparatus in Figure 7 to investigate the percentage of oxygen in the atmosphere.

The initial volume of air in the measuring cylinder was 18.0 cm³.

The student left the apparatus overnight.

The volume of gas in the measuring cylinder the next day was 14.5 cm³.

To the nearest whole number, what percentage of the air has reacted with the iron wool?

Describe one improvement the student could make to this method to ensure that all of the oxygen in the measuring cylinder has reacted.

When hydrocarbon fuels are burned, the products are water and carbon dioxide.

Describe what needs to be done to the apparatus in Figure 8 to collect the water and show that carbon dioxide has been produced.

A hydrocarbon, C_xH_y, is burned in excess oxygen, forming 26.4 g of carbon dioxide and 5.4 g of water.

The relative formula mass of C_xH_y is 78.

Calculate the molecular formula of the hydrocarbon C_xH_y.

(relative atomic masses: H = 1.0, C = 12; relative formula masses: H₂O = 18, CO₂ = 44)

molecular formula =_........

Magnesium is a metal.

State one physical property of magnesium.

Which element is in the same group of the periodic table as magnesium? Use the periodic table to help you answer this question.

Magnesium atoms have 12 electrons.

Complete the electronic configuration of a magnesium atom.

The electronic configuration of a chlorine atom is 2.8.7

Explain how the electronic configuration of chlorine is linked to its period in the periodic table.

1.20 g of magnesium reacts completely with 3.55 g of chlorine to form magnesium chloride.

Calculate the empirical formula of the magnesium chloride.

(relative atomic masses: Mg = 24.0, C l = 35.5)

You must show your working.

Sodium reacts with chlorine to form sodium chloride, which contains ionic bonds.

Hydrogen reacts with chlorine to form hydrogen chloride, which contains covalent bonds.

Figure 9 shows dot and cross diagrams of these compounds.

Describe the differences between an ionic bond and a covalent bond.

Figure 11 shows the structure of a molecule of compound S.

Use Figure 11 to deduce the empirical formula of compound S.

The melting points of three samples of S are shown in Figure 12.

State whether each of these samples, A, B and C, is pure or impure and justify your answers using the information in Figure 12.

A scientist uses chromatography in an investigation of compound S.

In the conditions used, compound S has an R_f value of 0.22.

Calculate the distance the spot of compound S moves if the solvent front has moved by 2.4 cm.

*(c) A solution of sodium chloride in water needs to be separated to obtain a sample of pure, dry sodium chloride and a sample of pure water.

Figure 13 shows the boiling points of sodium chloride and water.

Explain this difference in boiling points in terms of the structure and bonding of sodium chloride and water and how this difference is used to choose a method to separate sodium chloride solution into pure, dry sodium chloride and pure water.

Crude oil is a mixture of hydrocarbons.

Crude oil can be separated into useful fractions by the process of fractional distillation in a fractionating column.

Figure 15 shows a fractionating column, the fractions obtained and the trend in viscosity of the fractions.

Which row shows the correct uses for bitumen, diesel oil and fuel oil?

Explain the trend in the viscosity of the fractions.

Hydrocarbon X was cracked to form one molecule of hexane, C₆H₁₄, and one molecule of alkene Y.

The relative formula mass of Y is 56. The empirical formula of Y is CH₂.

Deduce the molecular formula of hydrocarbon X.

Show your working.

(relative atomic masses: H = 1.0, C = 12)

*(c) Large quantities of methane are used as a fuel.

Figure 16 shows a Bunsen burner.

Methane can be used as fuel for the Bunsen burner.

The air-hole on the chimney of the Bunsen burner can be opened and closed.

Explain the effect of opening and closing the air-hole of the Bunsen burner on the products of combustion of methane and the harm that using large quantities of methane as a fuel can cause.

An atom of aluminium has an atomic mass of 27.

Aluminium has an atomic number of 13.

State the number of electrons, neutrons and protons in this atom.

Aluminium reacts with bromine to form aluminium bromide. A sample of aluminium bromide contains 1.35 g of aluminium atoms and 12.00 g of bromine atoms.

Calculate the empirical formula of this sample of aluminium bromide.

(relative atomic masses: A l = 27.0, Br = 80.0)

Gallium is in the same group in the periodic table as aluminium and in the same period in the periodic table as bromine.

State in which group and period of the periodic table gallium can be found.

You may want to refer to the periodic table.

Gallium had not been discovered when Mendeleev created his first periodic table.

Figure 9 shows some properties of gallium that Mendeleev predicted and some of the actual properties of gallium.

Describe how Mendeleev predicted these properties of gallium.

This question is about oxygen.

The percentage of oxygen in today’s atmosphere is greater than the percentage of oxygen in the Earth’s early atmosphere.

