Answer:
The concentration the student should write down in her lab is 2.2 mol/L
Explanation:
Atomic mass of the elements are:
Na: 22.989 u
S: 32.065 u
O: 15.999 u
Molar mass of sodium thiosulfate, Na2S2O3 = (2*22.989 + 2*32.065 + 3*15.999) g/mol = 158.105 g/mol.
Mass of Na2S2O3 taken = (19.440 - 2.2) g = 17.240 g.
For mole(s) of Na2S2O3 = (mass taken)/(molar mass)
= (17.240 g)/(158.105 g/mol) = 0.1090 mole.
Volume of the solution = 50.29 mL = (50.29 mL)*(1 L)/(1000 mL)
= 0.05029 L.
To find the molar concentration of the sodium thiosulfate solution prepared we use the formula:
= (moles of sodium thiosulfate)/(volume of solution in L)
= (0.1090 mole)/(0.05029 L)
= 2.1674 mol/L
The given question is incomplete. The complete question is :
Which of the following Group 17 elements is the least reactive
a) Flourine
b) Chlorine
c) Astatine
d) Iodine
Answer: c) Astatine
Explanation:
Halogen is the name given to Group 17 family with general electronic configuration of 
which have 7 valence electrons and thus easily gain one electron to attain stable configuration.
As we move down the group from flourine to chlorine to bromine to iodine to astatine , the valence shell moves farther from nucleus and thus tendency to accept the electron decreases and thus reactivity also decreases.
Thus Astatine is the least reactive of all.
![pH=-\log_{10} [H_3O^+] \Rightarrow [H_3O^+]=10^{-pH} \\ \\ pH=2.8 \\ \ [H_3O^+]=10^{-2.8} \approx 1.58 \times 10^{-3}](https://tex.z-dn.net/?f=pH%3D-%5Clog_%7B10%7D%20%5BH_3O%5E%2B%5D%20%5CRightarrow%20%5BH_3O%5E%2B%5D%3D10%5E%7B-pH%7D%20%5C%5C%20%5C%5C%0ApH%3D2.8%20%5C%5C%0A%5C%20%5BH_3O%5E%2B%5D%3D10%5E%7B-2.8%7D%20%5Capprox%201.58%20%5Ctimes%2010%5E%7B-3%7D)
The [H₃O⁺] of the solution is approximately 1.58 × 10⁻³ M.
We should describe a little bit the legend.
A - Element - we should have circles with same color and not bonded together (argon gas).
B - Compound - here we may have circles with same or different color bonded together (water or oxygen which is a diatomic molecule).
C - Mixture of elements - circles with different colors not not bonded together (mixture of noble gases).
D - Mixture of compounds - circles with same or different color bonded together but we should see two or more types of connectivity between circles (mixture of water and ethanol).
E - Mixture of elements and compounds - circles with same or different color bonded together mixed with circles with same color and not bonded together (a mixture between oxygen which is a diatomic molecule and noble gas like argon).
Now we may answer the question:
1) B
2) C
3) D
4) D
5) A
6) B
7) B
8) E
9) E
10) D
11) B
12) D
13) D
14) D
15) D
Answer:
Roxanne said it was because chlorine is highly electronegative and sodium has a low ionization energy and that the ions Na and cr both have full electron shells.
