[sveioen]

Hey all,

doing some chemistry, and was hoping someone could check that the work I've done so far is correct!

1. 50.00 g NaCl equals...
Mm_NaCl = 22.99 + 35.45 = 58.44 g/mol
n = m / mm = 50.0g / 58.44 g/mol = 0.85 mol
and a total of
N = n * N_A = 0.85 mol * 6.023 * 10²³ = 5.12*10²³ ions.

2. 115 mL of a 0.3M solution of acetic acid is diluted by a certain amount of destilled water. After the dilution the concentration is 0.125M. How much water was added?

n= c * V = 0.300 M * 0.115 L = 0.0345 mol
V= 0.0345 mol / 0.125 mol/L = 0.276 L
ΔV = 0.276 L – 0.115 L = 0.161 L

3. Titration of 25 mL of ethanol solution (in water) with unknown concentration. After adding 23.46 mL of 0.200M permanganate the colour turns violet. What is the concentration of the ethanol solution?

Reaction: 5CH3CH2OH + 4MnO4^– + 12H⁺  → 5CH3COOH + 4Mn2⁺ + 11H2O

Moles of permanganate added:
n = c * V = 0.200 M * 23.46*10^-3 L = 4.692*10^-3 mol.
Since the ratio is 5:5 (or 1:1) the amount of ethanol present is the same, 4.692*10^-3 mol. So the concentration of the ethanol solution is:
C = 4.692*10^-3 mol / 25.00*10^-3 L = 0.18768 M

Appreciate any feedback!

[Borek]

N = n * N_A = 0.85 mol * 6.023 * 10²³ = 5.12*10²³ ions.

Close, but NaCl means TWO ions. No idea how the questions was worded.

5CH3CH2OH + 4MnO4^– + 12H⁺  → 5CH3COOH + 4Mn2⁺ + 11H2O

Since the ratio is 5:5 (or 1:1)

Assuming reaction is OK (no idea if oxidation ends here) ratio is not 5:5.

[sveioen]

N = n * N_A = 0.85 mol * 6.023 * 10²³ = 5.12*10²³ ions.

Close, but NaCl means TWO ions. No idea how the questions was worded.

The questions was "How many ions (in total) are there in 50 g of NaCl?". I found how many moles 50 g of NaCl equals, and times that with Avogadro's number. Sounds good?

5CH3CH2OH + 4MnO4^– + 12H⁺  → 5CH3COOH + 4Mn2⁺ + 11H2O

Since the ratio is 5:5 (or 1:1)

Assuming reaction is OK (no idea if oxidation ends here) ratio is not 5:5.

The reaction scheme was provided, so it's probably correct. However, am I considering the wrong reactant/product? It is Mn2⁺ which causes the color to change, right? So from the coefficients, 5 moles of CH3CH2OH reacts with 4 moles of Mn2⁺. Does this mean I have to use 5/4*n_{permanganate added}? So the concentration would be c= ((5/4)*4.692*10^-3 mol) / 25.00*10^-3 L?

[Borek]

Sounds good?

No. Have you actually read what I wrote?

However, am I considering the wrong reactant/product? It is Mn2⁺ which causes the color to change, right?

No, it is excess permanganate. Using 5:5 you can calculate how much Mn²⁺ was produced, you are interested in amount of ethanol. 5:4 is OK.