Answer to Katy

Katy, which problem needs balancing?

Answers to Katy

Hi Katy,
In the problem of amalgam fillings, Saliva is working as the conducting medium, so it's equivalent to the solutions and salt bridge in a galvanic cell
As for the question about the galvanic cell, this is true. The galvanic cell stops when the anode strip depletes or when ions of the cathode deplete.

Copper plating

Check this out, it's the experiment of copper plating a quarter...

Answers to Katy

Hi Katy, concerning the reaction between nitrogen and hydrogen gas to produce ammonia
N2 + H2 → NH3
The oxidation number of N decreases from zero to -3, this is reduction.
(N + 3e → N-3) × 2 so 2N + 6e→ 2N-3
(H → H+ + 1e) × 6 so 6H → 6H+ + 6e
2N + 6H → 2N-3 + 6H+
so the balanced equation:
N2 + 3H2 → 2NH3

The other question: The cell in which electroplating occurs is called an electrolytic cell. Eectroplating is a form of electrolysis.Whenever you are passing an electric current to start a chemical reaction, electrolysis is involved.

Third question: Electrolysis of water in the presence of KNO3
Cathode 1/2 reaction:
2H2O + 2e → H2 + 2OH-
in this 1/2 reaction, the O.N. of H decreases from +1 to 0. this is reduction. But only 2 hydrogens of the 4 hydrogens in the reactants were reduced. The other 2 hydrogens were neither oxidized nor reduced. In the compound OH-, the oxidation number of H is +1, which indicates that the O.N. of the 2 hydrogens in 2OH- did not change from that of reactant.
Reduction 1/2 reaction:
2H2O → O2 + 4H+ + 4e
in this 1/2 reaction, the O.N. of oxygen increased from -2 to 0, so this is oxidation. On the other hand, the oxidation number of hydrogen in the reactants and products is the same: +1
As for the question about the galvanic cell,
In the anode half cell, the amount of cations in the solution are increasing (remember that the atoms of the metal are being oxidized to cations) , so the amount of positive charges increases, therefore, anions flow from the salt bridge to maintain electric neutrality at this half cell.
conversely, cations flow from the salt bridge to the cathode half cell solution, because the solution is losing cations (cations are reduced to atoms), and the amount of anions in solution (sulfate ions for exampe if the solution is zinc sulfate) is becoming much more than the cation.
If you're question is: why do ions flow from salt bridge to maintain electric neutrality? What makes them flow in the first place?
Well, this would be an advanced question...flow of ions is controlled by a special diffusion called Fickian diffusion...If you like to read about it, you can..but it's not required from you this year

Answer to Katy

Katy, an electrolytic cell is a cell that converts electric energy to chemical energy.
This means, that if an electric current gives rise to a chemical reaction, then we have an electrolytic cell, so the word electrolysis is used.
In the case of electrolysis of water, we gave the cell a voltage that decomposed water into hydrogen gas and oxygen gas.
In the case of electroplating, we gave the cell a voltage so that the chemical reaction of electroplating took place.
In both cases, we have an electric current that is used to allow the occurance of an oxidation-reduction reaction. So both cells are called electrolytic cells

YouTube - Galvanic cell

YouTube - Galvanic cell

Click on the hyperlink to watch the galvanic cell animation

Chemistry Problem (4)

Galvanic effect of the amalgam filling
Amalgam fillings are made of a combination of metals including silver, tin, copper and mercury. Amalgam is extremely durable and able to withstand the grinding and chewing of your back teeth over long periods of time. However, researches have shown that the presence of mercury in amalgam fillings is dangerous, especially when mercury is found in an area close to the human brain. Mercury is extremely toxic to the nervous system, kidneys, and livers. Mercury may result in defects in fetuses for pregnant women. People with an amalgam filling in their mouths have experienced mild electric shocks when the amalgam came in contact with an aluminum foil, aluminum fork or spoon. Since saliva contains electrolytes, it works as a conductor of the formed electric current. The reaction between mercury and aluminum is summarized by the following equation:
Al +Hg+→ Al 3+ + Hg
a) Prove that this reaction is redox.
b) Write the oxidation and reduction half-reactions, then the overall redox reaction.
c) Identify the metal that has more tendency to lose electrons in this reaction, and the metal that has less tendency to lose electrons.
d) Explain the feeling of electric shock in people with amalgam fillings.
e) It is said that Aluminum and mercury form a "battery" effect in your mouth. Explain this statement.
f) Refer to the passage to answer these questions:
i) What is the medium that conducts the formed electric current in your mouth? Why?
ii) Why are amalgam fillings used in dentistry?
iii) What are the toxic effects of mercury to humans?
g) Based on this information, would you approve using amalgam fillings in your teeth? Why?
*picture was taken from naturaldentistry.us

