Chemistry

LEARNING OBJECTIVES

After reading this unit, you will be able to:

•define an electrolyte and a non-electrolyte.

•give examples of weak and strong electrolytes and non-electrolytes.

•state applications of electrolytes in daily life.

KNOWLEDGE GAIN

     

Trophies and medals are electroplated with gold and silver.

9.1 ELECTROLYTE AND NON-ELECTROLYTE

ACTIVITY 9.1: Distinction between Electrolyte and Non-electrolyte

Materials Required : Salt (NaCl) solution, sugar solution, pure water, 3 nine-volt cells, 6 carbon electrodes, 3 bulbs, 3 beakers and wires.

•Take 3 beakers. Label them A, B and C.

•Half-fill the beaker A with pure water, half-fill the beaker B with sugar solution, half-fill the beaker C with salt solution.

•Set all apparatuses as shown in figures.

Do you know, why bulb glows only in the sodium chloride solution?

In Activity 9.1, you will observe that only sodium chloride solution conducts electricity. This is because the solution contains ions—Na+ and Cl–. Sodium chloride (NaCl) ionizes into Na+ and Cl– in water. It is an electrolyte. Pure water and sugar solution do not contain any ion. So they do not conduct electricity. Sugar is a non-electrolyte.

Non-electrolytes are covalent compounds that do not dissociate into ions when they are dissolved in water. They dissolve in water as molecules. Sugar and urea are good examples of non-electrolytes.

              

Electrolytes are compounds whose aqueous solution contains ions. In other words, a substance that dissociates into ions when they are dissolved in water. For example, sodium chloride, magnesium chloride, copper sulphate and ammonium chloride. All electrolytes are divided into two groups—strong electrolytes and weak electrolytes.

           

EXERCISE 9.1

1. Pure water and sugar solution do not contain __________.

2. Non-electrolytes are _____________compounds.

3. Give two examples of non-electrolytes.

4. What do you mean by electrolytes?

5. Sodium chloride is an example of electrolyte.

                                              (True or False)

9.2 DEFINITION OF ELECTROLYSIS

Electrolysis is the process by which ionic substances are decomposed (broken down) into simpler substances when an electric current is passed through them. Ions are free to move when an ionic substance is dissolved in water. In Unit 5, we have already studied the electrolysis of water.

9.3 STRONG ELECTROLYTE

An electrolyte which is completely ionized in water and thus produces a large amount of ions is called strong electrolyte. For example, hydrochloric acid, nitric acid and sulphuric acid, sodium hydroxide and potassium hydroxide.

These electrolytes have high electrical conductivity (Figure 9.2) because of high concentration of ions in their solution.

        

Hydrochloric acid, sulphuric acid and nitric acid are also called mineral acids. The acids prepared from the minerals of the earth are called mineral acid. These are very strong acid and react very rapidly with metals, metal carbonates and metal hydrogen carbonates. In laboratory, these acids are mixed with water to dilute them.

While using mineral acids, follow all safety measures and handle them very carefully because they cause severe burns on skin and eat up clothes, wood, metals and stone due to their corrosive nature. These are never stored in metal containers. Mineral acids are stored in containers made up of glass.

EXERCISE 9.2

1. What do you mean by strong electrolytes?

2. __________ and __________ are mineral acids.

3. Give two examples of strong electrolytes.

4. Write two safety measures to use sulphuric acid.

5. In laboratory, dilutes acids are stored in metallic container.

                                                                  (True or False)

9.4 WEAK ELECTROLYTE

An electrolyte which is partially ionized in water and thus produces a small amount of ions is called weak electrolyte. For example, acetic acid, carbonic acid, sulfurous acid, organic acid, ammonium hydroxide, calcium hydroxide and magnesium hydroxide. These electrolytes react quite slowly with metals, metal carbonates, and metal hydrogen carbonates.

Weak electrolytes have low electrical conductivity (Figure 9.3) because of low concentration of ions in their solution.

                       

Organic Acids

The acids present in fruits are called organic acids. Organic acids occur naturally. Examples of organic acids are citric acid, lactic acid, oxalic acid and tartaric acid. Organic acids are weak acids. It is not harmful to eat fruits containing organic acids.

Sources of organic acids

•Citric acid is present in citrus fruits such as lemons and oranges.

                             

•Lactic acid is present in curd or sour milk.

•Oxalic acid is present in tomatoes.

