A nucleus of mass number 81 contains 46 neutrons
Mass number=number of protons+number of neutrons
81=number of protons+ 46
number of protons=81-46
number of protons=35
In an atom, number of electrons=number of protons=35
So, the element is ⁸¹Br₃₅ .
Atomic ion of Br, having 36 electrons in it will be:
⁸¹Br⁻₃₆
The symbol for this atomic ion will be Br and charge on the ion will be -ve.
Valence electrons are the electrons in the outermost shell, or energy level, of an atom. For example, oxygen has six valence electrons, two in the 2s subshell and four in the 2p subshell. We can write the configuration of oxygen's valence electrons as 2s²2p⁴
Answer:
2:1
1.2 × 10² g
Explanation:
Step 1: Write the balanced combustion equation
CH₄ + 2 O₂ ⇒ CO₂ + 2 H₂O
Step 2: Establish the appropriate molar ratio
According to the balanced equation, the molar ratio of O₂ to CH₄ is 2:1.
Step 3: Calculate the moles of CH₄ required to react with 15 moles of O₂
We will use the previously established molar ratio.
15 mol O₂ 1 mol CH₄/2 mol O₂ = 7.5 mol CH₄
Step 4: Calculate the mass corresponding to 7.5 moles of CH₄
The molar mass of CH₄ is 16.04 g/mol.
7.5 mol × 16.04 g/mol = 1.2 × 10² g
Freezing point depression is a colligative property.
The formula that rules it is:
ΔT f = Kf * m
Where m is the molality of the solution => m = moles of solute / Kg of solvent
=> m = 0.31 mol / 0.175 kg = 1.771 m
And kf = 1.86 °C/m
=> ΔTf = 1.771 m * 1.86 °C / m = 3.3 °C
=> Freezing point of the solution = normal freezing point of water - 3.3 °C = 0 - 3.3°C = - 3.3°C.
Answer: -3.3 °C
