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प्रश्न
Grills of doors and windows are always painted before they are used.
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उत्तर
- Usually, grills of doors and windows are made of iron.
- Iron objects get rusted on exposure to moist air.
- Since air always contains moisture, iron grills get rusted.
- Painting iron objects prevents rusting, hence iron grills of doors and windows are painted before they are used.
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संबंधित प्रश्न
Balance the chemical equation.
\[\ce{HNO3 +Ca(OH)2 -> Ca(NO3)2 + H2O}\]
2 mL of sodium hydroxide solution is added to a few pieces of granulated zinc metal taken in a test tube. When the contents are warmed, a gas evolves which is bubbled through a soap solution before testing. Write the equation of the chemical reaction involved and the test to detect the gas. Name the gas which will be evolved when the same metal reacts with dilute solution of a strong acid.
Balance the following equation:
\[\ce{Mg(OH)2 + HCl -> MgCl2 + H2O}\]
Balance the following equation:
\[\ce{Al2(SO4)3 + NaOH -> Al(OH)3 + Na2SO4}\]
With the help of an appropriate example, justify that some of the chemical reactions are determined by a change in colour.
Give a chemical equation for the reaction involved in the above case.
State one characteristic of the chemical reaction which takes place when quicklime is treated with water.
Write a balanced chemical equation with state symbols for the following reaction:
Barium chloride solution reacts with sodium sulphate solution to give insoluble barium sulphate and a solution of sodium chloride.
Write word equation for the following skeletal equation:
\[\ce{Zn + HCl -> ZnCl2 + H2}\]
The step(s) necessary for determining the percentage of water absorbed by raisins is/are:
Balance the equation stepwise.
NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + H2O(l)
What is the limitation of the reaction given in question 2?
Write word equation for the following molecular equation:
FeSO4 + 2NaOH →Na2SO4 + Fe(OH)2 ↓
Word equation:
State why [↓] indication is seen after Fe(OH)2 and not after Na2SO4
A chemical reaction is generally accompanied by certain external indications or characteristics. These include – change of – (a) colour (b) state (c) smell (d) evolution of gas (e) formation of precipitate (f) evolution or absorption of heat. With reference to change of colour – state the change in colour seen when the following are heated – mercury [II] oxide.
Balance the following simple equation:
Mg + N2 → Mg3N2
Balance the following simple equation:
Fe + H2O ⇌ Fe3O4 + H2
Balance the following simple equation:
H2 + O2 → H2O
In the chemical equation the _______ are written on the left-hand side.
Which of the following is not a physical change?
Three beakers labelled as A, B and C each containing 25 mL of water were taken. A small amount of NaOH, anhydrous CuSO4 and NaCl were added to the beakers A, B and C respectively. It was observed that there was an increase in the temperature of the solutions contained in beakers A and B, whereas in case of beaker C, the temperature of the solution falls. Which one of the following statement(s) is(are) correct?
- In beakers A and B, exothermic process has occurred.
- In beakers A and B, endothermic process has occurred.
- In beaker C exothermic process has occurred.
- In beaker C endothermic process has occurred.
To balance the following chemical equation the value of x and y should respectively be:
\[\ce{2NaOH + xAl_2O_3->yNaAlO_2 + H_2O}\]
