CBSE Class 7 Science Acid Bases and Salts Worksheet Set A

Read and download free pdf of CBSE Class 7 Science Acid Bases and Salts Worksheet Set A. Download printable Science Class 7 Worksheets in pdf format, CBSE Class 7 Science Chapter 5 Acids, Bases and Salts Worksheet has been prepared as per the latest syllabus and exam pattern issued by CBSE, NCERT and KVS. Also download free pdf Science Class 7 Assignments and practice them daily to get better marks in tests and exams for Class 7. Free chapter wise worksheets with answers have been designed by Class 7 teachers as per latest examination pattern

Chapter 5 Acids, Bases and Salts Science Worksheet for Class 7

Class 7 Science students should refer to the following printable worksheet in Pdf in Class 7. This test paper with questions and solutions for Class 7 Science will be very useful for tests and exams and help you to score better marks

Class 7 Science Chapter 5 Acids, Bases and Salts Worksheet Pdf


Acid Bases and Salts 

To understand the process of neutralization.
 
Question 1- What will be the color of basic solution after the addition of phenolphthalein?
Answer- Pink.
 
Question 2- Name the products of neutralization.
Answer- Salt and water.
 
EXERCISE
 
Question 1- Fill In The Blanks.
 
(i) Acids are sour in taste.
(ii) Litmus and turmeric extract are natural indicators.
(iii) Phenolphthalein is colorless in acidic solution.
(iv) Reaction between an acid and a base is called neutralization reaction.
(v) Ant’s sting has formic acid.
(vi) Excess secretion of hydrochloric acid in stomach, is called acidity.
(vii) Milk of magnesia is used in case of acidity.
 
 
Question 2- Match The Column ‘A’ With Column ‘B’.

7th.sci.eng.july.aug.new 3

 
Question 3. Choose The Correct Answer.
 
(i). Vinegar contains :
a) Acetic acid (✓)   b) Lactic acid   c) Citric acid   d) Tartaric acid
 
(ii). Tamarind contains :
a) Acetic acid   b) Lactic acid   c) Citric acid   d) Tartaric acid (✓)
 
(iii). The example of natural indicator is :
a) Litmus   b) Turmeric extract   c) China rose petals d) All the above (✓)
 
(iv). The color of blue litmus in acidic solution is :
a) Purple   b) Blue   c) Red (✓)   d) Pink
 
(v). Amla contains :
a) Ascorbic Acid (✓)   b) Quick lime   c) Calamine   d) All the above
 
 
Question 4- Write True Or False.
 
(i) Citric acid is found in tamarind. (False)
(ii) Ant’s sting has oxalic acid. (False)
(iii) Turmeric extract gives reddish brown color in basic solution. (True)
(iv) Sodium hydroxide turns blue litmus red. (False)
(v) Organic matter is used to treat acidic soil. (True)
 
 
Question 5- Very Short Answer Type Questions.
 
(i) Which acid is secreted in our stomach?
Answer- Hydrochloric acid.
 
(ii) Name any two ant acids.
Answer- Baking soda and milk of magnesia.
 
(iii) What type of substances are used as ant bites?
Answer- Formic acid.
 
(iv) Name any two citrus fruits.
Answer- Orange and lemon.
 
(v) Why is it essential to treat acidic products?
Answer- Because acidic products pollute soil and water.
 
 
Question 6- Short Answer Type Questions.
 
(i) Name the source from which litmus solution is obtained. What is the use of this solution?
Answer- Litmus solution is obtained from Lichens. Litmus solution is used to test whether a substance is acidic or basic in nature.
 
(ii) Is the distilled water acidic/basic/neutral? How would you verify it?
Answer- Distilled water is neutral and one can easily test it with the help of litmus paper. When we dip blue or red litmus paper in distilled water, there will not be any change in the color.
 
