Question 11 Mark
Calculate the molecular mass of hydrogen bromide $(HBr).$
$($Atomic masses: $H = 1u; Br = 80u)$
AnswerMolecular mass of hydrogen bromide $(HBr)$
$= 1 × H + 1 × Br$
$= (1 + 80)u$
$= 81u$
View full question & answer→Question 21 Mark
If the valency of hydrogen is $1$ and that of nitrogen is $3,$ work out the formula for ammonia.
Answer$\ \text{Symbols}:\ \ \ \ \ \text{H}\ \ \ \ \ \ \ \ \ \text{N}\\ {\text{Valencies}}:\ +1\ \ \ \ -3$
So, chemical formula of ammonia is $\mathrm{NH}_3$
View full question & answer→Question 31 Mark
Work out the formulae for the following compounds:
`Sodium oxide.
AnswerSodium oxide:
$\ \text{Symbols}:\ \ \ \ \ \text{Na}\ \ \ \ \ \ \ \text{O}\\ {\text{Valencies}}:\ +1\ \ \ \ -2$
Thus, the formula of sodium oxide is $\mathrm{Na_2O}$
View full question & answer→Question 41 Mark
How many molecules are present in one gram molecular mass of a substance?
Answer$6.002 \times 10^{23}$
View full question & answer→Question 51 Mark
Give two symbols which have been derived from the “English names” of the elements.
Question 61 Mark
Give the names and symbols of five familiar substances which you think are elements.
Answer
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Elements
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Symbols
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Hydrogen
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$H$
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Helium
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$He$
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Lithium
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$Li$
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Beryllium
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$Be$
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Boron
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$B$
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View full question & answer→Question 71 Mark
Name the law of chemical combination: Which was given by Lavoisier.
AnswerThe law of chemical combination proposed by Lavoisier is well known as the law of conservation of mass.
View full question & answer→Question 81 Mark
What name is given to the number $6.022 \times 10^{23}$?
View full question & answer→Question 91 Mark
Which particular atom of the above element is used for this purpose$?$
AnswerAtom with $6$ neutrons and $6$ protons in its nucleus so that its mass number is $12.$
View full question & answer→Question 101 Mark
What do the symbols, $\mathrm{H}_2, \mathrm{~S}$ and $\mathrm{O}_4$ mean in the formula $\mathrm{H}_2 \mathrm{SO}_4$ ?
Answer$\mathrm{H}_2$ represents two atoms of hydrogen, one atom of sulphur and four atoms of oxygen.
View full question & answer→Question 111 Mark
What do we call those particles which have more or less electrons than the normal atoms?
Question 121 Mark
Explain the difference between $2N$ and $\mathrm{N}_2$.
Answer$2N$ represents two separate atoms of nitrogen and $\mathrm{N}_2$ represents one molecule of nitrogen.
View full question & answer→Question 131 Mark
Stat the chemical symbols for the following elements: Sodium, Potassium, Iron, Copper, Mercury, Silver.
Answer
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Elements
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Symbols
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Sodium
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$Na$
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Potassium
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$K$
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Iron
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$Fe$
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Copper
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$Cu$
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Mercury
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$Hg$
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Silver
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$Ag$
|
View full question & answer→Question 141 Mark
What is a group of $6.022 \times 10^{23}$ particles known as?
View full question & answer→Question 151 Mark
Name the unit in which the radius of an atom is usually expressed.
AnswerThe radius of an atom is usually expressed in nanometre (nm).
View full question & answer→Question 161 Mark
Find the mass of $2$ moles of oxygen atoms$?$
AnswerMass of $2$ moles of oxygen atoms $= 2 × 16 = 32g$
View full question & answer→Question 171 Mark
Work out the formula for magnesium hydrogencarbonate.
Answer$\ \text{Symbols}:\ \ \ \ \ \text{Mg}\ \ \ \ \ \ \text{HCO}_3\\ {\text{Valencies}}:\ \ +2\ \ \ \ \ \ \ -1$
Thus, the resulting compound is $\mathrm{Mg}\left(\mathrm{HCO}_3\right)_2$
View full question & answer→Question 181 Mark
Write the relation between nanometer and metre.
