Answer:
Number of molecules = 2.61 x 10²³
Explanation:
Given:
Volume of tetra-chloride = 42 ml
Density = 1.59 g/ml
Find:
Number of molecules
Computation:
Mass = Volume of tetra-chloride x Density
Mass = 42 x 1.59
Mass = 66.78
Molecular mass of tetra-chloride = 154 g/mol
Moles = 66.78 / 154
Moles = 0.4337
0.4337 mole = 0.4337 x Avogadro number
0.4337 mole = 0.4337 x 6.022 x 10²³
Number of molecules = 2.61 x 10²³
There are 30 protons and 39 neutrons in the nucleus.
This must me the isotope of an element with an atomic mass close to 69 u.
The only candidates are Zn and Ga.
Zn has a zinc-69 isotope with mass 68.926 u.
Ga has a gallium -69 isotope with mass 68.925 u.
The isotope is probably

.
It has 30 protons and 39 neutrons.
Given, the density of water is 0.9975 g/ml. Density of water is mass of water per unit volume. Mass of 1 ml of water supposed to be 0.9975 g from density of water. So, mass of 10 ml of water is (0.9975 X 10) g= 9.975 g. From graduated cylinder, mass of 10 ml water is measured to be 9.955 g. So, error for mass of 10 ml water= (9.975-9.955)=0.02 g. Percentage of error for 10 ml water is
= 0.2. Error in the mass for the 10 ml of water is 0.2 %.
Benzene reacts with O₂ to produce CO₂ and H₂O, i.e.
C₆H₆ + 7.5 O₂ → 6 CO₂ + 3 H₂O
According to equation,
78.11 g (1 mole) C₆H₆ reacts to produce = 264 g (6 moles) of CO₂
Hence,
7.80 g C₆H₆ when reacted will produce = X g of CO₂
Solving for X,
X = (7.80 g × 264 g) ÷ 78.11 g
X = 26.36 g of CO₂
Theoretical Yield:
26.36 g of CO₂ produced is theoretical yield which shows 100% reaction between benzene and oxygen.
Actual Yield:
According to statement the actual amount of CO₂ produced is 3.0 g of CO₂.
%age Yield:
%age Yield = (Actual Yield ÷ Theoretical Yield) × 100
Putting Values,
%age Yield = (3.00 g ÷ 26.36 g) × 100
%age Yield = 11.38 %