Raveena covered a beaker of boiled water with a metal tray as shown in the diagram.
The beaker and metal tray were then removed from the tripod stand and left on the table. After two minutes, which of the following can be observed?
When the water vapours strike the cooler walls of container, they condense and form water droplets on the inner surfaces of metal tray and the beaker. This process is called condensation.
Sudha took lemon juice in two flasks. She put salt in flask I and washing soda in flask II. She observed lots of bubbles in flask II but nothing in flask I. What could be the reason for this?
Lemon juice (acid) reacts with washing soda (base) and liberates carbon dioxide gas i.e., a new substance is formed. Thus, it is a chemical change. Whereas, addition of salt in lemon juice is a physical change as only salt gets dissolved in lemon juice, no chemical reaction takes place.
Study the given Venn diagram carefully.
The centre point X represents
Boiling of an egg is a chemical, irreversible and slow change.
A metallic piece (X) is dropped into copper sulphate solution. After some time, the blue colour of the solution changes to green. The change which has occurred is
Metal (X), iron reacts with blue coloured solution of copper sulphate and forms a "new substance (green coloured solution of iron sulphate) and cannot be converted back to the original solution. Thus, it is an irreversible and chemical change.
Read the given passage and fill in the blanks by choosing an appropriate option. Iron nails when new are grey and bright. When exposed to (i), they get covered with a (ii) coating. This process is called (iii) and it is a (iv) change.
Mark the incorrect statement.
Changes which occur again and again after fixed intervals of time are known as periodic changes. For example, change of day and night, occurrence of full moon, beating of heart, oscillation of pendulum of clock, high and low tides in sea, etc. Changes which do not repeat themselves at regular intervals are called non-periodic changes. You cannot predict when will they reoccur. For example, occurrence of earthquake, accidents, sneezing, rusting of iron, growing of a tree, etc.
Few changes are given below. Mark the correct option from the codes given below.
(i) Milk is set to form curd.
(ii) Batter is steamed to form idlis.
(iii) Water is boiled to form steam.
(iv) Salt is dissolved in water to form solution.
A change in which a substance undergoes a change in its physical properties is called a physical change. It is generally reversible and in such a change, no new substance is formed. For example, boiling of water, dissolving of salt in water, melting an ice cube. A change in which one or more new substances are formed by means of a chemical reaction is called a chemical change. It is generally irreversible. For example, setting of milk into curd, making idlis, rusting of iron, cooking of food, etc.
Nitu mixed some iron filings with sulphur powder in a China dish. She heated the contents of China dish. What did she observe during the experiment?
On heating, iron reacts with sulphur to form black solid of iron sulphide. This is an irreversible, chemical change.
What is common among the following phenomena?
1. Blinking of traffic lights.
2. Rotation of blades of a fan.
3. Swinging of pendulum of a clock.
All these changes occur again and again after fixed intervals of time, hence are periodic changes.
Observe the two figures given below. In figure I, a solution of sugar in water is heated and in figure II, only sugar is being heated. What is the correct sequence of changes taking place?
In figure I, evaporation of water from sugar solution is a physical change because there is only change in state of matter from liquid (sugar solution) to solid state (crystals of sugar). In figure II, when sugar is heated, it turns black due to the formation of a new substance and it cannot be reversed. Therefore, it is a chemical change.
Rohan tore a sheet of paper into pieces and then burnt them. Identify the irreversible change taking place in the process.
Study the flowchart carefully.
(i) Melting of ice (i) Cutting of paper
(ii) Blowing of balloon (ii) Flowering of bud
Which of the following is correct?
The water formed after melting of ice can be frozen again to form ice. If the air inside the blown balloon is allowed to escape, then the balloon regains its original shape. So, both these changes are reversible changes. While changes like cutting of paper and flowering of bud cannot be reversed and hence, are irreversible.
A potter shapes pots out of clay (Process 1). He then bakes the pots in an oven (Process 2). Which of the following statements is correct?
Match the column I with column II and choose the correct option from the codes given below:
Digestion of food in our body - Slow change
Earthquake - Natural, undesirable change
Falling of stone - Fast change
Change of seasons - Natural, desirable change
Consider the following phenomena:
(i) Forest fire
(ii) Growth of plants
(iii) Low and high tides
(iv) Occurrence of a rainbow
(vi) Opening of a morning glory flower.
Which of the above phenomena can be classified as periodic changes?
Periodic changes are the changes which keep repeating themselves after a regular period of time. So, low and high tides and opening of a morning glory flower are the examples of periodic changes.
Observe the given figure carefully and choose the correct statement,
Processes (i) and (ii) involve absorption of heat while processes, (iii), (iv) and (v) involve evolution of heat.
Swati classified a few changes occurring around us as shown in the table.
Which of the changes is/are classified correctly?
Opening of a bud is a chemical and irreversible process.
Read the given statements and mark the correct option.
Statement 1: While fixing a metal rim on a wooden wheel of a cart, the size of the metal rim is kept slightly smaller than that of the wooden wheel.
Statement 2: Metals expand on heating and contract on cooling.
While fixing the metal rim, it is heated. It becomes slightly larger in size and can be fixed into the wooden wheel. On cooling, it contracts and fits tightly on to the wheel.
Study the given Venn diagram.
Identify points 1, 2 and 3.
Observe the given processes 1 and 2 carefully.
Which of the following statements are correct?
I. Bubbles are formed in process 1 while no bubble formation takes place in process 2.
II. Process 1 is slow while process 2 is fast.
Ill. Process 1 occurs at 100oC while process 2 can occur at any temperature.
Process 1 is boiling which is a fast process while process 2 is evaporation which is a slow process.