(iii) Describe the process of neutralization with the help of an example.
Answer- When an acid is mixed with a base, and then they react with each other to form the salt and water with the release of energy and cancel each other's effect. This process is neutralization process.
                          Acid + Base → Salt + Water + Heat
Example:
NaOH + HCl → NaCl + H2O + Heat
 
(iv) Name any two common acids and two common bases.
Answer-
Acids- Citric acid, hydrochloric acid, sulphuric acid.
Bases- Sodium hydroxide, Magnesium hydroxide, Calcium hydroxide.
 
(v) What are indicators? Write their types and two examples of each.
Answer-
Indicators- These are special type of substances used to test whether a substance is acidic or basic.
Indicators give different color in acid and base.
Types- (1) Natural Indicators- Litmus, turmeric, china rose petals etc.
(2) Synthetic Indicators- Phenolphthalein, methyl orange etc.
 
 
Question 7- Long Answer Type Questions.
 
(i) State differences between acids and bases.
Answer-
                Acids                                                                             Bases
1. They are sour in taste.                                                 1. They are bitter in taste.
2. They change blue litmus into red.                                2. They change red litmus into blue.
3. They turn china rose extract dark pink.                      3. They turn china rose extract dark green.
4. They give no color change with phenolphthalein.      4. They give pink color with phenolphthalein.
5. For example lemon and orange have acid.                  5. For example soap and baking soda are bases.
 
(ii) Name the acid present in (i) Vinegar, (ii) tamarind, (iii) citrus fruits and (iv) curd.
Answer- (i) Vinegar- Acetic acid.
(ii) Tamarind- Tartaric acid.
(iii) Citrus fruits- Citric acid.
(iv) Curd- Lactic acid.
 
(iii) You are given hydrochloric acid solution, sodium hydroxide solution and water in three different bottles. How would you check which bottle has which compound?
Answer- We will take three turmeric indicator paper strips. Then we will put some drops from all the three solutions on different strips. The solution which turn the turmeric indicator red, is basic i.e. sodium hydroxide.
Now put some drops from other two bottles on this red paper. The solution which turns this red turmeric paper to yellow is acidic i.e. hydrochloric acid. Remaining solution is water which does not change the color of turmeric indicator in both conditions.

Question. What do you understand by the terms, acid and base?
Answer. 
(a) Acids are defined as compounds which contain one or more hydrogen atoms, and when dissolved in water, they produce hydronium ions (H3O+), the only positively charged ions.
(b) Hydronium ion
(c) H3O+

Question. Explain the formation of hydronium ion. Write the ionization of sulphuric acid showing the formation of hydronium ion.
Answer. Hydronium ions: They are formed by the reaction of H+ (from acid) and water. It reacts with water to form H3O+ (Hydronium ion).
H+ + H2O → H3O+
Ionization of sulphuric acid showing the formation of hydronium ion:

Question. Water is never added to acid in order to dilute it why?
Answer. If water is added to a concentrated acid, the heat generated causes the mixture to splash out and cause severe burns. Thus, water is never added to acid in order to dilute it.

Question. Define the term ‘basicity’ of an acid. Give the basicity of: nitric acid, sulphuric acid and phosphoric acid.
Answer.  Basicity: The basicity of an acid is defined as the number of hydronium ions (H3O+) that can be produced by the ionization of one molecule of that acid in aqueous solution.
The basicity of following compounds are:
Nitric acid: Basicity = 1
Sulphuric acid: Basicity =2
Phosphoric acid: Basicity =3

Question. Give two examples of each of the following:
(a) oxy-acid
(b) hydracids
(c) monobasic acid
(d) dibasic acid
(e) tribasic acid
Answer. 
(a) Oxyacids: - HNO3, H2SO4
(b) Hydracid:- HCl, HBr
(c) Monobasic acid:- HCl, HBr
(d) Dibasic acid: - H2SO4 , H2CO3
(e) Tribasic acid:- H3PO4, H3PO3

Question. Name the:
(a) acidic anhydride of the following acids:
(i) sulphurous acid
(ii) nitric acid
(iii) phosphoric acid
(iv) carbonic acid
(b) acids present in vinegar, grapes and lemon
(c) (i) ion that turns blue litmus red,
(ii) ion that turns red litmus blue.
Answer. 
(a) The anhydride of following acids are:
(i) Sulphurous acid: SO2
(ii) Nitric acid: N2O5
(iii) Phosphoric acid: P2O5
(iv) Carbonic acid : CO2
(b) Acids present in following are:
Vinegar: Acetic acid
Grapes: Tartaric acid and Malic acid
Lemon: Citric acid
(c) (i) H+ ion turns blue litmus red.
(ii) OH- ion turns red litmus blue.

