Class 7 Science Answers to Acids,Bases and Salts Test Paper-1

M.M: 39 marks                       Dated: 31/05/2011

Time:  45 minutes

Q 1: Write True or False for the following plus write the correct answer for the false statements: (1 mark each x 10 = 10 marks)

       i. The word acid comes from the latin word “acere” which means bad – False (Acere means to taste sour).

     ii.  Substances which are bitter in taste and feel soapy on touching are called salts – False (Correct answer is Substances which are bitter in taste and feel soapy on touching are called bases).

   iii.  Acids turn red litmus blue – False (Correct answer is Acids turn blue litmus red).

   iv.  Neutral solutions are more acidic and less basic – False (Neutral solutions are neither acidic nor basic and thus they are called neutral).

     v. Sodium hydroxide turns red litmus to blue – True (Sodium hydroxide is a base and bases turns red litmus to blue).

   vi. The symbol for sodium is S – False (Symbol for sodium is Na).

 vii.  The symbol for potassium is K - True.

viii.  The sting of an ant contains an acid called acetic acid – False (The sting of an ant contains an acid called Formic acid).

   ix. The formula for sodium hydroxide is NaH – False (The formula for sodium hydroxide is NaOH).

     x. The formula for hydrochloric acid is HoCl – False (The formula for hydrochloric acid is HCl).

Q 2: Fill in the blanks  (1 mark each x 16 = 16 marks)

       i.  The formula of sodium chloride is NaCl.

     ii.  The formula of sulphuric acid is H2SO4.

   iii.   Acid + Base -------------> Salt + Water.

   iv.   Name of one common antacid is Milk of Magnesia, Mg (OH)2.

     v.  The formula of water is H2O.

   vi.   The formula of nitric acid is HNO3.

 vii.    In case of neutral substances, when one drop of their solution is put on either blue litmus or red litmus paper, there is no change in the colour of litmus paper.

viii. Bases turns red litmus to blue.

   ix. A base which is soluble in water is called an alkali.

     x. Sulphuric acid is used in making storage batteries for cars, buses, trucks, inverters.

   xi.  Carbonic acid is sued in fizzy soft drinks and soda water. (Formula of Carbonic acid is H2CO3)

 xii.   Lactic acid is present in curd and in sour milk. (Formula of lactic acid is C3H6O3)

xiii.  Tartaric acid is present in tamarind, unripe grapes, and unripe mangoes.

xiv.  Oxalic acid is majorly present in spinach.

  xv. Organic acids are the naturally occurring acids which are found in various types of plants and animals.

xvi.  Acids turn blue litmus to red.

Q 3: Name one natural and one synthetic indicator.                                                    (1 mark)

A 3: Some of the natural indicators are litmus (obtained from lichen and is purple in colour), red cabbage leaves, petals of petunia or geranium and turmeric solution (obtained from natural products).

Some of the synthetic Indicators – methyl orange and phenolphthalein (These are prepared and are not natural, watch out for the spelling of phenolphthalein).

Q 4: Write names of two neutral substances. 

 (1 mark)

A 4: Pure distilled water and Sodium chloride solution, NaCl (common salt) are examples of neutral substances. Some more neutral substances are (it is better to know more) sugar, calcium 
carbonate and calcium chloride etc. are neutral.

Q 5: Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.                                                    (2 marks)

A 5: The nature of the given solution can be basic or neutral.

Basic and neutral solutions do not change the colour of blue litmus paper. Since blue litmus remains blue after dipping in the solution, the solution will be either basic or neutral in nature.

To know more about the solution type, put a drop of this solution on a red litmus paper. If it turns blue, then the above solution is basic in nature and if no colour change occurs, then it is definitely a neutral solution.

Q 6: What is meant by acid rain? How is acid rain caused? What two damages are caused by acid rain?   (3 marks)

A 6: Rain containing acid in the form of mild (not very strong) sulphuric acid and nitric acid due to chemical reaction of rain water with sulphur dioxide and nitrogen oxide is called acid rain.

Human activities such as release of sulphur dioxide by power plants and release of nitrogen oxide by burning of fossil fuels (petrol, diesel and coal) and their mixing with rain water are responsible for acid rain. The sulphur dioxide n air react with water to form sulphuric acid and nitrogen oxide react with rain water to form nitric acid.

Acid rain causes following damages:

1. Aquatic plants and animals may die due to acid mixing in sea and river water.

2. Causes damage to trees at high elevations (heights).

3. Causes damage to buildings and old historical monuments.

4. The sulphur dioxide and nitrogen dioxide give rise to respiratory problems such as asthma,headaches, and irritation in eye, nose, and throat.

Q 7: Name two materials which should be added to acidic soil to reduce the acidity. Give reason.  

(3 marks)

A 7: Lime (Calcium carbonate), wood ashes and oyster shells can be added to make soil basic and reduce its acidity.

Lime is an alkali and thus neutralises the acidic effect and thus reduces the acidity. Wood ashes and oyster shells are also used to make the soil basic and reduce its acidity.

Q 8: What are three types of salts? Give one example of each type of salt.                    (3 marks)

A 8: A salt is a product formed by the neutralization of an acid by a base.

Three types of salt are:

1. Acidic
2. Basic
3. Neutral

Example of acidic salt is NH4Cl (Ammonium chloride).

Example of basic salt is Na2CO3 (Sodium carbonate).

Example of neutral salt is NaCl (Sodium chloride).