Answer is: 3,4
Chemical reaction: HNO₂ + NaOH → NaNO₂ + H₂O.
c₀(HNO₂) = 1,2 M = 1,2 mol/dm³.
c₀(NaNO₂) = 0,8 M = 0,8 mol/dm³.
V₀(HNO₂) = V₀(NaNO₂) = 1 dm³ = 1 L.
c₀(NaOH) = 0,5 M = 0,5 mol/dm³.
n₀(HNO₂)= 1,2 mol/dm³ · 1 dm³ = 1,2 mol.
n₀(NaNO₂) = 0,8 mol/dm³ · 1 dm³ = 0,8 mol.
V(NaOH) = 400 mL · 0,001 dm³/mL = 0,4 dm³.
n₀(NaOH) = c₀(NaOH) · V₀(NaOH).
n₀(NaOH) = 0,5 mol/dm³ · 0,4 dm³ = 0,2 mol.
n(HNO₂) = 1,2 mol - 0,2 mol = 1 mol.
n(NaNO₂) = 0,8 mol + 0,2 mol = 1 mol.
c(HNO₂) = 1 mol ÷ 1,4 dm³ = 0,714 mol/dm³.
c(NaNO₂) = 1 mol ÷ 1,4 dm³ = 0,714 mol/dm³.
pH = pKa + log (c(HNO₂) / c(NaNO₂)).
pH = 3,4 + log (0,714 mol/dm³ / 0,714 mol/dm³) = 3,4.
Answer:
As you haven't explained what measurements you took before solving this problem, I will explain the general procedure to evaluate the efficiency of a kettle. I hope it helps you. I´ll send an attachement file with the full answer, since I couldn't write it here.
I assume that the material that is going to be heated in the kettle is water.
1- You have to boil water in it and take the time it takes to its boiling point (in seconds).
2- You have to evaluate the amount of energy the water absorbed Q with the efficiency formula which I explain in the attachement file.
3- Divide Q by the time it took to bring the water to boiling so you can have the power it consumed.
4- You divide the last value you obtained by the Kettles's power rating.
5- Multiply the last value by 100 to obtain a percentage value of efficiency.
Explanation:
Efficiency is the ration of a machine's useful work, in this case how much energy the water absorbed to get to its boiling point divided by the time it took to get to this point, and the total energy expended, in this case the kettles's power rating.
The red sign pops up on the side of the bus.
At the equivalence point, the NaF completely reacts with the HCl
The correct option that gives the equivalence point when titrating NaF solution with HCl(aq), occur at a pH value is option c);
c) <u>Below 7 because it is determined by HF (aq)</u>
Reason:
The ionic equation of the reaction taking place in the titration is presented as follows;
- Na⁺ (aq) + F⁻ (aq) + H⁺ (aq) + Cl⁻(aq) → HF (aq)+ Na⁺(aq) + Cl⁻(aq)
Therefore, by removing the spectator ions, we get;
Therefore;
The net ionic equation is the formation of hydrofluoric acid, HF, which is a
weak acid, therefore, the pH value will be <u>below 7 because it is determined </u>
<u>by HF</u>
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Learn more about equivalence point here: titration
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Answer:
Ag2S
Explanation:
10.8 gm of silver, 12.4 gm of silver sulfide, so 12.4 -10.8 = 1,6 gm of sulfur
silver atomic weight is 108, sulfur atomic weight is 32 so
10.8/108; = 0.10 mole Ag 1.6/32 = 0.05 mole sulfur
so there is a 2:1 ratio of silver to sulfur, so the compound is 2 silver 1 sulfur or Ag2S