Acid and base

Question 1

how to dry a solid from aq solution

Answer 1

1. filter the mixture
2. wash it with DI water
3. dry in oven

Question 2

what is standard solution

Answer 2

solutions with accurately known concentrations

use to determine concentrations of other reagent

Question 3

why back titration is needed

Answer 3

no suitable indicator
reaction rate is slow
insoluble in water

Question 4

why its not appropriate to rinse the conical flask with acid

Answer 4

Some H+ ions remain in the flask, and more alkali than actually required is used to reach the titration end point.

Question 5

how to prepare a 250cm3 of standard solution

Answer 5

to dissolve the solid by adding deionized water to the solid in a beaker
Transfer the solution with rinsing with deionized water into a 250cm3 volumetric flask and add deionized water until the lower meniscus of water level reaches the graduation mark of the flask.
Shake thoroughly.

Question 6

how to perform crystallisation

Answer 6

Evaporate the filtrate, allow solid crystallize out

Collect crystals and then dry it with a filter paper.

Question 7

what is alkali

Answer 7

Alkali is water soluble substance reacts with acid to give salt and water only

Question 8

is all acidic compound contain H?

Answer 8

no
acidic =/= acid
CO2 SO2 is acidic

Question 9

what is titrant analyte and titre

Answer 9

titrant in burette
analyte in conical flask
titre is the volume/concentration of the solution determined

Question 10

NH4Cl acidic or alkaline?

Answer 10

acidic

Question 11

XHSO4 acidic or alkaline?

Answer 11

acidic

Question 12

is NaOH/ Na2O a salt

Answer 12

no
OH- and O2- are not come from anion of any acid
salt = metal cation or NH4+ + anion formed from acid

Question 13

what is basicity?

Answer 13

basicity of an acid is the maximum number of H+ ion which can be produced from 1 acid molecule / the number of ionizable H atom in one acid molecule

Question 14

what shd be done when conc acid spill to the skin

Answer 14

wash it with running cold water

Question 15

how to dilute a conc acid

Answer 15

add conc acid slowly to a large amount of water with constant stirring

if water is added to conc acid, a lot of heat is released and the heat can cause splashing out of the corrosive acid solution.

Question 16

difference between drying agent and dehydrating agent

Answer 16

drying agent –> physical change (CaO / anhydrous CaCl2)

dehydrating agent –> chemical change (conc H2SO4)

Question 17

which gas does anhydrous CaCl2 cannot dry

Answer 17

NH3

Question 18

why use an inverted funnel when passing HCl gas to water

Answer 18

prevent sucking back of water as HCl is soluble in water

Question 19

Na2SO3 acidic or alkaline?

Answer 19

alkaline

Question 20

NaHSO3 acidic or alkaline?

Answer 20

alkaline

Question 21

why theres no observable change when Ca2+ + NH3

Answer 21

OH- concentration too low in NH3

Question 22

why the boiling tube should be tilted downward in an experiment

Answer 22

prevent the condensed water from flowing back into the hot boilng tube which would cause cracking of the tube

Question 23

how NH3 can be collected

Answer 23

upward delivery as NH3 is less dense than air

or gas syringe (百搭）

Question 24

why cant we use acid when alkali spill to our skin

Answer 24

neutralization is highly exothermic

it causes burning of our skin

Question 25

what does the strength of acid depends on?

Answer 25

the degree of ionization to form H+

Question 26

what does the strength of alkali depends on?

Answer 26

the degree of ionization to form OH-

Question 27

factors that affect the pH of an aicd

Answer 27

concentration strength (strong or weak) basicity

Question 28

why some soil is acidic

Answer 28

acid rain | acidic fertiliser

Question 29

what can be used to neutralise acidic soil

Answer 29

CaO CaOH CaCO3 as they are not very soluble in water so it wont make the soil too alkaline

Question 30

why nitrogen is present in fertiliser

Answer 30

nitrogen is required for the formation of amino acid

Question 31

why we should wash the salt prepared with cold DI water

Answer 31

to remove any soluble impurity | help reduce the loss of the salt

Question 32

what is volumetric analysis

Answer 32

its a method used to determine quantity or concentration of a substance by titration

Question 33

what is requirement of primary standard

Answer 33

highly pure stable in air and solution does not absorb water or carbon dioxide in air

Question 34

why conc H2SO4 cant be primary standard

Answer 34

it absorb water so it cannot weigh out accurately

Question 35

how to prepare a primary standard

Answer 35

from a solid | from diluting a more concentrated standard solution

Question 36

titration of solution A against solution B | A or B in burette?

Answer 36

B in burette | A in conical flask

Question 37

burette must hold

Answer 37

strong acid/ strong alkali

Question 38

how the end point between the neutralization of weak acid and weak alkali be determined

Answer 38

measuring the temperature change and plot a graph

Question 39

why diluting chemical in titration

Answer 39

to save chemicals

Question 40

what is the state of citric acid in room temperature

Answer 40

solid

Question 41

describe the procedure that should be followed when preparing a burette containing HCl

Answer 41

rinse the burette with distilled water then with the hydrochloric acid fill the burette with the hydrochloric acid, making sure that the space between the tap and the tip of the burette is filled with the acid so there is no air bubbles in the burette Also, the meniscus should not be above the zero mark