Explain what caused this change to happen.

Magnesium reacts with oxygen from the air to form magnesium oxide.

A student carries out an investigation to determine the mass of magnesium oxide formed when a known mass of magnesium reacts completely with oxygen.

This is the method the student used.

step 1 find the mass of a crucible and lid

step 2 put a known mass of magnesium into the crucible and put the lid on

step 3 heat for five minutes using a roaring Bunsen burner flame

step 4 let the crucible, lid and contents cool down

step 5 find the final mass of the crucible, lid and contents

Explain how the student could check that the magnesium had reacted completely with oxygen.

In another experiment, it was found that 1.24 g of phosphorus reacted completely with 1.60 g of oxygen to form phosphorus oxide.

The relative formula mass of this phosphorus oxide is 284.

Deduce the molecular formula of this phosphorus oxide.

You must show your working.

(relative atomic masses: O = 16, P = 31)

molecular formula =_........

A student uses the apparatus shown in Figure 10 to investigate the percentage of oxygen in the atmosphere.

The apparatus was left for a few days.

Explain one change the student would see after a few days.

Explain one change that can be made to the apparatus in Figure 10 to allow the student to calculate the percentage of oxygen in the atmosphere.

The scientist John Dalton lived over 200 years ago.

John Dalton suggested an early model of atoms.

When Dalton first described atoms he said that

• all elements are made of atoms

• atoms are not formed of any smaller particles

• all atoms of the same element are identical.

Give two differences between Dalton’s model of atoms and today’s model of atoms.

Dalton also investigated different gases.

One of the gases that Dalton investigated was ethene.

The structure of one molecule of ethene is shown in Figure 8.

Give the molecular formula and the empirical formula of ethene.

Another gas that Dalton investigated was chlorine.

Chlorine gas reacts with water. The two products are a solution of hydrogen chloride and the substance HC l O.

Complete the balanced equation for this reaction, including the three missing state symbols.

Hydrogen chloride solution is acidic.

The formulae of four ions are shown in Figure 9.

Give the formula of the ion in Figure 9 that causes the hydrogen chloride solution to be acidic.

An acid reacts with an alkali.

Give the name of this type of reaction.

Describe what you would see when some copper carbonate powder is added to a beaker of dilute sulfuric acid.

The scientist John Dalton lived over 200 years ago.

John Dalton suggested an early model of atoms.

When Dalton first described atoms he said that

• all elements are made of atoms

• atoms are not formed of any smaller particles

• all atoms of the same element are identical.

Give two differences between Dalton’s model of atoms and today’s model of atoms.

Dalton also investigated different gases.

One of the gases that Dalton investigated was ethene.

The structure of one molecule of ethene is shown in Figure 2.

Give the molecular formula and the empirical formula of ethene.

Another gas that Dalton investigated was chlorine.

Chlorine gas reacts with water. The two products are a solution of hydrogen chloride and the substance HC l O.

Complete the balanced equation for this reaction, including the three missing state symbols.

Hydrogen chloride solution is acidic.

The formulae of four ions are shown in Figure 3.

Give the formula of the ion in Figure 3 that causes the hydrogen chloride solution to be acidic.

An acid reacts with an alkali.

Give the name of this type of reaction.

Fluorine, chlorine, bromine and iodine are elements in group 7 of the periodic table.

State the name given to the group 7 elements.

Name one other element that is in group 7. Use the periodic table on the back of this exam paper to help you.

Which element is liquid at room temperature and pressure?

Which element is dark-grey in colour at room temperature and pressure?

Tin reacts with chlorine to form tin chloride. A sample of tin chloride contains 1.19 g of tin and 1.42 g of chlorine.

Calculate the empirical formula of this tin chloride.

(relative atomic masses: C l = 35.5, Sn = 119.0)

You must show your working.

empirical formula of this tin chloride =_........

Tin also reacts with fluorine. The reaction between fluorine and tin is much more vigorous than the reaction between chlorine and tin.

Figure 8 shows the electronic configurations of fluorine and chlorine.

Explain, in terms of their electronic configurations, why fluorine reacts with tin more vigorously than chlorine reacts with tin.

Some metals are found in the Earth’s crust as uncombined elements. Reactive metals are found in ores.

In ores, metals are combined with other elements.

Which of these metals is found as the uncombined element in the Earth’s crust?

Give two advantages of recycling metals rather than extracting metals from their ores.

An ore of iron is mostly iron oxide, Fe₂O₃. Iron can be extracted from this iron oxide by heating it with carbon.

Balance this equation for the reaction that takes place.

Most copper ores are described as low grade. This means that the percentage of copper in the ore is very small.

5000 kg of one copper ore was found to contain 42.5 kg of copper.

