Question 12 Marks
Calculate the number of atoms of the following:
52 moles of Ar
Answer1 mole of $\mathrm{Ar}=6.022 \times 10^{23}$ atoms of Ar
$\therefore 52 \mathrm{~mol}$ of $\mathrm{Ar}=52 \times 6.022 \times 10^{23}$ atoms of Ar
$=3.131 \times 10^{25}$ atoms of Ar
View full question & answer→Question 22 Marks
How many significant figures should be present in the answer of the following calculations?
$\frac{0.02856×298.15×0.112}{0 5785}$
Answer $\frac{0.02856×298.15×0.112}{0 5785}$
Least precise number of calculation = 0.112
$\therefore$ Number of significant figures in the answer
= Number of significant figures in the least precise number
= 3
View full question & answer→Question 32 Marks
In a reaction
$\mathrm{A}+\mathrm{B}_2 \rightarrow \mathrm{AB}_2$
Identify the limiting reagent, if any, in the following reaction mixtures. 300 atoms of $A+200$ molecules of $B$.
AnswerA limiting reagent determines the extent of a reaction.
It is the reactant which is the first to get consumed during a reaction, thereby causing the reaction to stop and limiting the amount of products formed.
According to the given reaction, 1 atom of A reacts with 1 molecule of B.
Thus, 200 molecules of B will react with 200 atoms of A, thereby leaving 100 atoms of A unused.
Hence, B is the limiting reagent.
View full question & answer→Question 42 Marks
In a reaction,
$\mathrm{A}+\mathrm{B}_2 \rightarrow \mathrm{AB}_2$
Identify the limiting reagent, if any, in the following reaction mixtures.
2.5mol A + 5mol B.
AnswerA limiting reagent determines the extent of a reaction.
It is the reactant which is the first to get consumed during a reaction, thereby causing the reaction to stop and limiting the amount of products formed.
According to the reaction, 1mol of atom A combines with 1mol of molecule B.
Thus, 2.5mol of A will combine with only 2.5mol of B and the remaining 2.5mol of B will be left as such.
Hence, A is the limiting reagent.
View full question & answer→Question 52 Marks
In three moles of ethane ($\mathrm{C}_2 \mathrm{H}_6$), calculate the following:
Number of moles of carbon atoms.
Answer1 mole $\mathrm{C}_2 \mathrm{H}_6$ contains two moles of C - atoms.
$\therefore$ No. of moles of C-atoms in 3 moles of $\mathrm{C}_2 \mathrm{H}_6$.
$=2 \times 3$
$=6$
View full question & answer→Question 62 Marks
How many significant figures should be present in the answer of the following calculations?
5 × 5.364
Answer 5 × 5.364
Least precise number of calculation = 5.364
$\therefore$ Number of significant figures in the answer = Number of significant figures in 5.364
= 4
View full question & answer→Question 72 Marks
In a reaction
$\mathrm{A}+\mathrm{B}_2 \rightarrow \mathrm{AB}_2$
Identify the limiting reagent, if any, in the following reaction mixtures.
$5 \mathrm{mol}\mathrm{~A}+2.5 \mathrm{~mol} \mathrm{~B}$.
AnswerA limiting reagent determines the extent of a reaction.
It is the reactant which is the first to get consumed during a reaction, thereby causing the reaction to stop and limiting the amount of products formed.
1mol of atom A combines with 1mol of molecule B.
Thus, 2.5mol of B will combine with only 2.5mol of A.
As a result, 2.5mol of A will be left as such.
Hence, B is the limiting reagent.
View full question & answer→Question 82 Marks
A sample of drinking water was found to be severely contaminated with chloroform, $\mathrm{CHCl}_3$, supposed to be carcinogenic in nature. The level of contamination was 15ppm (by mass).
Express this in percent by mass.
Answer1 ppm is equivalent to 1 part out of 1 million $\left(10^6\right)$ parts.
$\therefore$ Mass percent of 15 ppm chloroform in water
$=\frac{15}{10^6} \times 100$
$=1.5 \times 10^{-3} \%$
View full question & answer→Question 92 Marks
If 10 volumes of dihydrogen gas reacts with five volumes of dioxygen gas, how many volumes of water vapour would be produced?