Question. What do you understand by the statement ‘acetic acid is a monobasic acid?
Answer.  Acetic acid is a monobasic acid which on ionization in water produce one hydronium ion per molecule of the acid.

Question.
(a) Give a balanced equation for reaction of nitrogen dioxide with water.
(b) How many types of salts does dibasic acid produce when it reacts with caustic soda solution? Give equation(s)
Answer. 
(a) 2NO2 + H2O ⟶ HNO2 + HNO3
(b) Two types of salts are produced when dibasic acid reacts with caustic soda. One is acidic salt and other normal salt.
Acid salts:
H2SO4 + NaOH ⟶ NaHSO4 + H2O
Normal salts:
H2SO4 + 2NaOH ⟶ Na2SO4 + 2H2O

Question. Carbonic acid gives an acid salt but hydrochloric acid does not. Explain.
Answer. 
The strength of an acid is the extent to which the acid ionizes or dissociates in water.
The strength of an acid depends on the degree of ionization and concentration of hydronium ions [H3O+] produced by that acid in aqueous solution.

Question. What do you understand by the strength of an acid? On which factor does the strength of an acid depend?
Answer. 
(a) Carbonic acid is a dibasic acid with two replaceable hydrogen ions; therefore it forms one acid salt or one normal salt.
Hydrochloric acid is a monobasic acid with one replaceable hydrogen ion and so forms only one normal salt.
(b) Strength of an acid is the measure of concentration of hydronium ions it produces in its aqueous solution. Dil. HCl produces high concentration of hydronium ion compared to that of concentrated acetic acid. Thus, dil. HCl is stronger acid than highly concentrated acetic acid.
(c) H3PO3 is not a tribasic acid because in oxyacids of phosphorus, hydrogen atoms which are attached to oxygen atoms are replaceable. Hydrogen atoms directly bonded to phosphorus atoms are not replaceable.
(d) The salt produced is insoluble in the solution so the reaction does not proceed. Hence, we do not expect lead carbonate to react with hydrochloric acid.
(e) NO2 is called double acid anhydride because two acids – nitrous acid and nitric acid – are formed when it reacts with water.
2NO2 + H2O → HNO2 + HNO3

Question. Dil. HCl acid is stronger than highly concentrated acetic acid. Explain.
Answer.  Acid rain is a by-product of a variety of human activities which release oxides of sulphur and nitrogen in the atmosphere. Burning of fossil fuels, coal, oil, petrol and diesel produces sulphur dioxide and nitrogen oxide which pollute the air. Polluted air also contains many oxidising agents which produce oxygen because of excessive heat. This oxygen combines with the oxides of sulphur and nitrogen and rain water to form acids.
2SO2 + O2 + 2H2O → 2H2SO4
4NO2 + O2 + 2H2O → 4HNO3

Question. How is an acid prepared from a
(a) Non-metal
(b) Salt?
Give an equation for each.
Answer. 
Acids are prepared from non-metals by their oxidation. For example :
Sulphur or phosphorus is oxidized by conc. Nitric acid to form sulphuric acid or phosphoric acid.
S + 6HNO3 H2SO4 + 2H2O + 6NO2
P + 5HNO3 H3PO4 + H2O + 5NO2
Acids are prepared from salt by displacement reaction. For example :
Nitric acid is prepared by using H2SO4 and sodium chloride.
NaCl + H2SO4 NaHSO4 + HNO3