Calculate the percentage of copper in this ore.

percentage of copper in ore =_........

In one stage of the extraction of lead from its ore, lead oxide is heated strongly with carbon.

The equation for the reaction is

Explain, using this equation, which substance has been oxidised in this reaction.

A titanium ore was analysed and found to contain 12 g of titanium atoms combined with 8.0 g of oxygen atoms.

Calculate the empirical formula of this titanium compound. (relative atomic masses: Ti = 48, O = 16)

You must show your working.

empirical formula =_........

Titanium and iron are examples of transition metals.

Figure 6 shows the percentage abundance of each isotope in a sample of titanium.

Calculate the relative atomic mass of titanium in this sample.

Iron, when heated in air, reacts with oxygen to form iron oxide.

This reaction is an example of

The equipment shown in Figure 7 can be used to find the mass of oxygen that combines with iron.

Describe how the equipment shown in Figure 7 could be used to find the mass of oxygen that combines with 0.500 g of iron wool in a crucible and lid of known mass.

2.24 g of iron combines with 0.96 g of oxygen to form an oxide of iron.

Determine the formula of this oxide of iron and use it to complete the balanced equation.

(relative atomic masses: Fe = 56.0, O = 16.0)

You must show your working.

balanced equation for the reaction is

Using the letters A, E, G, J, X and Z

give the letters of the two elements that are non-metals

give the letters of two elements in period 2

give the letter of an element that normally forms an ion with a charge of +1.

Element E has an atomic number of 5. In a sample of E there are two isotopes. One isotope has a mass number of 10 and the other isotope has a mass number of 11.

Explain, in terms of subatomic particles, what is meant by the term isotopes.

All atoms of element E in this sample contain

Element X has an atomic number of 18.

State the electronic configuration of an atom of element X.

In an experiment, 3.5 g of element A reacted with 4.0 g of element G to form a compound.

Calculate the empirical formula of this compound. (relative atomic masses: A = 7, G = 16)

You must show your working.

Ethene, C₂H₄, is an unsaturated hydrocarbon.

Explain why ethene is an unsaturated hydrocarbon.

A sample of ethene is burned completely in oxygen.

Write the balanced equation for this reaction.

Ethene can be polymerised to form poly(ethene).

Describe what you would see when a sample of ethene and a sample of poly(ethene) are shaken with separate, small volumes of bromine water.

A different hydrocarbon has a relative formula mass of 84. It has an empirical formula of CH₂.

Deduce the molecular formula of this hydrocarbon.

You must show your working.

(relative atomic masses: H=1, C=12)

The molecular formula of butene is C₄H₈.

Which of the following is the empirical formula of butene?

Calculate the relative formula mass of butene, C₄H₈.

(relative atomic masses: H = 1, C = 12)

relative formula mass_........

When burnt completely in air, butene forms carbon dioxide and water.

Balance the equation for this reaction by putting numbers in the spaces provided.

Describe the test to show that a gas is carbon dioxide.

Substance X is a gas at room temperature. It is a simple molecular, covalent substance.

Which row of the table shows the properties that substance X is most likely to have?

Diamond has a giant covalent structure.

State one property of diamond that is the result of its giant covalent structure.

Lithium, sodium and potassium are reactive metals in group 1 of the periodic table.

Sodium metal tarnishes in air to form a layer of sodium oxide on its surface. 0.92 g of sodium combined with 0.32 g of oxygen in this oxide.

Calculate the empirical formula of this sodium oxide. (relative atomic masses: O = 16, Na = 23)

You must show your working.

Sodium reacts with water to form sodium hydroxide in solution and hydrogen.

Complete the balancing of the equation for this reaction and add the state symbols for each substance.

In an experiment equal-sized pieces of lithium, sodium and potassium are added to separate samples of water.

A flame is produced only with potassium because potassium

*(ii) A teacher demonstrated this experiment.

The results are shown in Figure 14.

Describe, in detail, how the teacher would demonstrate this experiment safely, showing how the results give the order of reactivity of the metals.

Lithium, sodium and potassium are reactive metals in group 1 of the periodic table.

Sodium metal tarnishes in air to form a layer of sodium oxide on its surface. 0.92 g of sodium combined with 0.32 g of oxygen in this oxide.

Calculate the empirical formula of this sodium oxide. (relative atomic masses: O = 16, Na = 23)

You must show your working.

Sodium reacts with water to form sodium hydroxide solution and hydrogen.

Complete the balancing of the equation for this reaction and add the state symbols for each substance.

In an experiment equal-sized pieces of lithium, sodium and potassium are added to separate samples of water.

A flame is produced only with potassium because potassium

Explain, in terms of electronic configurations, the increase in reactivity from lithium to sodium to potassium.