Electrolisis and Voltaic Cell

Electrochemical Cells

An extremely important class of oxidation and reduction reactions are used to provide useful electrical energy in batteries. A simple electrochemical cell can be made from copper and zinc metals with solutions of their sulfates. In the process of the reaction, electrons can be transferred from the zinc to the copper through an electrically conducting path as a useful electric current.

An electrochemical cell can be created by placing metallic electrodes into an electrolyte where a chemical reaction either uses or generates an electric current.

 Electrochemical cells which generate an electric current are called voltaic cells or galvanic cells, and common batteries consist of one or more such cells. In other electrochemical cells an externally supplied electric current is used to drive a chemical reaction which would not occur spontaneously. Such cells are called electrolytic cells.

Voltaic Cells

An electrochemical cell which causes external electric current flow can be created using any two different metals since metals differ in their tendency to lose electrons. Zinc more readily loses electrons than copper, so placing zinc and copper metal in solutions of their salts can cause electrons to flow through an external wire which leads from the zinc to the copper.

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As a zinc atom provides the electrons, it becomes a positive ion and goes into aqueous solution, decreasing the mass of the zinc electrode. On the copper side, the two electrons received allow it to convert a copper ion from solution into an uncharged copper atom which deposits on the copper electrode, increasing its mass. The two reactions are typically written

Zn(s) -> Zn²⁺(aq) + 2e^- Cu²⁺(aq) + 2e^- -> Cu(s)

The letters in parentheses are just reminders that the zinc goes from a solid (s) into a water solution (aq) and vice versa for the copper. It is typical in the language of electrochemistry to refer to these two processes as "half-reactions" which occur at the two electrodes.

Zn(s) -> Zn2+(aq) + 2e-

The zinc "half-reaction" is classified as oxidation since it loses electrons. The terminal at which oxidation occurs is called the "anode". For a battery, this is the negative terminal.

The copper "half-reaction" is classified as reductionsince it gains electrons. The terminal at which reduction occurs is called the "cathode". For a battery, this is the positive terminal.

Cu2+(aq) + 2e- -> Cu(s)

In order for the voltaic cell to continue to produce an external electric current, there must be a movement of the sulfate ions in solution from the right to the left to balance the electron flow in the external circuit. The metal ions themselves must be prevented from moving between the electrodes, so some kind of porous membrane or other mechanism must provide for the selective movement of the negative ions in the electrolyte from the right to the left.

Energy is required to force the electrons to move from the zinc to the copper electrode, and the amount of energy per unit charge available from the voltaic cell is called the electromotive force (emf) of the cell.

Energy per unit charge is expressed in volts (1 volt = 1 joule/coulomb).

Clearly, to get energy from the cell, you must get more energy released from the oxidation of the zinc than it takes to reduce the copper. The cell can yield a finite amount of energy from this process, the process being limited by the amount of material available either in the electrolyte or in the metal electrodes.

For example, if there were one mole of the sulfate ions SO₄^2- on the copper side, then the process is limited to transferring two moles of electrons through the external circuit. The amount of electric charge contained in a mole of electrons is called the Faraday constant, and is equal to Avogadro's number times the electron charge:

Faraday constant = F = N_Ae = 6.022 x 10²³ x 1.602 x 10^-19 = 96,485 Coulombs/mole

The energy yield from a voltaic cell is given by the cell voltage times the number of moles of electrons transferred times the Faraday constant.

Electrical energy output = nFE_cell

The cell emf E_cell may be predicted from the standard electrode potentials for the two metals. For the zinc/copper cell under the standard conditions, the calculated cell potential is 1.1 volts.

Senses in sentences

When talking or writing, it is possible to make use of our five senses. It is also possible to exclude the senses from the what is said, leading to a more objective way of speaking. Sensory language references and stimulates the senses, thus:

1.  The party was so exciting

         The party is frequently described as very colorful. "And already the halls and salons and verandas are            gaudy with primary colors.the orchestra is playing yellow cocktail music.the seachange of faces and              voices and color." 


