Salts

Question 1

what is the solubility rule for nitrates?

Answer 1

all nitrates are soluble

Question 2

what is the solubility rule for SPA salts?

Answer 2

all SPA salts are soluble

Question 3

what are SPA salts?

Answer 3

Sodium
Potassium
Ammonium

Question 4

what is the solubility rule for chlorides?

Answer 4

all chlorides are soluble except lead (II) chloride and silver chloride

Question 5

what is the solubility rule for sulfates?

CLB

Answer 5

all sulfates are soluble except for calcium sulfate, lead (II) sulfate and barium sulfate (CLB)

Question 6

what is the solubility rule for carbonates?

Answer 6

all carbonates are insoluble except for SPA salts

Question 7

if the salt insoluble, what is the method of preparation?

Answer 7

precipitation

Question 8

if the salt is soluble, what are the two methods of preparation?

Answer 8

• acid with excess insoluble reagent

- titration

Question 9

if the salt is soluble but not a SPA salt, what is the method of preparation?

Answer 9

acid with excess insoluble reagent (AIR)

Question 10

if the salt is a soluble SPA salt, what is the method of preparation?

Answer 10

titration

Question 11

what is the condition for precipitation?

Answer 11

2 soluble salts

Question 12

what are the two soluble salts?

Answer 12

____ nitrate and sodium ____

Question 13

describe the process of precipitation

Answer 13

• add equal volumes of aqueous ____ nitrate and aqueous ____
• white ppt of ____ is formed
• filter mixture to obtain ____ as residue
• wash residue with distilled water
• dry crystals between pieces of filter paper

Question 14

why must we use two solutions to prepare this insoluble salt? why can we not use the same insoluble reagents as the AIR method?

Answer 14

• salt formed in precipitation method is insoluble, unlike the salt formed in AIR method which is soluble
• because this is an insoluble salt, if we use insoluble reagents instead of the solution, the salt produced will form a layer over the reagents and prevent it from reacting further

Question 15

what is the condition for acid excess insoluble reagent (AIR) method?

Answer 15

acid + metal/ metal hydroxide/metal oxide

Question 16

describe the process of AIR method

Answer 16

• warm acid in beaker, add excess reagent
• filter, heat till solution till saturation
• obtain crystals and dry between filter paper

Question 17

why must an excess insoluble reagent be used?

Answer 17

to ensure that all the acid is fully reacted

Question 18

what observation would show that the reaction has stopped?

Answer 18

when there is no more effervescence

Question 19

why was the mixture filtered off after the reaction had stopped?

Answer 19

to remove all the excess (insoluble reagent) as residue

Question 20

why was the filtrate heated to one third of its volume?

Answer 20

to obtain a concentrated solution of (the salt)

Question 21

why was the filtrate cooled?

Answer 21

to allow the crystals of (the salt) to form

Question 22

to prepare CuSO4, so we can react H2SO4 withe CuO, Cu(OH)2 or CuCO3 but cannot react with Cu metal why?

Answer 22

copper is an unreactive metal and it will not react with H2SO4

Question 23

what is the condition for titration?

Answer 23

acid + alkali

Question 24

describe titration

Answer 24

• pipette out 25.0cm3 of dilute alkali, titrate acid in burette till phenolphthalein indicator till change from pink to colourless, take note of amount of acid added
• repeat titration without indicator and add acid
• heat solution till saturated
• leave to cool, obtain crystals, dry

Question 25

why is titration method chosen for this particular salt?

Answer 25

as the salt and both the reagents used to prepare the salts are soluble

Question 26

what is the purpose of adding the indicator?

Answer 26

to find out the accurate volumes of acid and alkali needed for complete neutralisation

Question 27

why is the indicator not added thereafter?

Answer 27

the indicator would be an impurity in the salt solution