Question. Name an acid used:
(a) to flavor and preserve food,
(b) in a drink,
(c) to remove ink spots,
(d) as an eyewash
Answer. 
(a) SO2 +H2O H2SO3
(b) P2O5 +3H2O 2H3PO4
(c) CO2 + H2O H2CO3
(d) SO3 + H2O H2SO4

Question. Give equations to show how the following are made from their corresponding anhydrides.
(a) sulphurous acid
(b) phosphoric acid,
(c) carbonic acid
(d) sulphuric acid
Answer. 
(a) Citric acid
(b) Carbonic acid
(c) Oxalic acid
(d) Boric acid

Question. What do you understand by an alkali? Give two examples of:
(a) strong alkalis
(b) weak alkalis
Answer. 
An alkali is a basic hydroxide which when dissolved in water produces hydroxyl ions (OH-) as the only negatively charged ions.
(a) Strong alkalis: Sodium hydroxide , Potassium hydroxide
(b) Weak alkalis: Calcium hydroxide , Ammonium hydroxide

Question. What is the difference between:
(a) an alkali and a base,
(b) an alkali and a metal hydroxide?
Answer. 
(a) An alkali and a base:
1. Alkalis are soluble in water whereas bases may be or may not be soluble in water.
2. All alkalis are bases but all bases are not alkalis.
(b) An alkali and metal hydroxide :
1. Alkalis are soluble in water whereas metal hydroxides may be or may not be soluble in water

Question. Define in terms of ionization:
(a) an acid
(b) an alkali
Answer. 
(a) An acid: Acids are defined as compounds which when dissolved in water produce hydronium ions.
(b) An alkali: Alkalis are compounds which when dissolved in water produces hydroxyl ions.

Question. Name the ions furnished by:
(a) bases in solution,
(b) a weak alkali
(c) an acid
Answer. 
(a) Bases in solution give hydroxide ion.
(b) Weak alkali gives hydroxide ions.
(c) An acid gives a hydronium ion.

Question. Give one example in each case:
(a) A basic oxide which is soluble in water,
(b) A hydroxide which is highly soluble in water,
(c) A basic oxide which is insoluble in water,
(d) a hydroxide which is insoluble in water,
(e) A weak mineral acid,
(f) a base which is not an alkali
(g) An oxide which is a base,
(h) A hydrogen containing compound which is not an acid,
(i) A base which does not contain a metal ion.
Answer. 
(a) Barium oxide
(b) Sodium hydroxide
(c) Manganese oxide
(d) Cupper hydroxide
(e) Carbonic acid
(f) Ferric hydroxide
(g) Copper oxide
(h) Ammonia
(i) Ammonium hydroxide


CBSE Class 7 Science Chapter 5 Acid Bases and Salts Very Short Answer

Question. What are neutral solutions? 
Answer. The solutions which do not change the colour of either red or blue litmus are called neutral solutions.

Question. Where we find the oxalic acid? 
Answer. Oxalic acid is found in spinach

Question. Define phenolphthalein? 
Answer. An indicator we have not used so far is called phenolphthalein.

Question.Where we find potassium hydroxide? 
Answer. Potassium hydroxide found in the soap.

Question. Define neutralisation? 
Answer. The reaction between an acid and

 

CBSE Class 7 Science Chapter 5 Acid Bases and Salts Short Answer

Question. What is the effect of the indicator on acidic basic and neutral solution 
Answer. When it is used as an indicator, its colour changes to green in basic solution and dark pink colour in acidic solutions. In neutral solution it colour does not change.
Phenolphthalein solution is colourless. When it comes in contact with basic solution, its colour changes to pink.

Question. What do you understand by the term indicators? 
Answer. Indicators are substances that change colour when they are added to acidic or alkaline solutions. Litmus, phenolphthalein, and methyl orange are all indicators that are commonly used in the laboratory.

Question. How does litmus detect acidic and basic solution? 
Answer. The main use of litmus is to test whether a solution is acidic or basic. Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic or alkaline conditions, with the colour change occurring over the pH range. Neutral litmus paper is purple.

