Some Basic Concepts Flashcards
A mixture contains particles of two or more pure substances which may be present in it in any ratio. Hence, their composition is……….
variable
In a homogeneous mixture, the components completely mix with each other. This means particles of components of the mixture are uniformly distributed throughout the bulk of the mixture and its composition is uniform throughout
True
In………………the composition is not uniform throughout and sometimes different components are visible.
heterogeneous mixture
Earlier, two different systems of measurement, i.e., the…………System and the …………… System were being used in different parts of the world.
English
Metric
Assertion: The metric system, which originated in France in late eighteenth century, was more convenient.
Reason: It was based on the decimal system.
Both are correct and correct explanation
National Metrology Institute (NMI), which maintains standards of measurements. This responsibility has been given to the National Physical Laboratory (NPL),
New Delhi
True
The International System of Units (in French Le Systeme International d’Unités — abbreviated as SI) was established by the ……….. General Conference on Weights and Measures (CGPM from ConferenceGenerale des Poids et Measures).
11th
Assertion: Mass standard is defined as the mass of platinum-iridium (Pt-Ir) cylinder that is stored in an airtight jar at International Bureau of Weights and Measures in Sevres, France
Reason: Pt-Ir was chosen for this standard because it is highly resistant to chemical attack and its mass will not change for an extremely long time.
Both are correct
X-rays to determine the atomic density of a crystal of ultrapure silicon, has an accuracy of about 1 part in 10^6 but has not yet been adopted to serve as a standard
True
In 1960 the length of the metre was defined as 1.65076373 × 10^6 times the wavelength of light emitted by a………..laser.
krypton
Significant figures are meaningful digits which are known with certainty plus one which is estimated or uncertain.
True
The total number of digits in a number, including the last digit that represents the uncertainty of the result.
Thermometer of different types of
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Significant figures
All non-zero digits are significant.
Zeros preceding to first non-zero digit are not significant. Such zero indicates the position of decimal point.
Zeros between two non-zero digits are significant.
Zeros at the end or right of a number are significant, provided they are on the right side of the decimal point.
Counting the numbers of object, for example, 2 balls or 20 eggs, have infinite significant figures as these are exact numbers and can be represented by writing infinite number of zeros after placing a decimal i.e., 2 = 2.000000 or 20 = 20.000000.
100 has only……..significant figure, but 100. has……….. significant figures and 100.0 has………..significant figures.
one
three
Four
In numbers written in scientific notation, all digits are significant e.g., 4.01×10^2 has………….significant figures
three
Accuracy refers to the closeness of various measurements for the same quantity.
Precision is the agreement of a particular value to the true value of the result.
Both are incorrect
Vice versa is true
Precision refers to the closeness of various measurements for the same quantity. However, accuracy is the agreement of a particular value to the true value of the result.
In multiplication and division the result must be reported with no more significant figures as in the measurement with the few significant figures.
True
Number of significant figures in answer shall be equal to significant figures in number with minimum significant figures
Rounding off rules
If the rightmost digit to be removed is more than 5, the preceding number is increased by one.
If the rightmost digit to be removed is less than 5, the preceding number is not changed
If the rightmost digit to be removed is 5, then the preceding number is not changed if it is an even number but it is increased by one if it is an odd number
Law of conservation of mass
It states that matter can neither be created nor destroyed.
This law was put forth by Antoine Lavoisier in 1789.
He performed careful experimental studies for combustion reactions and reached to the conclusion that in all physical and chemical changes, there is no net change in mass during the process. Hence, he reached to the conclusion that matter can neither be created nor destroyed.
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 irrespective of the source.
Law of Multiple Proportions
This law was proposed by Dalton in 1803.
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.
Gay Lussac’s Law of Gaseous Volumes
This law was given by Gay Lussac in 1808.
He observed that when gases combine or are produced in a chemical reaction they do so in a simple ratio by volume, provided all gases are at the same temperature and pressure.
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 :
- Matter consists of indivisible atoms.
- All atoms of a given element have identical properties, including identical mass. Atoms of different elements differ in mass.
- Compounds are formed when atoms of different elements combine in a fixed ratio.
- Chemical reactions involve reorganisation of atoms. These are neither created nor destroyed in a chemical reaction.
Dalton’s theory could explain the laws of chemical combination. However, it could not explain the laws of gaseous volumes. It could not provide the reason for combining of atoms, which was answered later by other scientists.