Answer $1 \text{ nanometre} = \frac{1}{109}\text{metre}$
or
$1 \text{ nanometre} = 10^{-9}\text{ metre}$
View full question & answer→Question 191 Mark
Write the full form of $IUPAC.$
AnswerThe full form of $IUPAC$ is International Union of Pure and Applied Chemistry.
View full question & answer→Question 201 Mark
What are the building blocks of matter?
AnswerAtoms and molecules are the building blocks of matter.
View full question & answer→Question 211 Mark
What name is given to the amount of substance containing $6.022 \times 10^{23}$ particles (atoms, molecules or ions) of a substance?
View full question & answer→Question 221 Mark
Name the scientist who gave atomic theory of matter.
AnswerJohn Dalton proposed the atomic theory of matter.
View full question & answer→Question 231 Mark
What do we call those particles which are formed: By the gain of electrons by atoms?
AnswerAnions are formed by the gain of electrons by atoms.
View full question & answer→Question 241 Mark
Convert $12g$ of oxygen gas into moles.
AnswerGiven mass of oxygen $= 12g$ Molar mass of oxygen $= 32g$ No. of moles $=\frac{\text{Given mass}}{\text{Molar mass}}=\frac{12\text{g}}{32\text{g}}=0.375$
View full question & answer→Question 251 Mark
Write down the formulae for the following compounds: Calcium oxide.
AnswerCalcium oxide: $CaO$
View full question & answer→Question 261 Mark
Define ‘formula mass’ of a compound.
AnswerThe formula mass of an ionic compound is the relative mass of its 'formula unit' as compared with the mass of a Carbon$-12$ atom taken as $12$ units.
View full question & answer→Question 271 Mark
State whether the following statement is true or false: The symbol of element cobalt is $CO.$
AnswerFalse. The symbol for the element Cobalt is $Co,$ as the second letter of the symbol of an element has to be in the lower case.
View full question & answer→Question 281 Mark
An element $X$ of valency $3$ combines with another element $Y$ of valency $2.$ What will be the formula of the compound formed?
Answer$\ \text{Symbols}:\ \ \ \ \ \text{X}\ \ \ \ \ \ \text{ Y}\\ {\text{Valencies}}:\ \ \ \ \ 3\ \ \ \ \ \ \ 2$
Thus, the resulting compound is $\mathrm{X}_2 \mathrm{Y}_3$
View full question & answer→Question 291 Mark
- In what form does oxygen gas occur in nature?
- In what form do noble gases occur in nature?
Answer
- Oxygen gas occurs as a diatomic molecule in nature.
- Noble gases occur as mono atomic gases in nature.
View full question & answer→Question 301 Mark
Name the scientist who gave: Law of constant proportions.
AnswerLaw of constant proportions was proposed by Joseph Proust.
View full question & answer→Question 311 Mark
Calculate the molecular mass of ethanoic acid, $CH_3COOH$. $($Atomic masses: $C = 12u; H = 1u; O = 16u)$
AnswerMolecular mass of ethanoic acid $(CH_3COOH) = 1 \times C + 3 \times H + 1 \times C + 2 \times O + 1 \times H = 12 + 3 + 12 + 32 + 1 = 60u$
View full question & answer→Question 321 Mark
Give one major drawback of Dalton’s atomic theory of matter.
AnswerThe major drawback of Dalton’s atomic theory is that atoms were thought to be indivisible. But, it is not true since atoms are divisible.
View full question & answer→Question 331 Mark
Define atomic mass of an element.
AnswerThe atomic mass of an element is the relative mass of its atom as compared with the mass of a carbon$-12$ atom taken as $12$ units.
View full question & answer→Question 341 Mark
What is the name of a particle which contains 10 electrons, 11 protons and 12 neutrons?
AnswerIts $\mathrm{Na}^{+}$, the sodium ion.
