Scottish National 5 (Nat 5) Chemistry Syllabus

What happens to the concentration of $\ce{H+}$ and $\ce{OH-}$ ions when an acid is diluted with water?

Diluting an acid lowers the concentration of $\ce{H+}$ ions, so the pH rises towards 7 (but never reaches or exceeds 7). The $\ce{OH-}$ concentration increases slightly.

Write the general word equation for the neutralisation of an acid by a base/alkali.

acid + base → salt + water. For an alkali: $\ce{H+ + OH- -> H2O}$.

Name the salt and other products formed when hydrochloric acid reacts with sodium carbonate.

Sodium chloride, water and carbon dioxide: $$\ce{2HCl + Na2CO3 -> 2NaCl + H2O + CO2}$$

What salt is produced when sulfuric acid reacts with a metal hydroxide (e.g. potassium hydroxide)?

A sulfate salt (and water). For example: $$\ce{H2SO4 + 2KOH -> K2SO4 + 2H2O}$$

Define a 'homologous series'.

A homologous series is a group (family) of compounds with the same general formula, similar chemical properties, and showing a gradual change in physical properties as the molecular size increases. Successive members differ by $\ce{CH2}$.

Give the general formula of the alkanes and the alkenes.

Alkanes: $C_nH_{2n+2}$ (saturated). Alkenes: $C_nH_{2n}$ (unsaturated, contain a C=C double bond).

What is the difference between a saturated and an unsaturated hydrocarbon, and how can you test for unsaturation?

A saturated hydrocarbon has only single C–C bonds; an unsaturated one contains at least one C=C double bond. Unsaturation is tested with bromine water, which is rapidly decolourised (orange/brown to colourless) by an unsaturated compound.

Name and give the formula of the first three members of the alkanes.

Methane $\ce{CH4}$, ethane $\ce{C2H6}$, propane $\ce{C3H8}$.

What is the general formula of the cycloalkanes?

$C_nH_{2n}$ — the same general formula as the alkenes, but cycloalkanes are saturated ring structures.

Name the homologous series with the general formula $C_nH_{2n+1}OH$ and give its functional group.

The alcohols (alkanols). Functional group is the hydroxyl group, $\ce{-OH}$.

Name the homologous series with general formula $C_nH_{2n+1}COOH$ and its functional group.

The carboxylic acids (alkanoic acids). Functional group is the carboxyl group, $\ce{-COOH}$.

What products are formed and what type of products are these when an alcohol and a carboxylic acid react?

They form an ester and water in a condensation (esterification) reaction. Esters are used as flavourings and fragrances in consumer products.

What is meant by a 'consumer product' in chemistry, and name a typical example studied at Nat 5.

A consumer product is a substance made and used by people in everyday life, such as alcohols (in fuels/solvents), carboxylic acids, esters (flavours/perfumes), soaps, detergents and fragrances.

Why is ethanol widely used as a solvent and a fuel?

Ethanol is a good solvent because it can dissolve both polar and non-polar substances, and it is a useful fuel because it is flammable and burns to release energy producing $\ce{CO2}$ and water.

What is a fossil fuel, and name the three main fossil fuels.

A fossil fuel is a finite (non-renewable) fuel formed over millions of years from the remains of dead plants and animals. The three main ones are coal, crude oil (petroleum) and natural gas.

Write the general word equation for the complete combustion of a hydrocarbon.

hydrocarbon + oxygen → carbon dioxide + water. e.g. $$\ce{CH4 + 2O2 -> CO2 + 2H2O}$$

What is produced during incomplete combustion of a hydrocarbon, and why is one product dangerous?

Incomplete combustion (limited oxygen) produces carbon monoxide $\ce{CO}$ and/or carbon (soot) plus water. Carbon monoxide is toxic because it binds to haemoglobin and prevents the blood carrying oxygen.

Name three pollutants released when fossil fuels are burned and a problem each causes.

Carbon dioxide ($\ce{CO2}$ – greenhouse effect/global warming); sulfur dioxide ($\ce{SO2}$ – acid rain); oxides of nitrogen ($\ce{NO_x}$ – acid rain/smog); carbon monoxide ($\ce{CO}$ – toxic gas).

Why is the energy from fuels a major reason crude oil is fractionally distilled?

Fractional distillation separates crude oil into fractions of similar boiling-point hydrocarbons; the smaller, more volatile fractions are valuable, flammable fuels (e.g. petrol, kerosene, diesel) used to release energy.