2. Morning came and the people arrived.

The cool morning sun cast long fingers of shadow and light across the green field as our visitors tramped across rough and the dewy grass. Objective language seeks to engage the logical mind, but not the senses, which are considered too emotional. It is thus common in such as legal, scientific and business writing Senses in language Language can make reference to any or all senses by deliberate use of appropriate sensory words. Note that these can be both direct description and also sensory metaphors. Sight The visual sense is referenced by talking about light and dark, shades and hues, visible shape and appearance. Her brilliant red blouse fitted her slim figure like a glove. Sound Auditory senses are triggered by reference to loudness, timbre, actual words spoken, and so on. He shouted harsh approval at the sound of her pure warbling Italian soprano. Feeling Tactile feeling and emotional feeling are closely connected, as we sense our emotions as tensions and other physical bodily experiences. His heart thumped as he grasped the meaning of her smile. Taste and smell Our gustatory senses are closely linked and are often used in the metaphoric sense. She could stomach his words no longer and smelled a bitter rat in his intent. Smell in particularly is powerfully evocative sense and can easily trigger early memories.

The old grandfather and his little grandson

The Old Grandfather and

His Little Grandson

Leo Tolstoy

The grandfather had become very old. His legs would not carry him, his eyes could not see, his ears could not hear, and he was toothless. When he ate, bits of food sometimes dropped out of his mouth. His son and his son's wife no longer allowed him to eat with them at the table. He had to eat his meals in the corner near the stove.

One day they gave him his food in a bowl. He tried to move the bowl closer; it fell to the floor and broke. His daughter-in-law scolded him. She told him that he spoiled everything in the house and broke their dishes, and she said that from now on he would get his food in a wooden dish. The old man sighed and said nothing.

A few days later, the old man's son and his wife were sitting in their hut, resting and watching their little boy playing on the floor. They saw him putting together something out of small pieces of wood. His father asked him, "What are you making, Misha?"
The little grandson said, "I'm making a wooden bucket. When you and Mamma get old, I'll feed you out of this wooden dish."
The young peasant and his wife looked at each other, and tears filled their eyes. They were ashamed because they had treated the old grandfather so meanly, and from that day they again let the old man eat with them at the table and took better care of him.

Tell vs Show Sentences

Add sight

She smelled of wet cigarettes and bacon. As they slowly climbed the long, steep staircase, the only sound was his grandmothers' labored breathing and the mournful creak of the wooden stairs.
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tell vs show

1.  Tell sentence

"Mrs Jones love gardening."

 Writing which "shows" generally incorporates vivid descriptive detail in order to help the reader evaluate evidence in order to make the appropriate judgments.


Show sentences

From the moment she woke up in the morning, Mrs. Jones smiled at the thought of her garden. Most mornings, she'd scald her mouth trying to gulp down her coffee so that she could get outside while the ground was still damp from the morning dew. Once she knelt down in the soil, she lost track of all time and all concerns of her body. She would work well into the evening, barely noticing when the nails of her left hand would break to the point of bleeding. Mrs. Jones' Jones jeans were always stained on the knees with thick mud, and her arms were always bruised and scraped. But she didn't mind a bit.


2.  Tell sentence

     Dennis Rodman is a poor role model.

Show sentences
 
Dennis Rodman continues to break the rules of the NBA. He is rude to officials, excessively violent on and off the court, and has publicly claimed he holds no remorse for his actions.

vivid adjectives to develop sensory description

Descriptive writing provides literary texture to a story. Texture shows rather than tells. A writer shows the reader through the senses of sight, hearing, smell, taste, and touch, as well as through emotional feelings.

Descriptive details enable the reader to visualize elements in the story.

Vivid adjectives and active verbs help the writer to develop specific sensory descriptions.

 For example:
  The woman on the beach watched the sun set over the ocean. TELLS

 Shades of neon illuminated the edges of clouds, backlit by the sizzling sun that slipped beneath a cerulean sea. SHOWS


 #Notice that sentences that TELL tend to be direct. They are objective. Sentences that TELL record verifiable facts as a scientist or journalist might.

 Sentences that SHOW are subjective; they may be influenced in part by the writer’s personal experiences. Sentences that SHOW create mental images, and elicit emotional response.

How to change weak verbs to strong verbs

TO REWRITE SENTENCES USING STRONG VERBS:

1. Underline any use of Be, Is, Are, Was, Been, Being, Were, Has, Have, Having, Had.
   John is the manager of the produce department.
2. Look for a noun or adjective that you can convert to a strong verb.
   John is the manager of the produce department. ("manager," noun -- predicate nominative)
3. Rewrite the sentence using that strong verb.
   John manages the produce department.

