Nat5 Chemistry - Acids + Bases

What is the pH scale?

The pH scale gives an indication of the hydrogen ion concentration. It is a continuous scale that runs from 0 - 14 with pure water and neutral solutions having a pH of 7.

What do universal indicator and pH paper measure?

They measure how much acid or aqueous alkali is in a solution.

What device should you use if you need a more accurate measurement of acidity and alkalinity?

A pH meter

What is an example of an everyday acid?

Vinegar

What is an example of an everyday alkali?

Laundry detergent/baking soda

What would happen if you put a dry substance on pH paper?

Nothing, because dry solids and gases do not change the colour of pH paper.

What is the chemical name for water?

Hydrogen oxide

What bonds hold water together?

Covalent bonds

Why does water conduct electricity?

Water does conduct electricity poorly because water doesn't just consist of molecules but it also consists of a small number of ions.

What equation demonstrates how water conducts electricity by the way a small number of molecules split up?

H20 (l) ⇌ H+ (aq) + OH− (aq)

What does it mean when water "dissociates"

When water disociates, a molecule of water splits into its ions.

What does the ⇌ symbol mean?

The ⇌ symbol means that the reaction is reversible and occurs in both directions.

What can each water molecule form?

Each water molecule can form one hydrogen ion and one hydroxide ion

What is the concentration of hydrogen ions compared to the concentration of hydroxide ions in water?

The concentration of hydrogen ions and the concentration of hydroxide ions is the same in water since it is neutral.

What is the pH of acidic solutions?

Acidic solutions have a pH of less than 7. Acids have more hydrogen ions than hydroxide ions.

What is the chemical formula of hydrochloric acid?

HCl (aq)

What is the chemical formula of sulfuric acid?

H2SO4 (aq)

What is the chemical formula of nitric acid?

HNO3 (aq)

What is the chemical formula of phosphoric acid?

H3PO4

What pH do alkaline solutions have?

Alkaline solutions have a pH greater than 7. Alkaline solutions have more hydroxide ions than hydrogen ions.

What is the chemical formula of sodium hydroxide solution?

NaOH (aq)

What is the chemical formula of potassium hydroxide solution?

KOH (aq)

What is the chemical formula of calcium hydroxide solution?

Ca(OH)2 (aq)

How is a solution formed?

A solution is formed when a solute dissolves in a solvent.

What is a solvent?

the substance in which the solute dissolves

What is a solute?

the substance that is dissolved

What is a concentrated solution?

A concentrated solution is a solution which has a lot of the dissolved solute in a certain volume of solvent.

How can you dilute a solution?

By adding water

What happens if you add water to an acid?

It will be a more dilute acid. It will decrease the concentration of hydrogen ions. It will increase the pH.

When are acids formed?

Acids are formed when soluble non-metal oxides dissolve in water.

What is a base?

A base is a substance that neutralises an acid.

What can bases be?

Bases can be metal oxides, metal hydroxides, and metal carbonates. These are ionic compounds, and, therefore, solids at room temperature.

What is an example of a common base that is a gas?

Ammonia

What are alkalis?

Alkalis are solutions of soluble bases.

How are most alkalis made?

Most alkalis are made by dissolving a metal oxide in water - though only those in Group 1 are very soluble.

word equation for acids

(soluble) non-metal oxide + water -----> acid

word equation for alkalis

(soluble) metal oxide + water -----> metal hydroxide

What is neutralisation?

Neutralisation is the reaction of an acid with a base to form water. Salt is also formed in this reaction.

Examples of everyday neutralisation reactions

Vinegar on a wasp sting / treatment of stomach indigestion

word equation of acid and metal oxide neutralisation

acid + metal oxide -----> salt + water

word equation of acid and metal hydroxide neutralisation

acid + metal hydroxide -----> salt + water

word equation of acid and metal carbonate neutralisation

acid + metal carbonate -----> salt + water + carbon dioxide

What are spectator ions?

Spectator ions are ions that remain the same on the reactant and product side of the equation.

Why do we remove spectator ions in an equation?

To only show the reacting species

What is a precipitation reaction?

A precipitation reaction is when two solutions are mixed and a solid is formed.

What is the solid formed in a precipitation reaction called?

A precipitate

What do you do if you have more than one ion of a substance that is not a compound?

You put the number in front of it as you cannot use brackets. E.g 2H+

How does the precipitate get its name?

The precipitate gets its name from the metal ion in one solution and the negative ion in the other.

E.g silver nitrate (aq) + sodium chloride (aq) -----> silver chloride (s) + sodium nitrate (aq)

What can volumetric titrations be used for?

Volumetric titrations can be used to produce a soluble salt. They are a very accurate method for carrying out neutralisation reactions. In an acid-base titration, the concentration of the acid or base can be determined by accurately measuring the volumes used in the neutralisation reaction.

What two pieces of equipment are needed for accurate titration?

Burette and pipette

When is neutralisation complete?

Neutralisation is complete when the hydrogen ions from the acid have been cancelled out with the same number of hydroxide ions from the alkali.

What does an indicator do?

An indicator can be added to show the end point of the reaction through a colour change.

Why is the actual titration repeated multiple times?

To give a more reliable value for the volume to be used in the calculation. The first titration is used to find the rough volume and is often incorrect. With this rough volume known, a second and third titration can be carefully carried out, adding acid very slowly near the end point.

What is the actual volume used in the calculation?

The concordant values

What are the concordant values?

The concordant values are values that are within 0.2 cm³ of each other and the rough volume is ignored.