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Chemistry 1 Marks Question

The s-block Elements · Haryana Board (HBSE) STD 11 Science (Haryana - English Medium). 81 questions.

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Question 11 Mark
Write balanced equations for reactions between:
$\text{KO}_2$ and water.
Answer
$2\text{KO}_2+2\text{H}_2\text{O}\xrightarrow{\ \ \ \ \ }2\text{KOH}+\text{H}_2\text{O}_2+\text{O}_2$
or $4\text{KO}_{2(\text{s})}+2\text{H}_2\text{O}_{(\text{l})}\xrightarrow{\ \ \ \ \ }4\text{KOH}_{(\text{aq})}+3\text{O}_{2(\text{g})}$
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Question 21 Mark
Comment on each of the following observations:
Lithium is the only alkali metal to form a nitride directly.
Answer
Lithium is a very strong reducing agent. As a result, it directly combines with nitrogen to form its nitride $\left(\mathrm{Li}_3 \mathrm{N}\right)$.
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Question 31 Mark
Write balanced equations for reactions between:
$\text{Na}_2\text{O}$ and $\text{CO}_2$.
Answer
$\text{Na}_2\text{O}+\text{CO}_2\xrightarrow{\ \ \ \ \ \ }\text{Na}_2\text{CO}_3$
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Question 41 Mark
Write balanced equations for reactions between:
$\text{Na}_2\text{O}_2$ and water.
Answer
$\text{Na}_2\text{O}_2+2\text{H}_2\text{O}\xrightarrow{\ \ \ \ \ }2\text{NaOH}+\text{H}_2\text{O}_2$
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Question 51 Mark
Why are alkali metals strong reducing agents?
Answer
It is because of low ionisation enthalpy. They can lose electrons easily, that is why they are strong reducing agents.
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Question 61 Mark
Name the alkali metal which shows diagonal relationship with magnesium.
Answer
Lithium shows diagonal relationship with magnesium due to similar charge over radius ratio.
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Question 71 Mark
Arrange the following in order of their increasing covalent character:
MCI, MBr, ME, MI (where M is alkali metal.)
Answer
MF < MCI < MBr < MI, lesser the difference in electronegativity, more will be covalent character.
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Question 81 Mark
How does the basicity of oxides of group 2 increases down the group?
Answer
The basicity increases down the group
$\text{BeO}<\text{MgO}<\text{CaO}<\text{SrO}<\text{BaO}\\ \text{Amphoteric}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Strongly basic}$
Among the oxides of alkaline earth metals, BeO is amphoteric while other oxides are basic in nature. The decrease in basic character of oxides from Be to Ba is because of decrease in polarising power with increase in ionic size.
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Question 91 Mark
When is a cation highly polarising? Which alkali metal has highest polarising power?
Answer
Smaller the cation, higher the charge, high will be the polarising power. $\text{Li}^+$ has highest polarising power in group 1 due to smallest size.
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Question 101 Mark
How would you distinguish between
  1. $\mathrm{Be}(\mathrm{OH})_2$ and $\mathrm{Ba}(\mathrm{OH})_2$
  2. $\mathrm{BeSO}_4$ and $\mathrm{BaSO}_4$
Answer
  1. $\mathrm{Be}(\mathrm{OH})_2$, beryllium hydroxide is soluble in aqueous sodium hydroxide solution whereas $\mathrm{Ba}(\mathrm{OH})_2, ($barium hydroxide$)$ does not, because $\mathrm{Be}(\mathrm{OH})_2$ is amphoteric in nature.
$\text{Be(OH)}_2+2\text{NaOH}\xrightarrow{ \ \ \ \ \ \ \ \ }\text{Na}_2[\text{Be(OH)}_4]\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Sodium beryllate}$
  1. $\mathrm{BeSO}_4$ is soluble in water whereas $\mathrm{BaSO}_4$ is insoluble in water.
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Question 111 Mark
Name any two ores of magnesium.
Answer
Magnesite $\left(\mathrm{MgCO}_3\right)$, dolomite $\left(\mathrm{CaCO}_3 \cdot \mathrm{MgCO}_3\right)$.
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Question 121 Mark
What is magnesia cement? Give its composition.
Answer
When a saturated solution of magnesium chloride is mixed with magnesium oxide, it sets to a hard mass. This hard mass is known as magnesia cement. Its composition is $\mathrm{MgCl}_2 \cdot 5 \mathrm{MgO} \cdot \mathrm{H}_2 \mathrm{O}$.
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Question 131 Mark
Why are alkali metals soft?
Answer
They are soft metals due to less force of attraction between positively charged kernels and valence electrons cloud and due to large atomic size, i.e., weak metallic bond.
