How many oxygen atoms are in 2.30 g of quartz?
2 answers:
Answer:
4.61 * 10²² oxygen atoms
Explanation:
- Quartz is the common name of a silicon mineral, SiO₂.
- To solve the problem, we need to calculate the molar mass (MM) of quartz:
MM = AtomicMass of Si + 2 * AtomicMass of O
MM = 28.08 + 2 * 16
MM = 60.08 g/mol
- Then we can calculate how many moles of quartz are in 2.30 g:
2.30 g * = 0.0383 mol
- Then we use <em>Avogadro's number </em>calculate the number of oxygen atoms in 0.0383 mol of SiO₂, keeping in mind the number of O per quartz molecule:
0.0383 mol SiO₂ * = 4.61 * 10²² atoms of O
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Answer:
1) After adding 15.0 mL of the HCl solution, the mixture is before the equivalence point on the titration curve.
2) The pH of the solution after adding HCl is 12.6
Explanation:
10.0 mL of 0.25 M NaOH(aq) react with 15.0 mL of 0.10 M HCl(aq). Let's calculate the moles of each reactant.
There is an excess of NaOH so the mixture is before the equivalence point. When HCl completely reacts, we can calculate the moles in excess of NaOH.
NaOH + HCl ⇒ NaCl + H₂O
Initial 2.5 × 10⁻³ 1.5 × 10⁻³ 0 0
Reaction -1.5 × 10⁻³ -1.5 × 10⁻³ 1.5 × 10⁻³ 1.5 × 10⁻³
Final 1.0 × 10⁻³ 0 1.5 × 10⁻³ 1.5 × 10⁻³
The concentration of NaOH is:
NaOH is a strong base so [OH⁻] = [NaOH].
Finally, we can calculate pOH and pH.
pOH = -log [OH⁻] = -log 0.040 = 1.4
pH = 14 - pOH = 14 - 1.4 = 12.6