5 - acids

Question 1

Define acid

Answer 1

An acid is a proton donor

Question 2

How do we know if a substance is an acid if we have the chemical formula?

Answer 2

It contains H+ ions

Question 3

What happens when you put an acid in water?

Answer 3

It releases H+ ions and the other negative ion

Question 4

What are the chemical formulae of the 4 main acids?

Answer 4

Hydrochloric = HCl

Sulphuric = H~2 SO~4

Nitric = HNO~3

Ethanoic = CH~3 COOH

Question 5

What does dissociate mean?

Answer 5

When an acid is put into water and the ions are released into the water

Question 6

What makes an acid strong or weak?

Answer 6

A strong acid completely dissociates

A weak acid partially dissociates

Question 7

What is a H+ ion physically?

Answer 7

Just a proton

Question 8

Define base

Answer 8

A proton accepter

Question 9

What are the main examples of bases?

Answer 9

Hydroxides, oxides, ammonia etc.

Question 10

Define alkali

Answer 10

A type of base which dissolves in water to release OH- ions

basically, a hydroxide

Question 11

What is the only common alkaline gas?

Answer 11

Ammonia

Question 12

What happens when ammonia is put in water?

Answer 12

Ammonium ions and hydroxide ions are released

Question 13

Define salt

Answer 13

A substance which is formed when a H+ ion from an acid is replaced by another positive ion (could be metal ion)

Question 14

What happens when a salt and base react?

Answer 14

Salt and water are formed

Question 15

What are the salts formed by the 4 main acids?

Answer 15

Hydrochloric –> chloride

Sulphuric –> sulphate

Nitric –> nitrate

Ethanoic –> ethanoate

Question 16

What is the state of matter of acids, bases and salts?

Answer 16

acids are aqueous

salts are usually aqueous unless specified otherwise

Bases are either aqueous or solids

Question 17

How do the 4 main acids dissociate?

Answer 17

H~2 SO~4 –> 2H+ + SO~4 2-

HCl –> H+ + Cl-

HNO~3 –> H+ + NO~3-

CH~3 COOH –> H+ + CH~3 COO-

Question 18

What is the ionic equation for all reactions between acids and alkalis?

Answer 18

H+ + OH- –> H~2 O

Question 19

What is the ionic equation between acids and bases?

Answer 19

Find the salt and deduce which 2 ions it’s made from

You write that those 2 ions go to the salt

That is the ionic equation

Question 20

What happens when a acid reacts with a metal?

Answer 20

Acid + metal –> salt + hydrogen gas

Question 21

When happens when an acid reacts with a carbonate?

Answer 21

Acid + carbonate –> salt + carbon dioxide + water

Question 22

What happens when an acid reacts with ammonia?

Answer 22

Ammonia + acid –> ammonium salt (and nothing else)

Question 23

What happens when an acid reacts with any other base?

Answer 23

Acid + base –> salt + water

Question 24

Describe how to prepare a standard solution

Answer 24

Weigh the solid accurately

Dissolve the solid in a beaker but don’t fill it

Transfer the solution to a volumetric flask and rinse traces of solution from the beaker to the flask

Carefully fill the volumetric flask to the graduation line (read the meniscus at eye level)

Invert the flask several times to ensure the solution is well mixed

Question 25

Describe the method of titration

Answer 25

Using a pipette, we measure a volume of the standard solution into a conical flask

The other solution is placed in a burette and the volume is recorded

A few drops of indicator is added to the solution in the conical flask

The solution in the burette is added to the conical flask until the reaction has just completed (this is the equivalence point) and we see a different colour

The volume of solution added from the burette is calculated (this is called the titre)

The experiment is repeated until 2 titres are concordant to 0.1 cm^3

The mean titre is calculated to 1 decimal place and only concordant titres are used in the mean

Question 26

Explain the effect on the titre of filling the flask above the graduation line

Answer 26

This would cause the standard solution to be less concentrated

This means the titre volume would be larger in order to neutralise the standard solution

Question 27

Explain the effect on the titre of not inverting the flask

Answer 27

The concentration would now be inaccurate because it wouldn’t be the same throughout the standard solution

This causes the titre to be simply inaccurate

Question 28

Explain the effect of the burette readings being taken from the top of the meniscus

Answer 28

Looking at the readings from above will give less accuracy in the readings because it is harder to differentiate between the different reading marks

This would cause the calculated titre to be less accurate than if the readings were taken at eye level