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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
On what basis is a chemical equation balanced?
How will you indicate Endothermic reaction in a chemical equation?
Write complete balanced equation for the following reaction:
Calcium (solid) + water (liquid) 
Calcium Hydroxide (solution) + Hydrogen (gas)
When hydrogen is passed over copper oxide, copper and steam are formed. Write a balanced equation for this reaction and state which of the chemicals are compounds.
Carbon monoxide reacts with hydrogen under certain conditions to form methanol (CH3OH). Write a balanced chemical equation for this reaction indicating the physical states of reactants and product as well as the conditions under which this reaction takes place.
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.
Give one example of a chemical reaction characterised by formation of a precipitate.
When metal X is treated with a dilute acid Y, then a gas Z is evolved which burns readily by making a little explosion.
(a) Name any two metals which can behave like metal X.
(b) Name any two acids which can behave like acid Y.
(c) Name the gas Z.
(d) Is the gas Z lighter than or heavier than air?
(e) Is the reaction between metal X and dilute acid Y, exothermic or endothermic?
(f) By taking a specific example of metal X and dilute acid Y, write a balanced chemical equation for the reaction which takes place. Also indicate physical states of all the reactants and products.
The removal of oxygen from a substance is called:
(a) oxidation
(b) corrosion
(c) reduction
(d) rancidity
Write word equation for the following skeletal equation:
\[\ce{FeCl2 + Cl2 -> FeCl3}\]
Write your observation for the following chemical reaction and name the product formed:
When sugar is heated.
Write your observation for the following chemical reaction and name the product formed :
When dilute acetic acid is poured on baking soda.
Write symbolic representation for the following word equation and balance them :
Aluminium + Chlorine → Aluminium chloride.
Balance the following equation. Also name the product formed.
`"NaNO"_3 → "NaNO"_2 + "O"_2` Name of product (s)
Show the formation of Na2O by the transfer of electrons.
Balance the following equation:
Zn + KOH → K2ZnO2 + H2
Write the balanced chemical equation of the following reaction.
barium chloride + sulphuric acid → barium sulphate + hydrochloric acid
Define: Endothermic 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.
What is thermit process?
Write word equation for the following molecular equation:
\[\ce{CaCO3 + 2HCl ->[\triangle] CaCl2 + H2O + CO2 [g]}\]
Word equation:
State which characteristic does [g] in the above reaction indicate. The word equation of:
Give one example in the case where supplying energy [given below] is necessary for a chemical reaction.
Catalyst
Representation of the results of a chemical change – is a chemical equation.
For the equation: FeCl3 + 3NH4OH 3NH4Cl + Fe(OH)3 ↓
Answer the following:
Name the reactants and the products in the above equation.
Name the following:
The silvery residue obtained on heating mercury [II] oxide.
Name the following:
The gas evolved when a dilute acid is added to chalk [limestone].
Name the following:
Two gases which react under pressure in presence of a catalyst at elevated temperatures to give a gaseous product.
Give reason for the following:
Silver salts are kept in dark coloured bottles.
Write word equation for the following chemical reaction given below. Also state the observation seen in the case.
\[\ce{2SO2 + O2 ⇌[V2O5][450°C] 2SO3}\]
Balance the following simple equation:
\[\ce{Ca(OH)2 + HNO3 -> Ca(NO3)2 + H2O}\]
Balance the following simple equation:
Al + H2SO4 → Al2(SO4)3 + H2
Balance the following simple equation:
CaO + HCl → CaCl2 + H2O
Write a balanced equation for the following word equation:
Potassium nitrate → Potassium nitrite + Oxygen
Underline the compound in the equation given below, it is incorrectly balanced and write the correct balancing for the same.
Na2SO3 + HCl → 2NaCl + H2O + SO2
Write three steps of writing chemical equations with example?
What is called thermolysis reactions?
To balance the following chemical equation the value of x and y should respectively be:
\[\ce{2NaOH + xAl_2O_3->yNaAlO_2 + H_2O}\]
Why should a magnesium ribbon be cleaned before burning in air?
