Chemical Changes (except electrolysis)

Question 1

In aqueous solutions, what do acids produce?
In aqueous solutions, what do alkalis produce?

Answer 1

Hydrogen ions - acids
Hydroxide ions - alkalis

Question 2

What’s the difference between a base and an alkali?

Answer 2

Bases which are soluble in water are known as alkali. Some bases do not dissolve in water.

Question 3

What is below hydrogen in the reactivity series?

Answer 3

Copper
Silver
Gold
Platinum

Question 4

What is the product formed when acids react with a metal?

Answer 4

acid + metal —> salt + hydrogen

Question 5

What is the product formed when an acid reacts with a metal carbonate?

Answer 5

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

Question 6

What makes an acid strong or weak?

Answer 6

Strong acids fully ionise in an aqueous solution
Weak acids partially ionise in an aqueous solution

Question 7

What makes an acid concentrated or dilute?

Answer 7

Concentrated acids have a higher amount of acid molecules in a given volume of a solution.
Dilute acids have a lower amount of acid molecules in a given volume of a solution.

(even if the strength of the acid is the same)

Question 8

metal + oxygen —>

Answer 8

metal oxide

Question 9

What happens when you put an acid in an aqueous solution?

Answer 9

It ionises (splits) and produces hydrogen.
e.g, HCl produces hydrogen ions and chloride ions

Question 10

Recite the neutralisation reaction.

Answer 10

acid + base —> water + salt

Question 11

List the steps for obtaining copper sulfate crystals from copper oxide/carbonate and sulfuric acid.

Answer 11

• Set up the apparatus (gauze, bunsen burner, tripod, heatproof mat, solution inside the beaker) to do this reaction
• Pour in the sulfuric acid. It should be fully used up at the end of the reaction as it is a limiting reactant
• Heat the sulfuric acid untill it is nearly boiling with the bunsen burner
• Pour in some copper oxide/carbonate and stir it in. Eventually, the solution should turn blue
• Continue to pour in more and stir it untill there is excess remaining at the bottom of the solution.
• To crystalise, set up the crystilation apparatus (w/ evaporating basin)
• Gently heat the solution untill only half remains
• Cool the remainer of the solution to room temperatue and store in a cool, dry place.
• Gently pat the crystals dry.

Question 12

Name 3 weak acids and 3 strong acids:

Answer 12

Weak:
ethanoic acid
citric acid
carbonic acid

Strong:
hydrochloric acid
nitric acid
sulfuric acid

Question 13

What is an order of magnitude in terms of the pH scale?

Answer 13

As the pH scale decreases by 1 unit, the concentration of hydrogen ions increaces by 10x

Question 14

Recite the steps of the titration practical of (e.g,) nitric acid reacting with 25cm³ lithium hyroxide.

Answer 14

• Use a pippet to transfer 25cm³ of lithium hydroxide to a conical flask*(the conical flask reduces splashing) *
• Allow the liquid to drain out of the pippet, rather than blowing on it, so as to pour out the correct volume
• Add 5 drops of an indicator (e.g, methyl orange or phenolphthalein)
• Place the conical flask on a white tile (so as to see the color change clearly)
• Fill a burette with nitric acid
• Pour the nitric acid into the conical flask
• Swirl the solution (to ensure they mix)
• Once a color change is noticed, pour the nitric acid drop by drop untill the solution turns neutral
• Read the volume of acid added by the burette by becoming eye level to read the measurment from the bottom of the meniscus

carry out the practical again so as to calculate the mean of the results

Question 15

What is the formula used in titration calculations?

Answer 15

number of moles = concentration x volume