Observations That Help Us to Determine a Chemical Reaction

Q.

Write any two observations in an activity which may suggest that a chemical reaction has taken place. Give an example in support of your answer.

Q.

How do we come to know that a chemical reaction has taken place

Q.

Methane gas $\left({\text{CH}}_4\right)$ when burns with oxygen $\left({\text{O}}_2\right)$ gives carbon dioxide and water. Write the balanced chemical equation and provide the following information in terms of reactants and products in the equation. [5 Marks]

(a) no. of molecules
(b) no. of moles
(c) molar mass
(d) total mass of reactants and products
What does statement (d) infer?

Q. Ammonia gas reacts with hydrogen chloride gas to produce ammonium chloride. The physical state in which ammonium chloride is present is _________.

1. solid
2. liquid
3. gas
4. solution

Q.

Name two characteristics of the chemical reaction involving solutions of lead nitrate and potassium iodide.

Q.

The chemical reaction between quicklime and water is characterised by :
(a) evolution of hydrogen gas

(b) formation of slaked lime precipitate

(c) change in temperature of mixture

(d) change in colour of the product

Q.

Which of the following observations helps to determine whether a chemical reaction has taken place or not?

(i) Change in state.

(ii) Change in colour.

(iii) Change in shape

(iv) Evolution of gas.

(v) Change in temperature.

1. (i), (ii), (iii), (v)

2. (iii), (v)

3. (ii), (iii), (iv), (v)

4. (i), (ii), (iv), (v)

Q.

What change in colour is observed when white silver chloride is left exposed to sunlight state the type of chemical reaction in this change

Q.

9. What is charring of sugar? State whether it is a physical change or chemical change.

Q. Which of these given reactions is identified as a gas evolving reaction?

1. Reaction of zinc and sulphuric acid
2. Reaction of sodium hydroxide and sulphuric acid
3. Reaction of potassium iodide and lead nitrate
4. Reaction of quick lime and water

Q.

State one relevant observation for each of the following reactions:
Action of concentrated sulphuric acid on hydrated copper sulphate.

Q.

how do you come to know wether chemical reaction has taken place or not?

Q.

When ${\mathrm{H}}_2\mathrm{S}$ gas is bubbled through an aqueous solution of Copper(II) sulphate, a black precipitate of $\mathrm{CuS}$ is obtained. Write a balance reaction.

Q. When ferrous sulphate $\left({\text{FeSO}}_4\right)$ solution combines with sodium hydroxide $\text{(NaOH)}$, the chemical change is identified by the .

1. formation of gas
2. formation of ppt
3. absoprtion of heat

Q.

Why is the melting of wax a physical change while the burning of a candle is a chemical change?

Q.

State the chemical property of baking soda on which the following uses are based:
(i) as an antacid.
(ii) as a constituent of baking powder.

Q.

What do you understand by the following terms?

(a) Chemical Equation

Q. Which of the following are examples of exothermic processes?

1. Melting
2. Respiration
3. Burning
4. Evaporation

Q.

What is the colour of the precipitate formed when solution of ferrous sulphate is mixed with sodium hydroxide solution?

1. Dirty green

2. Dark blue

3. Dark brown

4. Dirty yellow

Q. Which of the following is not an observation that determines a chemical change?

1. 
   Evolution of a gas
2. 
   Change in temperature
3. 
   Formation of precipitate
4. 
   Change in mass

Q.

Why is it that burning of a candle involves both physical and chemical changes?

Q.

Name the reactant used for the preparation of Iron (II) sulfate?

Q.

Write the characteristics of chemical reactions.

Q.

Dissolving of quick lime in water is accompanied by:

1. Formation of precipitate

2. Evolution of heat

3. Change in state

4. Change in colour

Q.

Question 53
An element A reacts with water to form a compound B which is used in whitewashing. The compound B on heating forms an oxide C which on treatment with water gives back B. Identify A, B and C and give the reactions involved.

Q.

Melting of ice is an example of

1. Physical change

2. irreversible change

3. Chemical change

4. Undesirable change

Q.

State three characteristics that show a chemical reaction has occurred.

Q.

Digestion of food is a physical change

1. True
2. False

Q.

Write a balanced chemical reaction where the natural mixing of two colorless aqueous solutions produces a yellow precipitate.

Q. Which of these suggest that a chemical reaction may be occurring?

1. Change of colour
2. Change of state
3. Reduction of temperature
4. Release of a gas