Answer$\mathrm{H}_2$ and $\mathrm{O}_2$ react according to the equation.
$2 \mathrm{H}_2(\mathrm{g})+0_2(\mathrm{g}) \rightarrow 2 \mathrm{H}_2 \mathrm{O}(\mathrm{g})$
Thus, 2 volumes of $\mathrm{H}_2$ react with 1 volume of $\mathrm{O}_2$ to produce 2 volumes of water vapour. Hence, 10 volumes of $\mathrm{H}_2$ will react completely with 5 volumes of $\mathrm{O}_2$ to produce 10 volumes of water vapour.
View full question & answer→Question 102 Marks
Calculate the molecular mass of the following:
$\mathrm{CO}_2$
Answer$\mathrm{CO}_2$
The molecular mass of carbon dioxide, $\mathrm{CO}_2$
$=(1 \times \text { Atomic mass of carbon })+(2 \times \text { Atomic mass of oxygen })$
$=[1(12.011 \mathrm{u})+2(16.00 \mathrm{u})]$
$=12.011 \mathrm{u}+32.00 \mathrm{u}$
$=44.01 \mathrm{u} .$
View full question & answer→Question 112 Marks
Use the data given in the following table to calculate the molar mass of naturally occuring argon isotopes:
|
Isotope
|
Isotopic molar mass
|
Abundance
|
| ${ }^{36} \mathrm{Ar}$ |
$35.96755 \mathrm{g} \mathrm{~mol}^{-1}$ |
0.337%
|
| ${ }^{38} \mathrm{Ar}$ |
$37.96272 \mathrm{g} \mathrm{~mol}^{-1}$ |
0.063%
|
| ${ }^{40} \mathrm{Ar}$ |
$39.9624 \mathrm{g} \mathrm{~mol}^{-1}$ |
99.600%
|
AnswerMolar mass of argon,
$=\Big[\Big(35.96755\times\frac{0.337}{100}\Big)+\Big(37.96272\times\frac{0.063}{100}\Big)\\+\Big(39.9624\times\frac{90.60}{100}\Big)\Big]\text{g mol}^{-1}$
$=[0.121+0.024+39.802]\text{g mol}^{-1}$
$=39.947\text{g mol}^{-1}$
View full question & answer→Question 122 Marks
In a reaction
$\mathrm{A}+\mathrm{B}_2 \rightarrow \mathrm{AB}_2$
Identify the limiting reagent, if any, in the following reaction mixtures. $2 \mathrm{~mol} \mathrm{~A}+3 \mathrm{~mol} \mathrm{~B}$.
AnswerA limiting reagent determines the extent of a reaction.
It is the reactant which is the first to get consumed during a reaction, thereby causing the reaction to stop and limiting the amount of products formed.
According to the reaction, 1mol of A reacts with 1mol of B.
Thus, 2mol of A will react with only 2mol of B.
As a result, 1mol of B will not be consumed.
Hence, A is the limiting reagent.
View full question & answer→Question 132 Marks
A sample of drinking water was found to be severely contaminated with chloroform, $\mathrm{CHCl}_3$, supposed to be carcinogenic in nature. The level of contamination was 15 ppm (by mass).
Determine the molality of chloroform in the water sample.
Answer100 g of the sample contains $1.5 \times 10^{-3} \mathrm{~g}$ of $\mathrm{CHCl}_3$.
$\Rightarrow 1000 \mathrm{~g}$ of the sample contains $1.5 \times 10^{-2} \mathrm{~g}$ of $\mathrm{CHCl}_3$.
$\therefore$ Molality of chloroform in water
$=\frac{1.5 \times 10^{-1} \mathrm{~g}}{\text { Molar mass of } \mathrm{CHCl}_3}$
$=1.5 \times 10^{-3} \%$
Molar mass of $\mathrm{CHCl}_3=12.00+1.00+3(35.5)$
$=119.5 \mathrm{~g} \mathrm{~mol}^{-1}$
$\therefore$ Molality of chloroform in water $=0.0125 \times 10^{-2} \mathrm{~m}$
$=1.25 \times 10^{-4} \mathrm{~m}$
View full question & answer→Question 142 Marks
Calculate the molecular mass of the following:
$\mathrm{H}_2 \mathrm{O}$
Answer$\mathrm{H}_2 \mathrm{O} \text { : }$
The molecular mass of water, $\mathrm{H}_2 \mathrm{O}$
$=(2 \times \text { Atomic mass of hydrogen })+(1 \times \text { Atomic mass of oxygen })$
$=[2(1.0084)+1(16.00 \mathrm{u})]$
$=2.016 \mathrm{u}+16.00 \mathrm{u}$
$=18.016$
$=18.02 \mathrm{u} .$
View full question & answer→Question 152 Marks
What do you mean by significant figures?