View full question & answer→Question 351 Mark
Calculate the mass in grams of $0.17$ mole of hydrogen sulphide, $H_2S. ($Atomic masses: $H = 1u, S = 32u)$
Answer$1$ mole of $H_2S$ weights $= 34\ g$ So, $0.17$ mole of $H_2S$ will weigh$ = 34 \times 0.17\ g = 5.78\ g$
View full question & answer→Question 361 Mark
How many atoms are there in exactly $12g$ of carbon $-12$ element$? (C = 12u)$
Answer$6.022 \times 10^{23}$ atoms
View full question & answer→Question 371 Mark
An element $X$ has a valency of $4$ whereas another element $Y$ has a valency of $1 .$ What will be the formula of the compound formed between $X$ and $Y ?$
AnswerAs the valency of element $X$ is $4$ and that of $Y$ is $1 ,$ so the resulting formula is $X Y_4$.
View full question & answer→Question 381 Mark
Calculate the formulae masses of the following compounds: Sodium oxide, $Na_2O ($Given: Atomic masses: $Na = 23u; O = 16u; Al = 27u)$
AnswerMolecular mass of $Na_2O = (2 \times Na) + (1 \times O) = (2 \times 23) + (1 \times 16) = 62u$
View full question & answer→Question 391 Mark
Name the elements represented by the following symbols:
$Hg, Pb, Au, Ag, Sn.$
Answer
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Symbols
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Elements
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$Hg$
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Mercury
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$Pb$
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Lead
|
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$Au$
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Silver
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$Ag$
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Silver
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$Sn$
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Tin
|
View full question & answer→Question 401 Mark
The molecular formula of glucose is $C_6H_{12}O_6.$ Calculate its molecular mass. $($Atomic masses: $C = 12 u; H = 1 u; O = 16 u)$
AnswerMolecular formula of glucose $= C_6H_{12}O_6$ Molecular mass of glucose $= (6 \times C) + (12 \times H) + (6 \times O) = 72 + 12 + 96 = 180u$
View full question & answer→Question 411 Mark
What is the numerical value of Avogadro number?
Answer$6.002 \times 10^{23}$
View full question & answer→Question 421 Mark
If the valency of carbon is $4$ and that of sulphur is $2,$ work out the formula of the compound formed by the combination of carbon with sulphur. What is the name of this compound$?$
Answer$\ \text{Symbols}:\ \ \ \ \ \text{C}\ \ \ \ \ \ \ \ \ \text{S}\\ {\text{Valencies}}:\ +4\ \ \ \ -2$
Name and formula of the resulting compound is Carbon disulphide, $\mathrm{CS}_2$
View full question & answer→Question 431 Mark
What value has been given to the mass of this reference atom$?$
View full question & answer→Question 441 Mark
What do we call those particles which are formed:
By the loss of electrons by atoms?
Answer Cations are formed by the loss of electrons by atoms.
View full question & answer→Question 451 Mark
What is the mass of $0.2$ mole of oxygen atoms$?$
AnswerMass of $0.2$ moles of oxygen atoms $= 0.2 × 16 = 3.2g$
View full question & answer→Question 461 Mark
What is meant by 'a mole of carbon atoms'$?$
AnswerThe amount of substance, whose mass in grams is numerically equal to its atomic mass, is called gram atomic mass of that substance. Gram atomic mass of oxygen is $16g.$
View full question & answer→Question 471 Mark
Work out the formula for sulphur dioxide.
$($Valencies: $S = 4; O = 2)$
Answer$\ \text{Symbols}:\ \ \ \ \ \text{S}\ \ \ \ \ \ \ \ \ \text{O}\\ {\text{Valencies}}:\ +4\ \ \ \ -2$
Chemical formula of sulphur dioxide is $\mathrm{SO}_2$
View full question & answer→Question 481 Mark
How many atoms are present in one gram atomic mass of a substance?
AnswerOne mole of atoms ($6.002 \times 10^{23}$ atoms)
View full question & answer→Question 491 Mark
Name the scientist who gave:
Law of conservation of mass.
Answer Law of conservation of mass was proposed by Antoine Lavoisier.
View full question & answer→Question 501 Mark
An element $X$ has a valency of $2.$ Write the simplest formula for:
oxide of the element.
AnswerOxide of element: As valency of oxygen is $-2$ and that of element is $+2$ so, the resulting compound is $XO.$
View full question & answer→