Chemistry 101

[Mohit Pandey]

Hello to all!

My post is related to comparison of Modern Periodic Table and Mendeleev’s Periodic Table.

I am writing in question- answer form. It helps me in understanding the concepts more clearly.:

 

Why Mendeleev’s choice of formulae of compounds as the basis for deciding the position of an element in his table was a good one? How would this lead to elements with similar chemical properties being placed in the same group?

 

Mendeleev’s choice of formulae of compounds as the basis for deciding the position of an element in his table helped him in determining the valency of elements He placed elements whose formulae of oxides and hydrides were similar in the same group. Elements having same valence electrons have similar chemical properties. The position of an element in the periodic table tells us about the chemical reactivity. The valence electrons determine the kind and number of bonds formed by an element.

 

Am I correct?

[modest]

Are tannic acid and citric acid "humic acids" that would help sandy soil hold water?

 

Do Humic Substances Bolster Water and Nutrient Availability? - TurfGrass Trends

 

Tar

MA

 

I think you’re right, I think citric acid is good at binding metals (and nutrients) from water. I think this is the property of humic acid that plants are rather fond of. I’m sure there is more going on in humus with a lot of proteins, amino acids, and complex organic molecules. But, you are correct - Plants that are metal deficient are given a fertilizer solution of citric acid with metal ions because the acid will chelate (bind) the metals allowing them to be absorbed by the plant.

 

-modest

[learnin to learn]

wow i didnt know that!

[Mohit Pandey]

Nitric acid - Wikipedia, the free encyclopedia

Being a powerful oxidizing agent, nitric acid reacts violently with many organic materials and the reactions may be explosive. Depending on the acid concentration, temperature and the reducing agent involved, the end products can be variable. Reaction then takes place with all metals except the precious metal series and certain alloys. As a general rule of course, oxidizing reactions occur primarily with the concentrated acid, favouring the formation of nitrogen dioxide (NO2).

 

Cu + 4HNO3 → Cu(NO3)2 + 2NO2 + 2H2O

The acidic properties tend to dominate with dilute acid, coupled with the preferential formation of nitrogen oxide (NO).

 

3Cu + 8HNO3 → 3Cu(NO3)2 + 2NO + 4H2O

Since nitric acid is an oxidizing agent, hydrogen (H2) is rarely formed. Only magnesium (Mg) and calcium (Ca) react with cold, dilute nitric acid to give hydrogen:

 

Mg(s) + 2HNO3 (aq) → Mg(NO3)2 (aq) + H2 (g)

Ok . So it oxidises H2 produced to water. can anyone tell me the chemical equation with zinc, iron, etc in two stages? In first, hydrogen is produced and then in second, hyrogen is oxidised to water.

[modest]

Ok . So it oxidises H2 produced to water. can anyone tell me the chemical equation with zinc, iron, etc in two stages? In first, hydrogen is produced and then in second, hyrogen is oxidised to water.

 

 

Only magnesium and I guess ??calcium?? reduce the hydrogen ion with H2 and NO3 as products:

Red reduces blue:

Mg(s) + 2H+(aq) + 2NO3(aq) --> Mg2+(aq) + 2NO3-(aq) + H2(g)

 

Other metals reduce the NO3 ion instead of the H ion with water and (NO2, NO, N20 OH or NH4... depending on the metal) being a product:

Cu(s) + 4 H+(aq) + 2 NO3(aq) --> Cu2+(aq) + 2 NO2(g) + 2 H2O(l)

[Mohit Pandey]

I have two questions-

1. Chlor-Alkali Porcess

WHen electricity is passed through brine, then Cl2 is given off at anode and

H2 at cathode.

2Nacl + H2O---H2 + Cl2+ 2NaOH

 

Electrolytic Reduction

Sodium is obtained by electrolysis of its molten chloride. Na is deposited at cathode and Cl is libeated at anode .

 

Is there any difference between the two situations? Isn't the reactant(initial substance) same in both?

 

2.Metals act as reducing or oxidising agent? Non-metals act as reducing or oxidising agent ?

I have read about reduction and oxidation reaction in terms of loss or gain of hydrogen and oxygen only, not in terms of loss or gain of electrons. Please try to explain such that a student of Higher School can understand.

[modest]

I have two questions-

1. Chlor-Alkali Porcess

WHen electricity is passed through brine, then Cl2 is given off at anode and

H2 at cathode.

2Nacl + H2O---H2 + Cl2+ 2NaOH

 

Electrolytic Reduction

Sodium is obtained by electrolysis of its molten chloride. Na is deposited at cathode and Cl is libeated at anode .

 

Is there any difference between the two situations? Isn't the reactant(initial substance) same in both?

 

The reactants are different. In the electrolysis of molten NaCl there is no water - it is molten sodium chloride. This would obviously mean there can be no hydrogen gas produced or sodium hydroxide. This is why it's always important to put (aq) in your equations when they are in solution - it often makes a difference. I notice you didn't do that above - also, your H20 needs balanced on the left side (sorry, I used to tutor chemistry)

 

In the chlor-alkali process the sodium chloride is in a water solution (brine). There is also the practical difference of a membrane in the chlor-alkali process but that is probably a bit beyond the point.

 

2.Metals act as reducing or oxidising agent? Non-metals act as reducing or oxidising agent ?

I have read about reduction and oxidation reaction in terms of loss or gain of hydrogen and oxygen only, not in terms of loss or gain of electrons. Please try to explain such that a student of Higher School can understand.

