DAV Class 7 Science Chapter 3 Chemical Substances and Processes Question Answer Notes
DAV Class 7 Science Chapter 3 Chemical Substances and Processes Question Answer Notes Solution by Expert Science Teacher. DAV Class 7 Science 3rd Chapter Chemical Substances and Processes for Students of DAV Schools.
Lesson No 3
Chemical Substances and Processes
A.) Fill in the blanks.
Answer: (1) pure substances (2) chemical formula (3) H2O (4) oxygen, moisture (5) chemical reaction (6) salt, water
B.) Write True or False for the following statements.
1.) All matter is made up of atoms. True
2.) Compounds are substances consisting of two or more elements chemically combined in a fixed ratio. True
3.) The symbol of element copper is Cu. True
4.) Formula of sodium chloride is written as ClNa. False
5.) The chemical formula of aluminium sulphate is Al2SO4. False
6.) New substance formed in a chemical reaction is called product. True
7.) Magnesium hydroxide is an acid. False
Answer: (1) True (2) True (3) True (4) False, it is Nacl (5) False , the formula is Al2(SO4)3 (6) True (7) False, It is a base.
C.) Tick the correct option.(write the questions)
Answer:
1.) silver
2.) one atom of hydrogen, one atom of nitrogen, and three atoms of oxygen.
3.) Mg3(PO4)2
4.) displacement reaction
5.) CaO
D.) Answer the following questions in brief.
1.) What are elements?
Answer: elements are substances that are made up of similar atoms.
2.) Give the chemical symbol of iron and chlorine.
Answer: Iron – Fe and chlorine – Cl
3.) Write the chemical formulae of the following compounds:
(a) Aluminium oxide (b) Zinc acetate
Answer:
(a) Al2O3
(b) (CH3COO)2Zn
4.) Balance the following equation:
Ca(OH)2 + HCl → CaCl2 + H2O
Answer: Ca(OH)2 + 2HCl → CaCl2 + 2H2O
5.) What does a chemical equation represent?
Answer: Chemical equations show chemical reactions and the chemical formulae of the reactants.
6.) What are reactants and products in a chemical equation?
On the left side of the arrow in a chemical reaction we write the chemical formulas of substances that react hence they are known as reactant, whereas on the right hand of the arrow we have the result of reaction hence they are known as product.
7.) Give one example of a combination reaction.
Answer: carbon reacting with oxygen to form carbon dioxide
C + O2 → CO2
E.) Answer the following questions.
1.) Write the steps involved in writing the chemical formula of calcium phosphate.
Answer:
First we need to know the chemical symbols for the calcium and phosphate ions.
Ca²+ (calcium), (PO4)³– (phosphate)
Their respective charges need to be intercrossed , thus their respective subscript also interchanges.
Ca2+ X (PO4)3- → Ca3(PO4)2
2.) How is a chemical change different from a physical change?
Answer: in a chemical reaction we usually see a different substance or product being formed whereas in physical reaction no new product is formed. The new product formed during the chemical reaction has a different chemical composition.
3.) Neutralisation reaction is a chemical change. Justify this statement with the help of an example.
Answer: For a neutralisation reaction an acid and base react to form a salt and water, these are new products whose chemical composition are unique. Thus , neutralisation reaction is a chemical change.
Example –
NaOH + HCl → NaCl + H2O
4.) Define a decomposition reaction and give an example of the same.
Answer: a reaction in which more than one product is obtained from one of the reactants.
The decomposition of water into hydrogen and oxygen is an example of decomposition reaction.
2H2O → 2H2 + O2
5.) Classify the following reactions into different types, giving reason.
Answer:
a.) Combination reaction, since two or more chemicals form a new substance
B.) Neutralisation reaction, since an acid and a base react to form a salt and water
C.) Displacement reaction, As copper displaces silver from silver nitrate solution
D.) Decomposition reaction, since the chemical is broken into its constituent chemicals.
More Extra Questions for Preparation
Q.1.) Fill in the blanks.
1.) Substances made up of positively and negatively charged particles called ions.
2.) Chemical formula of glucose is C6H12O6.
3.) Substances which undergo a chemical change in a reaction are called reactants.
4.) Mixture is not pure substances.
5.) Element is a pure substance which is made up of atoms of same kind.
Q.2.) Write the symbols of the following.
1.) Iron
Answer – Fe2+
2.) Phosphate
Answer – PO4
3.) Sodium
Answer – Na+
4.) Zinc
Answer – Zn 2+
5.) Chloride
Answer – Cl –
Q.3.) Identify the type of reaction with explanation.
1.) 2H2O + 2H2(g) + O2(g)
Answer – It is decomposition reaction, because in these more than one product is obtained.
2.) NaoH (aq) + HCl(aq) —–> Nacl + H2O
Answer – It is neutralization reaction, because the reaction is between an acid and base.
Q.4.) Write types of reaction.
Answer –
a.) Combination reaction
b.) Decomposition reaction
c.) Displacement reaction
d.) Neutralization reaction
5.) Write the formula of Sodium oxide.
Answer – Symbol of sodium is Na +1
Symbol of oxygen is O2-
Na+1 O 2- ———> Na2O1 = Na2O
Q.6.) Define the following.
1.) Ions
Answer – Substances are made up of positively and negatively charged particles called ions.
2.) Products
Answer – The new substances formed after a chemical reaction.
3.) Pure substances
Answer – Materials which are made up of same kind of particle are called pure substances.
4.) Combination reaction
Answer – A chemical reaction in which two or more substances combine to form a new substance.
Q.7.) Explain why iron nail is seen brown when crystal of copper sulphate is added.
Answer –
1.) The blue colour of solution changes into light green and a brown coating appears on the iron nail.
2.) This happens because iron displaces copper from copper sulphate and forms iron sulphate this is green in colour.
3.) Copper deposits as a brown coating on the iron nail.
Q.8.) True or false.
1.) A sodium hydroxide is an acid.
Answer – False
2.) When iron comes in contact with moisture and air it gets rusted.
Answer – True
3.) The symbol of Ammonium is NH4+.
Answer – True
4.) Na is negatively charged ion.
Answer – False
Q.9.) Complete the following.
1.) H2(g) + OO2(g) ——-> H2O
2.) 2Na + Cl2 ——> 2Nacl
3.) C(s) + O2(g) ——> Co2(g)
Can you please send 10 assertion/reason questions of this chapter