Unit 1 - Acids and Bases T4

Question 1

pH scale

Answer 1

The pH scale measures the acidity or alkalinity of a solution. A pH less than 7 is acidic. Alkalis dissolve in water to give a pH greater than 7. A pH equal to 7 indicates a neutral solution. It is a measure of hydrogen ion concentration.

Question 2

Bases

Answer 2

A substance that can neutralise an acid.

Question 3

Forming alkali

Answer 3

When a metal oxide/ hydroxide/ carbonate is dissolved in water.
Metal oxide/ hydroxide/ carbonate must be soluble, can be found in data booklet.

Question 4

Forming acids

Answer 4

Dissolve a soluble non metal in water

Question 5

Hydrogen ions

Answer 5

H + Found most abundantly in acids compared to alkalis

Question 6

Hydroxide ions

Answer 6

OH- found most abundantly in alkali compared to acids.

Question 7

Neutral solutions

Answer 7

Have equal no. of hydrogen and hydroxide ions.

Question 8

Acid bonding

Answer 8

Bonds like ionic however hydrogen acts like a metal so loses electron.

Question 9

Alkali bonding

Answer 9

Bonds like ionic hydroxide is non metal so gains electron.

Question 10

Water and neutral solutions

Answer 10

Water molecules can break down into hydroxyl and hydrogen ions. 99% of water is H2O however 1% is hydroxide and hydrogen ions.
It is a reversible reaction as hydroxide and hydrogen ions can form H2O molecules as well.
It is called an equilibrium and is present in water and aqueous solutions.

Question 11

Aqueous solutions

Answer 11

Solution where the solvent is water. Solvent - dissolver.

Question 12

Diluting acids and bases

Answer 12

Adding water to an acid or base will change its pH. Adding water to any substance will add both hydrogen and hydroxide ions as both are present in equal concentrations in water. When an acidic solution is diluted with water the concentration of H+ ions decreases and the pH of the solution increases towards 7, opposite for bases.

Question 13

Neutralisations

Answer 13

the reaction of an acid with a base that results in the pH moving towards 7. It is a useful process that occurs in everyday life such as in the treatment of acid indigestion and the treating of acidic soil by adding lime.
Neutralisation also moves the pH of an alkali down towards seven.
Several different bases can neutralise acids, and water is always produced as a result of these reactions.
During neutralisation the H+ ion from the acid joins with the OH- ion from the alkali. This is why water is formed in these reactions.

Question 14

Equations for neutralisations

Answer 14

Acid + metal oxide ——> salt + water.
Acid + metal hydroxide——> salt + water.
Acid + metal carbonate ——> salt + water + carbon dioxide.

Question 15

Examples of acids

Answer 15

Hydrochloric acid - H+Cl-
Nitric acid - H+(No3)-
Sulfuric acid - H2+(So4) 2-
Phosphoric acid - H3+(Po4)3-

Question 16

Examples of alkalis / bases

Answer 16

Sodium Hydroxide - Na(OH)
Sodium Oxide - NaO
Sodium Carbonate Na2(CO3)

Question 17

Naming salts

Answer 17

To name the salt, the metal ion from the alkali (or base) replaces the hydrogen ion from the acid - (alkali to front, acid to back).

Question 18

Spectator Ions

Answer 18

Ions that are present during reaction but are unchanged by reaction. Can be seen by new state or new compound produced.

Question 19

Titrations

Answer 19

A titration experiment can be carried out to accurately measure the volume of substances that react in chemical reactions. This technique is commonly used in neutralisation reactions and can also be used to calculate an unknown concentration (of either the acid or alkali).

Question 20

Titration apparatus.

Answer 20

Apparatus - white tile, burette, pipette filler and pipette and conical flask.

Question 21

Titration steps

Answer 21

1. If the sample is a solid, it is weighed using an accurate balance, and then dissolved to make up a known volume of solution (usually 100cm3).
2. A pipette is used to measure accurately a volume of this solution - for 3
   example, 10cm . A safety pipette filler is used to draw solution into the
   pipette. This is emptied into a conical flask.
3. A few drops of an indicator may be added to the conical flask. This will show
   a change of colour when the titration is complete. Flask is placed on white tile so colour change can easily be seen.
4. A second chemical is placed in a burette. This other solution is of a chemical
   that will react with the synthesised chemical sample in the conical flask. Often
   the solution in the burette is an acid of a precise, known concentration.
5. The solution from the burette is run into the conical flask. The solution is
   added one drop at a time, with swirling to mix the solutions as the end-point is approached. Eventually, a colour change shows that the correct amount has been added to react completely with the synthesised chemical in the sample.
6. The volume of solution added from the burette is noted. The titration results can then be used to calculate the amount of the synthesised chemical in the sample, and therefore find its purity.

Question 22

Calculations involving titrations

Answer 22

When asked to find a good volume of unknown solution disregard rough titre as it is unreliable. Titration volumes within 0.5 cm3 are considered to be concordent.

Question 23

Common household acids

Answer 23

Vinegar, citric acids.

Question 24

Common household alkalis.

Answer 24

Oven cleaner, drain unblocker.

Question 25

Conductivity on acids and alkalis.

Answer 25

They conduct as ions are free to move, higher concentration of ions means that it’ll conduct better. Conductivity decreases as pH of solution moves toward 7. I.e pH1 will conduct better than pH6, pH 12 will conduct better than pH 5.

Question 26

Salts

Answer 26

Ionic substances that can be produced by neutralisation reactions.