Question. How acids are different form salts? 
Answer. 1. An acid is a substance which dissolved in water ionizes and releases hydrogen ions whereas a salt is a compound formed by the partial or complete replacement of the ionisable hydrogen atoms of an acid by a metallic ion.
2. Acid turns blue litmus paper to red whereas in salts there is no effect on litmus paper.

Question. What is china rose and why it is used as indicators 
Answer. China rose converts acidic solution to dark pink, basic solutions to green colour and has no colour change for neutral solutions. China rose is a natural indicator and is used to identify the acidic or basic nature of a solution.

 

CBSE Class 7 Science Chapter 5 Acid Bases and Salts Long Answer

Question. Explain neutralisation in everyday life? 
Answer. Neutralisation in everyday life are:
1. Indigestion: Our stomach contains hydrochloric acid, but too much of acid in the stomach causes indigestion. Sometimes indigestion is painful. To relieve indigestion, we take an antacid such as milk of magnesia, which contains magnesium hydroxide.
2. Factory wastes: Factory waste is neutralised before depositing it into the water bodies. Factory wastes are neutralized before disposing into water bodies because, factory wastes often contain acid. If it reaches a river, the acid will kill aquatic life. This is prevented by adding a base called slaked lime.
3. Soil treatment: Excessive uses of chemical fertilisers make the soil acidic. Plants do not grow well when the soil is either too acidic or too basic. When the soil is too acidic. It is treated with the bases like quick lime or slaked lime. If the soil is basic is organic matter is added to it.
4. Ant bite: when an ant bites it injects the acidic liquid into the skin. The effect of the acid can be neutralized by rubbing most baking soda.

Question. How litmus paper is different from pH paper? 
Answer. 1. pH paper is an indicator that can be used to determine the pH value of a solution whereas a litmus paper is an indicator that is used to determine the acidity or the basicity of a solution.
2. pH papers can give the exact pH value of a solution whereas litmus papers cannot give a value for the pH of a solution.
3. pH papers give more precise results whereas litmus papers give a less precise indication.
4. pH papers can give a range of colours in the presence of solutions with different pH values whereas litmus papers can give only two colours.

Question. State the difference between acid and base? 
Answer. 1. Acids are sour in taste whereas bases are bitter to taste.
2. Acids do not change the colour of turmeric indicator whereas bases turn the colour of turmeric indicator to red.
3. Acids do not change the colour of red litmus whereas bases turn red litmus blue.
4. Acids have pH value less than 7 whereas bases have pH value greater than 7.
5. Acids do not give soapy touch whereas bases give soapy touch.

Question. Explain about the natural indicators around us? 
Answer. Natural Indicator is a type of indicator that can be found naturally and can determine whether the substance is an acidic substance or a basic substance. Some examples of natural indicators are red cabbage, turmeric, grape juice, turnip skin, curry powder,
cherries, beetroots, onion, tomato, etc.
1. Litmus paper: When you want to determine the acidity or alkalinity of a liquid or water-soluble gas, the easiest way is to perform a litmus test. The test requires litmus papers, which are narrow strips of paper treated with chemical solutions that are sensitive to pH changes.
2. Turmeric as indicator: Turmeric, a common spice in curry, as an indicator for acidity and basicity. Turmeric is yellow in acid and neutral substances, but turns bright red with bases. Learners can use their indicator to test household chemicals and determine which are basic.

Question. Distinguish between acidic salt and basic salts?
Answer. 1. Acidic salts are ionic compounds that can form acidic solutions upon dissolution in water whereas basic salts are ionic compounds that can form basic solutions upon dissolution in water.
2. Acidic salts are less than pH 7.0 whereas basic salts are higher than pH 7.0.
3. Acidic salts reactivity forms protons whereas basic salts reactivity has force water molecules to remove hydroxide ions.
4. Acidic salts examples are ammonium salts, sodium bi sulphate and calcium oxalate whereas basic salts examples are: sodium bi carbonate, sodium sulphide etc.

 

 

Please click on below link to download CBSE Class 7 Science Acid Bases and Salts Worksheet Set A

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