F4chem acids and bases 40point

1.aqueous alkalis react with carbon dioxide.

alkali + CO2 --> CO3 +H2O

e.g.2NAOH(aq) + CO2 (g) --> CaCO3(s) + H2O(l)

圖片參考:http://imgcld.yimg.com/8/n/HA08177970/o/7012031800...

Referring to the diagram above,what is the meaning of the last sentence,"it

can be used for the absorption of carbon dioxide in gas analysis."

Can anyone explain it?

2.

圖片參考:http://imgcld.yimg.com/8/n/HA08177970/o/7012031800...

The above diagram shows the electrolysis of sodium chloride in chlor-alkali industry.It manufactures hydrogen,chlorine,sodium hydroxide and other products.

i.Why titanium and nickel are used as anode and cathode respectively?

ii.Nickel forms cation,how can it attract H+ ions?

3.Concentrated hydrochloric acid is a volatile liquid,which gives out white

fumes(acid mist:hydrogen chloride gas).Cocentrated nitric acid has the

same property but concentrated sulphuric acid doesn't.

圖片參考:http://imgcld.yimg.com/8/n/HA08177970/o/7012031800...

i.Hydrogen chloride dissolves in water to form hydrochloric acid.

Why it gives out fumes when it is exposed to the air?It has already

dissolved in water.

iiWhy this phenomenon will not occur in dilute hydrochloric acid?

iii.What is the meaning of volatile?My textbook said"Concentrated sulphuric

acid has a high boiling point,so it doesn't give an acid mist when exposed

to air."Why a liquid with high boiling point is not volatile?

4.Concentrated acids and alkalis are very corrosive especially when they are

hot.Why?

更新:

5.Hydrogen chloride is a covalent molecular compound.

In the presence of water,it ionizes to form H+(aq)

i.Actually H+ and Cl- can react with each other to form hydrogen chloride

with a giant ionic structure(i.e ionic compound)

Why would they attract each other by covalent bonds?

更新 2:

ii.Mg(OH)2 (s) + 2HCl (aq) --> MgCl2(aq) +2H2O(l)

Mg(OH)2 (s) + 2H+(aq) +2Cl- (aq) --> Mg2+(aq) 2Cl-(aq) +2H2O(l)

2Cl- in both sides are cancelled.

Is 2H+(aq) reacts with 2OH-(aq) to form 2H2O(l)?

But water is a covalent molecular compound instead a ionic compound.

更新 3:

iii.I don't understand the process of ionization.How do ions form in a covalent

compound after adding it to water?

更新 4:

6.Fizzy drink tablets should be stored in a cool and dry place.

The aim of storing in a dry place is to reduce the contact of tablets with

moisture in the air.How about "cool"?

更新 5:

7.How to determine the basicity of an acid.

For example,ethanoic acid(CH3COOH).It is monobasic although it has two

hydrogen atoms in the molecule.Are there any methods to find the basicity

of some acids such as methanoic acid(HCOOH) and oxalic acid (COOH)2

更新 6:

8.From my book:

Baking powder for making cakes is usually a mixture of solid acid and sodium

hydrogencarbonate.In making cakes,water and a little baking powder are added to flour.

The flour paste is then heated in an oven.Baking powder gives CO2 gas due to following

two reactions:

更新 7:

H+(aq) + HCO3-(aq) --> CO2(g) + H2O(l)

2NaHCO3(s) --heat--> Na2CO3(s) + CO2(g) + H2O(l)"

更新 8:

i.NaHCO3 has dissolved in water already to give CO2 and H2O in the first reaction.

Why there is a second reaction?

ii.Na2CO3 is soluble in water,why it is (s) instead of (aq)?

2 個解答

評分
  • 匿名
    9 年前
    最愛解答

    I'll try to answer all of them...

    however, some of them is not sure

    I'll give them a bracket *()

    1.

    In some experiments

    We may need to absorb CO2

    It means that the reaction cannot be a standard test for CO2

    [cannot tell you is it CO2 or not]

    however, it can absorb CO2

    for example

    CH4 + 2O2 -> CO2 + 2H2O

    if you want to know the amount of CO2

    you may need NaOH [usually solid] to absorb it and measure its mass

    new mass - original mass = mass of CO2

    2.

    (Titanium and Nickel are both used as catalyst in order to speed up reaction)

    In electrolysis, neglect the ions formed [when the electrode is inert...]

    Ni is not used as form ions

    therefore, just consider the charge of the rod

    "H+ goes to cathode [cations go to cathode which is -vely charged in electrolysis]"

    3.

    This only happen in conc. HCl

    this is mainly because the conc. is too high and it may escape from the solution

    Besides, HNO3 will decomposed in this way

    4HNO3 -[Energy]-> 4NO2 + 2H2O + O2

    this is the reason why it is needed to store in a brown reagent bottle

    (I do think this is because the strong force between water molecule and H+ and Cl- ; Water is quite polar and it has H is slightly positive while O is slightly negative, this can attract H+ and Cl- well)

    Volatile means a substance will turn into gas form

    Just like alcohol, it will volatile and decrease in volume

    however, it is because the b.p. of alcohol is low

    In the case of H2SO4

    it is a liquid in pure form [HCl and NO2 is in gas form and they will form acid after dissolution]

    Therefore, even water is not present, it is a liquid

    as a result, there will not be "volatile"

    4.

    By collision theory

    Reactions speed up with the increase of temperature

    Besides, some acid have more properties when hot

    For example, H2SO4 have the ability of oxidation when hot

    Oxidizing is also one of the acidic property

    ---

    cannot post all....

    you may give me your email

    資料來源: SELF
  • 9 年前

    5. ionic bond is formed only when the components' difference in electronegativty is very hig

    electronegativity of H=2.1

    Cl=3.2

    difference=1.1

    compare to NaCl

    Na=0.9

    Cl=3.2

    difference=2.3

    therefore, the H-Cl bond isn't ionic(you may say it is very polar but not ionic at all !)

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