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Question 141 Mark
What product is obtained by reaction of CaO with C at high temperature?
Answer
$\text{CaO}+3\text{C}\xrightarrow[2273\text{k}]{\text{heat}}\text{CaC}_2+\text{CO}$.
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Question 151 Mark
Mention the main constituents of Portland cement.
Answer
Dicalcium silicate (26%), tricalcium silicate (51%) and tricalcium aluminate (11%).
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Question 161 Mark
Arrange the alkaline earth's metal sulphate in decreasing order of solubility?
Answer
$\mathrm{MgSO}_4>\mathrm{CaSO}_4>\mathrm{SrSO}_4>\mathrm{BaSO}_4$ because smaller the cation, higher will be hydration energy.
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Question 171 Mark
Arrange LiCl, KCl, NaCl, CsCl in increasing order of ionic character.
Answer
CsH < RbH < KH < NaH < LiH.
Smaller the atom, stronger will be the bond with hydrogen, more stable.
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Question 181 Mark
Lithium is the only alkali metal that forms nitride directly on reaction with air. Explain.
Answer
$\mathrm{Li}^{+}$ion being small in size can easily stabilize small nitride ion $\mathrm{N}^{3-}$, however other alkali metal ions because of their larger size cannot stabilise smaller nitride ion. Thus, only lithium forms nitride.
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Question 201 Mark
Why is sulphur estimated as $\mathrm{BaSO}_4$ and not as $\mathrm{MgSO}_4$​​​​​​​?
Answer
$\mathrm{BaSO}_4$ is insoluble in water whereas $\mathrm{MgSO}_4$ is soluble in water. Therefore, sulphur is converted into and then converted into white precipitate of $\mathrm{BaSO}_4$.
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Question 211 Mark
Why does Be resemble Al?
Answer
Be resembles Al because charge over radius ratio is similar, i.e., they have similar polarizing power.
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Question 221 Mark
Give the chemical formula of quick lime, slaked lime and lime water.
Answer
Quick lime is CaO , slaked lime is $\mathrm{Ca}(\mathrm{OH})_2$ and lime water is an aqueous solution of $\mathrm{Ca}(\mathrm{OH})_2$.
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Question 231 Mark
The second ionization enthalpy of Ca is higher than first and yet calcium forms $\mathrm{CaCl}_2$ and not CaCl , why?
Answer
The hydration energy of $\mathrm{Ca}^{2+}$ overcomes the second ionisation energy of Ca , that is why Ca forms $\mathrm{CaCl}_2$ and not $\mathrm{CaCl} . \mathrm{Ca}^{+}$is not stable.
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Question 241 Mark
What is epsom salt? What is the action of heat on it?
Answer
$\text{MgSO}_4\cdot7\text{H}_2\text{O};$
$\text{MgSO}_4\cdot7\text{H}_2\text{O}\xrightarrow[-6\text{H}_2\text{O}]{423\text{K}}\text{MgSO}_4\cdot\text{H}_2\text{O}\\ \xrightarrow[-\text{H}_2\text{O}]{573\text{K}}\text{MgSO}_4\xrightarrow{\text{Heat}}\text{MgO}+\text{SO}_3$
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Question 251 Mark
Complete the following reaction:
$\text{O}_2^{-}+\text{H}_2\text{O}\xrightarrow{\ \ \ }$
Answer
Superoxide react with water and form $\mathrm{H}_2\mathrm{O}_2$ and $\mathrm{O}_2$.
$2\text{O}_2^{-}+2\text{H}_2\text{O}\xrightarrow{\ \ \ }2\text{OH}^-+\text{H}_2\text{O}_2+\text{O}_2$
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Question 261 Mark
What happens when K burns in air? Give chemical equation.
Answer
$\text{K}+\text{O}_2\overrightarrow{}\text{KO}_2$ potassium superoxide will be formed.
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Question 271 Mark
Which member of the alkaline earth metals family has:
  1. Least reactivity
  2. Lowest density
  3. Highest boiling point
  4. Maximum reduction potential?
Answer
  1. $Be$
  2. $Ca$
  3. $Be$
  4. $Be$
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Question 291 Mark
Why is $\mathrm{KO}_2$ used in oxygen cylinder in space and submarines?
Answer
It is because it absorbs $\mathrm{CO}_2$ and increases oxygen content.
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Question 301 Mark
Why do lithium salts show least electrical conductance in aqueous solution?
Answer
It is because $\text{Li}^+$ are most hydrated due to smaller size, hence their mobility is least, hence conductivity is least.
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Question 311 Mark
Which magnesium compounds are the constituents of toothpaste?
