Some Basic Concepts of Chemistry - Online Test
Q1. Significant figures are
Answer : Option A
Explaination / Solution:
Significant digits are certain digits that have significance or meaning to certain digits in a number . Such digits help scientists to use them with more precise information about measurement and other numeric data. These digits also help them in rounding off very large or very small number
Q2. According to Gay Lussac’s Law of Gaseous Volumes,
" when gases combine or are produced in a chemical reaction they do so in a ______ ratio by volumes provided all gases are at same temperature and pressure."
Answer : Option A
Explaination / Solution:
Gay lussac’s law states 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 same temperature and pressure.
Mathematically , the law is expressed as ,
[ V / n ] = k
where V represents volume of the gas , n denotes number of moles of the gas & k is proportionality constant .
Thus, volume ratio must be related to the relative number of molecules.
This relationship was crucial in establishing the formula of simple molecules at a time when a distinction between atoms and molecules was not clearly understood.
Q3. According to Avogadro Law equal volumes ofall gases at the same temperature and pressure should contain ---------- number of molecules .
Answer : Option C
Explaination / Solution:
Avogadro's law states that " equal volumes of all gases at same temperature and pressure contain equal number of molecules. "
Q4. Molecular mass of a compound is the ------------- of atomic masses of elements present in a molecule .
Answer : Option B
Explaination / Solution:
Molecular mass is the sum of atomic masses of the elements present in a molecule.
For example ; Molecular mass of CO2 = atomic mass of one carbon atom & atomic mass of two oxygen atoms
=[ 12+2(16) ] u
= 44u.
Q5. A given compound always contains exactly the same proportion of elements by weight. This law is stated by
Answer : Option D
Explaination / Solution:
The observation was first made by French chemist Joseph Proust , based on certain experiments conducted between 1798 and 1804.
Proust made the above statement known as " Proust's law " or " Law of definite composition " or " Law of constant composition "
Q6. Avogadro's constant is the number of entities ( viz. atoms , molecules or ions ) present in ------------- mole of a substance.
Answer : Option B
Explaination / Solution:
Avagadro's constant represents the number of entities ( viz, atoms , molecules or ions ) present in 1 mole of a substance .
The constant ( denoted by N )
=6.022 x 1023
Q7. An empirical formula represents the simplest
Answer : Option C
Explaination / Solution:
In chemistry the empirical formula of a compound is the simplest positive integer ratio of atoms present in a compound.
However ,this differs from the chemical formula which expresses the number of atoms in each molecule of a compound ..
An empirical formula makes no mention of the arrangement of atoms in a compound.
It is standard for many ionic compounds like CaCl2 or for macro - molecules such as silicates etc.
Q8. Molecular formula represents
Answer : Option D
Explaination / Solution:
Molecular formula is the exact no. of atoms present in a molecule of a compound.
Molecular formula of a compound is related with its empirical formula as ,
Mollecular formula = ( Empirical formula ) n
where n represents a positive integer .
Q9. According to the law of conservation of mass, a balanced chemical equation
Answer : Option C
Explaination / Solution:
According to law of conservation of mass
total mass of reactants
= total mass of product
∴ the number . of atoms of each element in reactants
= number . of atoms of that element in products
Q10. Molarity is defined as,
Answer : Option C
Explaination / Solution:
Molarity is the most widely used method of expressing the strength or concentration of a solution .
It is denoted by ' M ' .
Molarity is defined as number of . of moles of solute present per litre of solution.
Mathematically ,
Molarity ( M )
= Number of moles of solute / Volume of solution in Litres
