Question 11 Mark
Calculate the molar mass of the following substances: Hydrochloric acid, $HCl.$
AnswerMolar mass of Hydrochloric acid $=$ Molar mass of $H\ +$ Molar mass of $Cl = 1 + 35.5 = 36.5\ g$.
View full question & answer→Question 21 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 31 Mark
What is the mass of.
$1$ mole of nitrogen atoms$?$
AnswerMass of one mole of nitrogen atoms is $14\ g.$
View full question & answer→Question 41 Mark
What is the mass of. $4$ mole of aluminium atoms $($Atomic mass of aluminium $= 27)?$
AnswerThe mass of $4$ moles of Aluminium atoms will be $(4 \times 27)\ g = 108\ g.$
View full question & answer→Question 51 Mark
Write the atomicity of the following:
$\mathrm{HNO}_3$
AnswerIn $\mathrm{HNO}_3$ , there are three atoms of oxygen, one atom of nitrogen and one atom of hydrogen sulphur constituting a molecule of $\mathrm{HNO}_3$ . Hence, the atomicity is five.
View full question & answer→Question 61 Mark
Give the symbols of the following elements.
- Aluminium
- Cobalt
- Arsenic
- Radon
AnswerI. The symbol of aluminium is $Al.$
II. The symbol of cobalt is $Co.$
III. The symbol of arsenic is $As.$
Iv. The symbol of radon is $Rn$.
View full question & answer→Question 71 Mark
Calculate the formula unit masses of $\mathrm{ZnO}, \mathrm{Na}_2 \mathrm{O}, \mathrm{K}_2 \mathrm{CO}_3$, given atomic masses of $\mathrm{Zn}=65 \mathrm{u}, \mathrm{Na}=23 \mathrm{u}, \mathrm{K}=39 \mathrm{u}, \mathrm{C}= 12 u ,$ and $\mathrm{O}=16 \mathrm{u}$.
AnswerFormula unit mass of $ZnO =($ Atomic mass of $Zn )+($ Atomic mass of $O$ )
$
=(65+16) u =81 u
$
Formula unit mass of $Na _2 O =(2 \times 23)+16$
$
=62 u
$
Formula unit mass of $K _2 CO _3=(2 \times 39)+12+(3 \times 16)$
$
=138 u
$
View full question & answer→Question 81 Mark
Give a brief description of the following: Ions.
AnswerCompounds composed of metals and nonmetals contain charged species. These charged particles or species are known as ions. There are two types of ions: Cations and Anions. The positively charged ions are known as cations and the negatively charged ions are known as anions.
View full question & answer→Question 91 Mark
Calculate the mass of the following: $7$ moles of sulphuric acid.
AnswerThe mass of sulpuric acid is $98g/mol.$
So, Mass $= 7\ mol × 98g/mol.$
The mass of sulphuric acid is $686g.$
View full question & answer→Question 101 Mark
If the valency of hydrogen is $1$ and that of nitrogen is $3$, work out the formula for ammonia.
AnswerIf the valency of hydrogen is $1$ and that of nitrogen is $3$, work out the formula for ammonia. Ammonia consists of nitrogen and hydrogen. Formula for ammonia can be worked out by crossing the valency of the constituent elements. Therefore, the formula of ammonia is $\mathrm{NH}_3$.
View full question & answer→Question 111 Mark
Work out the formulae for the following compounds:
Sodium oxide.
AnswerThe chemical formula for sodium oxide is $\mathrm{Na}_2\mathrm{O}$.
View full question & answer→Question 121 Mark
How many molecules are present in one gram molecular mass of a substance?
Answer$6.022 \times 10^{23}$ molecules
View full question & answer→Question 131 Mark
Define the following terms.
Molar mass.
Answer Molar mass is simply defined as the mass of one mole of any substance. The meaning of molar mass is how many grams are present in one mole of a particular substance. The periodic table provides the atomic masses used in the calculation of the molar mass. Avogadro's number tells the number of particles present per mole.
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Give two symbols which have been derived from the “English names” of the elements.
AnswerTwo examples of symbols which have been derived from the "English names" are Sulphur - $S$ and Aluminium - $Al$
View full question & answer→Question 151 Mark
Give the names and symbols of five familiar substances which you think are elements.
AnswerIron: $Fe ,$ Silver:$ Ag ,$ Oxygen: $O ,$ Hydrogen: $H ,$ Gold: $Au.$
View full question & answer→Question 161 Mark
Name the law of chemical combination: Which was given by Lavoisier.
