10.4.2 practice

[leonard martinez]

10.4.2 Practice: Chemical Reactions

Practice Assignment

Physical Science (S2965767)

Martinez Leonard

Points possible: 50

Date: 9/25/16

It's the weekend, and your mom and dad are at an all-day checkers tournament. Your parents just had a new pool put in (lucky you!), so you are thinking you will spend the day swimming and lounging in the water. However, your parents have another plan. They have decided that maintaining the pool will be your job - and they want you to get started today! When you complete that task, you are to prepare dinner for the family before they get home. And you thought having your parents gone all day was going to be fun!

I. The Pool (22 points)

You need to check the pool water's pH to make sure it is between 7 and 7.6. If it's above or below that, you need to add the appropriate chemicals to return the water's pH to this range. Let's see what you know about keeping up your pool!

1. What is pH, what do you use to test it, and why would it be important to keep the pH of swimming-pool water between 7 and 7.6? (4 points)

pH is the logarithm of the reciprocal of hydrogen-ion concentration in gram atoms per liter; provides a measure on a scale from 0 to 14 of the acidity or alkalinity of a solution.

We use it to test whether the solution is neutral,acidic,or basic.ph between 7 and 7.6 is alkalescent.it will not hurt kid's skin.

2. You test the pH of the pool's water. You discover that its pH is 6.5. Is the pool's water too acidic or too basic? Describe what this might do to the pool. (3 points)

Neither.

It is acidic solution.

Skin will be hurt in the acidic solution!

3. You need to raise the pH of the pool by adding sodium carbonate. (6 points)

a.Do you think sodium carbonate is an acid or a base? And why?(2 points)

an acid is defined as an element that breaks apart in water to produce positively charged hydrogen (H+) ions, while a base reacts with water to form negatively charged hydroxide (OH-) ions. Acids are defined as anything with a pH below seven, while a base is any solution with a pH higher than seven. The pH scale runs from zero to 14, meaning sodium carbonate with a pH of just over 11 is only a medium-strength baseou think sodium carbonate is an acid or a base, and why? (2 points)

b. What type of reaction will occur when sodium carbonate is added to the pool water to return its pH to the normal range, and what are the typical products of this type of reaction? (2 points)

sodium carbonate will cause water in the ;pool to go basic or raise pH . 

4. The other important part of maintaining a swimming pool is sanitation. In your pool, chlorine is used to sanitize its water. Chlorine is produced by the electrolysis of salt water. When electricity is passed through NaCl (salt) and H2O (water), the atoms dissociate into Cl2 (chlorine), NaOH (sodium hydroxide), and H2 (hydrogen). Chlorine is isolated in its gaseous form and used to create other compounds for sanitizing, bleaching, and the production of plastics and related products. (5 points)

a. Below is the unbalanced equation for this process. Balance the equation, and be sure to show your work. (3 points)

NaCl + H2O —→ Cl2 + NaOH + H2

2NaCl +2H2O ---> Cl2 + 2NaOH +H2

b. What type of reaction is this? Explain. (2 points)

electrolysis reaction. because if we  add salt NaCl in water it only dissolved. but if we pass electricity through it, then this reaction occurs.

5. You notice a thin film of insoluble solid floating on the surface of the pool's water. What type of reaction do you think caused this? According to this type of reaction, what would floating film be called? (4 points)

If there is a thin film of insoluble solid material floating on the surface of the pool's water, it's not a reaction, it is either the difference in density or the effect of the surface tension of the water

II. Making Dinner (28 points)

Now it's time to make dinner. On the menu tonight are fried chicken, green beans, and cornbread. Good thing you love to cook!

1. The first thing you need to do is turn on the burners, so you can fry the chicken and boil the water for green beans. You have a natural-gas (methane, CH4) stove. When you ignite a natural-gas stove, the methane reacts with oxygen (O2) to produce carbon dioxide and water vapor. (6 points)

a. Write a balanced equation for this reaction, and be sure to show your work. (4 points)

 CH4 + 2O2 ----> CO2 + 2H2O 

b. What type of reaction is this? Explain. (2 points)

 Combustion. A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide. 

