Acids, Alkalis, And Salts (Y11)

Question 1

What colour is litmus in acid and alkali?

Answer 1

Red in acid

Blue in alkali

Question 2

What colour is phenolphthalein in acid and alkali?

Answer 2

Clear in acid

Pink in alkali

Question 3

What colour is methyl orange is acid and alkali?

Answer 3

Pink/red in acid

Yellow in alkali

Question 4

What are acids?

Answer 4

• acids neutralises bases
• they dissolve in water
• they release H+ ions

Question 5

What do the number of H+ ions lost tell you about the acid?

Answer 5

• strong acids disassociate their H+ ions fully
• weak acids disassociate their H+ ions partially
• pH measures the number of H+ ions lost

Question 6

What are alkalis?

Answer 6

• dissolve in water

* release hydroxide(OH-) ions

Question 7

What are bases?

Answer 7

• don’t dissolve in water
• neutralise acids
E.g. Copper or iron oxide, zinc carbonate

Question 8

explain the add excess base method

Answer 8

Add excess base: (e.g. Making copper sulphate)

1. Add excess base to the acid until no more dissolves (warm acid if necessary)
2. Filter off excess base
3. Obtain dry salt from the solution

Question 9

Explain the titration method

Answer 9

Titration: (e.g. Hydrochloride acid and sodium hydroxide)

1. Measure out the alkali using a pipette, and pour into conical flask
2. Add acid via a Burnett to alkali, slowly, occasionally mixing, until indicator is neutral
3. Add the same volume of acid to the same amount of alkali WITHOUT indicator
4. Obtain dry salt from solution

Question 10

Explain the precipitation method

Answer 10

Precipitation: (e.g. Making lead iodide)
1. Make two solutions each containing an ion of the salt you want to make (these must be soluble)
2. Mix the solutions
3. Filter off the precipitate- the insoluble salt
4. Wash the precipitate with distilled water to remove any other salt solutions
5. Dry on filter paper or warm gauze
Example: sodium iodide + lead nitrate ➯ lead iodide + sodium nitrate
Colourless solution + colourless solution ➯ yellow precipitate + colourless solution

Question 11

What salts are soluble?

Answer 11

All nitrates
All chlorides except silver and lead
All sulfates except barium lead and calcium
Potassium, sodium and ammonium carbonates

Question 12

What salts are insoluble?

Answer 12

Silver chloride, lead chloride
Barium sulphate, lead sulphate, calcium sulphate
All carbonates except potassium, sodium, and ammonium

Question 13

How do you know what method to use to make a salt?

Answer 13

1. Is the salt soluble?
No: precipitation
Yes:
2:Is the base soluble? (I.e. Is it a hydroxide)
No: add excess base
Yes: titration

Question 14

How des the add excess base method work?

Answer 14

• mix acid and base
• add excess base until it no more dissolves
• filter
• heat to get rid of some water
• leave to crystallise
• wash w distilled water to get rid of any remaining acid/alkali

Question 15

How does titration work?

Answer 15

• measure out alkali using pipette and pour into conical flask
• add acid via a burette slowly, mixing occasionally, until indicator turns neutral
• repeat but w/o indicator
• heat solution to get rid of most of water
• filter to remove water
• allow to crystallise

Question 16

How does precipitation work?

Answer 16

• make two soluble solutions each containing an ion of the salt you want
• mix
• filter off the precipitate- the insoluble salt
• wash w distilled water to get rid of any other salt solutions
• dry on filter paper/warm gauze

Question 17

What is concentration?

Answer 17

Concentration (moldm-3) = moles / volume

Question 18

How do you work out concentration calculations?

Answer 18

• balance eq
• write in what we know and what we must find out
• work out mols of known
• use ole ratios to find mols of unknown
• using vol of unknown find conc of unknown