Answer Significant figures are meaningful digits which are known with certainty including the last digit whose value is uncertain.
For example,
In 11.2546g, there is 6 significant figures but here 11.254 are certain and 6 is uncertain and the uncertainty would be ±1 in the last digit.
Hence last uncertain digit is also included in Significant figures.
View full question & answer→Question 162 Marks
How many significant figures should be present in the answer of the following calculations?
0.0125 + 0.7864 + 0.0215
Answer 0.0125 + 0.7864 + 0.0215
Since the least number of decimal places in each term is four, the number of significant figures in the answer is also 4.
View full question & answer→Question 172 Marks
In three moles of ethane ($\mathrm{C}_2 \mathrm{H}_6$), calculate the following:
Number of molecules of ethane.
Answer1 mole $\mathrm{C}_2 \mathrm{H}_6$ contains six moles of H - atoms.
$\therefore$ No. of molecules in 3 moles of $\mathrm{C}_2 \mathrm{H}_6$.
$=3 \times 6.023 \times 1023$
$=18.069 \times 1023$
$=18484.59$
View full question & answer→Question 182 Marks
In three moles of ethane ($\mathrm{C}_2 \mathrm{H}_6$), calculate the following:
Number of moles of hydrogen atoms.
Answer1 mole $\mathrm{C}_2 \mathrm{H}_6$ contains six moles of H - atoms.
$\therefore$ No. of moles of C- atoms in 3 moles of $\mathrm{C}_2 \mathrm{H}_6$.
$=3 \times 6$
$=18$
View full question & answer→Question 192 Marks
Calculate the molecular mass of the following:
$\mathrm{CH}_4$
Answer$\mathrm{CH}_4$ :
The molecular mass of methane, $\mathrm{CH}_4$
$=(1 \times \text { Atomic mass of carbon })+(4 \times \text { Atomic mass of hydrogen })$
$=[1(12.011 \mathrm{u})+4(1.008 \mathrm{u})]$
$=12.011 \mathrm{u}+4.032 \mathrm{u}$
$=16.043 \mathrm{u}$.
View full question & answer→Question 202 Marks
Calculate the number of atoms in the following:
52u of He.
Answer 1 atom of He = 4u of He
Or,
4u of He = 1 atom of He
1u of He $=\frac{1}{4}$ atom of He
52u of He $=\frac{52}{4}$ atom of He
= 13 atoms of He.
View full question & answer→Question 212 Marks
In a reaction
$\mathrm{A}+\mathrm{B}_2 \rightarrow \mathrm{AB}_2$
Identify the limiting reagent, if any, in the following reaction mixtures.
100 atoms of A + 100 molecules of B.
AnswerA limiting reagent determines the extent of a reaction.
It is the reactant which is the first to get consumed during a reaction, thereby causing the reaction to stop and limiting the amount of products formed.
According to the given reaction, 1 atom of A combines with 1 molecule of B.
Thus, all 100 atoms of A will combine with all 100 molecules of B.
Hence, the mixture is stoichiometric where no limiting reagent is present.
View full question & answer→Question 222 Marks
What will be the mass of one ${ }^{12} \mathrm{C}$ atom in g?
Answer1 mol of ${ }^{12} \mathrm{C}$ atom $=6.022 \times 10^{23}$ atom $=12 \mathrm{~g}$
Thus, $6.022 \times 10^{23}$ atoms of 12 C have mass $=12 \mathrm{~g}$
$\therefore 1$ atom of ${ }^{12} \mathrm{C}$ will have mass $=\frac{12}{6.022 \times 10^{23}}$
$\mathrm{g}=1.9927 \times 10^{-23} \mathrm{~g}$
View full question & answer→Question 232 Marks
Calculate the number of atoms in the following:
52g of He.
