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Eva8 [605]
3 years ago
12

Phenolphthalein has a pka of 9.7 and is colorless in its acid form and pink in its basic form. part a for ph= 2.0 calculate [in−

]/[hin].
Chemistry
2 answers:
Tresset [83]3 years ago
8 0

Answer:

1.9953 × 10⁻⁸

Explanation:

Considering the Henderson- Hasselbalch equation for the calculation of the pH of the indicator as:

pH = pKa + log[In⁻]/[HIn]

Where Ka is the dissociation constant of the acid.

Given, pKa = 9.7

pH = 2.0

So,  

2.0 = 9.7 + log[In⁻]/[HIn]

log[In⁻]/[HIn]  = - 7.7

<u>[In⁻]/[HIn] = Antilog (-7.7) = 1.9953 × 10⁻⁸</u>

Karo-lina-s [1.5K]3 years ago
4 0
Use the h-h equation! 

pH = pKa + log[In-/HIn]
2.0 = 9.7 + log[In-/HIn]
-7.7 = log[In-/HIn]
10^-7.7 = [In-/HIn]
[In-/HIn] = 1.995 x 10^-8

Hope this helps!
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A chemistry graduate student is given 125.mL of a 1.00M benzoic acid HC6H5CO2 solution. Benzoic acid is a weak acid with =Ka×6.3
lubasha [3.4K]

Answer:

53.9 g

Explanation:

When talking about buffers is very common the problem involves the use of the Henderson Hasselbach formula:

pH = pKa + log [A⁻]/[HA]

where  [A⁻] is the concentration of the conjugate base of the weak acid HA, and [HA] is the concentration of the weak acid.

We can calculate pKₐ from the given kₐ ( pKₐ = - log Kₐ ), and from there obtain the ratio  [A⁻]/HA].

Since we know the concentration of HC6H5CO2 and the volume of solution, the moles and mass of KC6H5CO2  can be determined.

So,

4.63 = - log ( 6.3 x 10⁻⁵ ) + log [A⁻]/[HA] = - (-4.20 ) + log [A⁻]/[HA]

⇒ log [A⁻]/[HA]  = 4.63 - 4.20 =  log [A⁻]/[HA]

0.43 = log [A⁻]/[HA]

taking antilogs to both sides of this equation:

10^0.43 =  [A⁻]/[HA] = 2.69

 [A⁻]/ 1.00 M = 2.69 ⇒ [A⁻] = 2.69 M

Molarity is moles per liter of solution, so we can calculate how many moles of  C6H5CO2⁻ the student needs to dissolve  in 125. mL ( 0.125 L ) of a 2.69 M solution:

( 2.69 mol C6H5CO2⁻ / 1L ) x 0.125 L  = 0.34 mol C6H5CO2⁻

The mass will be obtained by multiplying 0.34 mol times molecular weight for KC6H5CO2 ( 160.21 g/mol ):

0.34 mol x 160.21 g/mol = 53.9 g

3 0
3 years ago
A tank at is filled with of sulfur tetrafluoride gas and of sulfur hexafluoride gas. You can assume both gases behave as ideal g
dangina [55]

The question is incomplete, the complete question is:

A 7.00 L tank at 21.4^oC is filled with 5.43 g of sulfur hexafluoride gas and 14.2 g of sulfur tetrafluoride gas. You can assume both gases behave as ideal gases under these conditions. Calculate the mole fraction and partial pressure of each gas. Round each of your answers to significant digits.

<u>Answer:</u> The mole fraction of sulfur hexafluoride is 0.221 and that of sulfur tetrafluoride is 0.779

<u>Explanation:</u>

The number of moles is defined as the ratio of the mass of a substance to its molar mass.  The equation used is:

\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}} ......(1)

  • <u>For sulfur hexafluoride:</u>

Given mass of sulfur hexafluoride = 5.43 g

Molar mass of sulfur hexafluoride = 146.06 g/mol

Putting values in equation 1, we get:

\text{Moles of sulfur hexafluoride}=\frac{5.43g}{146.06g/mol}=0.0372mol

  • <u>For sulfur tetrafluoride:</u>

Given mass of sulfur tetrafluoride = 14.2 g

Molar mass of sulfur tetrafluoride = 108.07 g/mol

Putting values in equation 1, we get:

\text{Moles of sulfur tetrafluoride }=\frac{14.2g}{108.07g/mol}=0.1314mol

Total moles of gas in the tank = [0.0372+ 0.1314] mol = 0.1686 mol

Mole fraction is defined as the moles of a component present in the total moles of a solution. It is given by the equation:

\chi_A=\frac{n_A}{n_A+n_B} .....(2)

where n is the number of moles

Putting values in equation 2, we get:

\chi_{SF_6}=\frac{0.0372}{0.1686}=0.221

\chi_{SF_4}=\frac{0.1314}{0.1686}=0.779

Hence, the mole fraction of sulfur hexafluoride is 0.221 and that of sulfur tetrafluoride is 0.779

7 0
3 years ago
Determine if the chemical equation is balanced or not balanced. 1N2 + 1H2&gt; NH3 ​
almond37 [142]

Answer:

Explanation:

7 0
3 years ago
Which of the following provides cell support in an animal cell? A. microtubule B. mitochondria C. lysosomes D. vacuole
Viktor [21]

Answer:

D.

Vacuole

Explanation:

Hope this helps:)

4 0
3 years ago
Negative ions are usually formed from: metals nonmetals
Lelechka [254]
Non metals are electronegative in nature whereas metals are electropositive. A non-metal accepts electron and gains negative charge whereas metals lose eletrons and gains positive charge. Hence correct answer is non-metals. Hope this helps!
3 0
3 years ago
Read 2 more answers
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