Answer:
Oxidation: Cr → Cr⁴⁺ + 4 e⁻
Reduction: 4 e⁻ + O₂ → 2 O²⁻
Explanation:
Let's consider the following redox reaction.
Cr + O₂ → CrO₂
Cr is oxidized. Its oxidation number increases from 0 to +4. The corresponding half-reaction is:
Cr → Cr⁴⁺ + 4 e⁻
O is reduced. Its oxidation number decreases from 0 to -2. The corresponding half-reaction is:
4 e⁻ + O₂ → 2 O²⁻
Answer:
431.38 mg protein / mL
Explanation:
This is an example of the <em>Kjeldahl method</em>, for nitrogen determination. All nitrogen atoms in the protein were converted to NH₃ which then reacted with a <u>known excess of HCl</u>. This excess was later quantified via titration with NaOH.
First we calculate the <u>total amount of H⁺ moles from HCl</u>:
- 0.0388 M HCl * 10.00 mL = 0.388 mmol H⁺
Now we calculate the <u>excess moles of H⁺</u> (the moles that didn't react with NH₃ from the protein), from the <u>titration with NaOH</u>:
- HCl + NaOH → H₂O + Na⁺ + Cl⁻
- 0.0196 M * 3.83 mL = 0.075068 mmol OH⁻ = 0.0751 mmol H⁺
Now we substract the moles of H⁺ that reacted with NaOH, from the total number of moles, and the result is the <u>moles of H⁺ that reacted with NH₃ from the protein</u>:
- 0.388 mmol H⁺ - 0.0751 mmol H⁺ = 0.313 mmol H⁺ = 0.313 mmol NH₃
With the moles of NH₃ we know the moles of N, then we can <u>calculate the mass of N</u> present in the aliquot:
- 0.313 mmol NH₃ = 0.313 mmol N
- 0.313 mmol N * 14 mg/mmol = 4.382 mg N
From the exercise we're given the concentration of N in the protein, so now we <u>calculate the mass of protein</u>:
- 4.382 mg * 100/15.7 = 27.91 mg protein
Finally we <u>calculate the protein concentration in mg/m</u>L, <em>assuming your question is in 647 μL</em>, we first convert that value into mL:
- 647 μL *
0.647 mL
- 27.91 mg / 0.647 mL = 431.38 mg/mL
Answer:
1.97 moles of Na contains greater number of atoms than 6.8 × 10²² atoms of Li.
Explanation:
To solve this problem we will first calculate the number of atoms contained by 1.97 moles of Na and then will compare it with 6.8 × 10²² atoms of Li.
As we know that 1 mole of any substance contains exactly 6.022 × 10²³ particles which is also called as Avogadro's Number. So in order to calculate the number of atoms contained by 1.97 moles of Na, we will use following relation,
Moles = Number of Atoms ÷ 6.022 × 10²³ atoms.mol⁻¹
Solving for Number of Atoms,
Number of Atoms = Moles × 6.022 × 10²³ Atoms.mol⁻¹
Putting values,
Number of Atoms = 1.07 mol × 6.022 × 10²³ Atoms.mol⁻¹
Number of Atoms = 1.18 × 10²⁴ Atoms of Na
Hence,
1.97 moles of Na contains greater number of atoms than 6.8 × 10²² atoms of Li.