AnswerThe law of chemical combination given by Lavoisier is known as the Law of conservation of mass.
View full question & answer→Question 171 Mark
Write the chemical formula using criss-cross method: Barium nitrate.
Question 181 Mark
What is wrong with the following symbols$?$ Give the correct symbol in case: Hydrogen $(Hg)$
AnswerCorrect name for hydrogen is $“H”.$ The symbol $“Hg”$ is used for mercury.
View full question & answer→Question 191 Mark
What name is given to the number $6.022 \times 10^{23}?$
AnswerIt is called Avogadro's number and is denoted by the sign $NA$ or $Q.$
View full question & answer→Question 201 Mark
Which particular atom of the above element is used for this purpose$?$
AnswerCarbon$-12$ atom is particularly used as a standard in the atomic mass scale.
View full question & answer→Question 211 Mark
Which of the following symbols of elements are incorrect$?$ Give their correct symbols. Carbon $c$
AnswerCarbon $c$ is incorrect symbol. Its correct symbol is $C.$
View full question & answer→Question 221 Mark
The visible universe is estimated to contain $10^{22}$ stars. How many moles of stars are present in the visible universe?
AnswerNumber of moles in $10^{22}$ stars $=10226.022×1023 = 0.0166$ moles.
View full question & answer→Question 231 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$\mathrm{H}_2 \mathrm{SO}_4$ is the formula for sulphuric acid. In this formula, $\mathrm{H}_2$ represents two atoms of hydrogen, $\mathrm{~S}$ represents one atom of sulphur and $\mathrm{O}_4$ represents four atoms of oxygen are involved in the formation of one molecule of sulphuric acid.
View full question & answer→Question 241 Mark
Find the ratio by mass of the combining elements in the following compounds.
$\mathrm{NH}_3$
AnswerNitrogen combines with hydrogen in the ratio of $14 : 3$ to form ammonia gas.
View full question & answer→Question 251 Mark
The symbols of some of the ions are given below: $\mathrm{Na}^{+}$ Using this information, find out the formulae of: Sodium carbonate
View full question & answer→Question 261 Mark
Write the formula of the following compound: Sodium bromide.
AnswerSodium Bromide is an inorganic compound with the chemical formula $NaBr.$
View full question & answer→Question 271 Mark
What helps in determining the formula of an ionic compound?
AnswerValency helps in determining the formula of an ionic compound. Valency can be used to find out how the atoms of an element will combine with the atoms of another element to form a compound.
View full question & answer→Question 281 Mark
What do we call those particles which have more or less electrons than the normal atoms?
AnswerThose particles which have more or less electrons than the normal atoms are called ions.
View full question & answer→Question 291 Mark
Calculate the mass of the following: $2$ moles of methane.
AnswerGiven:
Number of moles $=2$
Atomic mass of $CH _4=12+1 \times 4=16 g / mol$
To find out the mass of methane, apply the formula given:
Number of moles $=\frac{\text { Mass }}{\text { Molar mass }}$
$
\begin{aligned}
& \Rightarrow 2=\frac{\text { Mass }}{16 g / mol } \\
& \Rightarrow \text { Mass }=2 mol \times 16 g / mol \\
& \Rightarrow \text { Mass }=32 g
\end{aligned}
$
Thus, the mass of methane is $32 g$.
View full question & answer→Question 301 Mark
An element $X$ forms $X_2(CO_3)^3$ type compound. What is the formula of its phosphate and chloride?
View full question & answer→Question 311 Mark
Which of the following symbols of elements are incorrect? Give their correct symbols.
Sodium So
Answer Sodium So is incorrect symbol. Its correct symbol is Na.
View full question & answer→Question 321 Mark
Explain the difference between $\mathrm{2N}$ and $\mathrm{N}_2$.
Answer$\mathrm{N}_2$ is nitrogen gas and there is chemical bond between two nitrogen atoms. $\mathrm{2N}$ represents just two atoms of nitrogen that are not chemically bonded. Simply put, $\mathrm{2N}$ are two atoms of nitrogen, while $\mathrm{N}_2$ is one molecule of nitrogen.
View full question & answer→Question 331 Mark
What is meant by the term chemical formula?
AnswerThe chemical formula of a compound means the symbolic representation of the composition of a compound. A chemical formula for a molecule is represented by the group of symbols of the elements that constitute the molecule, and the number of atoms of each element present in one molecule.
View full question & answer→Question 341 Mark
Define the term ‘molecular mass'.