 

Redox reactions can be very confusing. Oxidizing does not always mean adding oxygen and reducing does not always mean adding hydrogen. The reducing agent can be anything that gives electrons to something else. The oxidizing agent can be anything that takes electrons from something else. Actually, I would honestly suggest you wait to learn redox in class if it is something you haven't started yet. I only say this because I'm afraid I will confuse you with a bad explanation. I just checked the wikipedia article on redox and it's quite good. If you can't wait, that would be a good place to start. But, let me warn you - it's something you've got to spend quite a bit of time on before you know it intuitively and nothing beats a good teacher with a chalkboard.

 

- modest

[Michaelangelica]

ligands are atoms or molecules that share its electons with a central ion.

Is that fair to other thingies?

 

PS modest

Thanks muchly (I can't give you more rep as mean, tight A*S*D, B**t*rd* wont let me)

I don't relaly understand; but it sounds GREAT!

[modest]

ligands are atoms or molecules that share its electons with a central ion.

Is that fair to other thingies?

 

Isn't it all just a big fight for electrons, this - chemistry :(

 

PS modest

Thanks muchly (I can't give you more rep as mean, tight A*S*D, B**t*rd* wont let me)

I don't relaly understand; but it sounds GREAT!

 

You are too kind.

"I dare do all that may become a man; Who dares do more is none"

[Mohit Pandey]

This is why it's always important to put (aq) in your equations when they are in solution - it often makes a difference. I notice you didn't do that above - also, your H20 needs balanced on the left side (sorry, I used to tutor chemistry)

 

Would I put NaCl(aq) in the equation even after I have shown H20 as a reactant? Should it be as Following?

2NaCl(aq) + H2O---2H2 + Cl2+ 2NaOH

 

Actually, I would honestly suggest you wait to learn redox in class if it is something you haven't started yet.

I think I can reduce your work by telling that I have already studied redox reactions. :(

[modest]

Would I put NaCl(aq) in the equation even after I have shown H20 as a reactant? Should it be as Following?

2NaCl(aq) + H2O---2H2 + Cl2+ 2NaOH

 

Sure you could put that on the NaCl, also the NaOH. And your hydrogen and chlorine are gas so you can put (g). This is sometimes redundant and unimportant, but it's sometimes significant - so always good practice to do it. Just think of the difference between sugar(l) and sugar(aq) - melted liquid sugar and dissolved sugar act very different.

 

2NaCl(aq) + 2H2O + energy -> Cl2(g) + H2(g) + 2NaOH(aq)

 

Notice that the product NaOH(aq) is in solution. If it came out as a precipitate it would be NaOH(ppt) so this can be useful information.

 

-modest

[Mohit Pandey]

1.Cu2O + HCl----

 

2.A solution of a substance X is used for white washing. Name the substance X.---- I am in doubt whether the answer should be quick lime or slaked lime. I know that after the reaction of water and quick lime, we get aqueous solution of slaked lime. So, is it solution of quick or slaked lime?

 

3.Please give chemical equation of the reaction between barium hydroxide and ammonium chloride. Is it an endothermic reaction?

[Mercedes Benzene]

1. Hint: This is a double displacement reaction....

 

2. The question asks you to name the substance in the solution, and you already said that the solution was slaked lime... so that's the answer. :)

 

3. Hint: Again, this is just a double displacement reaction. The ammonium hydroxide decomposes into ________ & __________.

[Mohit Pandey]

1. Cu2O + 2HCl--2CuCl + H2O.

 

2. You are thinking it too easy. :) I never said that the solution was slaked lime. In fact, I was telling you what I know. Can't we say that solution of quick lime ( that turns to slake lime) is used? I am saying this because the second part of this question(which I have not posted yet) asks to write the reaction of the substance X with water. So, the answer of second part is CaO + H2O---Ca(OH)2.

 

3. Ba(OH)2 + NH4Cl---NH4OH + BaCl2. Moreover, is it an endothermic reaction?

[freeztar]

For participants of this thread, I recommend using the [ce] tag when writing chemical equations. It makes it much easier. :)

 

For example, take this hypothetical reaction as an example (quote this post to see how I wrote it):

 

[ce]CO2 + H2O -> 2(OH) + CO[/ce]

 

In fact, it might be a good idea to have a sticky that explains this in detail.

 

Carry on folks... :hyper:

[Mercedes Benzene]

1. Cu2O + 2HCl--2CuCl + H2O.

 

2. You are thinking it too easy. :) I never said that the solution was slaked lime. In fact, I was telling you what I know. Can't we say that solution of quick lime ( that turns to slake lime) is used? I am saying this because the second part of this question(which I have not posted yet) asks to write the reaction of the substance X with water. So, the answer of second part is CaO + H2O---Ca(OH)2.

 

3. Ba(OH)2 + NH4Cl---NH4OH + BaCl2. Moreover, is it an endothermic reaction?

 

1. Not quite. There's something wrong with the products. Mind oxidation numbers.

 

2. Awkaward wording to blame.

 

4. Almost.... the [ce]NH4OH[/ce] decomposes...

Also, I don't know if you care about the net ionics, but if so, you need to take into account spectator ions.

 

And Freeztar, the use of the chemistry latex tags is discussed in our latex thread.... if I remember correctly. However, tomorrow I will add a sticky to the chemistry forums so it's more readily available.

[Mohit Pandey]

1.[ce] Cu2O + 2HCl - CuCl2 + H2O[/ce] Now, see if it is correct.

 

2. Please tell why quick lime cannot be the answer. I am asking can't we take the solution of CaO as the answer? I mean to say that [ce] Ca(OH)2[/ce] is a solution of CaO.

 

3.[ce] 2NH4Cl + Ba(OH)2 -> 2NH3 + BaCl2 + 2H2O.[/ce] But how can it be then a double displacement reaction like

[ce] BaCl2 + Na2SO4 - NaCl + BaSO4.[/ce]

I have learnt that compounds exchange their ions in a double displacement reaction . But in the present case, it is not like that.