Answer4 g of $\mathrm{He}=6.022 \times 10^{23}$ atoms of He
$\therefore 52 \mathrm{~g}$ of $\mathrm{He}=\frac{6.022 \times 10^{23} \times 52}{4}$ atoms of He
$=7.8286 \times 10^{24}$ atoms of He.
View full question & answer→Question 242 Marks
If 500mL of a 5M solution is diluted to 1500ml, what will be the molarity of the solution obtained?
Answer$\text{M}_1\text{V}_1=\text{M}_2\text{V}_2$
$500\times5=1500\times\text{M}_2$
$\text{M}_2=\frac{2500}{1500}$
$=\frac{5}{3}=1.66\text{M}.$
View full question & answer→Question 252 Marks
How many atoms of calcium are there in 2g of Ca?
(At. mass of Ca = 40u)
Answer1 mole of $\mathrm{Ca}=40 \mathrm{~g}=6.022 \times 10^{23}$ atoms
$2\text{g of ca}=\frac{6.022\times10^{23}}{40}\times2$
$=3.011\times10^{22}$
View full question & answer→Question 262 Marks
Volume of a solution changes with change in temperature, then, will the molality of the solution be affected by temperature? Give reason for your answer.
AnswerNo, molality of a solution does not change with temperature since mass remains unaffected by temperature.
Molelity, $\text{m}=\frac{\text{moles of solute}}{\text{weight of solvent(in g)}}\times100$
View full question & answer→Question 272 Marks
How many molecules are pre ent in one mole of oxygen gas at STP? Calculate its mass.
Answer1 mole of $\mathrm{O}_2$ gas contains $6.022 \times 10^{23}$ molecules.
1 mole of $\mathrm{O}_2$ gas at $\mathrm{STP}=32 \mathrm{~g}$.
View full question & answer→Question 282 Marks
1L of a gas at STP weighs 1.97g. What is molecular mass?
Answer1 L of gas at STP weighs $=1.97 \mathrm{~g}$
22.4 L of gas at STP weighs $=1.97 \times 22.4=44.128 \mathrm{~g} \mathrm{~mol}^{-1}$
View full question & answer→Question 292 Marks
What do you understand by stoichiometric coefficients in a chemical equation?
AnswerThe coefficients of reactants and products involved in a chemical equation represented by the balanced form, are known as stoichiometric coefficients.
e.g. $\mathrm{N}_2(\mathrm{g})+3 \mathrm{H}_2(\mathrm{g}) \rightarrow 2 \mathrm{NH}_3(\mathrm{g})$
The stoichiometric coefficients are 1, 3 and 2 respectively.
View full question & answer→Question 302 Marks
What will be the molarity of a solution. Which contains 5.58g of NaCl(s) per 500mL?
Answer$\text{M}=\frac{\text{W}_{\text{B}}}{\text{M}_{\text{B}}}\times\frac{100}{\text{Volume of solution in mL}}$
$=\frac{5.85}{58.5}\times\frac{1000}{500}=0.2\text{mol L}^{-1}$
View full question & answer→Question 312 Marks
How much copper can be obtained from 100 g of copper sulphate $\left(\mathrm{CuSO}_4\right)$ ?
Answer$\text { Molar mass of } \mathrm{CuSO}_4=63.54+32.06+(4 \times 16)=159.6 \mathrm{~g} \mathrm{~mol}^{-1}$
$159.6 \mathrm{g} \mathrm{~CuSO}_4 \text { contains }=63.54 \mathrm{~g} \mathrm{Cu}$
$1 \mathrm{g} \mathrm{~CuSO}_4 \text { contains }=\frac{63.54}{159.6} \mathrm{~g} \mathrm{Cu}$
$\therefore 100 \mathrm{g} \mathrm{~CuSO}_4 \text { contains }=\frac{63.54 \times 100}{159.6}$
$=39.81 \mathrm{g} \mathrm{~Cu}$
View full question & answer→Question 322 Marks
Calculate the number of grams of oxygen in 0.10 mol of $\mathrm{Na}_2 \mathrm{CO}_3 \cdot 10 \mathrm{H}_2 \mathrm{O}$.