Solution to Problem (4)

Solution:
a) In the reactants, the oxidation number of Al is zero (uncombined element) and the O.N. of Hg+ is +1 (the O.N. of an ion is equal to its charge)In the products, the O.N. of Al3+ is +3 (the O.N. of an ion is equal to its charge) while the O.N. of Hg is zero (uncombined element)the O.N. of Al increases from zero to +3, this is oxidation. The O.N. of Hg decreases from +1 to zero, this is reduction. Since this reaction involves a transfer of electrons between the reactants, then it is redox.
b) Al → Al3+ + 3e oxidation half reaction
(Hg+ + 1e → Hg) × 3 reduction half reaction
Overall redox reaction: Al + 3Hg+→ 3Hg+ Al3+
c) Since Al is the substance oxidized, then it has more tendency to lose electrons. Since Hg is the substance reduced, then it has less tendency to lose electrons.
d) Since the reaction between aluminum and mercury is a redox reaction, it involves a transfer of electrons, then an electric current is generated.
e) Chemical energy was converted into electric energy due to the reaction between mercury and aluminum, since they are two metals having different tendencies to lose electrons, saliva works as a solution that conducts electricity. This explains the word "battery".
f)
i) Saliva works as a conducting medium for the generated electric current, since it contains electrolytes (substances which are able to conduct electricity
ii) Amalgam fillings are used in dentistry since they are extremely durable and able to withstand the grinding and chewing of your back teeth over long periods of time.
iii) Mercury is extremely toxic to the nervous system, kidneys, and livers. Mercury may result in defects in fetuses for pregnant women
g) Of course not, since amalgam fillings contain mercury which is a highly toxic metal to human body, being able to damage vital organs in human body.

Answer to Katy

Dear Katy,
In this case, you will be told about the charge of the ion in the question.
don't worry, calm down.... you will do well

Answers to Amar and Katy

Hi all,
Amar, you can memorize the electrolysis half reactions in acidic and KNO3 media (because these are the only two cases that may come up)
Katy, the compounds I gave you are not molecular: for example MgSO4 is an ionic compound, Mg2+ is a metalic ion, and sulfate ion is a nonmetal. so the oxidation number of mg is equal to its charge. Did I answer your question? if not, tell me.

Reply to Amar

Amar, I corrected the exercise on the post carrying your name. You're right, it's 3O2 not 6O2 (error:))). Good luck to all, and study well

Answers to Firas

Hey Firas, don't apologize for your questions, this blog was made to answer your questions in the first place.
Q 1) The anode is the electrode that gets thinner since it loses electrons, so the atoms on the anode change into ions (from solid state (atoms) to aqueous state (ions))
On the other hand, the cathode is the electrode that gets thicker, since it gains electrons, so it attracts the cations of the metal from the solution, the cations will gain the electrons (be reduced) to become atoms (solids) which will stick on the cathode.
Q2) The word electrolyte doesn't mean catalyst. Electrolytes are substances that conduct electricity, in this case, they are the ions in the solution. We know that ions conduct electricity because they are charged particles.
Q3) A spontaneous reaction that proceeds on its own, while a non-spontaneous reaction cannot start by itself, it needs a form of energy to start. For example, decomposing water into hydrogen and oxygen gases requires either of these energies: heat (2000 C or an electric current). For this reason, decomposing water is a non-spontaneous reaction.
Q4) yes, for both types of electrolysis we use an electrolytic cell.
Remeber that an electrolytic cell is a cell the depends on a source of electricity (battery), it converts electric energy to a chemical energy.
Q5) yes, you can memorize it this way
Since the oxidant is the substance reduced, then for sure it is the substance whose O.N. decreased, and since the reductant is the substance oxidized, then for sure it is the substance whose O.N. inreased.
Q6) They can be memorized, since only 2 cases are required from you (electrolysis using KNO3 or H2SO4)

