English Medium कक्षा १० - CBSE Important Questions for Science

With the help of an appropriate example, justify that some of the chemical reactions are determined by Change in colour 

Give chemical equation for the reaction involved in the above case. 

With the help of an appropriate example, justify that some of the chemical reactions are determined by Change in temperature.

Give chemical equation for the reaction involved in the above case.

Answer the following question.
2 g of silver chloride is taken in a china dish and the china dish is placed in sunlight for some time. What will be your observation in this case? Write the chemical reaction involved in the form of a balanced chemical equation. Identify the type of chemical reaction.

Answer the following question.
What is observed when 2 mL of dilute hydrochloric acid is added to 1 g of sodium carbonate taken in a clean and dry test tube? Write a chemical equation for the reaction involved.

In a double displacement reaction such as the reaction between sodium sulphate solution and barium chloride solution:

1. exchange of atoms takes place
2. exchange of ions takes place
3. a precipitate is produced
4. an insoluble salt is produced

The correct option is:

When aqueous solutions of potassium iodide and lead nitrate are mixed an insoluble substance separates out. The chemical equation for the reaction involved is: 

Bronze is an alloy of ______.

Select the appropriate state symbols of the products given as X and Y in the following chemical equation by choosing the correct option from table given below: 

\[\ce{Zn_{(s)} + H_2SO_{4(l)} ->ZnSO_{4(X)} + H_{2(Y)}}\]

Give the structural formula of ethanol.

In an experiment to study the properties of ethanoic acid, a student takes about 3 mL of ethanoic acid in a dry test tube. He adds an equal amount of distilled water to it and shakes the test tube well. After some time he is likely to observe that

(A) a colloid is formed in the test tube.

(B) the ethanoic acid dissolves readily in water.

(C) the solution becomes light orange.

(D) water floats over the surface of ethanoic acid.

While studying saponification reaction, a student measures the temperature of the reaction mixture and also finds its nature using blue/red litmus paper. On the basis of his observations the correct conclusion would be

(A) the reaction is exothermic and the reaction mixture is acidic.

(B) the reaction is endothermic and the reaction mixture is acidic.

(C) the reaction is endothermic and the reaction mixture is basic.

(D) the reaction is exothermic and the reaction mixture is basic.

What are covalent compounds?

Consider the following comments about saponification reactions:

I. Heat is evolved in these reactions.

II. For quick precipitation of soap, sodium chloride is added to the reaction mixtures.

III. Saponification reactions are a special kind of neutralisation reactions.

IV. Soaps are basic salts of long-chain fatty acids.

The correct comments are

(a) I, II and III

(b) II, III and IV

(c) I, II and IV

(d) Only I and IV

What do you observe when you drop a few drops of acetic acid to test tubes containing

(a) phenolphthalein

(b) distilled water

(c) universal indicator

(d) sodium hydrogen carbonate powder

Explain why carbon forms compounds mainly by covalent bond.

A student adds 2 mL of acetic acid to a test tube containing 2 mL of distilled water. He then shakes the test tube well and leaves it to settle for some time. After about 5 minutes he observes that in the test tube there is :

(A) a clear transparent colourless solution

(B) a clear transparent pink solution

(C) a precipitate settling at the bottom of the test tube

(D) a layer of water the layer of acetic acid

State the reason to explain why covalent compounds "have low melting and boiling points."

When you add about 2 ml of acetic acid to a test tube containing an equal amount of distilled water and leave the test tube to settle after shaking its contents, what will you observe in the test tube after about 5 minutes?

(A) A white precipitate settling at its bottom

(B) A clear colourless solution

(C) A layer of water over the layer of acetic acid

(D) A layer of acetic acid over the layer of water

A student adds a few drops of ethanoic acid to test tubes X, Y and Z containing aqueous solutions of sodium chloride, sodium hydroxide and sodium carbonate, respectively. If he now brings a burning splinter near the mouth of the test tubes immediately after adding ethanoic acid in each one of them, in which of the test tube or test tubes the flame will be extinguished?

(A) X and Y

(B) Y and Z

(C) X and Z

(D) only Z

In order to study saponification reaction, we first prepare 20% solution of sodium hydroxide. If we record the temperature of this solution just after adding sodium hydroxide flakes to water and also test its nature using litmus, it may be concluded that the process of making this solution is

(A) exothermic and the solution is alkaline

(B) endothermic and the solution is alkaline

(C) endothermic and the solution is acidic

(D) exothermic and the solution is acidic