Answer1 mole of $\mathrm{Na}_2 \mathrm{CO}_3 \cdot 10 \mathrm{H}_2 \mathrm{O}$. Contains 13 moles of oxygen atoms.
0.1 mole of $\mathrm{Na}_2 \mathrm{CO}_3 .10 \mathrm{H}_2 \mathrm{O}$ contains $13 \times 0.1=1.3$ moles of oxygen atoms.
Mass of 1.3 moles of oxygen atoms $=1.3 \times 16=20.8 \mathrm{~g}$.
View full question & answer→Question 332 Marks
A measured temperature on Fahrenheit scale is 200° F. What will this reading be on Celsius scale?
Answer$\frac{\text{C}}{5}=\frac{\text{F}-32}{9}$
$\Rightarrow\frac{\text{C}}{5}=\frac{200-32}{9}$
$\Rightarrow\text{C}=\frac{5\times168}{9}$
$=\frac{840}{9}=93.3^\circ\text{C}.$
View full question & answer→Question 342 Marks
Vitamin C is known to contain $1.29 \times 10^{24}$ hydrogen atoms. Calculate the number of moles of hydrogen atoms.
AnswerNumber of moles of hydrogen $=\frac{\text{Number of atoms}}{6.022\times10^{23}}$
$=\frac{1.29\times10^{24}}{6.022\times10^{23}}$
$=\frac{12.9\times10^{23}}{6.022\times10^{23}}=2.14\text{mol}$
View full question & answer→Question 352 Marks
Write the relationship between empirical formula and molecular formula.
AnswerMolecular formula = n × Empirical formula where
$\text{n}=\frac{\text{Molar mass}}{\text{Empirical formula mass}}$
View full question & answer→Question 362 Marks
Calculate the volume of water that should be added to $25 \mathrm{~cm}^3$ of $10 \mathrm{M} \mathrm{H}_2 \mathrm{SO}_4$ to obtain $0.5 \mathrm{M} \mathrm{H} 2 \mathrm{SO}_4$ solution.
Answer$\text{M}_1\text{V}_1=\text{M}_2\text{V}_2$
$\Rightarrow10\times25=0.5\times\text{V}_2$
$\text{V}_2=\frac{250}{0.5}=500\text{mL}$
Volume of water
$=$ Volume of solution - Volume of solute
$=500-25=475 \mathrm{~cm}^3$
View full question & answer→Question 372 Marks
What is the mass percent of carbon in carbon dioxide?
AnswerMass % of carbon in $\text{CO}_2$
$=\frac{\text{Mass of carbon}}{\text{Mass of CO}_2}\times100$
$=\frac{12}{44}\times100=\frac{300}{11}=27.27\%$
View full question & answer→Question 382 Marks
How many moles arc there in 0.08L of hydrogen at STP?
AnswerNumber of moles $=\frac{\text{Volume at STP}}{22.4\text{L}}=\frac{0.08}{22.4}$
$=0.035\text{ moles.}$
View full question & answer→Question 392 Marks
How many atoms are present in 16g of ozone?
AnswerNumber of moles of $\text{O}_3=\frac{\text{Mass of O}_3}{\text{Molar mass of O}_3}$
$=\frac{16}{48}=\frac{1}{3}\text{mole}$
Number of atoms in 1 mole of $\mathrm{O}_3=3 \times 6.022 \times 10^{23}$ atoms
Number of atoms in $\frac{1}{3}$ mole of $\mathrm{O}_3$
$=3\times6.022\times10^{23}\times\frac{1}{3}$
$=6.002\times10^{23}\text{ atoms}.$
View full question & answer→Question 402 Marks
Define limiting reagent.
OR
What is limiting reactant in a reaction?
AnswerThe reactant which is entirely consumed when a reaction goes to completion. It is present in smaller amount than calculated by balanced chemical equation.
View full question & answer→Question 412 Marks
Calculate the percentage of nitrogen in $\mathrm{NH}_3$. (Atomic mass of $\mathrm{N}=14, \mathrm{H}=1 \mathrm{amu}$ )
Answer% of nitrogen in $\mathrm{NH}_3$
$=\frac{\text{Totaol mass of nitrogen}}{\text{Molar mass of NH}_3}\times100$
$=\frac{14}{17}\times100=\frac{1400}{17}=82.3\%$
View full question & answer→Question 422 Marks
Why is the law of Gay Lussac's not obeyed if any reactant or product is not a gas?