Answer to Amar's Question (Amar read this)

Hey Amar, you're right it's 3O2 not 6O2.
Hey Amar, how are you?
Combustion is burning. Any type of combustion requires oxygen. This year you're responsible for combustion of hydrocarbons. The complete combustion of hydrocarbons produces two substances: Carbon dioxide and Water, in addition to energy.
You might be asked to write the equation of the reaction of combustion of a hydrocarbon. You might also be asked to list the products formed. After your write the equation of the reaction, you must balance it.
Example: Try practicing these examples
Write the equations of combustion of each of ethane, ethene, and butyne.
Solution: (the idea is the same for all types of hydrocarbons: alkanes, alkenes, and alkynes)
1- Combustion of ethane:
C2H6 + 7/2O2 → 2CO2 + 3H2O
2- Combustion of ethene:
C2H4 + 3O2→ 2CO2 + 2H2O
3- Combustion of butyne:
C4H6 + 11/2O2 → 4CO2 + 3H2O
To balance the equation:
First, balance the carbons
Second, balance the hydrogens
Last, balance the oxygens

Chemistry Problem (3)

Studying the Galvanic Cell

Oxidation-Reduction reactions can be used to provide electricity. Various forms of cells and batteries produce electricity through a redox reaction. A device that converts chemical energy into electric energy is called a galvanic cell. In order to build a galvanic cell, we need two metal strips, one being more reactive than the other. Each of the two metals is dipped in a solution containing the ion specific to that metal. Then, the solutions are connected to each other by a salt bridge. The two metal strips are connected to the terminals of a voltmeter or a bulb. The figure above displays a galvanic cell.
1) Why can redox reactions produce electricity?
2) Using the passage:
- write examples of uses of redox reactions in daily life.

- define the galvanic cell

3) Can we use two metals of the same nature? Justify your answer.
4) The sketch above shows the direction of transfer of electrons. Label the anode and the cathode of the cell justifying your answer.

5) Given: the other electrode is Ag, the ion of Ag is Ag+, the ion of Zn is Zn2+. - Write the oxidation and reduction half reactions, and write the overall redox reaction.
6) Give the representation of this cell.
7) Which electrode becomes thinner? Which electrode becomes thicker? Justify your answer.

Solution to Chemistry Problem (3)

Solution:
1) Redox reactions can produce electricity since they involve a transfer of electrons.
2) - Various forms of batteries and cells produce electricity through redox reactions.- The galvanic cells is a device that converts chemical energy into electric energy
3) No, we can’t use metals of the same nature since one metal must have more tendency to lose electrons than the other in order for a galvanic cell to generate electricity.
4) Anode: (3) since it is the electrode that loses electrons
Cathode: (2) since it is the electrode that gains the electrons5)
Oxidation half reaction: Zn → Zn2+ + 2e
Reduction half-reaction: (Ag+ + 1e→ Ag) × 2
Overall Reaction: Zn + 2Ag+→ 2Ag + Zn2+
6) Zn/Zn2+-salt bridge - Ag+ /Ag
7) The anode becomes thinner, since it loses electrons so the atoms of zinc metal (solid) are oxidized to becomes zinc ions (aqueous), which become part of the solution.
The cathode becomes thicker, since silver ions (aqueous) are being reduced to become silver atoms (solid) on the silver strip making it thicker.

Chemistry Problem (2)

(figure was taken from self-teaching physics and chemistry guide to Dr. I. Abbas and Dr. A. Shaar)
The figure above corresponds to an electroplating sketch. We wish to coat the spoon with Silver.
a) How is energy converted in this cell? What do we call such cells?
b) Label the parts figure from (1) to (6).
c) To which pole of the battery is the anode connected? To which pole of the battery is the cathode connected?
d) The following solutions are available: AgNO3(aq) – CuSO4(aq) - Au(NO3)3(aq)Which solution is suitable to be used in the cell? Why are the other two solutions not suitable?
e) We electroplate objects for 2 purposes. What are they?
f) Write the oxidation and reduction half reactions involved in this process and write the overall redox reactions.