Answer
$\mathrm{Mg}(\mathrm{OH})_2$ and $\mathrm{MgCO}_3$ are the constituents of toothpaste.
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Question 321 Mark
Why does $\text{BeCl}_2$ fumes in moist air?
Answer
It is because it is covalent, gets hydrolysed forming HCI which fumes in moist air.
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Question 331 Mark
Arrange the alkaline earth metal carbonates in the decreasing order of thermal stability.
Answer
The decreasing order of thermal stability is $\mathrm{BaCO}_3>\mathrm{SrCO}_3>\mathrm{CaCO}_3>\mathrm{MgCO}_3>\mathrm{BeCO}_3$
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Question 341 Mark
Why are alkali metals used in photoelectric cells?
Answer
They have low ionisation enthalpy and can lose electrons when light falls on them, that is why they are used in photoelectric cells.
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Question 351 Mark
Why do alkali metals have low melting and boiling points?
Answer
It is due to weak metallic bonds which is due to bigger atomic size that is why they have low melting and boiling points.
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Question 361 Mark
Why does common salt becomes damp during rainy season?
Answer
It is due to presence of $\text{CaCl}_2$ and $\text{MgCl}_2$ as impurities which are hygroscopic.
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Question 371 Mark
Which colours are imparted to flame when the following elements are introduced in the flame one by one?
  1. Strontium.
  2. Barium.
  3. Calcium.
Answer
  1. Strontium $-$ brick red.
  2. Barium $–$ grassy green.
  3. Calcium $-$ Crimson red.
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Question 381 Mark
Write any two uses of $\text{NaHCO}_3$.
Answer
  1. It is a mild antiseptic for skin infections.
  2. It is used in fire extinguishers.
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Question 391 Mark
Write the chemical reactions involved in the formation of soda as from sodium carbonate (decarbohydrate).
Answer
$\text{Na}_2\text{CO}_3.10\text{H}_2\text{O}\xrightarrow{375\text{K}}\text{Na}_2\text{CO}_3.\text{H}_2\text{O}+9\text{H}_2\text{O}$
$\text{Na}_2\text{CO}_3.\text{H}_2\text{O}\xrightarrow{>373\text{K}}\text{Na}_2\text{CO}_3+\text{H}_2\text{O}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{(Soda)}$
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Question 401 Mark
Why is $\text{BeCl}_2$ soluble in organic solvents?
Answer
$\text{BeCl}_2$ is covalent, therefore, soluble in organic solvents.
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Question 411 Mark
Why is fly ash used as cement substitute.
Answer
Fly ash is waste product of iron industry and thermal power plants. Its properties are similar to cement because it mainly consist of calcium silicate, therefore, can be used as cement substitute.
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Question 421 Mark
Show by a chemical reaction that $\text{Na}_2\text{O}$ is a basic oxide.
Answer
$\text{Na}_2\text{O}\text{(s)}+2\text{HCL}\text{(aq)}\overrightarrow{\ \ \ \ \ \ \ \ \ } 2\text{NaCl}\text{(s)}+\text{H}_2\text{O}\text{(l)}\\\text{Sodium} \ \ \ \ \ \text{Hydrochloric} \ \ \ \ \ \text{Sodium}\ \ \ \ \ \ \ \text{Water}\\ \text{oxide}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{acid}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{chloride}$
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Question 441 Mark
It is necessary to add gypsum in the final stages of preparation of cement. Explain why?
Answer
Gypsum $\left(\mathrm{CaSO}_4 2 \mathrm{H}_2 \mathrm{O}\right)$ is added in the final stages of preparation of cement since when $\mathrm{H}_2 \mathrm{O}$ is added to cement it slows down the process of setting of cement so that it gets sufficiently hardened thereby imparting greater strength to it.
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Question 451 Mark
The function of sodium pump is biological process operating in each and every cell of the animals. Which of this pump?
Answer
$\text{K}^+$ are constituent of this pump.
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Question 461 Mark
Why are metals usually not found as nitrates in their ores?
Answer
It is because metal nitrates are highly unstable and highly soluble in water due to higher hydration energy than lattice energy. Therefore, rarely found as ores.
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Question 471 Mark
Sodium fire in the laboratory should not be extinguished by pouring water. Why?
Answer
This is because sodium produces hydrogen gas with water which catches fire because of the exothermic nature of the reaction.
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Question 481 Mark
The enamel is made up of which compound?
Answer
$\mathrm{Ca}_3\left(\mathrm{PO}_4\right)_2$, Calcium phosphate.
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Question 491 Mark
Name some impurities found in brine solution.
Answer
It contains sodium sulphate, calcium sulphate, calcium chloride and magnesium chloride as impurities.
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