Answer:
6.574 g NaF into 300ml (0.25M HF) => Bfr with pH ~3.5
Explanation:
For buffer solution to have a pH-value of 3.5 the hydronium ion concentration [H⁺] must be 3.16 x 10⁻⁴M ( => [H⁺] = 10^-pH = 10⁻³°⁵ =3.16 x 10⁻⁴M).
Addition of NaF to 300ml of 0.25M HF gives a buffer solution. To determine mass of NaF needed use common ion analysis for HF/NaF and calculate molarity of NaF, then moles in 300ml the x formula wt => mass needed for 3.5 pH.
HF ⇄ H⁺ + F⁻; Ka = 6.6 x 10⁻⁴
Ka = [H⁺][F⁻]/[HF] = 6.6 x 10⁻⁴ = (3.16 x 10⁻⁴)[F⁻]/0.25 => [F⁻] = (6.6 x 10⁻⁴)(0.25)/(3.16x10⁻⁴) = 5.218M in F⁻ needed ( = NaF needed).
For the 300ml buffer solution, moles of NaF needed = Molarity x Volume(L)
= (5.218M)(0.300L) = 0.157 mole NaF needed x 42 g/mole = 6.574 g NaF needed.
Check using the Henderson - Hasselbalch Equation...
pH = pKa + log ([Base]/[Acid]); pKa (HF) = 3.18
Molarity of NaF = (6.572g/42g/mole)/(0.300 L soln) = 0.572M in NaF = 0.572M in F⁻.
pH = 3.18 + log ([0.572]/[0.25]) ≅ 3.5.
One can also back calculate through the Henderson -Hasselbalch Equation to determine base concentration, moles NaF then grams NaF.
The missing part of the question is shown in the image attached
Answer:
C10H22(l) + 31/2 O2 (g)-----> 10CO2(g) + 11H2O(l)
V= 70.4L of CO2
Explanation:
Equation of the reaction is:
C10H22(l) + 31/2 O2 (g)-----> 10CO2(g) + 11H2O(l)
Number of moles of decane = mass/ molar mass
Molar mass of decane= 122gmol-1
n= 0.370×10^3g/122gmol-1= 3.0 moles
T= 13°C +273=286K
P= 1atm
R= 0.082 atmLK-1mol-1
From :
PV= nRT
V= nRT/P
V= 3.0×0.082×286/1
V= 70.4L of CO2
Answer:
There are 8 valence electrons
Explanation:
Answer:
Second order
Explanation:
Given that:
When the reaction A → B + C is studied, a plot 1/[A]t vs. time gives a straight line with a positive slope.
From the integration method for the second order of reaction.
Suppose that:
rate = k₂[A]²
∴
Therefore, a plot of the linear function 
versus t will be linear with a positive slope k₂ and the intercept on the concentration axis will be 
The linear plot for a second order reaction can be seen in theimage attached below.
