Answer:
Bohr's model of the hydrogen atom is based on three postulates:
1) An electron moves around the nucleus in a circular orbit,
2) An electron's angular momentum in the orbit is quantised,
3) The change in an electron's energy as it makes a quantum jump from one orbit to another is always accompanied by the emission or absorption of a photon. Bohr's model is semi-classical because it combines the classical concept of electron orbit (postulate 1) with the new concept of quantisation ( postulates 2 and ).
Answer:
23 and 56 minutes or 24 hours
Earth rotates once in about 24 hours with respect to the Sun, but once every 23 hours, 56 minutes, and 4 seconds with respect to other, distant, stars. Earth's rotation is slowing slightly with time; thus, a day was shorter in the past
Answer:
pH = 2.69
Explanation:
The complete question is:<em> An analytical chemist is titrating 182.2 mL of a 1.200 M solution of nitrous acid (HNO2) with a solution of 0.8400 M KOH. The pKa of nitrous acid is 3.35. Calculate the pH of the acid solution after the chemist has added 46.44 mL of the KOH solution to it.</em>
<em />
The reaction of HNO₂ with KOH is:
HNO₂ + KOH → NO₂⁻ + H₂O + K⁺
Moles of HNO₂ and KOH that react are:
HNO₂ = 0.1822L × (1.200mol / L) = <em>0.21864 moles HNO₂</em>
KOH = 0.04644L × (0.8400mol / L) = <em>0.0390 moles KOH</em>
That means after the reaction, moles of HNO₂ and NO₂⁻ after the reaction are:
NO₂⁻ = 0.03900 moles KOH = moles NO₂⁻
HNO₂ = 0.21864 moles HNO₂ - 0.03900 moles = 0.17964 moles HNO₂
It is possible to find the pH of this buffer (<em>Mixture of a weak acid, HNO₂ with the conjugate base, NO₂⁻), </em>using H-H equation for this system:
pH = pKa + log₁₀ [NO₂⁻] / [HNO₂]
pH = 3.35 + log₁₀ [0.03900mol] / [0.17964mol]
<h3>pH = 2.69</h3>
<em>Answer:</em>
<em>242 gram</em> of HF will be required for complete rex.
<em>Balance chemical equation:</em>
SiO2 + 4HF → SiF4 + 2H2O
<em>Data given</em>
mass of SiO2 = 182g
molar mass of SiO2=60.08
moles of SiO2 = mass/molar mass = 182/60.08 =3.02 moles
From balance chemcial equation
SiO2 : HF
1 : 4
3.02 = 4 × 3.02 = 12
mass of HF= no. of moles × molar mass
mass of HF = 12.08×20 =<em> 242 g</em>
The balance equation for the reaction between sodium bicarbonate and hydrochloric acid:
The reactants and react in the ratio 1:1. So we use the mass of sodium bicarbonate and molar mass to find the number of moles produced.
.
.
Again we use the fact that the stochiometric ratio are 1:1:1:1:1, hence the moles of are 24.977moles.
So we used the ideal gas law , where P is the pressure, V is the volume, R the gas constant, is and T is the temperature in kelvins. We make V the subject
The answer is supposed to be in L, , so