                            

•Tartaric acid is present in unripe grapes and tamarind.

                         

EXERCISE 9.3

1. What do you mean by weak electrolytes?

2. Write three examples of weak electrolytes.

3. The acids present in fruits are called __________.

4. Name the acid present in              

          (a) milk                          (b) lemon.

5. Why weak electrolytes have low electrical conductivity?

9.5 CONDUCTIVITY OF ELECTRICITY BY ELECTROLYTES

ACTIVITY 9.2: Identifying the Conductivity of Electricity by Electrolytes

Chemicals Required

Hydrochloric acid, aqueous ammonia, Sodium chloride solution, Sugar solution, Calcium hydroxide solution, Ethanol, Sodium hydroxide solution, tap water, Acetic acid (ethanoic acid), distilled water.

Materials Required

Homemade conductivity tester, and beaker (50 ml).

Procedure

Prepare your homemade conductivity tester as given below.

Materials

•1 light emitting diode (LED)

•1 kW resistor

•1 nine-volt battery

•1 battery connector

•1 piece of fiber board or plywood

•1 rubber band

•Half meter black wire and half meter red wire

•Tape

             

•Take about 25 ml hydrochloric acid in a 50 ml beaker.

•Dip the open wire ends in the beaker to test if they conduct electricity.

•Observe the brightness of the LED in tester.

•Compare your observation with the given table.

•Light will glow if the electrolyte is strong or weak or it is a non-electrolyte.

•Repeat the activity with each sample.

•Make an appropriate report of your observation.

Caution

Be careful not to touch the exposed wire of the electrodes that are used for testing!

9.6 APPLICATION OF ELECTROLYTES

ACTIVITY 9.3

Research and make presentations about the applications of electrolytes in daily life.

The following are application of electrolytes:

•Sodium chloride (NaCl) is more commonly known as “salt” or “table salt,” and is the major ingredient in the edible salt that is sprinkled on food to make it taste better. Sodium chloride is present in the ocean and is the main thing that makes ocean water taste so salty.

•Nitric acid (HNO₃) is a corrosive acid. It is used in the manufacture of fertilizer. It is also used as one of the ingredients in certain types of liquid rocket fuel.

• Hydrochlroic acid (HCl) is a strong acid widely used in the chemical industry.

•Calcium chloride (CaCl₂) is also a salt and is different from the table salt. Calcium chloride is a compound made of calcium and chloride, and is one of the types of salt used to control ice on sidewalks and roadways. The compound is often produced from limestone.

•Potassium nitrate (KNO₃) is used in a wide variety of substances. It can be used as a food additive, but is also an ingredient in various types of rocket fuels and in fireworks. Potassium nitrate was an ingredient in gun powder for many years.

•Sodium hydroxide (NaOH) is an important ingredient in many detergents, soaps, and drain cleaners. It is highly dangerous because of its ability to decompose lipids and proteins in skin, causing burns when not handled properly.

•Sulphuric acid (H₂SO₄) is used in car batteries to get the electricity to flow. Like sodium hydroxide, it can cause very severe chemical burns when it comes into contact with skin, so it is very important to handle with extreme caution.

•Ammonium chloride (NH₄Cl) is a main component of dry cell. Dry cell is commonly known as Leclanché cell. The other electrolyte used in dry cell is manganese dioxide (MnO₂).

•Sodium acetate (CH₃COONa) is an electrolyte that includes sodium as a main ingredient. It is often used to seal concrete so that it is protected against bad weather. It is also used as an ingredient in certain types of foods, such as salt and vinegar potato chips, because of its salty and tangy flavour when mixed with other seasonings.

•Magnesium hydroxide (Mg(OH)₂) is also known as milk of magnesia because of its milk-like appearance. It is a main component of many types of laxatives and antacids, and in underarm deodorants and antiperspirants. It can also be applied to the scalp for dandruff control.

EXERCISE 9.4

1. Fill in the Blanks

(a) Nitric acid is a __________ acid.    (b) Sodium hydroxide is used in the making __________ and __________.

(c) __________ is used in car batteries for electricity.       (d) __________ is a main component of dry cell.

(e) Magnesium hydroxide is also known as __________.

9.7 SUMMARY

•Electrolytes are compounds whose aqueous solution contains ions.

•Electrolytes are grouped into—strong electrolytes and weak electrolytes.

•An electrolyte which ionized completely in water is called strong electrolyte.

For example, H₂SO₄, HCl and HNO₃.

