List of top Science Questions on Chemical Reactions

In the following reaction, what is the name of compound ‘A’? \[ \text{NaCl} + \text{NH}_3 + \text{H}_2\text{O} + \text{CO}_2 \rightarrow \text{A} + \text{NH}_4\text{Cl} \]
While burning a magnesium ribbon in air, list two safety measures which should be followed. Also state two observations of this activity.

Select from the following a statement which is not true about the burning of magnesium ribbon in air:

In which of the following reactions is a combination reaction taking place?
I. CuO + H$_2$ $\xrightarrow{\Delta}$ Cu + H$_2$O
II. ZnO + C → Zn + CO
III. 4Na + O$_2$ → 2Na$_2$O
IV. CH$_4$ + 2O$_2$ → CO$_2$ + 2H$_2$O
i) Write balanced equations for the following reactions:
(a) Aluminum + Copper chloride → Aluminum chloride + Copper:
(b) Magnesium + Hydrochloric acid → Magnesium chloride + Hydrogen:
Complete the following chemical equation:
\(\underline{\hspace{2cm}}\) + CO_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O}
Why do we balance a chemical equation? Name and state the law that suggests the balancing of a chemical equation. Balance the following chemical equation: \[ {Zn} + {H}_3 {PO}_4 \rightarrow {Zn}_3 {(PO}_4{)}_2 + {H}_2 \]
Assertion (A): Concentrated nitric acid is diluted by adding water slowly to acid with constant stirring.
Reason (R): Concentrated nitric acid is easily soluble in water.
In the light of the above statements, choose the most appropriate answer from the options given below:
Write the chemical formula of bleaching powder. Write the balanced chemical equation for its preparation. List three uses.
When barium chloride and sodium sulphate react together in aqueous solution, an insoluble substance is formed with sodium chloride in the aqueous solution. This reaction is an example of:
Example of thermal decomposition reaction are:
  1. \( \text{2AgCl} \rightarrow \text{2Ag} + \text{Cl}_2 \)
  2. \( \text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2 \)
  3. \( \text{2H}_2\text{O} \rightarrow \text{2H}_2 + \text{O}_2 \)
  4. \( \text{2KClO}_3 \rightarrow \text{2KCl} + \text{3O}_2 \)
Show the formation of calcium chloride by the transfer of electrons from one element to the other. Atomic Number of calcium and chlorine is 20 and 17 respectively.
Name the compound used in black and white photography. State whether the reaction that occurs is exothermic or endothermic. Give justification for your answer.

Name an alcohol and a carboxylic acid having two carbon atoms in their structures. Draw their structures and state how this alcohol and carboxylic acid can be converted into a carboxylic acid. What happens when these two compounds react in the presence of an acid? Write chemical equations for the reactions involved in the two cases mentioned above. 

Glucose reacts with oxygen in the cells of our body and provides energy.
Natural gas is burnt in air.
Steam is passed over red hot iron.

The colour of the solution observed after about 1 hour of placing iron nails in copper sulphate solution is: 

The colour of the solution observed after about 1 hour of placing iron nails in copper sulphate solution is:
How is washing soda obtained from sodium chloride? Give the chemical equations of the reactions involved in the process.

Common salt is a very important chemical compound for our daily life. It’s chemical name is sodium chloride and it is used as a raw material in the manufacture of caustic soda, washing soda, baking soda etc. It is also used in the preservation of pickles, butter, meat etc.
(i) Name the acid and the base from which common salt can be obtained. 
(ii) State the nature (acidic/basic/neutral) of sodium chloride. Give reason for the justification for your answer. 
(iii) (A) What happens when electric current is passed through an aqueous solution of sodium chloride (called brine)? 
Name the products obtained along with the corresponding places in the electrolytic cell where each of these products is obtained.

What happens when butane is burnt in air? Write the chemical equation for the reaction. Differentiate between the flames obtained when butane and butyne both are burnt in air in similar conditions.
Define a precipitation reaction. Give its example and also express the reaction that occurs in the form of a balanced chemical equation.
In which one of the following situations a chemical reaction does not occur?
In order to prepare dry hydrogen chloride gas in a humid atmosphere, the gas produced is passed through a guard tube (drying tube) which contains: