Chemistry Case study (4 Marks)

Read the passage given below and answer the following questions from 1 to 5.
After having some idea about the terms atomsand molecules, it is appropriate here tounderstand what do we mean by atomic andmolecular masses.One atomicmass unit is defined as a mass exactly equal to one-twelfth of the mass of one carbon – 12 atom.Molecular mass is the sum of atomic masses of the elements present in a molecule. It is obtained by multiplying the atomic mass of each element by the number of its atoms and adding them together. Some substances, such as sodium chloride, do not contain discrete molecules as their constituent units. In such compounds, positive (sodium ion) and negative (chloride ion) entities are arranged in a three dimensional structure. The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.02214076× 10²³ elementary entities. This number is the fixed numerical value of the Avogadro constant, N_A , when expressed in the unit mol–1 and is called the Avogadro number. The amount of substance, symbol n, of a system is a measure of the number of specified elementary entities. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles. It may be emphasised that the mole of a substance always contains the same number of entities, no matter what the substance may be. In order to determine this number precisely, the mass of a carbon–12 atom was determined by a mass spectrometer and found to be equal to 1.992648 × 10^–23 g. Knowing that one mole of carbon weighs 12 g, the number of atoms in it is equal to:
        12 g /mol C-12       .
1.992648 × 10²³  g / C- 12 atom. = 6.0221367 × 10²³ atoms/mol.
The mass of one mole of a substance in grams is called its molar mass. the molar mass in grams is numerically equal to atomic molecular/formula mass in u.An empirical formula represents the simplestwhole number ratio of various atoms present ina compound, whereas, the molecular formulashows the exact number of different types ofatoms present in a molecule of a compound. If the mass per cent of variouselements present in a compound is known, its empiricalformula can be determined. Molecular formulacan further be obtained if the molar mass isknown.Many a time, reactions are carried out with the Amounts of reactants that are different than The amounts as required by a balanced chemical reaction. In such situations, one Reactant is in more amount than the amount required by balanced chemical reaction. The reactant which is present in the least amount Many a time, reactions are carried out with the
amounts of reactants that are different than the amounts as required by a balanced chemical reaction. In such situations, one reactant is in more amount than the amount required by balanced chemical reaction. The reactant which is present in the least amount gets consumed after sometime and after that further reaction does not take place whatever be the amount of the other reactant. Hence, the reactant, which gets consumed first, limits the amount of product formed and is, therefore, called the limiting reagent.

1. One atomic mass unit (amu) is defined as a mass exactly equal to one-twelfth of the mass of one …atom.

1. Hydrogen – 1
2. Carbon – 12
3. Oxygen -12
4. Chlorine – 35

2. The mass of one mole of a substance in grams is called its..

1. Atomic mass
2. Molecular Weight
3. Molecular mass
4. Molar mass.

3. … is the sum of atomic massesof the elements present in a molecule.

1. Atomic mass
2. Molecular Weight
3. Molecular mass
4. Molar mass.

4. One mole contains exactly …elementary entities.

1. 02214076 × 10²¹
2. 02214076 × 10²²
3. 6.02214076 × 10²³
4. 02214076 × 10²⁴

5. For which of the following compound , formula mass is preferred instead of molecular mass?

1. NaCl
2. C2H6
3. N2
4. H2O​

The uncertainty in the experimental or the calculated values is indicated by mentioning the number of significant figures. Significant figures are meaningful digits which are known with certainty plus one which is estimated or uncertain. The uncertainty is indicated by writing the certain digits and the last uncertain digit. there are certain rules for determining the Number of significant figures. These are Stated below:

• All non-zero digits are significant. For Example in 285cm, there are three Significant figures and in 0.25 mL, there are two significant figures.
• Zeros preceding to first non-zero digit are not significant. such zero indicates the position of decimal point. thus, 0.03 has one significant figure and 0.0052 has two significant figures.
• Zeros between two non-zero digits are significant. thus, 2.005 has four Significant figures.
• Zeros at the end or right of a number are significant, provided they are on the right side of the decimal point. For example, 0.200 g has three significant figures. But, if otherwise, the terminal zeros are not significant if there is no decimal point.

Precision refers to the closeness of various measurements for the same quantity. However, accuracy is the agreement of a particular valueto the true value of the result.

LAWS OF CHEMICALCOMBINATIONS- The combination of elements to form compounds is governed by the following five basic laws.