2. While you're busy frying chicken, you realize you need to start boiling water for the green beans. Hey ? where's the water? I guess you're going to have to make that, too! You just need a little hydrogen (H2) and oxygen (O­2) to make water (H2O). (6 points)

a. Write a balanced equation for this reaction. Be sure to show your work. (4 points)

Because H2 will react with O2 vigorously, so in order to produce some water by this way, you need a sealed vase or sth like that with H2 and O2 inside. Using electricity current to trigger the reaction. Once it is triggered, it will react spontaneously and produce H2O. 

2H2(g) + O2(g) => 2H2O(l) 

b. What type of reaction is this? Explain. (2 points)

 This is an oxidation-reduction reaction because H2 is oxidised by O2 and O2 is reduced by H2.

3. Now that you've got water, you're ready to cook the green beans. You grab an aluminum pan and start boiling water. You throw in the nutritious green beans, full of iron and vitamins, and cook until they are just tender. After a few minutes, you taste some of the beans. Yuck! The beans taste like an aluminum soda can! Some sort of chemical reaction has happened. As an equation, it looks like this:

beansFe(aq) + Al(s) → beansAl(aq) + Fe(s) (7 points)

a. What type of reaction is this? Explain what you think happened. (3 points)

 It is an oxidation-reduction reaction as well. 

Al is more active than Fe so it pushed Fe in bean out and replaced it. This result in the taste like aluminium can of the beans. 

b. This is also another type of reaction. What is it? Give another common example of this type of reaction. (2 points)

 This is also called substitution reaction when Fe atoms in bean are replaced by Al atoms from outside. They switch there places. 

e.g: 2AgNO3 + BaCl2 = 2AgCl (precipitate) + Ba(NO3)2 

c. Do you think it is OK to eat the green beans? Explain why, or why not. (2 points)

 No! It is not OK. Aluminium is a toxic for our body. If we eat bean with Al inside, we can be poisoned. 

4. Now you just have to make the cornbread. You pull out your grandmother's recipe. You see that it calls for vinegar (HC2H3O2) and baking soda (NaHCO3) as a leavening agent (to make it rise). The reaction between vinegar and baking soda looks like this:

HC2H3O2(aq) + NaHCO3(aq) → NaC2H3O2(aq) + H2CO3(aq) (6 points)

a. What type of substance is vinegar? What type of substance is baking soda? (2 points)

 Vinegar is an acid or more precisely, it is a carboxylic acid (turn litmus into red). 

NaHCO3 is a salt and it is basic (it can turn litmus into blue). 

b. This type of reaction can be classified at least two ways. What are they? Explain. (4 points)

This reaction can be called as neutralisation reaction because the vinegar is acidic and NaHCO3 is basic so when react, both of them neutralise each other to form salt and a weaker acid which is not stable H2CO3 and quickly form H2O and CO2. 

Other way to call it is substitution reaction because there is a replacement of atoms when Na atom replaces H atom in -COOH group of the acid and vice versa. 

5. Now you just need to clean up the greasy stove and countertops. (3 points)

a. Should you use a cleaner that contains an acid or a base? Explain. (2 points)

You should use an base because the greasiness after cooking is because of lipid. If you use base, one reaction can occur which is called saponification reaction. This is due to the base has reacted with the lipid to form salt and alcohol and this is easier to be removed by water then. More important, the reaction is one way and is irreversible like the reaction between acid and lipid. So using base is much more convenient. 

b. Give the chemical name of a common example of an acid or a base used to clean grease. (1 point)

 NaOH: Sodium hydroxide.

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[djshotte...@gmail.com]

what did you get for a grade?

[leonard martinez]

I got a 48/50 if I remember correctly 

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