•Strong electrolytes have high electrical conductivity.

•An electrolyte which ionized partially in water is called weak electrolyte.

For example, CH₃COOH, Ca(OH)₂ and Mg(OH)₂

.•Weak electrolytes have low electrical conductivity.

•Electrolysis is the passage of a direct electric current through an ion-containing solution.

•The acids present in fruits are called organic acid.

•The acids prepared from the minerals of the earth are called mineral acids.

•Sulfuric acid is used in car batteries.

•Ammonium chloride and manganese dioxide are used in Leclanché cell.

9.8 GLOSSARY

•Antacid: a medicine used in acidity.

•Antiperspirants: a substance that is applied to the skin, especially under the arms, to reduce sweating.

•Concrete: a building material made from a mixture of broken stone or gravel, sand, cement, and water.

•Corrosive: a substance that gradually destroys living tissues on other matter.

•Dandruff: small pieces of dead skin in a person’s hair.

•Deodorants: a substance which removes unpleasant smells, especially bodily odors.

•Detergents: a water-soluble cleansing agent which combines with impurities and dirt to make them more soluble.

•Diode: a semiconductor device with two terminals, typically allowing the flow of current in one direction only.

•Ingredient: any of the foods or substances that are combined to make a particular dish.

•Laxative: a medicine used to treat and prevent constipation.

•Lipids: an important component of living cells, a fatty acids that stores energy in living cells.

•Severe: causing very great pain.

•Sprinkle: a small quantity or amount of something scattered over an object or surface.

•Tangy: having a strong, piquant flavor or smell.

•Urea: a water-soluble compound containing nitrogen, carbon, oxygen and hydrogen used as fertilizer.

9.9 UNIT ASSESSMENT

I. Multiple Choice Questions

1. Sugar solution does not contain

(a) atom (b) molecule (c) ion (d) none of these

2. Sodium chloride and copper sulphate are examples of

(a) electrolytes (b) compounds (c) both (a) and (b) (d) elements

3. Sucrose and urea are good examples of

(a) strong electrolyte (b) weak electrolyte (c) non-electrolyte (d) all of these

4. During electrolysis of water, hydrogen gas is produced _________ as compared with oxygen.

(a) two times (b) three times (c) four times (d) five times

5. Generally, strong electrolytes react very rapidly with

(a) metals (b) metal carbonates (c) metal hydrogen carbonates (d) all of these

6. Citric acid and tartaric acid are examples of

(a) mineral acid (b) organic acid (c) only (a) (d) only (b)

7. Choose the weak electrolyte(s).

(a) Carbonic acid (b) Ammonium hydroxide (c) Calcium hydroxide (d) All of these

8. Choose the mineral acid.

(a) Sulfuric acid (b) Hydrochloric acid (c) Nitric acid (d) All of these

9. Choose the correct statement(s).

(a) Hydrochloric acid is widely used in chemical industry (b) Magnesium hydroxide is also known as milk of magnesia (c) Nitric acid is used in the manufacture of fertilizer

(d) All of the above

10. Electrolyte used in car batteries to get the electricity is ______ .

(a) sulphuric acid (b) nitric acid (c) sodium acetate (d) calcium chloride

II. Open Ended Questions

1.Give two examples of

(a) Electrolytes            (b) Non-electrolytes

2. Distinguish between strong and weak electrolytes. Give examples.

3. Explain non-electrolytes.

4. What do you mean by organic acid and mineral acid?

5. How is strong acid stored in laboratory?

6. Carry out an experiment to differentiate between electrolytes and non-electrolytes.

7. Name the electrolyte used in/as

(a) car batteries (b) fertilizer (c) table salt (d) detergents

8. What are the applications of electrolytes in daily life?

III. Practical-based Questions

Look at the figures and answer the following questions.

1. Which of the beakers contains non-electrolyte?

(a) Beaker A (b) Beaker B (c) Beaker C (d) All of these

2. Which beaker contains solution of weak electrolyte?

(a) Beaker A (b) Beaker B (c) Beaker C (d) All of these

3. Which beaker contains solution of strong electrolyte?

(a) Beaker A (b) Beaker B (c) Beaker C (d) All of these

4. Which beaker contains solution of organic acid?

(a) Beaker A (b) Beaker B (c) Beaker C (d) None of these

5. The beaker B may contain

(a) Pure water (b) Glucose solution (c) Urea solution (d) All of these