AnswerThe molecular mass of a substance is the relative mass of its molecule as compared to the mass of the Carbon$-12$ atom taken as $12-$units. Molecular mass is the total mass of a compound. It is equal to the sum of the atomic masses or mass numbers of each element present in a compound or molecule.
View full question & answer→Question 351 Mark
Calculate the mass of the following: $10$ moles of hydrogen cyanide.
AnswerGiven:
Number of moles $=10$
Atomic mass of $HCN =1+12+14=27 g / mol$
To find out the mass of hydrogen cyanide, apply the formula given:
$
\begin{aligned}
& \text { Number of moles }=\frac{\text { Mass }}{\text { Molar mass }} \\
& \Rightarrow 10=\frac{\text { mass }}{27 g / mol } \\
& \Rightarrow \text { Mass }=10 mol \times 27 g / mol \\
& \Rightarrow \text { Mass }=270 g
\end{aligned}
$
Thus, the mass of hydrogen cyanlde Is $270 g$.
View full question & answer→Question 361 Mark
Stat the chemical symbols for the following elements: Sodium, Potassium, Iron, Copper, Mercury, Silver.
AnswerSodium $: Na,$ Potassium $: K,$ Iron $: Fe,$ Copper $: Cu,$ Mercury $: Hg,$ Silver $: Ag$
View full question & answer→Question 371 Mark
What is a group of $6.022 \times 10^{23}$ particles known as?
AnswerA group of $6.022 \times 10^{23}$ particles is known as one mole.
View full question & answer→Question 381 Mark
Write the molecular formulae for the following compounds. Aluminium $(III)$ nitrate.
AnswerThe molecular formula of the compound is $Al\ NO\ 3\ 3 .$
View full question & answer→Question 391 Mark
Name the unit in which the radius of an atom is usually expressed.
AnswerThe radius of an atom is usually expressed in 'nanometres'.
View full question & answer→Question 401 Mark
Give the formulae of the compounds formed from the following set of element: Potassium and oxygen.
Question 411 Mark
Give the formulae of the compounds formed from the following set of element: Nitrogen and magnesium.
Question 421 Mark
Express the following in kilograms. $5.84 \times 10^{-3}mg$
Answer$5.84 \times 10-3 \mathrm{mg} \rightarrow 5.84 \times 10-9 \mathrm{~kg}$.
View full question & answer→Question 431 Mark
What is wrong with the following symbols$?$ Give the correct symbol in case: Copper $(Co)$
AnswerCorrect symbol for copper is $Cu.$ The symbol $“Co”$ is used for cobalt.
View full question & answer→Question 441 Mark
Find the mass of $2$ moles of oxygen atoms$?$
View full question & answer→Question 451 Mark
Work out the formula for magnesium hydrogencarbonate.
AnswerA compound, $Mg(HCO3)2,$ that is stable only in solution. It is formed by the action of carbon dioxide on a suspension of magnesium carbonate in water: $MgCO3(s)+CO2(g)+H2O(l) → Mg(HCO3)2(aq)$ On heating, this process is reversed.
View full question & answer→Question 461 Mark
What is wrong with the following symbols$?$ Give the correct symbol in case: Sodium $(So)$
AnswerSodium $So$ is incorrect symbol. Its correct symbol is $Na.$
View full question & answer→Question 471 Mark
Give a brief description of the following: Atomic mass unit.
AnswerAn atomic mass unit is defined as accurately $1/12$ the mass of a carbon$-12$ atom. The carbon$-12$ atom has six neutrons and six protons in its nucleus. It is represented as $a.m.u$ or $u$ (unified). It is a unit of mass used to express atomic masses.
View full question & answer→Question 481 Mark
Write the relation between nanometer and metre.
AnswerThe relation between nanometer and meter is $1$ nanometer $= 10−9m.$
View full question & answer→Question 491 Mark
Write the molecular formulae for the following compounds. Iron $(III)$ sulphide.
AnswerOxidation state of sulphide is $−2$ and that of iron is given as $+3.$ Therefore, to balance the charges, molecular formula will be $Fe2S3.$
View full question & answer→Question 501 Mark
Calculate the molar mass of the following compound:
$\mathrm{Na}_2 \mathrm{CO}_3$
AnswerTo put it another way, the molar mass is the overall mass in grams of all the particles that make up a mole of a specific molecule. When we add all the totals, we get $(46+12+48)=106$. Hence, the molar mass of $Na_ 2 CO_ 3$ thus becomes $106 \mathrm{~g} / \mathrm{mole}$.
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