What is an addition reaction, and what reagent commonly adds across a C=C double bond?

An addition reaction is where atoms add across the carbon–carbon double bond of an unsaturated molecule, opening it to form a single bond. Reagents such as hydrogen ($\ce{H2}$), bromine ($\ce{Br2}$) or water can add. e.g. $$\ce{C2H4 + H2 -> C2H6}$$

What is hydrogenation, and give an industrial use of it.

Hydrogenation is the addition of hydrogen across a C=C double bond, converting an unsaturated compound into a saturated one. It is used industrially to turn unsaturated vegetable oils into solid/spreadable fats (e.g. margarine).

Write the products of the addition reaction between ethene and bromine.

Ethene reacts with bromine to form 1,2-dibromoethane: $$\ce{C2H4 + Br2 -> C2H4Br2}$$

Place these metals in order of increasing reactivity: copper, magnesium, zinc, sodium.

Increasing reactivity: copper < zinc < magnesium < sodium.

Describe what is seen when a reactive metal reacts with dilute acid, and name the gas produced.

The metal fizzes/effervesces and dissolves, producing a salt and hydrogen gas. The hydrogen gas gives a 'squeaky pop' with a lit splint: $$\ce{Mg + 2HCl -> MgCl2 + H2}$$

Explain why only metals below hydrogen in the reactivity series (e.g. copper) do not react with dilute acids.

A metal only displaces hydrogen from an acid if it is more reactive than hydrogen. Unreactive metals such as copper, silver and gold are below hydrogen, so they do not react with dilute acids to give hydrogen.

What is an electrochemical (displacement) cell's basic principle for producing electricity?

When two different metals are connected in an electrolyte, electrons flow through the external circuit from the more reactive metal to the less reactive metal, generating a current. The bigger the reactivity difference, the larger the voltage.

Define a 'displacement reaction' for metals.

A displacement reaction is one in which a more reactive metal displaces (pushes out) a less reactive metal from a solution of its compound, e.g. $$\ce{Zn + CuSO4 -> ZnSO4 + Cu}$$

How are very reactive metals such as aluminium and sodium extracted from their ores, and why?

They are extracted by electrolysis of the molten ore/compound, because they are too reactive to be displaced by heating with carbon (their compounds are very stable).

What is a polymer, and what is the small repeating unit it is made from called?

A polymer is a very large (long-chain) molecule made by joining together many small molecules. The small molecules are called monomers, and the joining process is polymerisation.

Describe addition polymerisation and name a polymer made this way.

In addition polymerisation many small unsaturated monomers (containing C=C double bonds) join together by opening their double bonds to form one long saturated polymer chain, with no other product. e.g. ethene → poly(ethene).

What problem do most synthetic plastics/polymers cause for the environment?

Most synthetic polymers are non-biodegradable, so they are not broken down by microorganisms and persist in landfill/oceans. Burning them can also release toxic gases (e.g. $\ce{CO}$, $\ce{HCl}$).

What is a fertiliser, and which three essential elements do fertilisers commonly provide?

A fertiliser is a substance that restores essential elements to the soil to promote plant growth. The three key elements are nitrogen (N), phosphorus (P) and potassium (K).

Name the industrial process that makes ammonia, and write its equation.

The Haber process makes ammonia from nitrogen and hydrogen: $$\ce{N2 + 3H2 <=> 2NH3}$$ (reversible, with a catalyst, high pressure and moderate temperature).

Why is ammonia important for fertilisers, and what is made when ammonia is oxidised industrially?

Ammonia ($\ce{NH3}$) is a soluble source of nitrogen used to make nitrogen-containing fertilisers (e.g. ammonium salts). When oxidised (Ostwald process) it forms nitrogen dioxide/nitric acid, which is used to make nitrate fertilisers.

Name the flame colours produced by lithium, sodium and potassium ions in a flame test.

Lithium gives a red flame, sodium gives a yellow/orange flame, and potassium gives a lilac (purple) flame.

In chemical analysis, what is a precipitate, and how is it used to identify ions?

A precipitate is an insoluble solid formed when two solutions are mixed. Adding a chosen reagent forms a precipitate of a characteristic colour, allowing specific ions to be identified by the colour and presence of the solid.

Describe the titration technique used to find the concentration of an acid or alkali.

A known volume of one solution is measured into a flask with an indicator; the other solution is added from a burette until the indicator just changes colour (end-point). Concentration is then calculated using $$n = C \times V$$ and the balanced equation, repeating to get concordant titres.