Chemical Reactions

Q. Complete the following reaction:
$\text{Mg}+{\text{O}}_2\to$ _______

1. Magnesium oxide
2. Magnesium dioxide
3. Magnesium hydroxide
4. Magnesium carbonate

Q.

Write one of the reaction for each of the following characteristics

change of colour

Q. What do you observe when:
(e) an iron nail is kept in tap water for few days

Q. Fill in the blanks:
(d) Chemical change occurs as a result of between two substances.

Q.

When magnesium is burned in the air , a powdery ash X is formed. x on dissolving with water forms Y . What are Y and X

Q.

What happens when the magnesium ribbon is burnt in oxygn

Q. This gas has a rotten egg smell

1. Hydrogen sulphide
2. Hydrogen
3. Ammonia
4. Oxygen

Q. Chemical reactions involve _____ changes.

1. Temporary
2. Chemical
3. Physical
4. A and C

Q. Fill in the blanks:

(a) A new substance is always formed in a ______ change.

Q. Define:
(ii) a chemical change

Q.

Nitrogen reacts with hydrogen under high temperature and pressure and forms ammonia. Which type of change is undergone in the given example?

1. A natural change

2. A physical change

3. An electric change

4. A chemical change

Q. When vinegar is added to baking soda, confirms the occurrence of a chemical change.

1. evolution of gas
2. change in colour
3. change in state

Q. What happens when a solution of an acid is mixed with a solution of a base in a test tube?
(i) The temperature of the solution increases
(ii) The temperature of the solution decreases
(iii) The temperature of the solution remains the same
(iv) Salt formation takes place

1. (i) only
2. (i) and (iii)
3. (ii) and (iii)
4. (i) and (iv)

Q. <!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> We need to be cautious while using acids in laboratory.

1. False
2. True

Q. Identify the type of reaction in the given images:

1. 
2. 
3. 
4. 

Q. When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.​ [2 marks]

Q. The unbalanced equation is

1. $2H_2{O}_2\to 2H_{2}O+O_2$
2. $CaO+H_{2}O\to Ca(OH{)}_2$
3. $2Mg+O_2\to 2MgO$
4. $H_2+O_2\to 2H_{2}O$

Q. Chromatography is used to separate:

1. molecules
2. mixtures
3. compounds
4. atoms

Q. An element with the atomic number $19$ will most likely combine chemically with the element whose atomic number is :

1. $18$
2. $11$
3. $17$
4. $20$

Q. Explain Combination reaction with examples.

Q. What is chromatography? ​

Q.

When carbon dioxide is passed through limewater, it turns milky due to the formation of ____________.

Q. Define combination reaction.

Q. A scientist while working on an experiment found a compound with chemical formula $Fe(HC{O}_3{)}_3$. What is its atomicity?

1. 8
2. 6
3. 16
4. 15

Q. what happens when magnesium burns in air ? write the chemical equstion.

Q. Which of the following are correct with respect to chemical reactions?
(i) Chemical composition changes
(ii) Formation of new products takes place
(iii) We can’t obtain the intial reactants by simple physical means like filtering, dissolving etc.

1. Only (i) and (ii)
2. All (i), (ii) and (iii)
3. Only (ii) and (iii)
4. Only (i) and (iii)

Q.

List the observations that helps us to determine when a chemical reaction has taken place.

Q. When vinegar is added to baking soda, confirms the occurrence of a chemical change.

1. change in state
2. evolution of gas
3. change in colour

Q. <!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> A word equation consists of symbols of the reactants and the products.

1. True
2. False

Q. Which one of the following processes involve chemical reactions?
(i) Filling of LPG gas under pressure in gas cylinders
(ii) Liquefaction of air
(iii) Rusting of an iron object
(iv) Ripening of fruits