1. Law of Conservation of Mass-This law was put forth by Antoine Lavoisierin 1789. He performed careful experimental studies for combustion reactions and reached to the conclusion that in all physical andchemical changes, there is no net change inmassduring the process. Hence, he reachedto the conclusion that matter can neither becreated nor destroyed. This is called ‘Law ofConservation of Mass’.
2. Law of Definite Proportions-This law was given by, a French chemist, Joseph Proust. He stated that a given compound always contains exactly the same proportion of elements by weight.
3. Law of Multiple Proportions-This law was proposed by John Dalton. According to this law, if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in the ratio of small whole numbers. For example, hydrogen combines with oxygen to form two compounds, namely, water and hydrogen peroxide.

Hydrogen + Oxygen→ Water

2g                 16g       18g

Hydrogen + Oxygen → Hydrogen Peroxide

    2g                  32g        34g

Here, the masses of oxygen (i.e., 16 g and 32 g), which combine with a fixed mass of hydrogen (2g) bear a simple ratio, i.e., 16:32 or 1:2.

4. Gay Lussac’s Law of Gaseous Volumes-This law was given by Gay Lussac in 1808. Heobserved that when gases combine or are produced in a chemicalreaction they do so in asimple ratio by volume,provided all gases are at the same temperature and pressure.
5. Avogadro’s Law – In 1811, Avogadro proposed that equal volumes of all gases at the same temperature and pressure should contain equal number of molecules.

In 1808, Dalton published ‘A New System of Chemical Philosophy’, in which he proposed the following :

1. Matter consists of indivisible atoms.
2. All atoms of a given element have identical properties, including identical mass. Atoms of different elements differ in mass.
3. Compounds are formed when atoms of different elements combine in a fixed ratio.
4. Chemical reactions involve reorganisati on of atoms. These are neither created nor destroyed in a chemical reaction.

1. … refers to the closeness of variousmeasurements for the same quantity.

1. Accuracy
2. Reliability
3. Precision
4. Uncertainty

2. Law of Conservation of mass was put forth by ….in 1789.

1. Joseph Proust
2. Antoine Lavoisier
3. Joseph Louis
4. Gay Lussac

3. Which of the following number has twosignificant figures.

1. 0.0052
2. 052
3. 52
4. 0052

4. … is the agreement of a particular valueto the true value of the result.

1. Accuracy
2. Reliability
3. Precision
4. Uncertainty

5. Law of Multiple Proportions proposed by....

1. Joseph Proust
2. Antoine Lavoisier
3. Joseph Louis
4. John Dalton

Read the passage given below and answer the following questions from 1 to 5.
Quantitative measurement of properties isreaquired for scientific investigation. Earlier, two different systems of measurement, i.e., the English System and the Metric System were being used indifferent parts of the world. The metric system, which originated in France in late eighteenth century. The SI system has seven base units. these are listed as follow.

	Base Physical Quantities	Unit
1	Length	Metre – m
2	Mass	Kilogram – kg
3	Time	Second – s
4	Electric current	Ampere-  A
5	Thermodynamic Temperature	Kelvin – K
6	Amount of substance	Mole – mol
7	Luminous intensity	Candela- cd

Here , Mass of a substance is the amount of matter present in it, while weight is the force exerted by gravity on an object. Density of a substance is its amount of mass per unit volume. The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.02214076 × 10²³ elementary entities. This number is the fixed numerical value of the Avogadro constant, NA, when expressed in the unit per moland is called the Avogadro number. The amount of substance, symbol n, of a system is a measure of the number of specified elementary entities. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles.There are three common scales to measure temperature — °C (degree celsius), °F (degree fahrenheit) and K (kelvin). Here, K is the SIunit. Generally, the thermometer with celsius scale are calibrated from 0° to 100°, where these two temperatures are the freezing point and the boiling point of water, respectively. The fahrenheit scale is represented between 32° to 212°.
The temperatures on two scales are related to each other by the following relationship:
°F =  9 (°C) + 32
5
The kelvin scale is related to celsius scaleas follows:
K = °C + 273.15