Solution to Chemistry Problem (2)

a) In the electroplating cell, energy was converted from electrical to chemical. Cells that convert electric energy to chemical energy are called electrolytic cells.

b) (1): anode (2): cathode (metal to be coated) (3): DC power supply or battery (4): solution containing Ag+ (the ion of the coating metal) (5) electrolytic cell (6): connecting wires

c) the anode is connected to the positive pole of the battery while the cathode is connected to the negative pole of the battery since the anode is the (+) pole (loses electrons) while the cathode is the negative pole (gains electrons) of the cell.

d) AgNO3 is the suitable solution since it contains Ag+ ion which is the ion of Ag metal, the other solution are not suitable because they do not contain the ion of the coating metal.

e) We electroplate objects to:
- protect them from corrosion since the coating metal would be more corrosion-resistant

- give objects a more attractive appearance

f) oxidation half reaction: Ag→ Ag+ + 1e

reduction half reaction Ag+ + 1e → Ag

The overall reaction would be: Ag + Ag+→ Ag+ + Ag

Solution to Redox Reactions Problem:

equation 1: In the reactants, the O.N. of Mg is O (uncombined element), while in the products the O.N. of Mg in MgSO4 is +2 (the O.N. of ions is equal to its charge, and the ion of Mg is Mg2+)
so, the O.N. of Mg increased from O to +2, then this is oxidation. Note: O.N. stands for oxidation number.
the O.N. of H in the reactant is +1, while the O.N. of H in the products (H2 gas) is O since it's an uncombined element. the O.N. of H decreases from +1 to O, so this is reduction. Since this reactions involves a transfer of electrons between the reactants and products, then it's a redox reaction.
equation 2: In the reactants the O.N. of Cu is zero (uncombined element) while the O.N. of N in HNO3 is +5 (the sum of Oxidation number of atoms or ions in a compound is equal to zero), so O.N.(H)+O.N.(N) + 3×O.N.(O)=0 , by substituion: 1 + O.N.(N) + 3×(-2)=0 so O.N(N) = +5.
In the products, the O.N. of Cu in Cu(NO3)2 is +2 (the O.N. of ions is equal to their charge, and we have Cu2+ ion in this case), while the O.N. of nitrogen in NO is +2 (since the sum of O.N. of O and N is 0).
In sum, the oxidation number of Cu increased from O to +2, this is oxidation, while the O.N. of N decreased from +5 to +2, this is reduction. Since this reaction involves a transfer of electrons between reactants, then this is a redox reaction.
equation 3: In the reactants the O.N. of Zn is equal to O (uncombined element), while the O.N. of H is +1. In the products, the O.N. of Zn is +2 while the O.N. of H is O (uncombined element).
In sum, the O.N. of Zn increased from 0 to +2, so this is oxidation, while the O.N. of H decreased from +1 to O, so this is reduction. Since this reaction involves a transfer of electrons between reactants, then it is a redox.
equation 4: In the reactants the O.N. of H is +1 while the O.N. of Mg is O (uncombined element). In the products, the O.N. of Mg is +2 while the O.N. of H is O.
In sum, the O.N. of Mg increased from O to +2, so this is oxidation, while the O.N. of H decreased from +1 to O so this is reduction. Since this reaction involves a transfer of electrons between reactants, then it's redox

Chemistry problem

Show that the following equations represent redox reactions:

equation 1: Mg + H2SO4 → MgSO4 +H2
equation 2: 3Cu + 8HNO3→ 3 Cu(NO3)2 + 2NO + 4 H2O
equation 3: 2H2SO4 + Fe→ Fe(SO4) + SO2 + H2O
equation 4: 2HCL + Mg → MgCl2 + H2

Welcome, students!

Hello to all, this blog was prepared to answer your questions while studying chemistry for the official examination.

Every now and then, I'll post a problem along with the solution. Try to solve the problem first, then have a look at the solution.