Science
Class 8
Topic: Elements And Compounds
Reinforcement Worksheet
Name:_____________________Sec:_______________________Date:_____________________
Q1.Choose the best answer.
1. Which of the following is an element?
a) steam b) sugar c)dry ice d) sulphur
2. Which of the following is an element but NOT a metal?
a) Oxygen b) copper c) aluminium d) salt
3. Which element can be found as charcoal, diamond or graphite?
a) Carbon b) nitrogen c) zinc d) phosphorus
4. Which metal is present in the liquid state at room temperature?
a) Helium b) bromine c) mercury d) lithium
5. Which substance does not have fixed melting and boiling points?
a) Water b) sugar c) ink d) sodium
6. Which of the following best supports the fact that air is a mixture?
a) The oxygen in the air is easily removed during combustion.
b) Air contains different elements.
c) The water vapour is a chemical compound.
d) The composition of the air remains almost constant throughout the world.
7. A compound contains
a) Different kinds of atoms mixed together.
b) The same kind of atom mixed together.
c) Different kinds of atoms chemically combined together.
d) The same kind of atom chemically combined together.
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Q2. Fill in the blanks.
a) Elements are classified into metals,__________ and __________
b) A _____________ is a substance which can not further divide by chemical reaction.
c) The most found element in the air is_______________
d) In the periodic table, elements are arranged in columns called______________
Q3. Complete the given statements.
(a)Rust is formed when iron objects are left out in the air. The iron reacts with the oxygen in the
air, forming iron oxide. Rust be can turned back into iron, by mixing it with carbon and heating
it. I think rust is _____________________ (an element / a mixture / a compound) because
______________________________________________________________________________
(b)Helium is a gas. There are tiny amounts of helium in the air. Helium does not burn, and will
not react with any other chemicals. It cannot be split up by chemical reactions. It think helium
is _____________________ (an element / a mixture / a compound) because
______________________________________________________________________________
Q4. Match the Columns.
A
1) A Compound used in photosynthesis
2) An element present both in air and water
3) A metal which is liquid at room temperature
4) A metal used for making cooking pot
5) A non metal used in air balloon
a)
b)
c)
d)
e)
B
Mercury
Helium
Carbon dioxide
Aluminum
oxygen
Q5. Are these statements true or false. Rewrite the false statement.
a) Elements are made of two or more different types of atoms.
___________________________________________________________________________
b) Mixtures have a definite composition.
___________________________________________________________________________
c) Compounds can be represented using a formula.
___________________________________________________________________________
d) A mixture of salt and water will boil at a higher temperature than pure water.
___________________________________________________________________________
e) Compounds can be decomposed on heating.
___________________________________________________________________________
f) The two most abundant elements in the Universe are Hydrogen & Helium.
___________________________________________________________________________
g) Chemical symbol for Copper is Co.
___________________________________________________________________________
h) Vertical columns in the periodic table are called periods.
___________________________________________________________________________
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i) Elements in the same group in the periodic table share similar chemical properties.
___________________________________________________________________________
j) Compounds can only be broken into simpler substances by chemical reactions.
___________________________________________________________________________
Q6a. Complete the following table:
Compounds
Elements they are made of
(i) Water
(ii) Carbon Dioxide
(iii) Ammonia
(iv) Iron Sulphide
(v) Sulphur Dioxide
Models of Compound
b. Classify the following as Elements (Metals and non-metals) and compound.
Carbondioxide, Iron, Sulphur, Helium, Nitrogen, Copper Sulphate, Copper, Oxygen, Aluminium, Carbon
Elements
Metals
Non-metals
Compounds
c. Write two properties on the basis of which you differentiate metals from non-metals.
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
d. The formula of Aluminium sulphate is Al2(SO4)3
i) How many elements are present in the above formula.
__________________________________________________________________________
ii) State the number of atoms of each element.
__________________________________________________________________________
__________________________________________________________________________
e. When Magnesium burns in air a white ash is formed.
i) Write a word equation for the reaction
__________________________________________________________________________
__________________________________________________________________________
ii) Is this a physical or a chemical change? Give two reasons.
__________________________________________________________________________
__________________________________________________________________________
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Q7. When copper carbonate is heated copper oxide and a gas are formed. The gas when
passed through lime water turns it milky as shown in the diagram below.
i) Which gas is produced that turns lime water milky?
__________________________________________________________________________
ii) Write a word equation for the above reaction.
__________________________________________________________________________
Q8. An alloy is a mixture of elements.
The table shows the mass of each element present in 100 g of five different alloys, bronze,
solder, steel, stainless steel and brass.
[4]
(a) Which alloy in the table above contains an element which is a non-metal?
______________________________________________________________________________
(b) Which two alloys in the table contain only two metals?
____________________________________ and ______________________________________
(c) Another alloy called nichrome contains only the elements chromium and nickel.
100 g of nichrome contains 20 g of chromium.
How much nickel does it contain? _______________ g
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Q9. Identify each of the following picture as an element E or a compound C.
Q10. Below is the first 36 elements in the periodic table with their atomic numbers.
(a) Give the symbol for one example of each of the following:
(i) a metal .............................(ii) an inert gas.......................
(iii)a non-metal in liquid state.............................
(b) Find chlorine in the table above. (i) What is the atomic number of Chlorine? .....................
(ii) What is the group number................................?
Q11. Different elements have different properties, some of which are shown below:
• Electrical insulator
• Good thermal conductor
• Poor thermal conductor
• High melting point
• Good electrical conductor
• Shiny
• Ductile
• Malleable
a) Gold is a metal. Give two properties of gold from the list above which make it a
good material to use as jewellery.
1 ...............................................................................................................................
2 ...............................................................................................................................
b) Krypton is a gas used inside a light bulb. Give two properties of krypton from the
list above which make it a good material to use.
1 ...............................................................................................................................
2 ...............................................................................................................................
c) Tungsten is used to make the filament inside a light bulb. Give two properties
from the list above which make it a good material to use.
(2)
1 ...............................................................................................................................
2 ...............................................................................................................................
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Q12. A science teacher showed her class three experiments, A, B and C. The experiments and
the word equations for the reactions that took place are shown below.
All the experiments were done in a fume cupboard.
(a) From the substances in experiments A, B and C, above, give the name of:
(i) three metallic elements; __________________________________________________
(ii) three non-metallic elements; ______________________________________________
(iii) two compounds. ________________________ and ________________________
(b) In experiment B, the iron filings weighed 2.0 g at the beginning of the experiment and the
iron sulphide produced weighed 2.8 g.
Explain this increase in mass.
______________________________________________________________________________
______________________________________________________________________________
(c) Complete the word equation for the chemical reaction in experiment C.
copper + chlorine → ____________________________
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