AnswerIf any reactant or product is a liquid or solid, the volume occupied by them is extremely small as compared to the gas and hence, the law is not obeyed.
View full question & answer→Question 432 Marks
How many gram of $\mathrm{Na}_2 \mathrm{CO}_3$ should be dissolved to make $100 \mathrm{~cm}^3$ of $0.15 \mathrm{M} \mathrm{~Na}_2 \mathrm{CO}_3$ solution?
Answer$1000 \mathrm{~cm}^3$ of $0.15 \mathrm{M} \mathrm{~Na}_2 \mathrm{CO}_3$ contains $\mathrm{Na}_2 \mathrm{CO}_3=0.15 \mathrm{~mol}$
$100 \mathrm{~cm}^3$ of $0.15 \mathrm{M} \mathrm{~Na}_2 \mathrm{CO}_3$ will contain $\mathrm{Na}_2 \mathrm{CO}_3$
$=\frac{0.15}{1000} \times 100=0.015 \mathrm{~mol}$
(Molar mass of $\mathrm{Na}_2 \mathrm{CO}_3=106 \mathrm{~g} \mathrm{~mol}^{-1}$ )
Mass of $\mathrm{Na}_2 \mathrm{CO}_3=0.015 \times 106=1.59 \mathrm{~g}$
View full question & answer→Question 442 Marks
What does the following prefixes stand for:
- Pico.
- Nano.
- Micro.
- Deci.
Answer$a. 10^{-12}$
$b. 10^{-9}$
$c. 10^{-6}$
$d. 10^{-1}$
View full question & answer→Question 452 Marks
If the density of a solution is $3.12 \mathrm{~g} \mathrm{~mL}^{-1}$, what is the mass of 1.5 mL solution in significant figures.
Answer$\text { Mass of solution }=\text { Volume of solution } \times \text { density }$
$=1.5 \mathrm{~mL} \times 3.12 \mathrm{~g} \mathrm{~mL}^{-1}$
$=4.680 \mathrm{~g}=4.7 \mathrm{~g}$.
View full question & answer→Question 462 Marks
Calculate the percentage by mass of water in sodium carbonate crystals. $\left(\mathrm{Na}_2 \mathrm{CO}_3 \cdot 10 \mathrm{H}_2 \mathrm{O}\right)$.
Answer$\%\text{ of H}_2\text{O}\text{ in Na}_2\text{CO}_310\text{H}_2\text{O}$
$=\frac{\text{Total mass of }\text{H}_2\text{O}}{\text{Molar mass}}\times100$
$\%\text{ of CaCO}_3=\frac{180}{286}\times100=62.9\%$
View full question & answer→Question 472 Marks
Calculate the number of moles of NaOH in $27 \mathrm{~cm}^3$ of 0.15M NaOH solution.
Answer$\text{M}=\text{n}\times\frac{1000}{\text{Volume of solution in cm}^3}$
$\Rightarrow0.15=\text{n}\times\frac{1000}{27\text{cm}^3}$
$\Rightarrow\text{n}=0.00405\text{ moles}.$
View full question & answer→Question 482 Marks
Calculate the average atomic mass of hydrogen using the following data:
|
Isotope
|
% Natural abundance
|
Molar mass
|
| ${ }^1 \mathrm{H}$ |
99.985
|
1
|
| ${ }^2 \mathrm{H}$ |
0.015
|
2
|
AnswerAverage atomic mass
$=\frac{\text{Abundance of }^1\text{H}\times\text{Atimic mass + Abudance of }^2\text{H}\times\text{Atomic mass}}{100}$
$=\frac{99.985\times1+0.015\times2}{100}=\frac{100.015}{100}=1.00015\text{u}$
View full question & answer→Question 492 Marks
How is the term material different from matter?
AnswerAnything which has mass and occupies space is called matter. However, material corresponds to the matter which has specific uses e.g. glass, cement etc.
View full question & answer→Question 502 Marks
What is the difference between molality and molarity?
AnswerMolarity is concentration of a substance that is calculated as the number of moles of solute that is dissolved in 1 liter of solution while molality is concentration of a substance that is calculated as the number of moles of solute found in 1kg of solvent.
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