National 5 Chemistry | Unit 1 Part 4 | Acids and Bases

Acid

Acids are substances which ==produce H+ (aq) ions== when ==dissolved in water==.

Alkali

Alkalis are substances which ==produce OH- (aq) ions== when ==dissolved in water==.

Base

A base is a compound that ==neutralises an acid==. Bases that are dissolved in water are alkalis.

When a solution has pH < 7, it is:

Acidic

When a solution has pH > 7, it is:

Alkaline

When a solution has pH = 7, it is:

Neutral

If \[H+\] = \[OH-\] then pH…

pH = 7 (neutral)

If \[H+\] > \[OH-\] then pH…

pH < 7 (acidic)

If \[H+\] < \[OH-\] then pH…

pH > 7 (alkaline)

An acidic solution will contain more _____ ions than _____ ions.

Hydrogen (H+); hydroxide (OH-)

An alkaline solution will contain more _____ ions than _____ ions.

Hydroxide (OH-); hydrogen (H+)

In neutral solutions (pH 7), the concentration of hydrogen ions is _____ to the concentration of hydroxide ions.

Equal

In water and aqueous solutions, there is an _____ between hydrogen and hydroxide ions and _____ molecules.

Equilibrium; water

Elements react with oxygen to form…

Oxides

What type of solution is formed when a non-metal oxide dissolves in water?

Non-metals form ==acidic== solutions.

What does hydrogen (non-metal) form when it is burned to form an oxide?

Hydrogen burns to form an oxide with a ==pH of 7==.

Some metal oxides are soluble in water. When these dissolve, they form _____ _____, which are _____.

Metal hydroxides; alkaline

Ammonia is a clear, colourless, pungent gas that dissolves in water to form _____ _____, which is an _____ solution.

Ammonium hydroxide; alkaline

The chemical equation for ammonia dissolving in water is:

NH3 + H2O → NH4OH

Explain the difference between ammonia and ammonium:

Ammonia (NH3) is a covalent molecular, while ammonium (NH4) is an ion.

Do insoluble metal hydroxides alter the pH of water?

==No==, insoluble metal hydroxides don’t alter the pH of water.

Which element is common to all acids?

Hydrogen (H+)

Acids have what type of bonding and why?

==Acids are ionic== because they can ==conduct electricity==.

Do dilute acids conduct electricity?

==Yes==, dilute acids conduct electricity.

What type of particle has to be present in order for a solution to conduct electricity?

==Ions== must be present.

Electrolysis

The ==separation of ionic compounds== into its elements by running an electric current through it.

In the electrolysis of an acid, what gas is produced at the negative electrode?

==Hydrogen==, because it has a ==positive charge== and are therefore attracted to the negative electrode.

The ion-electron equation showing the formation of hydrogen gas is:

2H+ (aq) + 2e- → H2(g)

Explain why dry pH paper is unaffected by hydrogen chloride gas but the gas turns moist pH paper red:

Hydrogen chloride gas is a ==covalent molecular==, so when it comes in contact with moisture the ==covalent bonds break to form ions==.

The concentration of H+ (aq) ions _____ and the pH _____ towards _____ as an acid is diluted.

Decreases; increases; 7

The concentration of OH- (aq) ions _____ and the pH _____ towards _____ as an alkali is diluted.

Decreases; decreases; 7

What type of bonding and structure is in water?

Water is a ==covalent molecular==.

Water is expected not to conduct electricity because it has no electrons free to move. Why can pure water conduct electricity?

There are a small number of ions present in pure water, as H2O can be broken down to ==H+ and OH- ions==.

The equation for the dissociation of water is:

H2O (l) ⇋ H+ (aq) + OH- (aq)

Neutralisation

When a base and an acid react to form a neutral solution (water) and a salt.

The equation for neutralisation is:

Acid + alkali → salt + water

Spectator ion

An ion that is present in a reaction but is not involved.

Ionic equations can be written for:

\-Neutralisation reactions

\-Precipitation reactions

The equation for the reaction of acids with metal oxides is:

Acid + metal oxide → salt + water

The equation for the reaction of acids with metal carbonates is:

Acid + metal carbonate → salt + water + carbon dioxide