Always use good grammar in English when you write, but do not neglect using strong verbs for strong writing and a more robust writing style.

How to start Descriptive

Types of Papers: Narrative/Descriptive

To write a narrative essay, you’ll need to tell a story (usually about something that happened to you) in such a way that he audience learns a lesson or gains insight.

To write a descriptive essay, you’ll need to describe a person, object, or event so vividly that the reader feels like he/she could reach out and touch it.

Tips for writing effective narrative and descriptive essays:

• Tell a story about a moment or event that means a lot to you--it will make it easier for you to tell the story in an interesting way!
• Get right to the action!  Avoid long introductions and lengthy descriptions--especially at the beginning of your narrative.
• Make sure your story has a point! Describe what you learned from this experience.
• Use all five of your senses to describe the setting, characters, and the plot of your story. Don't be afraid to tell the story in your own voice.  Nobody wants to read a story that sounds like a textbook!

How to Write Vivid Descriptions

Having trouble describing a person, object, or event for your narrative or descriptive essay?  Try filling out this chart:

What do you smell?	What do you taste?	What do you see?	What do you hear?	What might you touch or feel?

Remember:  Avoid simply telling us what something looks like--tell us how it tastes, smells, sounds, or feels!

Consider this…

• Virginia rain smells different from a California drizzle.
• A mountain breeze feels different from a sea breeze.
• We hear different things in one spot, depending on the time of day.
• You can “taste” things you’ve never eaten: how would sunscreen taste?

Using Concrete Details for Narratives

Effective narrative essays allow readers to visualize everything that's happening, in their minds.  One way to make sure that this occurs is to use concrete, rather than abstract, details. 

Concrete Language…	Abstract Language…
…makes the story or image seem clearer and more real to us.	...makes the story or image difficult to visualize.
…gives us information that we can easily grasp and perhaps empathize with.	…leaves your reader feeling empty, disconnected, and possibly confused.

The word “abstract” might remind you of modern art.  An abstract painting, for example, does not normally contain recognizable objects.  In other words, we can't look at the painting and immediately say "that's a house" or "that's a bowl of fruit."  To the untrained eye, abstract art looks a bit like a child's finger-painting--just brightly colored splotches on a canvas.

Avoid abstract language—it won’t help the reader understand what you're trying to say!

Examples:

Abstract:  It was a nice day. 
Concrete:  The sun was shining and a slight breeze blew across my face. 

Abstract:  I liked writing poems, not essays. 
Concrete:  I liked writing short, rhythmic poems and hated rambling on about my thoughts in those four-page essays. 

Abstract:  Mr. Smith was a great teacher.
Concrete:  Mr. Smith really knew how to help us turn our thoughts into good stories and essays.

Descriptive Sentences

VIVID VS. VAGUE LANGUAGE

The sensory details you select in your writing should create for your reader the same picture you have in your mind. Instead of using vague, general words, your sensory language should be concrete and sensory-packed. This makes the difference between vivid and and vague language. Take a look at the comparison between vague and vivid sentences.

Vague	Vivid
The food was unappetizing.	The pale turkey slices floated limply in a pool of murky fat.
The sprinkler was refreshing.	The cool water from the sprinkler sprayed our hot faces.
The traffic was heavy.	Our old car puffed as Main Street became clogged with a line of clamoring motorists.

WHAT TO AVOID WHEN USING SENSORY DETAIL

• Too many adjectives—retain only the most powerful words in your writing, deleting any unnecessary words
• Too many adverbs—verbs are stronger than adverbs. She strolled into the room is more powerful than She walked casually into the room.
• Clichéd figures of speech—overused language, such as green with envy, signals a lack of imagination. Use fresh, descriptive words that go against rote thinking.

Now, consider this paragraph with all five sensory descriptors: sight, sound, smell, taste, and touch.

My sister and I walked along the boardwalk one afternoon on our vacation. The hot boards warmed our bare feet. We watched the foam-covered waves topple over each other and then slide back into sea. The crashing water competed with the exuberant yells from the seagulls. We bought a perfectly oval fluff of pink cotton candy that dissolved sweetly in our mouths. Afterwards, we walked along the edge of the water, letting the warm salty air blow our hair away from our necks as the cool water lapped over our toes.

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