1. The metric system,which originated in … in late eighteenthcentury.

1. Ukraine
2. German
3. Russia
4. France

2. The SI system has …. base units.

1. 7
2. 3
3. 9
4. 1

3. The symbol for SI unit of thermodynamic temperature is …

1. Kelvin
2. K
3. Degree Celsius
4. °C

4. A prefix giga equivalents to:

1. 10⁹
2. 10¹⁰
3. 10¹¹
4. 10¹²

5. The fahrenheit scale is represented between..

1. 0°F to 100°F
2. 32°F to 212°.F
3. 15° F to 373° F

Read the passage given below and answer the following questions from (i) to (v).
The identity of a substance is defined not only by the types of atoms or ions it contains, but by the quantity of each type of atom or ion. The experimental approach required the introduction of a new unit for amount of substances, the mole, which remains indispensable in modern chemical science. The mole is an amount unit similar to familiar units like pair, dozen, gross, etc. It provides a specific measure of the number of atoms or molecules in a bulk sample of matter. A mole is defined as the amount of substance containing the same number of discrete entities (atoms, molecules, ions, etc.) as the number of atoms in a sample of pure 12C weighing exactly 12g. One Latin connotation for the word “mole” is “large mass” or “bulk,” which is consistent with its use as the name for this unit. The mole provides a link between an easily measured macroscopic property, bulk mass, and an extremely important fundamental property, number of atoms, molecules and so forth. The number of entities composing a mole has been experimentally determined to be 6.02214179 × 10²³.
6.02214179 × 10²³, a fundamental constant named Avogadro’s number (NA ) or the Avogadro constant in honor of Italian scientist Amedeo Avogadro. This constant is properly reported with an explicit unit of “per mole,” a conveniently rounded version being 6.022×10²³/mol. Consistent with its definition as an amount unit, 1 mole of any element contains the same number of atoms as 1 mole of any other element. The masses of 1 mole of different elements, however, are different, since the masses of the individual atoms are drastically different. The molar mass of an element (or compound) is the mass in grams of 1 mole of that substance, a property expressed in units of grams per mole (g/mol).
The following questions are multiple choice questions. Choose the most appropriate answer:

1. A sample of copper sulphate pentahydrate contains 8.64g of oxygen. How many grams of Cu is present in the sample?

1. 0.952g
2. 3.816g
3. 3.782g
4. 8.64g

2. A gas mixture contains 50% helium and 50% methane by volume. What is the percent by \ weight of methane in the mixture?

1. 19.97%
2. 20.05%
3. 50%
4. 80.03%

3. The mass of oxygen gas which occupies 5.6 litres at STP could be:

1. Gram atomic mass of oxygen
2. One fourth of the gram atomic mass of oxygen
3. Double the gram atomic mass of oxygen
4. Half of the gram atomic mass of oxygen

4. What is the mass of one molecule of yellow phosphorus? (Atomic mass of phosphorus = 30)

1. 1.993 x 10^-22 mg
2. 1.993 x 10^-19 mg
3. 4.983 x 10^-20 mg
4. 4.983 x 10^-23 mg

5. The number of moles of oxygen in 1L of air containing 21% oxygen by volume, in standard conditions is:

1. 0.186 mol
2. 0.21 mol
3. 2.10 mol
4. 0.0093 mol

Read the passage given below and answer the following questions from 1 to 5.
Chemistry is the science of molecules and theirtransformations. It is the science not so much of the one hundred elements but of the infinite variety of molecules thatmay be built from them. Chemistry plays a central role in science andis often intertwined with other branches ofscience.to understand thebasic concepts of chemistry, which begin withthe concept of matter. Let us start with thenature of matter. matter can exist in threephysical states viz. solid, liquid and gas.Particles are held very close to each otherin solids in an orderly fashion and there is notmuch freedom of movement. In liquids, theparticles are close to each other but they canmove around. However, in gases, the particlesare far apart as compared to those present insolid or liquid states and their movement iseasy and fast. different states of matter exhibitthe following characteristics:

1. Solids have definite volume and definiteshape.
2. Liquids have definite volume but do nothave definite shape. They take the shapeof the container in which they are placed.
3. Gases have neither definite volume nordefinite shape. They completely occupy thespace in the container in which they are placed.

Matter can be classified as mixture or pure substance. A mixture may be homogeneous or heterogeneous. Pure substances can further be classified into elements and compounds. Particles of an element consist of only one type of atoms. These particles may exist as atoms or molecules. When two or more atoms of different elements combine together in a definite ratio, the molecule of a compound is obtained.
Every substance has unique or characteristic properties. These properties can be classified into two categories — physical properties, such as colour, odour, melting point, boiling point, density, etc., and chemical properties, like composition, combustibility, ractivity with acids and bases, etc. Physical properties can be measured or observed without changing the identity or the composition of the substance. The measurement or observation of chemical properties requires a chemical change to occur. Measurement of physical properties does not require occurance of a chemical change.

1. Which of the following state of matter have definite volume but do not have definite shape?

1. Solid
2. Liquid
3. Gas
4. Plasma

2. Particles are held very close to each other in … in an orderly fashion and there is not much freedom of movement.

1. Liquid
2. Gas
3. Solid
4. Plasma

3. Particles of …. consist of only one type of atom.

1. Compound
2. Mixture
3. Element
4. All the above

4. Water molecule comprises …hydrogen atoms and … oxygen atom.

1. One, two
2. Three, one
3. One, three
4. Two, one

5. Which of the following is not an example of Physical Properties of substance.?

1. Odour
2. Melting point
3. Density
4. Composition