Scottish National 4 (Nat 4) Chemistry (National 4) Syllabus

What is the pH scale used for, and what is its range?

It measures how acidic or alkaline a solution is, running from about $0$ to $14$.

What pH values indicate acidic, neutral and alkaline solutions?

Acidic: pH less than $7$; neutral: pH equal to $7$; alkaline: pH greater than $7$.

What colour does universal indicator turn in a strong acid and in a strong alkali?

Red in a strong acid, and blue/purple (violet) in a strong alkali.

Name two common laboratory acids and two common alkalis.

Acids: hydrochloric acid $\ce{HCl}$ and sulfuric acid $\ce{H2SO4}$. Alkalis: sodium hydroxide $\ce{NaOH}$ and potassium hydroxide $\ce{KOH}$.

What is neutralisation?

A reaction between an acid and a base (or alkali) that moves the pH towards $7$, producing a salt and water.

Write the general word equation for the reaction of an acid with a metal hydroxide (alkali).

acid + metal hydroxide $\rightarrow$ salt + water, e.g. $\ce{HCl + NaOH -> NaCl + H2O}$.

What two products form when an acid reacts with a metal carbonate?

A salt, water and carbon dioxide gas, e.g. acid + carbonate $\rightarrow$ salt + water + $\ce{CO2}$.

What happens to the pH of an acid when water is added to dilute it?

The pH rises towards $7$ as the acid becomes more dilute (less concentrated).

What is combustion?

Combustion is the reaction of a substance with oxygen, releasing energy (it is an exothermic reaction); burning fuels in oxygen is combustion.

What is a fossil fuel? Name three examples.

A fuel formed over millions of years from the remains of dead organisms; examples are coal, oil and natural gas.

What two products are formed when a hydrocarbon burns completely in plenty of oxygen?

Carbon dioxide and water, e.g. $\ce{CH4 + 2O2 -> CO2 + 2H2O}$.

Why is incomplete combustion dangerous?

When there is not enough oxygen, the poisonous gas carbon monoxide ($\ce{CO}$) and soot (carbon) are produced instead of only carbon dioxide.

Name two pollutants released by burning fossil fuels and a problem each causes.

Sulfur dioxide ($\ce{SO2}$) and nitrogen oxides cause acid rain; carbon dioxide ($\ce{CO2}$) contributes to the greenhouse effect / global warming.

What is a hydrocarbon?

A compound containing only the elements hydrogen and carbon, e.g. methane $\ce{CH4}$.

What is a plastic (polymer) and how is it made?

A plastic is a synthetic material made of very large molecules (polymers) formed by joining together many small molecules called monomers in a process called polymerisation.

What is the difference between a thermoplastic and a thermosetting plastic?

Thermoplastics soften when heated and can be reshaped repeatedly; thermosetting plastics set hard on heating and cannot be re-melted or reshaped.

Give one advantage and one disadvantage of plastics.

Advantage: they are light, cheap, waterproof and easily moulded. Disadvantage: most are non-biodegradable and made from finite crude oil, causing pollution.

What does "biodegradable" mean?

A biodegradable material can be broken down naturally by microorganisms (bacteria/fungi) in the environment.

What is corrosion, and what is the special name for the corrosion of iron?

Corrosion is a chemical reaction at the surface of a metal with substances in the air; the corrosion of iron is called rusting.

What two substances are needed for iron to rust?

Both oxygen (from the air) and water must be present for iron to rust.

State the chemical reactivity order of these metals from most to least reactive: copper, magnesium, zinc, iron.

Magnesium $>$ zinc $>$ iron $>$ copper (magnesium most reactive, copper least).

What do reactive metals like magnesium and zinc produce when they react with dilute acid?

A salt and hydrogen gas, e.g. $\ce{Mg + 2HCl -> MgCl2 + H2}$.

How can you test for hydrogen gas?

A lighted splint held at the mouth of the test tube gives a squeaky "pop" with hydrogen gas.

What is the reaction of a metal with oxygen called, and what is the product?

It is called oxidation; the metal forms a metal oxide, e.g. $\ce{2Mg + O2 -> 2MgO}$.

Name two methods used to prevent iron from rusting.

Any two of: painting, oiling/greasing, coating with plastic, galvanising (coating with zinc), or electroplating.

What is an alloy? Give an example.

An alloy is a mixture of a metal with one or more other elements to improve its properties, e.g. steel (iron + carbon) or brass (copper + zinc).

Why are fertilisers added to soil?

They replace essential elements (such as nitrogen, phosphorus and potassium) used up by crops, helping plants grow faster and increasing crop yield.

What environmental problem can be caused by fertilisers washing into rivers and lochs?

Algal bloom / eutrophication — excess nutrients cause rapid algae growth that uses up oxygen in the water, killing fish and other aquatic life.

What is the difference between a dependent (measured) and an independent (changed) variable in an experiment?

The independent variable is the one you deliberately change; the dependent variable is the one you measure as a result. All other variables are kept constant (controlled).

Why should an experiment be repeated and an average taken?

Repeating measurements and averaging improves reliability and reduces the effect of random errors, giving more trustworthy results.